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Compact Cassette tape types and formulations

January 01, 1970

Audio compact cassettes use magnetic tape of three major types which differ in fundamental magnetic properties, the level of bias applied during recording, and the optimal time constant of replay equalization. Specifications of each type were set in 1979 by the International Electrotechnical Commission (IEC): Type I (IEC I, 'ferric' or 'normal' tapes), Type II (IEC II, or 'chrome' tapes), Type III (IEC III, ferrichrome or ferrochrome), and Type IV (IEC IV, or 'metal' tapes). 'Type 0' was a non-standard designation for early compact cassettes that did not conform to IEC specification.

Differences in tape colour of most common tape formulations, top to bottom: ferric, ferricobalt, chromium dioxide and metal particle cassettes
Standardized notches for automatic tape selection. Top to bottom: Type I (and Type III), Type II, Type IV

By the time the specifications were introduced, Type I included pure gamma ferric oxide formulations, Type II included ferricobalt and chromium(IV) oxide formulations, and Type IV included metal particle tapes—the best-performing, but also the most expensive. Double-layer Type III tape formulations, advanced by Sony and BASF in the 1970s, never gained substantial market presence.

In the 1980s the lines between three types blurred. Panasonic developed evaporated metal tapes that could be made to match any of the three IEC types. Metal particle tapes migrated to Type II and Type I, ferricobalt formulations migrated to Type I. By the end of the decade performance of the best Type I ferricobalt tapes (superferrics) approached that of Type IV tapes; performance of entry-level Type I tapes gradually improved until the very end of compact cassette production.[1]

Specifications edit

 
Coercivity and remanence marked on the wrapper of a 'professional' cassette (TDK AM, ca. 1995). These are typical values for a microferric cassette.
 
MOL, SOL, bias noise and dynamic range marked on the wrapper of a superferric cassette (TDK AR, 1990s). The values approach the limits of ferric tape technology
 
Frequency response curves of a typical cassette tape showing the effects of different bias settings (after Roberson[2])

Magnetic properties edit

Magnetic recording relies on the use of hard ferrimagnetic or ferromagnetic materials. These require strong external magnetic fields to be magnetized, and retain substantial residual magnetization after the magnetizing field is removed.[3] Two fundamental magnetic properties, relevant for audio recording, are:

  • Saturation remanence limits maximum output level and, indirectly, dynamic range of audio recordings.[4] Remanence of audio tapes, referred to quarter-inch tape width, varies from around 1100 G for basic ferric tapes to 3500 G for Type IV tapes;[5] advertised remanence of the 1986 JVC Type IV cassette reached 4800 G.[6]
  • Coercivity is a measure of the external magnetic flux required to magnetize the tape, and an indicator of the necessary bias level. The coercivity of audio tapes varies from 350 Oe to 1200 Oe. High-coercivity particles are more difficult to erase, bias and record, but also less prone to high-frequency losses during recording, and to external interference and self-demagnetization during storage.[5][7][8]

A useful figure of merit of tape technology is the squareness ratio of the hysteresis curve.[9] It is an indicator of tape uniformity and its linearity in analogue recording.[9] An increase in the squareness ratio defers the onset of compression and distortion, and allows fuller utilization of the tape's dynamic range within the limits of remanence.[9][10] The squareness ratio of basic ferric tapes rarely exceeds 0.75, and the squareness ratio of the best tapes exceeds 0.9.[9]

Electromagnetic properties edit

 
Hysteresis curves of Type I, CrO2 Type II and Type IV tapes.[11] On this chart, the vertical span is remanence (remaining magnetism), a rough indicator of maximum recording output level. The horizontal span shows coercivity ― how much flux it takes to magnetize the tapes

Manufacturers of bulk tape provided extremely detailed technical descriptions of their product, with numerous charts and dozens of numeric parameters. From the end user viewpoint, the most important electromagnetic properties of the tape are:

  • Maximum output levels, usually specified in dB relative to the nominal zero reference level of 250 nWb/m or the 'Dolby level' of 200 nWb/m. Often incorrectly called recording levels, these are always expressed in terms of the tape's output, thus taking its sensitivity out of the equation. Performance at low and middle, and at treble frequencies was traditionally characterized by two related but different parameters:
    • Maximum output level (MOL) is relevant at low and middle frequencies. It is usually specified at 315 Hz (MOL315) or 400 Hz (MOL400), and its value marks the point when the third harmonic coefficient reaches 3%.[12] Further magnetization of the tape is technically possible, but at the cost of unacceptable compression and distortion. For all types of tape, MOL reaches a maximum in the 125–800 Hz area, while dropping off below 125 Hz and above 800 Hz.[13] The maximum output of Type I tape at 40 Hz is 3–5 dB lower than MOL400,[14] while in Type IV tapes it is 6–7 dB lower.[15] As a result, ferric tapes handle bass-heavy music with apparent ease compared to expensive metal tapes. Double-layer Type III (IEC III, ferrichrome or ferrochrome) tape formulations were supposed to allow bass frequencies to be recorded deeper into the ferric layer, while keeping the high frequencies in the upper chromium oxide layer.
    • At treble frequencies the playback head cannot reliably reproduce harmonics of the recorded signal.[16] This makes distortion measurements impossible; instead of MOL, high-frequency performance is characterized by saturation output level (SOL), usually specified at 10 kHz (SOL10k).[16] Once the tape reaches saturation point, any further increase in recording flux actually decreases output to below SOL.[16]
  • Noise level, usually understood as bias noise (hiss) of a tape recorded with zero input signal, replayed without noise reduction, A-weighted and referred to the same level as MOL and SOL. The difference between bias noise and the noise of virgin tape is an indicator of tape uniformity. Another important but rarely quantified type of noise is modulation noise, which appears only in the presence of a recorded signal, and which cannot be reduced by Dolby or dbx noise reduction systems.[17]
  • Dynamic range, or signal-to-noise ratio, was usually understood as the ratio between MOL and A-weighted bias noise level.[16][18] High fidelity audio requires a dynamic range of at least 60–65 dB; the best cassettes tapes reached this threshold in the 1980s, at least partially eliminating the need for the use of noise reduction systems. Dynamic range is the most important property of the tape. The higher the dynamic range of music, the more demanding it is of tape quality; alternatively, heavily compressed music sources can do well even with basic, inexpensive tapes.[8]
  • Sensitivity of the tape, referred to that of an IEC reference tape and expressed in dB, was usually measured at 315 Hz and 10 kHz.[19]
  • Stability of playback in time. Low-quality or damaged cassette tape is notoriously prone to signal dropouts, which are absolutely unacceptable in high fidelity audio.[19] For high quality tapes, playback stability is sometimes lumped together with modulation noise and wow and flutter into an integral smoothness parameter.[20]

Frequency range, per se, is usually unimportant. At low recording levels (−20 dB referred to nominal level) all quality tapes can reliably reproduce frequencies from 30 Hz to 16 kHz, which is sufficient for high fidelity audio.[16] However, at high recording levels the treble output is further limited by saturation. At the Dolby recording level the upper frequency limit shrinks to a value between 8 kHz for a typical chromium dioxide tape, and 12 kHz for metal tapes; for chromium dioxide tapes, this is partially offset by lower hiss levels.[16] In practice, the extent of the high-level frequency range is not as important as the smoothness of the midrange and treble frequency response.[19]

Standards edit

 
A mark on prerecorded chromium dioxide cassette intended for replay as Type I (Decca Records, 1980s)
 
IEC I compatibility logo (BASF, 1981). These logos, advanced by BASF and the IEC, didn't catch on and were soon abandoned

The original specification for Compact Cassette was set by Philips in 1962–1963. Of the three then available tape formulations that matched Philips requirements, the BASF PES-18 tape became the original reference.[21] Other chemical companies followed with tapes of varying quality, often incompatible with the BASF reference. By 1970, a new, improved generation of tapes firmly established themselves on the market, and became the de facto reference for aligning tape recorders — thus the compatibility issue worsened even further.[21] In 1971 it was tackled by the Deutsches Institut für Normung (DIN), which set the standard for chromium dioxide tapes. In 1978 the International Electrotechnical Commission (IEC) enacted the comprehensive standard on cassette tapes (IEC 60094). One year later the IEC mandated the use of notches for automatic tape type recognition.[21] Since then, the four cassette tape types were known as IEC I, IEC II, IEC III and IEC IV.[21] The numerals follow the historical sequence in which these tape types were commercialized, and do not imply their relative quality or intended purpose.[22]

An integral part of the IEC 60094 standard family is the set of four IEC reference tapes. Type I and Type II reference tapes were manufactured by BASF, Type III reference tapes by Sony, and Type IV reference tapes by TDK.[23] Unlike consumer tapes, which were manufactured continuously over the years, each reference tape was made in a single production batch by the IEC-approved factory.[23][19] These batches were made large enough to fill the need of the industry for many years.[23] A second run was impossible, because chemists were unable to replicate the reference tape type formulation with proper precision.[23] From time to time, the IEC revised the set of references; the final revision took place in April 1994.[19] The choice of reference tapes, and the role of the IEC in general, has been debated. Meinrad Liebert, designer of Studer and Revox cassette decks, criticized the IEC for failing to enforce the standards and lagging behind the constantly changing market.[24] In 1987, Liebert wrote that while the market clearly branched into distinct, incompatible "premium" and "budget" subtypes, the IEC tried in vain to select an elusive "market average"; meanwhile, the industry moved forward, disregarding outdated references.[24] This, according to Liebert, explained sudden demand for built-in tape calibration tools that were almost unheard-of in the 1970s.[24]

From the end user viewpoint, the IEC 60094 defined two principal properties of each tape type:

  • Bias level for each type was set equal to the optimal bias of the relevant IEC reference tape, and sometimes changed when the IEC changed the reference tapes, though the BASF datasheet for the Y348M tape, approved as the IEC Type I reference in 1994, says that its optimal bias is exactly 0.0 dB from the previous reference (BASF R723DG). The IEC reference tape bias definition is: Using the relevant IEC reference tape and heads according to Ref. 1.1, the bias current providing the minimum third harmonic distortion ratio for a 1 kHz signal recorded at the reference level is the reference bias setting. Type II bias ('high bias') equals around 150% of Type I bias, Type IV bias ('metal bias') equals around 250% of Type I bias.[25] Real cassette tapes invariably deviate from the references and require fine tuning of bias; recording a tape with improper bias increases distortion and alters frequency response.[26] A 1990 comparative test of 35 Type I tapes showed that their optimal bias levels were within 1 dB of the Type I reference, while Type IV tapes deviated from the Type IV reference by up to 3 dB.[27] Some typical cassette deck frequency response curves showing the effects of different bias settings are provided in the relevant figure.
  • Time constant of replay equalization (often shortened to EQ) for Type I tapes equals 120 μs, as per the Philips specification. The time constant for Type II, III and IV tapes is set at a lower value of 70 μs. The purpose of replay equalization is to compensate for high-frequency losses during recording,[28] which, in case of ferric cassettes, usually start at around 1–1.5 kHz. The choice of time constant is a somewhat arbitrary decision, seeking the best combination of conflicting parameters — extended treble response, maximum output, minimum noise and minimum distortion.[29] High-frequency roll-off that is not fully compensated in the replay channel may be offset by pre-emphasis during recording.[29] Lower replay time constants decrease the apparent level of hiss (by 4 dB when stepping down from 120 to 70 μs), but also decrease apparent high-frequency saturation level, so the choice of time constants was a matter of compromise and debate. [30] "Hard" maximum and saturation levels, in terms of voltage output of playback head, remain unchanged. However, the high-frequency voltage level at the output of the replay equalizer decreases with a decrease in time constant.[citation needed] The industry and the IEC decided that it would be safe to decrease the time constant of Type II, III and IV tapes to 70 μs, because they are less prone to high-frequency saturation than contemporary ferric tapes.[29] Many disagreed, arguing that the risk of saturation at 70 μs is unacceptably high.[31] Nakamichi and Studer complied with the IEC, but provided an option for playing Type II and Type IV tapes using the 120 μs setting and matching pre-emphasis filters in the recording path. A similar pre-emphasis was applied by duplicators of prerecorded chromium dioxide cassettes; although loaded with Type II tape, these cassettes were packaged in Type I cassette shells and were intended to be replayed as Type I tapes.[8]

Type I edit

Type I, or IEC I, ferric or 'normal' cassettes were historically the first, the most common and the least expensive; they dominated the prerecorded cassette market.[8] The magnetic layer of a ferric tape consists of around 30% synthetic binder and 70% magnetic powder — acicular (oblong, needle-like) particles of gamma ferric oxide (γ-Fe2O3), with a length of 0.2 μm to 0.75 μm.[32] Each particle of such size contains a single magnetic domain.[33] The powder was and still is manufactured in bulk by chemical companies specializing in mineral pigments for the paint industry.[32] Ferric magnetic layers are brown in colour, whose shade and intensity depends mostly on the size of the particles.

