Compact Cassette tape types and formulations
Double-layer Type III tape formulations, advanced by Sony and BASF in the 1970s, never gained substantial market presence.
[3] Two fundamental magnetic properties, relevant for audio recording, are: A useful figure of merit of tape technology is the squareness ratio of the hysteresis curve.
[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.
[21] The numerals follow the historical sequence in which these tape types were commercialized, and do not imply their relative quality or intended purpose.
[23] A second run was impossible, because chemists were unable to replicate the reference tape type formulation with proper precision.
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.
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] 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).
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.
[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.
[9][42] Newer tapes consistently produced higher output with less distortion at the same levels of bias and audio recording signals.
[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.
Overall, superferrics are a good match to Type IV, especially in recording acoustical music with a wide dynamic range.
IEC Type II tapes are intended for recording using high (150% of normal) bias and replay with the 70 μs time constant.
[52] In the middle of 1960s, DuPont created and patented an industrial process for making fine ferromagnetic particles of chromium dioxide (CrO2).
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.
[59] 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.
[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.
With the short-lived 1988 Reference Super, even BASF started the manufacture and sale of Type II ferricobalt tapes.
[68] In practice, only Denon, Taiyo Yuden, and, for only a few years, TDK, ever attempted making Type II metal tape.
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).
[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.
[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.
[85] 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][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.
[79] 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.
Thus, these plots provide data on the linearity of the different tape formulations at both high and moderate recording levels.
Some representative measured performance characteristics of a small number of commercially available tape types are presented in the table below.