Type I tapes must be recorded with 'normal' (low) bias flux and replayed with a 120 μs time constant. Over time, ferric oxide technology developed continuously, with new, superior generations emerging around every five years.[34] Cassettes of various periods and price points can be sorted into three distinct groups: basic coarse-grained tapes; advanced fine-grained, or microferric, tapes; and highest-grade ferricobalt tapes, having ferric oxide particles encapsulated in a thin layer of cobalt-iron compound. Ferricobalt tapes are often called 'cobalt doped', however, this is historically incorrect. Cobalt doping in a strict sense involves uniform substitution of iron atoms with cobalt.[35] This technology has been tried for audio and failed, losing to chromium dioxide.[22] Later, the industry has chosen the far more reliable and repeatable process of cobalt adsorption — encapsulation of unmodified iron oxide particles in a thin layer of cobalt ferrite.[35]

The remanence and squareness properties of the three groups substantially differ, while coercivity remains almost unchanged at around 380 Oe (360 Oe for the IEC reference tape approved in 1979[36]). Quality Type I cassettes have higher midrange MOL than most Type II tapes, slow and gentle MOL roll-off at low frequencies, but less high-frequency headroom than Type II.[13] In practice, that means that ferric tapes have lower fidelity compared to chrome tapes and metal tapes at high frequencies, but are often better at reproducing the low frequencies found in bass-heavy music.

Basic ferric edit

 
Sony C60 compact cassette (1974)

Entry-level ferric formulations are made of pure, unmodified, coarse-grained ferric oxide. Relatively large (up to 0.75 μm in length), irregularly-shaped oxide particles have protruding branches or dendrites; these irregularities prevent tight packing of particles, reducing iron content of the magnetic layer and, consequently, its remanence (1300–1400 G) and maximum output level.[37] The squareness ratio is low, around 0.75, resulting in early but smooth onset of distortion.[37] These tapes, historically labeled and sold as 'low noise', have high levels of hiss and relatively low sensitivity; their optimal bias level is 1–2 dB lower than that of the IEC reference tape.

This group also includes most of the so-called 'Type 0' cassettes — a mixed bag of ferric tapes that do not meet the IEC standard or the original Philips specification.[25][38] Historically, informal 'Type 0' denoted early cassettes loaded with tape designed for reel-to-reel recorders.[25] In the 1980s, many otherwise decent and usable basic tapes were effectively demoted to 'Type 0' status when equipment manufacturers began aligning their decks for use with premium ferricobalts (the latter having much higher sensitivity and bias).[38] In the 21st century, 'Type 0' denotes all sorts of low-quality, counterfeit or otherwise unusable cassettes. They require unusually low bias, and even then only a few of them perform on par with quality Type I tapes.[25] A 'Type 0' tape, if it is usable at all, is incompatible with Dolby noise reduction: with the Dolby decoder engaged, the tape sounds dull, resulting from its poor sensitivity causing severe Dolby mistracking.[38]

Microferric edit

In the beginning of the 1970s, gradual technological improvements over the previous decade resulted in the second generation of Type I tapes. These tapes had uniformly needle-shaped, highly orientable particles (HOP) of much smaller size, around 0.25 μm in length, hence the trade term microferrics.[9] Their uniform shape allowed very dense packing of particles, with less binder and more particles per unit volume,[9] and a corresponding rise in remanence to around 1600 G. The first microferric (TDK SD) was introduced in 1971, and in 1973 Pfizer began marketing patented microferric powder that soon became an industry standard.[39] In the 20th century, Pfizer had a strong mineral pigment division, with factories in California, Illinois and Indiana. In 1990 Pfizer sold its iron-oxide business to Harrisons & Crosfield of the United Kingdom.[40] The next step was to align needle-shaped particles in parallel with the flux lines generated by the recording head; this was done by controlled flow of liquid magnetic mix over substrate (rheological orientation),[9] or by applying a strong magnetic field while the binder was curing.[41]

Typical microferric cassettes of the 1980s had less hiss and at least 2 dB higher MOL than basic Type I tapes, at the cost of increased print-through.[42] Noise and print-through are interrelated, and directly depend on the size of oxide particles. A decrease in particle size invariably decreases noise and increases print-through. The worst combination of noise and print-through occurs in highly irregular formulations containing both unusually large and unusually small particles.[43] Small improvements continued for thirty years, with a gradual rise of squareness ratio from 0.75 to over 0.9.[9][42] Newer tapes consistently produced higher output with less distortion at the same levels of bias and audio recording signals.[9] The transition was smooth; after the introduction of new, superior tape formulations, manufacturers often kept older ones in production, selling them in different markets or under different, cheaper, designations. Thus, for example, TDK ensured that its premium microferric AD cassette was always ahead of entry-level microferric D, having finer particles and lower noise.[44]

Ferricobalt Type I edit

The third, and best performing, class of ferric tapes is made of fine ferric particles encapsulated in a thin 30 Å layer of cobalt-iron mix, similar in composition to cobalt ferrite.[45] The first cobalt-doped cassettes, introduced by 3M in 1971, had exceptionally high sensitivity and MOL for the period, and were an even match for contemporary chromium dioxide tapes[46] — hence the trade name superferrics. Of many competing cobalt-doping technologies, the most widespread was low-temperature encapsulation of ferric oxide in aqueous solution of cobalt salts with subsequent drying at 100–150 °C.[45][47] Encapsulated microferric particles retain needle-like shape and can be tightly packed into uniform anisotropic layers.[45][47] The process was first commercialized in Japan in the early 1970s.[48]

The remanence of ferricobalt cassettes is around 1750 G, resulting in around 4 dB gain in MOL and 2–3 dB gain in sensitivity compared to basic Type I tapes; their hiss level is on par with contemporary microferric formulations. The dynamic range of the best ferricobalt cassettes (true superferrics) equals 60–63 dB, and the MOL at lower frequencies exceeds the MOL of Type IV tapes. Overall, superferrics are a good match to Type IV, especially in recording acoustical music with a wide dynamic range.[49][38] This was reflected in the price of top-of-the-line superferric tapes like Maxell XLI-S or TDK AR-X, which by 1992 matched the price of 'entry-level' metal tapes.

Type II edit

 
The TDK KR (Krom) was the company's only chrome tape ever made. In 1974-1975, as soon as TDK had ferricobalt technology going, they killed chrome production altogether.
 
All Type II cassettes made by TDK after 1975 (SA, SA-X, SA-XS shown) were ferricobalts, not chromes

IEC Type II tapes are intended for recording using high (150% of normal) bias and replay with the 70 μs time constant. All generations of Type II reference tapes, including the 1971 DIN reference that pre-dated the IEC standard, were manufactured by BASF. Type II has been historically known as 'chromium dioxide tape' or simply 'chrome tape', but in reality most Type II cassette tapes do not contain chromium.[50] The "pseudochromes" (including almost all Type IIs made by the Big Three Japanese makers — Maxell, Sony and TDK) are actually ferricobalt formulations optimized for Type II recording and playback settings.[50][51] A true chrome tape may have a distinctive 'old crayon' smell, more specifically, any oil or wax chalks that have chrome dioxide pigments in them like chrome yellow, which is missing in "pseudochromes". Both kinds of Type II tapes have, on average, lower high-frequency MOL and SOL, and higher signal-to-noise ratio than quality Type I tapes.[52] This is caused by the midrange and treble pre-emphasis applied during recording to match the 70 μs equalization at playback.[52]

Chromium dioxide edit

In the middle of 1960s, DuPont created and patented an industrial process for making fine ferromagnetic particles of chromium dioxide (CrO2). The first CrO2 tapes for data and video appeared in 1968.[41] In 1970, BASF, who would become the main proponent of CrO2, launched its chrome cassette production;[51] in the same year Advent introduced the first cassette deck with chrome capability and Dolby noise reduction. The combination of low noise CrO2 tape with companding noise reduction brought a revolutionary improvement to compact-cassette sound reproduction, almost reaching the high fidelity level. However, CrO2 tape required redesign of the bias and replay equalization circuitry. This problem was resolved during the 1970s,[53] but three unsolved issues remained: the cost of making CrO2 powder, the cost of royalties charged by DuPont, and the pollution effects of hexavalent chromium waste.[54][51]

The reference CrO2 tape, approved by the IEC in 1981, is characterized by coercivity of 490 Oe (high bias) and remanence of 1650 G.[55][48] Retail CrO2 cassettes had coercivity in the range from 400 to 550 Oe.[56] Owing to the very 'clean', uniform shape of the particles, chrome tapes easily attain an almost perfect squareness ratio of 0.90.[48][57] 'True chromes', not modified by the addition of ferric additives or coatings, have very low and euphonic hiss (bias noise), and very low modulation noise at high frequencies.[58][8] Double-layer CrO2 cassettes have the lowest absolute noise among all the audio formulations; these cassettes generate less noise at 4.76 cm/s than a ferric tape at 19.05 cm/s.[53] Their sensitivity is usually also very high, but MOL is low, on par with basic Type I tapes. CrO2 tape does not tolerate overload very well: the onset of distortion is sharp and dissonant, so recording levels should be set conservatively, well below MOL.[58] At low frequencies, the MOL of CrO2 tapes rolls off faster than in ferric or metal tapes, hence the reputation of 'bass shyness'. CrO2 cassettes are best fit for recording dynamic music with rich harmonic content and relatively low bass levels;[58] their dynamic range is a good fit for recording from uncompressed digital sources[34] and for music with extended quiet passages.[8] Good ferric tapes may have the same or higher treble SOL, but CrO2 tapes still sound subjectively better owing to lower hiss and modulation noise.[59]

Ferricobalt Type II edit

 
Sony Chrome compact cassette (1976)
 
BASF Chrome Extra II cassette (1988)
 
Frequency response and noise level of the Nakamichi SX Type II cassette tape tested using a Nakamichi 600 two-head cassette deck

After the introduction of CrO2 cassettes, Japanese companies began developing a royalty-free alternative to DuPont's patent, based on an already established cobalt doping process.[48] A controlled increase in cobalt content causes an almost linear increase in coercivity, thus a Type II "pseudochrome" tape can be made by simply adding around 3% cobalt to a Type I ferricobalt tape.[35] By 1974 the technology was ready for mass production, and TDK and Maxell introduced their classic "pseudochromes" (TDK SA and Maxell UD-XL), while killing their true chrome lines (TDK KR and Maxell CR). By 1976, ferricobalt formulations took over the video tape market,[60] and eventually they became the dominant high-performance tape for audio cassette.[51] Chromium dioxide disappeared from the Japanese domestic market,[51] although chrome remained the tape of choice for high fidelity cassette duplication among the music labels. In consumer markets, chrome coexisted as a distant second with "pseudochromes" until the very end of the cassette era. Ferricobalt technology developed continuously: in the 1980s Japanese companies introduced 'premium' double-layered ferricobalts with exceptionally high MOL and SOL; in the middle of the 1990s TDK launched the first and only triple-coated ferricobalt, the SA-XS.[61][62]

The electromagnetic properties of Type II ferricobalts are very close to those of their Type I cousins. Owing to the use of 70 μs replay equalization, the hiss level is lower, but so is the treble saturation level. The dynamic range of Type II ferricobalts, according to the 1990 tests, lies between 60 and 65 dB. The coercivity of 580–700 Oe and remanence of 1300–1550 G are close to the CrO2 reference tape, but the difference is big enough to cause compatibility problems.[50] TDK SA was the informal reference in Japan. TDK advertisements boasted that "more decks are aligned to SA than any other tape", but there is very little first-hand information on which tapes were actually used at the factories. Japanese manufacturers provided lists of recommended tapes but did not disclose their reference tapes. There is, however, enough indirect information converging on TDK SA. For example, in 1982, when Japanese-owned Harman Kardon sent samples for Dolby certification, they were aligned to the IEC CrO2 reference. However, production copies of the same models were aligned to TDK SA.[63] Since the Japanese already dominated both the cassette and hi-fi equipment markets, incompatibility further undermined the market share of European-made cassette decks and CrO2 cassettes.[64] In 1987, the IEC resolved the compatibility issue by appointing a new Type II reference tape U 564 W, a BASF ferricobalt with properties that were very close to contemporary TDK tapes. With the short-lived 1988 Reference Super, even BASF started the manufacture and sale of Type II ferricobalt tapes.[65][66]

Metal particle Type II edit

The coercivity of iron-cobalt metal particle mix, precipitated from aqueous solutions, depends on the cobalt content. A change in cobalt content from 0% to 30% causes a gradual rise in coercivity from around 400 Oe (Type I level) to 1300 Oe (Type IV level); alloyed iron-cobalt particles can reach a coercivity of 2200 Oe.[67] This makes possible manufacturing of metal particle tapes conforming to Type II and even Type I biasing requirements.[68]

In practice, only Denon, Taiyo Yuden, and, for only a few years, TDK, ever attempted making Type II metal tape. These rare expensive cassettes were characterized by high remanence, approaching that of Type IV tapes (2600 G); their coercivity of 800 Oe was closer to Type II than Type IV tapes, but still quite far from either type reference.[69] Independent tests of the 1990 Denon and Taiyo Yuden tapes placed them at the very top of the Type II spectrum — if the recording deck could cope with unusually high sensitivity and provide unusually high bias current.[70]

Type III edit

In 1973, Sony introduced double-layer ferrichrome tapes having a five-micron ferric base coated with one micron of CrO2 pigment.[71][51] The new cassettes were advertised as 'the best of both worlds' — combining the good low-frequency MOL of microferric tapes with good high-frequency performance of chrome tapes.[42][22] The novelty became part of the IEC standard, codenamed Type III; the Sony CS301 formulation became the IEC reference.[23] However, the idea failed to attract followers. Apart from Sony, only BASF, Scotch and Agfa introduced their own ferrichrome cassette tapes.[72]

These expensive ferrichrome tapes never gained substantial market share, and after the release of metal tapes they lost their perceived exclusivity.[51][42] Their place in the market was taken over by superior and less expensive ferricobalt formulations.[51][42] By 1983, tape deck manufacturers stopped providing an option for recording Type III tapes.[23] Ferrichrome tape remained in the BASF and Sony lineups until 1984[72] and 1988,[73] respectively.

The use of ferrichrome tapes was complicated by the conflicting rationale of the playback of these tapes. Officially, they were intended to be played back using 70 μs equalisation. The information leaflet that Sony included in each box of ferrichrome cassette tapes recommended that, "If the selector has two positions, NORMAL and CrO2, set it to the NORMAL position."[74] (which applies 120 μs equalisation). The leaflet notes that the high frequency range will be enhanced and that the tone control should be adjusted to compensate. The same leaflet recommends that if the playback machine offers a 'Fe-Cr' selection, that this should be selected. On Sony's machines, this automatically selects 70 μs equalisation. The service manual for the Sony TC-135SD, which was one of the few cassette decks offering a 'Fe-Cr' position, shows the tape type selector switch paralleling the ferrichrome equalisation selection with that of chrome dioxide (70 μs).[75] Neither Sony nor BASF cassette tapes feature the notches on the back surface that automatically select 70 μs equalisation on those machines that featured an automatic detection system.

Type IV edit

Metal particle Type IV edit

 
 
Top-of-the-line Type IV cassettes were packaged in expensive, precision-engineered shells. The TDK MA-R shell (left) had a rigid alloy frame, the Sony Metal Master (right) had ceramic shell halves and a ceramic tape guide insert
 
Frequency response and noise analysis of Nakamichi ZX Metal Particle Type IV cassette tape using the Nakamichi LX-5 three-head cassette deck

Pure metal particles have an inherent advantage over oxide particles due to 3–4 times higher remanence, very high coercivity and far smaller particle size, resulting in both higher MOL and SOL values.[76][77] First attempts to make metal particle (MP) tape, rather than metal oxide particle tape, date back to 1946; viable iron-cobalt-nickel formulations appeared in 1962.[56] In the early 1970s, Philips began development of MP formulations for the Compact Cassette.[64] Contemporary powder metallurgy could not yet produce fine, submicron size particles, and properly passivate these highly pyrophoric powders.[78][79] Although the latter problems were soon solved,[78] the chemists did not convince the market in terms of the long-term stability of MP tapes; suspicions of inevitable early degradation persisted until the end of the cassette era.[56] The fears did not materialize,[56] and most metal particle tapes survived decades of storage just as well as Type I tapes; however, signals recorded on metal particle tapes do degrade at about the same rate as in chromium tapes, around 2 dB over the estimated lifetime of the cassette.[80][81]

Metal particle Compact Cassettes, or simply 'metal' tapes, were introduced in 1979 and were soon standardized by the IEC as Type IV.[56][79] They share the same 70 μs replay time constant as Type II tapes, and can be correctly reproduced by any deck equipped with Type II equalization.[19] Recording onto a metal tape requires special high-flux magnetic heads and high-current amplifiers to drive them.[19][79] Typical metal tape is characterized by remanence of 3000–3500 G and coercivity of 1100 Oe, thus its bias flux is set at 250% of Type I level.[42][56][82][19] Traditional glass ferrite heads would saturate their magnetic cores before reaching these levels. "Metal capable" decks had to be equipped with new heads built around sendust or permalloy cores, or the new generation of glass ferrite heads with specially treated gap materials.[83]

Metal particle tapes, particularly top-of-the-line double coated tapes, have record high midrange MOL and treble SOL, and the widest dynamic range coupled with the lowest distortion.[84] They were always expensive, almost exclusive, out of reach of most consumers.[84] They excel at reproducing fine nuances of uncompressed acoustic music, or music with very high treble content, like brass and percussion.[84][8] However, they need a high quality, properly aligned deck to reveal their potential.[84][8] First-generation metal particle tapes were consistently similar in their biasing requirements, but by 1983 newer formulations drifted away from each other and the reference tape.[85]

Metal evaporated edit

Unlike wet coating processes, metal evaporated (ME) media are fabricated by physical deposition of vaporized cobalt or cobalt-nickel mix in a vacuum chamber.[86] There is no synthetic binder to hold particles together; instead, they adhere directly to polyester tape substrate.[86][79] An electron beam melts source metal, creating a continuous directional flow of cobalt atoms towards the tape.[86] The zone of contact between the beam and the tape is blown with a controlled flow of oxygen, which helps formation of polycrystalline metal-oxide coating.[86] A massive liquid-cooled rotating drum, which pulls the tape into the contact zone, protects it from overheating.[86]

Metal evaporated coatings, along with barium ferrite, have the highest information density of all rerecordable media.[87] The technology was introduced in 1978 by Panasonic, initially in the form of audio microcassettes, and matured through the 1980s.[87][79] Metal evaporated media established itself in analogue (Hi8) and digital (Digital8, DV and MicroMV) videotape market, and data storage (Advanced Intelligent Tape, Linear Tape Open).[87] The technology seemed promising for analogue audio recording; however, very thin metal evaporated layers were too fragile for consumer cassette decks, the coatings too thin for good MOL,[79] and manufacturing costs were prohibitively high. Panasonic Type I, Type II and Type IV metal evaporated cassettes, introduced in 1984, were sold for only a few years in Japan alone, and remained unknown in the rest of the world.[79]

Measured performance characteristics edit

 
Comparison of typical MOL, SOL, and 0-dB frequency responses for sample Type I, Type II, and Type IV cassette tapes
 
Frequency response plots of some sample Type I, Type II, and Type IV cassette tapes

During the many years that cassette decks were popular, many audio magazines published comparative measurements of the performance characteristics of the wide variety of different tapes that were available in the marketplace.[88][89][90][91][92][93] [94] These measurements typically included parameters such as MOL, SOL, frequency response at 0-dB and −20-dB re Dolby Level, signal-to-noise ratio, modulation noise, bias level, and sensitivity. The first figure shows frequency response plots for sample Type I, Type II, and Type IV cassette tapes comparing their MOL, SOL, and 0-dB performance.

The second figure shows the frequency response performance of typical Type I, Type II, and Type IV cassette tapes, obtained for a number of different input signal levels, using a high quality Pioneer CT-93 stereo cassette deck from the 1990s.[95][94] For each of the three tape formulations, the record/replay characteristics of the cassette deck were aligned with the relevant IEC Reference Tape, and each tested tape was measured with the bias and equalization unchanged from that reference position. The record/replay frequency response was tested at four levels: +6 VU, 0 VU, −10 VU and −20 VU (Dolby Level is marked at +3 VU for the CT-93). Thus, these plots provide data on the linearity of the different tape formulations at both high and moderate recording levels. It is interesting to note that the Type I tape shows +6 VU and at 0 VU responses that are much flatter than that of the Type II tape. At +6 VU, the Type II tape displays significant amounts of signal level compression across the entire frequency range, reducing to about 2 dB of signal compression between 80 Hz and 1 kHz.

Some representative measured performance characteristics of a small number of commercially available tape types are presented in the table below.[90][88]

Maximum Output Level
(dB re 400-Hz Dolby Level)
3% Harmonic
Distortion 		3% Twin-Tone
Intermodulation 		High-Frequency
−3 dB Point
(kHz)
Tape Type 100 400 1k 2k 5k 10k S/N
Ratio
(dBA) 		0-dB
Input
Level 		−20-dB
Input
Level 		Mod.
Noise
(dB) 		Bias
(dB) 		Sens.
(dB)
BASF LH-MI I +4.0 +4.8 +5.6 +0.8 −2.4 −8.8 58.3 10.6 — −45.7 +0.4 −0.3
Maxell UR I +3.9 +4.3 +4.4 +0.5 −2.5 −9.0 57.0 9.8 — −43.8 −0.5 0.0
Maxell UD-XL I I +6.5 +6.8 +6.8 +0.8 −2.0 −8.5 58.8 10.0 23.9 −46.3 +0.1 +0.9
Sony HF I +2.0 +2.4 +2.5 −0.9 −4.1 −10.3 54.3 8.9 — −36.1 −0.9 −1.0
TDK D I +2.6 +3.5 +4.5 0.0 −3.1 −9.6 55.5 9.3 22.9 −45.4 −0.1 −1.0
TDK AD I +3.8 +6.2 +6.2 +1.3 −1.7 −8.2 60.3 9.9 23.2 −44.3 +0.5 −0.3
BASF CR-Mll II +4.8 +5.4 +4.0 −4.0 −8.3 −12.8 63.0 7.3 — −51.0 +1.0 +1.0
Maxell UD-XL II II +4.4 +5.2 +5.1 −2.1 −5.6 −10.6 60.4 9.2 22.1 −48.0 −0.1 +1.7
Memorex CDXII II +5.7 +6.3 +6.1 −0.4 −3.1 −6.9 61.2 11.9 — −47.4 +1.3 +2.9
TDK SA II +3.4 +4.4 +4.9 −1.9 −5.7 −11.2 60.9 8.9 20.3 −47.2 +0.1 +1.1
TDK SA-X II +3.7 +4.4 +3.6 −2.8 −7.3 −11.5 63.2 7.8 23.8 −47.8 +1.0 +1.6
Maxell MX IV +8.0 +9.1 +9.5 +2.3 −1.9 −6.8 62.7 12.5 25.0 −50.4 +0.1 +0.8
Sony Metal-ES IV +8.8 +10.2 +10.3 +2.1 −2.4 −7.1 66.0 12.5 — −50.8 +0.6 +2.0

References edit

  1. ^ Ankosko, Bob (1993). "Tape Buying Gude". Stereo Review (March): 56 (JVC, Maxell prices).
  2. ^ Roberson, Howard A. (January 1981). "All That Data: Tape Deck Frequency Response And Headroom" (PDF). Audio. pp. 74–84.
  3. ^ Брагинский & Тимофеев 1987, p. 21.
  4. ^ Козюренко 1998, p. 23.
  5. ^ a b Jones & Manquen 2008, pp. 1066, 1068.
  6. ^ "Blank Tape Firms Ready Promotions". Billboard. 11 January 1986. p. 32.
  7. ^ Брагинский & Тимофеев 1987, p. 57.
  8. ^ a b c d e f g h Mitchell 1984, p. 42.
  9. ^ a b c d e f g h i Jones & Manquen 2008, pp. 1067, 1068.
  10. ^ Брагинский & Тимофеев 1987, pp. 29, 58–59.
  11. ^ Козюренко 1998, p. 22.
  12. ^ Козюренко 1998, p. 33.
  13. ^ a b Roberson 1990, p. 53.
  14. ^ Roberson 1990, p. 47.
  15. ^ Roberson 1990, p. 58.
  16. ^ a b c d e f Stark 1992, p. 46.
  17. ^ Козюренко 1998, p. 34.
  18. ^ Козюренко 1998, pp. 13–14.
  19. ^ a b c d e f g h Козюренко 1998, p. 32.
  20. ^ Roberson 1990, p. 48.
  21. ^ a b c d "History of Compact Cassette". 2012.
  22. ^ a b c Foster 1984, p. 456.
  23. ^ a b c d e f Feldman, Len (1983). "International Tape Standardization" (PDF). Modern Recording and Music. 9 (1): 28–29.
  24. ^ a b c Liebert, Meinrad (1987). "Revox B215 automatic calibration. The perfect compromise" (PDF). Swiss Sound (19): 4–6.
  25. ^ a b c d "A quick guide to tape types" (PDF). High Fidelity (11): 29. 1982.
  26. ^ Козюренко 1998, pp. 34–35.
  27. ^ Roberson 1990, pp. 47, 52, 58.
  28. ^ Burstein 1985, p. 74.
  29. ^ a b c Burstein 1985, p. 76.
  30. ^ Burstein 1985, pp. 76, 79.
  31. ^ Burstein 1985, pp. 79–80.
  32. ^ a b Mallinson 2012, p. 29.
  33. ^ Mallinson 2012, p. 24.
  34. ^ a b Jones 1985, p. 85.
  35. ^ a b c Camras 2012, p. 108.
  36. ^ "BASF International Reference Tape IEC I. Iron Oxide Tape - Batch R723DG". BASF. 1979. {{cite journal}}: Cite journal requires |journal= (help)
  37. ^ a b Jones & Manquen 2008, p. 1067.
  38. ^ a b c d Mitchell 1984, p. 43.
  39. ^ Clark 1999, p. 104.
  40. ^ "Pfizer sells iron-oxide pigment unit". The Morning Call. 1990-03-31.
  41. ^ a b Брагинский & Тимофеев 1987, p. 29.
  42. ^ a b c d e f Capel 2016, p. 116.
  43. ^ Jones & Manquen 2008, p. 1072.
  44. ^ Camras 2012, p. 116.
  45. ^ a b c Mallinson 2012, p. 31.
  46. ^ Free, John (1971). "How Good Are Those New Tapes?". Popular Science (November): 89, 130.
  47. ^ a b Брагинский & Тимофеев 1987, p. 173.
  48. ^ a b c d Mallinson 2012, p. 32.
  49. ^ Козюренко 1998, p. 27.
  50. ^ a b c Foster 1984, p. 457.
  51. ^ a b c d e f g h Kimizuka 2012, p. 227.
  52. ^ a b Roberson 1987, p. 57.
  53. ^ a b Free, J. (1977). "Cassette tapes for higher hi-fi". Popular Science (June): 50–53.
  54. ^ Брагинский & Тимофеев 1987, pp. 163–164, 183.
  55. ^ "BASF International Reference Tape IEC II. Chromium Dioxide Tape - Batch S4592A". BASF. 1981. {{cite journal}}: Cite journal requires |journal= (help)
  56. ^ a b c d e f Camras 2012, p. 33.
  57. ^ Jones & Manquen 2008, p. 1068.
  58. ^ a b c Козюренко 1998, pp. 28, 30.
  59. ^ Booth 1989, p. 65.
  60. ^ Kirsh, B. (17 February 1973). "Blank TV Tape Production Heats Up Chrome vs Cobalt Battle". Billboard. p. 38.
  61. ^ "TDK Europe 1995-1997". Vintagecassettes.com. 2005–2014.
  62. ^ Козюренко 1998, p. 29.
  63. ^ Hirsch, Julian (1982). "Harman Kardon hk705 Cassette Deck" (PDF). Stereo Review's Tape Recording & Buying Guide: 37–38.
  64. ^ a b "Cassette users set for another ride?" (25 August). New Scientist. 1977: 478. {{cite journal}}: Cite journal requires |journal= (help)
  65. ^ Block, Debbie (25 July 1992). "New Wine in Old Cassettes". Billboard. pp. TD-3, TD-7.
  66. ^ "BASF Chrome Tape Formulations". Vintagecassettes.com. 2005–2014.
  67. ^ Camras 2012, pp. 108, 113.
  68. ^ Camras 2012, pp. 113–114.
  69. ^ Booth 1989, p. 64.
  70. ^ Roberson 1990, pp. 58–59.
  71. ^ Eguchi, Hideo (1973). "Oxide+Chrome Blanks Add to Coatings Output". Billboard. No. October 6.
  72. ^ a b "BASF 1984". Vintagecassettes.com. 2005–2014.
  73. ^ "Sony 1988-89 Japan". Vintagecassettes.com. 2005–2014.
  74. ^ SONY information leaflet ref 3-780-439-11(1&2)
  75. ^ "Sony TC-135SD Stereo Cassette Deck (1975–76)". hifiengine.com.
  76. ^ Camras 2012, p. 111.
  77. ^ Mitchell 1984, p. 41.
  78. ^ a b Брагинский & Тимофеев 1987, p. 176.
  79. ^ a b c d e f g Kimizuka 2012, p. 228.
  80. ^ Bogart, John W. C. Van (1995). Magnetic Tape Storage and Handling. A Guide for Libraries and Archives (PDF). Commission on Preservation and Access. pp. 5, 7. ISBN 1887334408.
  81. ^ Bressan, F. (2019). "Chemistry for Audio Heritage Preservation: A Review of Analytical Techniques for Audio Magnetic Tapes". Heritage. 2 (2): 1559, 1568. doi:10.3390/heritage2020097. hdl:1854/LU-8609085.
  82. ^ Mallinson 2012, p. 33.
  83. ^ Козюренко 1998, pp. 32, 66.
  84. ^ a b c d Козюренко 1998, pp. 29, 31.
  85. ^ Foster 1984, p. 458.
  86. ^ a b c d e Jubert & Onodera 2012, pp. 69–70.
  87. ^ a b c Jubert & Onodera 2012, p. 67.
  88. ^ a b Roberson, Howard A. (September 1983). "Mass Tape Test: 77 Cassettes Rated" (PDF). Audio. pp. 34–44.
  89. ^ Beekhuyzen, Hans (July 1984). "Test 35 Cassettes". Audio & Techniek. pp. 53–69.
  90. ^ a b Roberson, Howard A. (June 1986). "Cassette Test Update: 49 Formulations" (PDF). Audio. pp. 74–84.
  91. ^ Roberson, Howard A. (November 1987). "Mass Cassette Test: We Review 35 New Tapes" (PDF). Audio. pp. 50–61.
  92. ^ Roberson, Howard A. (March 1990). "Greatest Cassette Test Ever: 88 Tapes Tested" (PDF). Audio. pp. 47–58.
  93. ^ Schüller, Peter (November 1990). "Grupen Dynamik Test 48 Cassetten". Stereoplay. pp. 62–83.
  94. ^ a b Challis, Louis (November 1991). "A Review of Current Cassette Tapes" (PDF). Electronics Australia. pp. 10–17.
  95. ^ Challis, Louis (October 1991). "Pioneer's CT-93 Stereo Cassette Deck" (PDF). Electronics Australia. pp. 8–13.

Bibliography edit

  • Booth, Stephen (1989). "Tale of the Tapes". Popular Mechanics (November): 63–65.
  • Burstein, Herman (1985). "The Whys and Hows of Cassette Equalization" (PDF). Audio (6): 72–81.
  • Camras, Marvin (2012). Magnetic Recording Handbook. Springer. ISBN 9789401094689.
  • Capel, Vivian (2016). Newnes Audio and Hi-Fi Engineer's Pocket Book. Newnes/Elsevier. ISBN 9781483102436.
  • Clark, Mark H. (1999). "Product Diversification". Magnetic Recording: The First 100 Years. IEEE Press. pp. 92–109. ISBN 9780780347090.
  • Foster, Edward (1984). "Statement on Copyright Aspects of Audio Recorders and Blank Tapes". Video and Audio Home Taping. Hearing Before the Subcommittee on Patents, Copyrights, and Trademarks, volume 4. U.S. Government Printing Office. pp. 443–467.
  • Hodges, R. (1978). "The Cassette: A Short History" (PDF). HiFi/Stereo Review (2): 26.
  • Jones, D.; Manquen, D. (2008). "Chapter 28. Magnetic Recording and Playback". Handbook for Sound Engineers, Fourth Edition. Focal Press / Elsevier. ISBN 9780240809694.
  • Jones, Mike (1985). "Cassette Quality: What is the industry doing?" (PDF). Audio (6): 82–86.
  • Jubert, P.-O.; Onodera, S. (2012). "Metal Evaporated Media". In Buschow, K.H.J. (ed.). Handbook of Magnetic Materials, vol. 20. Elsevier. pp. 65–122. ISBN 9780444563774.
  • Kefauver, Alan (2001). The Audio Recording Handbook. A-R Editions, Inc. pp. 253–263. ISBN 9780895794628.
  • Kimizuka, Masanori (2012). "Historical Development of Magnetic Recording and Tape Recorder" (PDF). National Museum of Nature and Science. Survey Reports on the Systemization of Technologies. 17 (August): 185–275.
  • Mallinson, John C. (2012). The Foundations of Magnetic Recording. Elsevier. ISBN 9780080506821.
  • Mitchell, Peter W. (1984). "Choosing Tape" (PDF). Stereo Review (March): 41–43.
  • Morton, David (2006). Sound Recording: The Life Story of a Technology. JHU Press. ISBN 9780801883989.
  • Stark, Craig (1992). "Choosing the Right Tape" (PDF). Stereo Review (March): 45–48.
  • Talbot-Smith, Michael (2013). Audio Engineer's Reference Book. CRC Press. ISBN 9781136119743.
  • Брагинский, Г. И.; Тимофеев, Е. Н. (1987). Технология магнитных лент [Magnetic Tape Technology] (in Russian). Химия. ISBN 5724500558.
  • Козюренко, Ю. И. (1998). Современные магнитофоны, плееры, диктофоны и наушники [Modern tape recorders, players, dictation devices and headphones] (in Russian). ДМК. ISBN 5898180087.

January 01, 1970
compact, cassette, tape, types, formulations, audio, compact, cassettes, magnetic, tape, three, major, types, which, differ, fundamental, magnetic, properties, level, bias, applied, during, recording, optimal, time, constant, replay, equalization, specificatio. Audio compact cassettes use magnetic tape of three major types which differ in fundamental magnetic properties the level of bias applied during recording and the optimal time constant of replay equalization Specifications of each type were set in 1979 by the International Electrotechnical Commission IEC Type I IEC I ferric or normal tapes Type II IEC II or chrome tapes Type III IEC III ferrichrome or ferrochrome and Type IV IEC IV or metal tapes Type 0 was a non standard designation for early compact cassettes that did not conform to IEC specification Differences in tape colour of most common tape formulations top to bottom ferric ferricobalt chromium dioxide and metal particle cassettesStandardized notches for automatic tape selection Top to bottom Type I and Type III Type II Type IV By the time the specifications were introduced Type I included pure gamma ferric oxide formulations Type II included ferricobalt and chromium IV oxide formulations and Type IV included metal particle tapes the best performing but also the most expensive Double layer Type III tape formulations advanced by Sony and BASF in the 1970s never gained substantial market presence In the 1980s the lines between three types blurred Panasonic developed evaporated metal tapes that could be made to match any of the three IEC types Metal particle tapes migrated to Type II and Type I ferricobalt formulations migrated to Type I By the end of the decade performance of the best Type I ferricobalt tapes superferrics approached that of Type IV tapes performance of entry level Type I tapes gradually improved until the very end of compact cassette production 1 Contents 1 Specifications 1 1 Magnetic properties 1 2 Electromagnetic properties 2 Standards 3 Type I 3 1 Basic ferric 3 2 Microferric 3 3 Ferricobalt Type I 4 Type II 4 1 Chromium dioxide 4 2 Ferricobalt Type II 4 3 Metal particle Type II 5 Type III 6 Type IV 6 1 Metal particle Type IV 6 2 Metal evaporated 7 Measured performance characteristics 8 References 9 BibliographySpecifications edit nbsp Coercivity and remanence marked on the wrapper of a professional cassette TDK AM ca 1995 These are typical values for a microferric cassette nbsp MOL SOL bias noise and dynamic range marked on the wrapper of a superferric cassette TDK AR 1990s The values approach the limits of ferric tape technology nbsp Frequency response curves of a typical cassette tape showing the effects of different bias settings after Roberson 2 Magnetic properties edit Magnetic recording relies on the use of hard ferrimagnetic or ferromagnetic materials These require strong external magnetic fields to be magnetized and retain substantial residual magnetization after the magnetizing field is removed 3 Two fundamental magnetic properties relevant for audio recording are Saturation remanence limits maximum output level and indirectly dynamic range of audio recordings 4 Remanence of audio tapes referred to quarter inch tape width varies from around 1100 G for basic ferric tapes to 3500 G for Type IV tapes 5 advertised remanence of the 1986 JVC Type IV cassette reached 4800 G 6 Coercivity is a measure of the external magnetic flux required to magnetize the tape and an indicator of the necessary bias level The coercivity of audio tapes varies from 350 Oe to 1200 Oe High coercivity particles are more difficult to erase bias and record but also less prone to high frequency losses during recording and to external interference and self demagnetization during storage 5 7 8 A useful figure of merit of tape technology is the squareness ratio of the hysteresis curve 9 It is an indicator of tape uniformity and its linearity in analogue recording 9 An increase in the squareness ratio defers the onset of compression and distortion and allows fuller utilization of the tape s dynamic range within the limits of remanence 9 10 The squareness ratio of basic ferric tapes rarely exceeds 0 75 and the squareness ratio of the best tapes exceeds 0 9 9 Electromagnetic properties edit nbsp Hysteresis curves of Type I CrO2 Type II and Type IV tapes 11 On this chart the vertical span is remanence remaining magnetism a rough indicator of maximum recording output level The horizontal span shows coercivity how much flux it takes to magnetize the tapes Manufacturers of bulk tape provided extremely detailed technical descriptions of their product with numerous charts and dozens of numeric parameters From the end user viewpoint the most important electromagnetic properties of the tape are Maximum output levels usually specified in dB relative to the nominal zero reference level of 250 nWb m or the Dolby level of 200 nWb m Often incorrectly called recording levels these are always expressed in terms of the tape s output thus taking its sensitivity out of the equation Performance at low and middle and at treble frequencies was traditionally characterized by two related but different parameters Maximum output level MOL is relevant at low and middle frequencies It is usually specified at 315 Hz MOL315 or 400 Hz MOL400 and its value marks the point when the third harmonic coefficient reaches 3 12 Further magnetization of the tape is technically possible but at the cost of unacceptable compression and distortion For all types of tape MOL reaches a maximum in the 125 800 Hz area while dropping off below 125 Hz and above 800 Hz 13 The maximum output of Type I tape at 40 Hz is 3 5 dB lower than MOL400 14 while in Type IV tapes it is 6 7 dB lower 15 As a result ferric tapes handle bass heavy music with apparent ease compared to expensive metal tapes Double layer Type III IEC III ferrichrome or ferrochrome tape formulations were supposed to allow bass frequencies to be recorded deeper into the ferric layer while keeping the high frequencies in the upper chromium oxide layer At treble frequencies the playback head cannot reliably reproduce harmonics of the recorded signal 16 This makes distortion measurements impossible instead of MOL high frequency performance is characterized by saturation output level SOL usually specified at 10 kHz SOL10k 16 Once the tape reaches saturation point any further increase in recording flux actually decreases output to below SOL 16 Noise level usually understood as bias noise hiss of a tape recorded with zero input signal replayed without noise reduction A weighted and referred to the same level as MOL and SOL The difference between bias noise and the noise of virgin tape is an indicator of tape uniformity Another important but rarely quantified type of noise is modulation noise which appears only in the presence of a recorded signal and which cannot be reduced by Dolby or dbx noise reduction systems 17 Dynamic range or signal to noise ratio was usually understood as the ratio between MOL and A weighted bias noise level 16 18 High fidelity audio requires a dynamic range of at least 60 65 dB the best cassettes tapes reached this threshold in the 1980s at least partially eliminating the need for the use of noise reduction systems Dynamic range is the most important property of the tape The higher the dynamic range of music the more demanding it is of tape quality alternatively heavily compressed music sources can do well even with basic inexpensive tapes 8 Sensitivity of the tape referred to that of an IEC reference tape and expressed in dB was usually measured at 315 Hz and 10 kHz 19 Stability of playback in time Low quality or damaged cassette tape is notoriously prone to signal dropouts which are absolutely unacceptable in high fidelity audio 19 For high quality tapes playback stability is sometimes lumped together with modulation noise and wow and flutter into an integral smoothness parameter 20 Frequency range per se is usually unimportant At low recording levels 20 dB referred to nominal level all quality tapes can reliably reproduce frequencies from 30 Hz to 16 kHz which is sufficient for high fidelity audio 16 However at high recording levels the treble output is further limited by saturation At the Dolby recording level the upper frequency limit shrinks to a value between 8 kHz for a typical chromium dioxide tape and 12 kHz for metal tapes for chromium dioxide tapes this is partially offset by lower hiss levels 16 In practice the extent of the high level frequency range is not as important as the smoothness of the midrange and treble frequency response 19 Standards edit nbsp A mark on prerecorded chromium dioxide cassette intended for replay as Type I Decca Records 1980s nbsp IEC I compatibility logo BASF 1981 These logos advanced by BASF and the IEC didn t catch on and were soon abandoned The original specification for Compact Cassette was set by Philips in 1962 1963 Of the three then available tape formulations that matched Philips requirements the BASF PES 18 tape became the original reference 21 Other chemical companies followed with tapes of varying quality often incompatible with the BASF reference By 1970 a new improved generation of tapes firmly established themselves on the market and became the de facto reference for aligning tape recorders thus the compatibility issue worsened even further 21 In 1971 it was tackled by the Deutsches Institut fur Normung DIN which set the standard for chromium dioxide tapes In 1978 the International Electrotechnical Commission IEC enacted the comprehensive standard on cassette tapes IEC 60094 One year later the IEC mandated the use of notches for automatic tape type recognition 21 Since then the four cassette tape types were known as IEC I IEC II IEC III and IEC IV 21 The numerals follow the historical sequence in which these tape types were commercialized and do not imply their relative quality or intended purpose 22 An integral part of the IEC 60094 standard family is the set of four IEC reference tapes Type I and Type II reference tapes were manufactured by BASF Type III reference tapes by Sony and Type IV reference tapes by TDK 23 Unlike consumer tapes which were manufactured continuously over the years each reference tape was made in a single production batch by the IEC approved factory 23 19 These batches were made large enough to fill the need of the industry for many years 23 A second run was impossible because chemists were unable to replicate the reference tape type formulation with proper precision 23 From time to time the IEC revised the set of references the final revision took place in April 1994 19 The choice of reference tapes and the role of the IEC in general has been debated Meinrad Liebert designer of Studer and Revox cassette decks criticized the IEC for failing to enforce the standards and lagging behind the constantly changing market 24 In 1987 Liebert wrote that while the market clearly branched into distinct incompatible premium and budget subtypes the IEC tried in vain to select an elusive market average meanwhile the industry moved forward disregarding outdated references 24 This according to Liebert explained sudden demand for built in tape calibration tools that were almost unheard of in the 1970s 24 From the end user viewpoint the IEC 60094 defined two principal properties of each tape type Bias level for each type was set equal to the optimal bias of the relevant IEC reference tape and sometimes changed when the IEC changed the reference tapes though the BASF datasheet for the Y348M tape approved as the IEC Type I reference in 1994 says that its optimal bias is exactly 0 0 dB from the previous reference BASF R723DG The IEC reference tape bias definition is Using the relevant IEC reference tape and heads according to Ref 1 1 the bias current providing the minimum third harmonic distortion ratio for a 1 kHz signal recorded at the reference level is the reference bias setting Type II bias high bias equals around 150 of Type I bias Type IV bias metal bias equals around 250 of Type I bias 25 Real cassette tapes invariably deviate from the references and require fine tuning of bias recording a tape with improper bias increases distortion and alters frequency response 26 A 1990 comparative test of 35 Type I tapes showed that their optimal bias levels were within 1 dB of the Type I reference while Type IV tapes deviated from the Type IV reference by up to 3 dB 27 Some typical cassette deck frequency response curves showing the effects of different bias settings are provided in the relevant figure Time constant of replay equalization often shortened to EQ for Type I tapes equals 120 ms as per the Philips specification The time constant for Type II III and IV tapes is set at a lower value of 70 ms The purpose of replay equalization is to compensate for high frequency losses during recording 28 which in case of ferric cassettes usually start at around 1 1 5 kHz The choice of time constant is a somewhat arbitrary decision seeking the best combination of conflicting parameters extended treble response maximum output minimum noise and minimum distortion 29 High frequency roll off that is not fully compensated in the replay channel may be offset by pre emphasis during recording 29 Lower replay time constants decrease the apparent level of hiss by 4 dB when stepping down from 120 to 70 ms but also decrease apparent high frequency saturation level so the choice of time constants was a matter of compromise and debate 30 Hard maximum and saturation levels in terms of voltage output of playback head remain unchanged However the high frequency voltage level at the output of the replay equalizer decreases with a decrease in time constant citation needed The industry and the IEC decided that it would be safe to decrease the time constant of Type II III and IV tapes to 70 ms because they are less prone to high frequency saturation than contemporary ferric tapes 29 Many disagreed arguing that the risk of saturation at 70 ms is unacceptably high 31 Nakamichi and Studer complied with the IEC but provided an option for playing Type II and Type IV tapes using the 120 ms setting and matching pre emphasis filters in the recording path A similar pre emphasis was applied by duplicators of prerecorded chromium dioxide cassettes although loaded with Type II tape these cassettes were packaged in Type I cassette shells and were intended to be replayed as Type I tapes 8 Type I editType I or IEC I ferric or normal cassettes were historically the first the most common and the least expensive they dominated the prerecorded cassette market 8 The magnetic layer of a ferric tape consists of around 30 synthetic binder and 70 magnetic powder acicular oblong needle like particles of gamma ferric oxide g Fe2O3 with a length of 0 2 mm to 0 75 mm 32 Each particle of such size contains a single magnetic domain 33 The powder was and still is manufactured in bulk by chemical companies specializing in mineral pigments for the paint industry 32 Ferric magnetic layers are brown in colour whose shade and intensity depends mostly on the size of the particles Type I tapes must be recorded with normal low bias flux and replayed with a 120 ms time constant Over time ferric oxide technology developed continuously with new superior generations emerging around every five years 34 Cassettes of various periods and price points can be sorted into three distinct groups basic coarse grained tapes advanced fine grained or microferric tapes and highest grade ferricobalt tapes having ferric oxide particles encapsulated in a thin layer of cobalt iron compound Ferricobalt tapes are often called cobalt doped however this is historically incorrect Cobalt doping in a strict sense involves uniform substitution of iron atoms with cobalt 35 This technology has been tried for audio and failed losing to chromium dioxide 22 Later the industry has chosen the far more reliable and repeatable process of cobalt adsorption encapsulation of unmodified iron oxide particles in a thin layer of cobalt ferrite 35 The remanence and squareness properties of the three groups substantially differ while coercivity remains almost unchanged at around 380 Oe 360 Oe for the IEC reference tape approved in 1979 36 Quality Type I cassettes have higher midrange MOL than most Type II tapes slow and gentle MOL roll off at low frequencies but less high frequency headroom than Type II 13 In practice that means that ferric tapes have lower fidelity compared to chrome tapes and metal tapes at high frequencies but are often better at reproducing the low frequencies found in bass heavy music Basic ferric edit nbsp Sony C60 compact cassette 1974 Entry level ferric formulations are made of pure unmodified coarse grained ferric oxide Relatively large up to 0 75 mm in length irregularly shaped oxide particles have protruding branches or dendrites these irregularities prevent tight packing of particles reducing iron content of the magnetic layer and consequently its remanence 1300 1400 G and maximum output level 37 The squareness ratio is low around 0 75 resulting in early but smooth onset of distortion 37 These tapes historically labeled and sold as low noise have high levels of hiss and relatively low sensitivity their optimal bias level is 1 2 dB lower than that of the IEC reference tape This group also includes most of the so called Type 0 cassettes a mixed bag of ferric tapes that do not meet the IEC standard or the original Philips specification 25 38 Historically informal Type 0 denoted early cassettes loaded with tape designed for reel to reel recorders 25 In the 1980s many otherwise decent and usable basic tapes were effectively demoted to Type 0 status when equipment manufacturers began aligning their decks for use with premium ferricobalts the latter having much higher sensitivity and bias 38 In the 21st century Type 0 denotes all sorts of low quality counterfeit or otherwise unusable cassettes They require unusually low bias and even then only a few of them perform on par with quality Type I tapes 25 A Type 0 tape if it is usable at all is incompatible with Dolby noise reduction with the Dolby decoder engaged the tape sounds dull resulting from its poor sensitivity causing severe Dolby mistracking 38 Microferric edit In the beginning of the 1970s gradual technological improvements over the previous decade resulted in the second generation of Type I tapes These tapes had uniformly needle shaped highly orientable particles HOP of much smaller size around 0 25 mm in length hence the trade term microferrics 9 Their uniform shape allowed very dense packing of particles with less binder and more particles per unit volume 9 and a corresponding rise in remanence to around 1600 G The first microferric TDK SD was introduced in 1971 and in 1973 Pfizer began marketing patented microferric powder that soon became an industry standard 39 In the 20th century Pfizer had a strong mineral pigment division with factories in California Illinois and Indiana In 1990 Pfizer sold its iron oxide business to Harrisons amp Crosfield of the United Kingdom 40 The next step was to align needle shaped particles in parallel with the flux lines generated by the recording head this was done by controlled flow of liquid magnetic mix over substrate rheological orientation 9 or by applying a strong magnetic field while the binder was curing 41 Typical microferric cassettes of the 1980s had less hiss and at least 2 dB higher MOL than basic Type I tapes at the cost of increased print through 42 Noise and print through are interrelated and directly depend on the size of oxide particles A decrease in particle size invariably decreases noise and increases print through The worst combination of noise and print through occurs in highly irregular formulations containing both unusually large and unusually small particles 43 Small improvements continued for thirty years with a gradual rise of squareness ratio from 0 75 to over 0 9 9 42 Newer tapes consistently produced higher output with less distortion at the same levels of bias and audio recording signals 9 The transition was smooth after the introduction of new superior tape formulations manufacturers often kept older ones in production selling them in different markets or under different cheaper designations Thus for example TDK ensured that its premium microferric AD cassette was always ahead of entry level microferric D having finer particles and lower noise 44 Ferricobalt Type I edit The third and best performing class of ferric tapes is made of fine ferric particles encapsulated in a thin 30 A layer of cobalt iron mix similar in composition to cobalt ferrite 45 The first cobalt doped cassettes introduced by 3M in 1971 had exceptionally high sensitivity and MOL for the period and were an even match for contemporary chromium dioxide tapes 46 hence the trade name superferrics Of many competing cobalt doping technologies the most widespread was low temperature encapsulation of ferric oxide in aqueous solution of cobalt salts with subsequent drying at 100 150 C 45 47 Encapsulated microferric particles retain needle like shape and can be tightly packed into uniform anisotropic layers 45 47 The process was first commercialized in Japan in the early 1970s 48 The remanence of ferricobalt cassettes is around 1750 G resulting in around 4 dB gain in MOL and 2 3 dB gain in sensitivity compared to basic Type I tapes their hiss level is on par with contemporary microferric formulations The dynamic range of the best ferricobalt cassettes true superferrics equals 60 63 dB and the MOL at lower frequencies exceeds the MOL of Type IV tapes Overall superferrics are a good match to Type IV especially in recording acoustical music with a wide dynamic range 49 38 This was reflected in the price of top of the line superferric tapes like Maxell XLI S or TDK AR X which by 1992 matched the price of entry level metal tapes Type II edit nbsp The TDK KR Krom was the company s only chrome tape ever made In 1974 1975 as soon as TDK had ferricobalt technology going they killed chrome production altogether nbsp All Type II cassettes made by TDK after 1975 SA SA X SA XS shown were ferricobalts not chromes IEC Type II tapes are intended for recording using high 150 of normal bias and replay with the 70 ms time constant All generations of Type II reference tapes including the 1971 DIN reference that pre dated the IEC standard were manufactured by BASF Type II has been historically known as chromium dioxide tape or simply chrome tape but in reality most Type II cassette tapes do not contain chromium 50 The pseudochromes including almost all Type IIs made by the Big Three Japanese makers Maxell Sony and TDK are actually ferricobalt formulations optimized for Type II recording and playback settings 50 51 A true chrome tape may have a distinctive old crayon smell more specifically any oil or wax chalks that have chrome dioxide pigments in them like chrome yellow which is missing in pseudochromes Both kinds of Type II tapes have on average lower high frequency MOL and SOL and higher signal to noise ratio than quality Type I tapes 52 This is caused by the midrange and treble pre emphasis applied during recording to match the 70 ms equalization at playback 52 Chromium dioxide edit In the middle of 1960s DuPont created and patented an industrial process for making fine ferromagnetic particles of chromium dioxide CrO2 The first CrO2 tapes for data and video appeared in 1968 41 In 1970 BASF who would become the main proponent of CrO2 launched its chrome cassette production 51 in the same year Advent introduced the first cassette deck with chrome capability and Dolby noise reduction The combination of low noise CrO2 tape with companding noise reduction brought a revolutionary improvement to compact cassette sound reproduction almost reaching the high fidelity level However CrO2 tape required redesign of the bias and replay equalization circuitry This problem was resolved during the 1970s 53 but three unsolved issues remained the cost of making CrO2 powder the cost of royalties charged by DuPont and the pollution effects of hexavalent chromium waste 54 51 The reference CrO2 tape approved by the IEC in 1981 is characterized by coercivity of 490 Oe high bias and remanence of 1650 G 55 48 Retail CrO2 cassettes had coercivity in the range from 400 to 550 Oe 56 Owing to the very clean uniform shape of the particles chrome tapes easily attain an almost perfect squareness ratio of 0 90 48 57 True chromes not modified by the addition of ferric additives or coatings have very low and euphonic hiss bias noise and very low modulation noise at high frequencies 58 8 Double layer CrO2 cassettes have the lowest absolute noise among all the audio formulations these cassettes generate less noise at 4 76 cm s than a ferric tape at 19 05 cm s 53 Their sensitivity is usually also very high but MOL is low on par with basic Type I tapes CrO2 tape does not tolerate overload very well the onset of distortion is sharp and dissonant so recording levels should be set conservatively well below MOL 58 At low frequencies the MOL of CrO2 tapes rolls off faster than in ferric or metal tapes hence the reputation of bass shyness CrO2 cassettes are best fit for recording dynamic music with rich harmonic content and relatively low bass levels 58 their dynamic range is a good fit for recording from uncompressed digital sources 34 and for music with extended quiet passages 8 Good ferric tapes may have the same or higher treble SOL but CrO2 tapes still sound subjectively better owing to lower hiss and modulation noise 59 Ferricobalt Type II edit nbsp Sony Chrome compact cassette 1976 nbsp BASF Chrome Extra II cassette 1988 nbsp Frequency response and noise level of the Nakamichi SX Type II cassette tape tested using a Nakamichi 600 two head cassette deck After the introduction of CrO2 cassettes Japanese companies began developing a royalty free alternative to DuPont s patent based on an already established cobalt doping process 48 A controlled increase in cobalt content causes an almost linear increase in coercivity thus a Type II pseudochrome tape can be made by simply adding around 3 cobalt to a Type I ferricobalt tape 35 By 1974 the technology was ready for mass production and TDK and Maxell introduced their classic pseudochromes TDK SA and Maxell UD XL while killing their true chrome lines TDK KR and Maxell CR By 1976 ferricobalt formulations took over the video tape market 60 and eventually they became the dominant high performance tape for audio cassette 51 Chromium dioxide disappeared from the Japanese domestic market 51 although chrome remained the tape of choice for high fidelity cassette duplication among the music labels In consumer markets chrome coexisted as a distant second with pseudochromes until the very end of the cassette era Ferricobalt technology developed continuously in the 1980s Japanese companies introduced premium double layered ferricobalts with exceptionally high MOL and SOL in the middle of the 1990s TDK launched the first and only triple coated ferricobalt the SA XS 61 62 The electromagnetic properties of Type II ferricobalts are very close to those of their Type I cousins Owing to the use of 70 ms replay equalization the hiss level is lower but so is the treble saturation level The dynamic range of Type II ferricobalts according to the 1990 tests lies between 60 and 65 dB The coercivity of 580 700 Oe and remanence of 1300 1550 G are close to the CrO2 reference tape but the difference is big enough to cause compatibility problems 50 TDK SA was the informal reference in Japan TDK advertisements boasted that more decks are aligned to SA than any other tape but there is very little first hand information on which tapes were actually used at the factories Japanese manufacturers provided lists of recommended tapes but did not disclose their reference tapes There is however enough indirect information converging on TDK SA For example in 1982 when Japanese owned Harman Kardon sent samples for Dolby certification they were aligned to the IEC CrO2 reference However production copies of the same models were aligned to TDK SA 63 Since the Japanese already dominated both the cassette and hi fi equipment markets incompatibility further undermined the market share of European made cassette decks and CrO2 cassettes 64 In 1987 the IEC resolved the compatibility issue by appointing a new Type II reference tape U 564 W a BASF ferricobalt with properties that were very close to contemporary TDK tapes With the short lived 1988 Reference Super even BASF started the manufacture and sale of Type II ferricobalt tapes 65 66 Metal particle Type II edit The coercivity of iron cobalt metal particle mix precipitated from aqueous solutions depends on the cobalt content A change in cobalt content from 0 to 30 causes a gradual rise in coercivity from around 400 Oe Type I level to 1300 Oe Type IV level alloyed iron cobalt particles can reach a coercivity of 2200 Oe 67 This makes possible manufacturing of metal particle tapes conforming to Type II and even Type I biasing requirements 68 In practice only Denon Taiyo Yuden and for only a few years TDK ever attempted making Type II metal tape These rare expensive cassettes were characterized by high remanence approaching that of Type IV tapes 2600 G their coercivity of 800 Oe was closer to Type II than Type IV tapes but still quite far from either type reference 69 Independent tests of the 1990 Denon and Taiyo Yuden tapes placed them at the very top of the Type II spectrum if the recording deck could cope with unusually high sensitivity and provide unusually high bias current 70 Type III editIn 1973 Sony introduced double layer ferrichrome tapes having a five micron ferric base coated with one micron of CrO2 pigment 71 51 The new cassettes were advertised as the best of both worlds combining the good low frequency MOL of microferric tapes with good high frequency performance of chrome tapes 42 22 The novelty became part of the IEC standard codenamed Type III the Sony CS301 formulation became the IEC reference 23 However the idea failed to attract followers Apart from Sony only BASF Scotch and Agfa introduced their own ferrichrome cassette tapes 72 These expensive ferrichrome tapes never gained substantial market share and after the release of metal tapes they lost their perceived exclusivity 51 42 Their place in the market was taken over by superior and less expensive ferricobalt formulations 51 42 By 1983 tape deck manufacturers stopped providing an option for recording Type III tapes 23 Ferrichrome tape remained in the BASF and Sony lineups until 1984 72 and 1988 73 respectively The use of ferrichrome tapes was complicated by the conflicting rationale of the playback of these tapes Officially they were intended to be played back using 70 ms equalisation The information leaflet that Sony included in each box of ferrichrome cassette tapes recommended that If the selector has two positions NORMAL and CrO2 set it to the NORMAL position 74 which applies 120 ms equalisation The leaflet notes that the high frequency range will be enhanced and that the tone control should be adjusted to compensate The same leaflet recommends that if the playback machine offers a Fe Cr selection that this should be selected On Sony s machines this automatically selects 70 ms equalisation The service manual for the Sony TC 135SD which was one of the few cassette decks offering a Fe Cr position shows the tape type selector switch paralleling the ferrichrome equalisation selection with that of chrome dioxide 70 ms 75 Neither Sony nor BASF cassette tapes feature the notches on the back surface that automatically select 70 ms equalisation on those machines that featured an automatic detection system Type IV editMetal particle Type IV edit nbsp nbsp Top of the line Type IV cassettes were packaged in expensive precision engineered shells The TDK MA R shell left had a rigid alloy frame the Sony Metal Master right had ceramic shell halves and a ceramic tape guide insert nbsp Frequency response and noise analysis of Nakamichi ZX Metal Particle Type IV cassette tape using the Nakamichi LX 5 three head cassette deck Pure metal particles have an inherent advantage over oxide particles due to 3 4 times higher remanence very high coercivity and far smaller particle size resulting in both higher MOL and SOL values 76 77 First attempts to make metal particle MP tape rather than metal oxide particle tape date back to 1946 viable iron cobalt nickel formulations appeared in 1962 56 In the early 1970s Philips began development of MP formulations for the Compact Cassette 64 Contemporary powder metallurgy could not yet produce fine submicron size particles and properly passivate these highly pyrophoric powders 78 79 Although the latter problems were soon solved 78 the chemists did not convince the market in terms of the long term stability of MP tapes suspicions of inevitable early degradation persisted until the end of the cassette era 56 The fears did not materialize 56 and most metal particle tapes survived decades of storage just as well as Type I tapes however signals recorded on metal particle tapes do degrade at about the same rate as in chromium tapes around 2 dB over the estimated lifetime of the cassette 80 81 Metal particle Compact Cassettes or simply metal tapes were introduced in 1979 and were soon standardized by the IEC as Type IV 56 79 They share the same 70 ms replay time constant as Type II tapes and can be correctly reproduced by any deck equipped with Type II equalization 19 Recording onto a metal tape requires special high flux magnetic heads and high current amplifiers to drive them 19 79 Typical metal tape is characterized by remanence of 3000 3500 G and coercivity of 1100 Oe thus its bias flux is set at 250 of Type I level 42 56 82 19 Traditional glass ferrite heads would saturate their magnetic cores before reaching these levels Metal capable decks had to be equipped with new heads built around sendust or permalloy cores or the new generation of glass ferrite heads with specially treated gap materials 83 Metal particle tapes particularly top of the line double coated tapes have record high midrange MOL and treble SOL and the widest dynamic range coupled with the lowest distortion 84 They were always expensive almost exclusive out of reach of most consumers 84 They excel at reproducing fine nuances of uncompressed acoustic music or music with very high treble content like brass and percussion 84 8 However they need a high quality properly aligned deck to reveal their potential 84 8 First generation metal particle tapes were consistently similar in their biasing requirements but by 1983 newer formulations drifted away from each other and the reference tape 85 Metal evaporated edit Unlike wet coating processes metal evaporated ME media are fabricated by physical deposition of vaporized cobalt or cobalt nickel mix in a vacuum chamber 86 There is no synthetic binder to hold particles together instead they adhere directly to polyester tape substrate 86 79 An electron beam melts source metal creating a continuous directional flow of cobalt atoms towards the tape 86 The zone of contact between the beam and the tape is blown with a controlled flow of oxygen which helps formation of polycrystalline metal oxide coating 86 A massive liquid cooled rotating drum which pulls the tape into the contact zone protects it from overheating 86 Metal evaporated coatings along with barium ferrite have the highest information density of all rerecordable media 87 The technology was introduced in 1978 by Panasonic initially in the form of audio microcassettes and matured through the 1980s 87 79 Metal evaporated media established itself in analogue Hi8 and digital Digital8 DV and MicroMV videotape market and data storage Advanced Intelligent Tape Linear Tape Open 87 The technology seemed promising for analogue audio recording however very thin metal evaporated layers were too fragile for consumer cassette decks the coatings too thin for good MOL 79 and manufacturing costs were prohibitively high Panasonic Type I Type II and Type IV metal evaporated cassettes introduced in 1984 were sold for only a few years in Japan alone and remained unknown in the rest of the world 79 Measured performance characteristics edit nbsp Comparison of typical MOL SOL and 0 dB frequency responses for sample Type I Type II and Type IV cassette tapes nbsp Frequency response plots of some sample Type I Type II and Type IV cassette tapes During the many years that cassette decks were popular many audio magazines published comparative measurements of the performance characteristics of the wide variety of different tapes that were available in the marketplace 88 89 90 91 92 93 94 These measurements typically included parameters such as MOL SOL frequency response at 0 dB and 20 dB re Dolby Level signal to noise ratio modulation noise bias level and sensitivity The first figure shows frequency response plots for sample Type I Type II and Type IV cassette tapes comparing their MOL SOL and 0 dB performance The second figure shows the frequency response performance of typical Type I Type II and Type IV cassette tapes obtained for a number of different input signal levels using a high quality Pioneer CT 93 stereo cassette deck from the 1990s 95 94 For each of the three tape formulations the record replay characteristics of the cassette deck were aligned with the relevant IEC Reference Tape and each tested tape was measured with the bias and equalization unchanged from that reference position The record replay frequency response was tested at four levels 6 VU 0 VU 10 VU and 20 VU Dolby Level is marked at 3 VU for the CT 93 Thus these plots provide data on the linearity of the different tape formulations at both high and moderate recording levels It is interesting to note that the Type I tape shows 6 VU and at 0 VU responses that are much flatter than that of the Type II tape At 6 VU the Type II tape displays significant amounts of signal level compression across the entire frequency range reducing to about 2 dB of signal compression between 80 Hz and 1 kHz Some representative measured performance characteristics of a small number of commercially available tape types are presented in the table below 90 88 Maximum Output Level dB re 400 Hz Dolby Level 3 Harmonic Distortion 3 Twin Tone Intermodulation High Frequency 3 dB Point kHz Tape Type 100 400 1k 2k 5k 10k S NRatio dBA 0 dBInputLevel 20 dBInputLevel Mod Noise dB Bias dB Sens dB BASF LH MI I 4 0 4 8 5 6 0 8 2 4 8 8 58 3 10 6 45 7 0 4 0 3 Maxell UR I 3 9 4 3 4 4 0 5 2 5 9 0 57 0 9 8 43 8 0 5 0 0 Maxell UD XL I I 6 5 6 8 6 8 0 8 2 0 8 5 58 8 10 0 23 9 46 3 0 1 0 9 Sony HF I 2 0 2 4 2 5 0 9 4 1 10 3 54 3 8 9 36 1 0 9 1 0 TDK D I 2 6 3 5 4 5 0 0 3 1 9 6 55 5 9 3 22 9 45 4 0 1 1 0 TDK AD I 3 8 6 2 6 2 1 3 1 7 8 2 60 3 9 9 23 2 44 3 0 5 0 3 BASF CR Mll II 4 8 5 4 4 0 4 0 8 3 12 8 63 0 7 3 51 0 1 0 1 0 Maxell UD XL II II 4 4 5 2 5 1 2 1 5 6 10 6 60 4 9 2 22 1 48 0 0 1 1 7 Memorex CDXII II 5 7 6 3 6 1 0 4 3 1 6 9 61 2 11 9 47 4 1 3 2 9 TDK SA II 3 4 4 4 4 9 1 9 5 7 11 2 60 9 8 9 20 3 47 2 0 1 1 1 TDK SA X II 3 7 4 4 3 6 2 8 7 3 11 5 63 2 7 8 23 8 47 8 1 0 1 6 Maxell MX IV 8 0 9 1 9 5 2 3 1 9 6 8 62 7 12 5 25 0 50 4 0 1 0 8 Sony Metal ES IV 8 8 10 2 10 3 2 1 2 4 7 1 66 0 12 5 50 8 0 6 2 0References edit Ankosko Bob 1993 Tape Buying Gude Stereo Review March 56 JVC Maxell prices Roberson Howard A January 1981 All That Data Tape Deck Frequency Response And Headroom PDF Audio pp 74 84 Braginskij amp Timofeev 1987 p 21 Kozyurenko 1998 p 23 a b Jones amp Manquen 2008 pp 1066 1068 Blank Tape Firms Ready Promotions Billboard 11 January 1986 p 32 Braginskij amp Timofeev 1987 p 57 a b c d e f g h Mitchell 1984 p 42 a b c d e f g h i Jones amp Manquen 2008 pp 1067 1068 Braginskij amp Timofeev 1987 pp 29 58 59 Kozyurenko 1998 p 22 Kozyurenko 1998 p 33 a b Roberson 1990 p 53 Roberson 1990 p 47 Roberson 1990 p 58 a b c d e f Stark 1992 p 46 Kozyurenko 1998 p 34 Kozyurenko 1998 pp 13 14 a b c d e f g h Kozyurenko 1998 p 32 Roberson 1990 p 48 a b c d History of Compact Cassette 2012 a b c Foster 1984 p 456 a b c d e f Feldman Len 1983 International Tape Standardization PDF Modern Recording and Music 9 1 28 29 a b c Liebert Meinrad 1987 Revox B215 automatic calibration The perfect compromise PDF Swiss Sound 19 4 6 a b c d A quick guide to tape types PDF High Fidelity 11 29 1982 Kozyurenko 1998 pp 34 35 Roberson 1990 pp 47 52 58 Burstein 1985 p 74 a b c Burstein 1985 p 76 Burstein 1985 pp 76 79 Burstein 1985 pp 79 80 a b Mallinson 2012 p 29 Mallinson 2012 p 24 a b Jones 1985 p 85 a b c Camras 2012 p 108 BASF International Reference Tape IEC I Iron Oxide Tape Batch R723DG BASF 1979 a href Template Cite journal html title Template Cite journal cite journal a Cite journal requires journal help a b Jones amp Manquen 2008 p 1067 a b c d Mitchell 1984 p 43 Clark 1999 p 104 Pfizer sells iron oxide pigment unit The Morning Call 1990 03 31 a b Braginskij amp Timofeev 1987 p 29 a b c d e f Capel 2016 p 116 Jones amp Manquen 2008 p 1072 Camras 2012 p 116 a b c Mallinson 2012 p 31 Free John 1971 How Good Are Those New Tapes Popular Science November 89 130 a b Braginskij amp Timofeev 1987 p 173 a b c d Mallinson 2012 p 32 Kozyurenko 1998 p 27 a b c Foster 1984 p 457 a b c d e f g h Kimizuka 2012 p 227 a b Roberson 1987 p 57 a b Free J 1977 Cassette tapes for higher hi fi Popular Science June 50 53 Braginskij amp Timofeev 1987 pp 163 164 183 BASF International Reference Tape IEC II Chromium Dioxide Tape Batch S4592A BASF 1981 a href Template Cite journal html title Template Cite journal cite journal a Cite journal requires journal help a b c d e f Camras 2012 p 33 Jones amp Manquen 2008 p 1068 a b c Kozyurenko 1998 pp 28 30 Booth 1989 p 65 Kirsh B 17 February 1973 Blank TV Tape Production Heats Up Chrome vs Cobalt Battle Billboard p 38 TDK Europe 1995 1997 Vintagecassettes com 2005 2014 Kozyurenko 1998 p 29 Hirsch Julian 1982 Harman Kardon hk705 Cassette Deck PDF Stereo Review s Tape Recording amp Buying Guide 37 38 a b Cassette users set for another ride 25 August New Scientist 1977 478 a href Template Cite journal html title Template Cite journal cite journal a Cite journal requires journal help Block Debbie 25 July 1992 New Wine in Old Cassettes Billboard pp TD 3 TD 7 BASF Chrome Tape Formulations Vintagecassettes com 2005 2014 Camras 2012 pp 108 113 Camras 2012 pp 113 114 Booth 1989 p 64 Roberson 1990 pp 58 59 Eguchi Hideo 1973 Oxide Chrome Blanks Add to Coatings Output Billboard No October 6 a b BASF 1984 Vintagecassettes com 2005 2014 Sony 1988 89 Japan Vintagecassettes com 2005 2014 SONY information leaflet ref 3 780 439 11 1 amp 2 Sony TC 135SD Stereo Cassette Deck 1975 76 hifiengine com Camras 2012 p 111 Mitchell 1984 p 41 a b Braginskij amp Timofeev 1987 p 176 a b c d e f g Kimizuka 2012 p 228 Bogart John W C Van 1995 Magnetic Tape Storage and Handling A Guide for Libraries and Archives PDF Commission on Preservation and Access pp 5 7 ISBN 1887334408 Bressan F 2019 Chemistry for Audio Heritage Preservation A Review of Analytical Techniques for Audio Magnetic Tapes Heritage 2 2 1559 1568 doi 10 3390 heritage2020097 hdl 1854 LU 8609085 Mallinson 2012 p 33 Kozyurenko 1998 pp 32 66 a b c d Kozyurenko 1998 pp 29 31 Foster 1984 p 458 a b c d e Jubert amp Onodera 2012 pp 69 70 a b c Jubert amp Onodera 2012 p 67 a b Roberson Howard A September 1983 Mass Tape Test 77 Cassettes Rated PDF Audio pp 34 44 Beekhuyzen Hans July 1984 Test 35 Cassettes Audio amp Techniek pp 53 69 a b Roberson Howard A June 1986 Cassette Test Update 49 Formulations PDF Audio pp 74 84 Roberson Howard A November 1987 Mass Cassette Test We Review 35 New Tapes PDF Audio pp 50 61 Roberson Howard A March 1990 Greatest Cassette Test Ever 88 Tapes Tested PDF Audio pp 47 58 Schuller Peter November 1990 Grupen Dynamik Test 48 Cassetten Stereoplay pp 62 83 a b Challis Louis November 1991 A Review of Current Cassette Tapes PDF Electronics Australia pp 10 17 Challis Louis October 1991 Pioneer s CT 93 Stereo Cassette Deck PDF Electronics Australia pp 8 13 Bibliography editBooth Stephen 1989 Tale of the Tapes Popular Mechanics November 63 65 Burstein Herman 1985 The Whys and Hows of Cassette Equalization PDF Audio 6 72 81 Camras Marvin 2012 Magnetic Recording Handbook Springer ISBN 9789401094689 Capel Vivian 2016 Newnes Audio and Hi Fi Engineer s Pocket Book Newnes Elsevier ISBN 9781483102436 Clark Mark H 1999 Product Diversification Magnetic Recording The First 100 Years IEEE Press pp 92 109 ISBN 9780780347090 Foster Edward 1984 Statement on Copyright Aspects of Audio Recorders and Blank Tapes Video and Audio Home Taping Hearing Before the Subcommittee on Patents Copyrights and Trademarks volume 4 U S Government Printing Office pp 443 467 Hodges R 1978 The Cassette A Short History PDF HiFi Stereo Review 2 26 Jones D Manquen D 2008 Chapter 28 Magnetic Recording and Playback Handbook for Sound Engineers Fourth Edition Focal Press Elsevier ISBN 9780240809694 Jones Mike 1985 Cassette Quality What is the industry doing PDF Audio 6 82 86 Jubert P O Onodera S 2012 Metal Evaporated Media In Buschow K H J ed Handbook of Magnetic Materials vol 20 Elsevier pp 65 122 ISBN 9780444563774 Kefauver Alan 2001 The Audio Recording Handbook A R Editions Inc pp 253 263 ISBN 9780895794628 Kimizuka Masanori 2012 Historical Development of Magnetic Recording and Tape Recorder PDF National Museum of Nature and Science Survey Reports on the Systemization of Technologies 17 August 185 275 Mallinson John C 2012 The Foundations of Magnetic Recording Elsevier ISBN 9780080506821 Mitchell Peter W 1984 Choosing Tape PDF Stereo Review March 41 43 Morton David 2006 Sound Recording The Life Story of a Technology JHU Press ISBN 9780801883989 Stark Craig 1992 Choosing the Right Tape PDF Stereo Review March 45 48 Talbot Smith Michael 2013 Audio Engineer s Reference Book CRC Press ISBN 9781136119743 Braginskij G I Timofeev E N 1987 Tehnologiya magnitnyh lent Magnetic Tape Technology in Russian Himiya ISBN 5724500558 Kozyurenko Yu I 1998 Sovremennye magnitofony pleery diktofony i naushniki Modern tape recorders players dictation devices and headphones in Russian DMK ISBN 5898180087 Retrieved from https en wikipedia org w index php title Compact Cassette tape types and formulations amp oldid 1213113846, wikipedia, wiki, book, books, library,

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