The Type II high bias audio cassette is actually much older a development than many people realise. The rise of the Type II tape is generally associated with the 1980s, but in fact, it was introduced, with a chromium dioxide (CrO2) tape formulation, at the dawn of the 1970s.
Chrome tapes were, technically, a big advancement from the start. Du Pont’s chromium dioxide formulation gave an undeniable increase in high frequency response over the often rather muffled tone of the existing Type I ferric cassette. This meant much better definition – a major improvement in fidelity, and an ability to preserve all the zing and sparkle at the treble end of the original sound.
Why didn’t the chrome cassette take off straight away? Well, because this was a time barely out of the 1960s, and the technology and standards of the day just weren’t sufficient to make any significant use of that extra frequency response. People would be recording from vinyl records, televisions, radios – most typically not via a direct, electronic feed, but simply via a cheap microphone on a tape recorder.
The original sound was already compromised by the inefficient ‘60s technology. The recording was then compromised further by the recording equipment and methods. By the time you accounted for the poor treble response of the typical playback system of the time (often with a single ‘full range’ speaker incapable of reproducing frequencies above 5 or 6KHz), any advantages the chrome cassette offered had been well and truly stripped out of the equation. Indeed, because the Type II chrome cassette was characteristically light on bass, there was an argument that Type Is, with their fuller bass range, would actually sound better on some 1960s equipment than the Type IIs. The chromium dioxide audio cassette was a great innovation, but it was born well before its time.
For these reasons, the mass market largely stuck with standard ferric tapes through the 1970s. The real battle was to reduce hiss in cassettes across the board, and reading the labels of 1970s cassettes, you get evidence of that. Boasts of ‘low noise’ (meaning, but not always delivering, less hiss) are very common, but there’s rarely anything relating to definition. People just weren’t sufficiently bothered about high frequency response, and in most cases didn’t have the means to exploit it even if they were. I was only a child in the 1970s, but my family bought plenty of cassettes – always of the Type I variety. I wasn’t aware then that there was such a thing as a chrome or Type II tape. In fact, Type Is weren’t identified as Type Is in the depths of the ‘70s. They were just ‘audio tapes’, and chromes were a specialist product.
The Type II cassette operated with different electronic parameters from the Type I. ‘High bias’ refers to one of these differences. During sound recording, a special, inaudibly high frequency is applied to audio tape, to facilitate the effective magnetisation of the particles. Changing the volume at which this frequency is applied, is known as altering the bias. The bias, then, is simply the volume at which this special frequency is applied during recording.
To clarify, the bias frequency can’t be heard by the listener – it’s only there to facilitate an accurate recording process. Changing the bias helps in optimising the tape’s particular formulation for best audible results – minimising distortion and so forth. Optimum quality for a chrome-formulated tape was obtained by recording with the bias frequency at higher volume than is the case with a standard ferric tape – hence, ‘high bias’.
The standard EQ setting also differed between Type I and blank Type II cassettes (although this isn’t usually the case with pre-recorded tapes). The EQ is another electronic variable, dealing with the equalisation of frequencies on an audio tape, as traded off against noise level. EQ is measured in microseconds.
Whereas Type I cassettes operated with an EQ of 120 microseconds, blank Type IIs usually have a 70 microsecond EQ. It seems, however, that for the first year or two of production (in the early ‘70s), Type II cassettes used the same EQ setting as Type Is. The switch to 70 microseconds appears to have been purely a noise reduction measure. Taking down the EQ would have reduced noise, but at the expense of some high frequency glassiness. Noise was a much bigger concern than super-high frequency response in the early ‘70s, hence the decision, as far as I can establish.
Years later, however, the EQ for pre-recorded Type II cassettes was established at 120 microseconds – again, the same as a Type I. By this time, Dolby noise reduction had been widely adopted to take care of overly present tape hiss, so the higher inherent noise level was no longer seen as a problem. The advantages to using 120 microseconds for pre-records concerned wider compatibility, better economy of manufacture, and of course an increase in high frequency sensitivity.
In the mid 1970s, TDK introduced an alternative to the chrome formulation, based around a cobalt / iron oxide formula, which they called Avilyn, or Super Avilyn. The electronic (bias/EQ) settings were the same as for a chrome tape, and this was still a Type II, but the sound was different. Less glassy and transparent than a typical BASF chrome, but still displaying very good definition and fidelity. As time went on, other manufacturers adopted these cobalt mix formulations, and the Type II cassette progressively moved away from chrome. Chrome kings BASF held onto the real chromium dioxide formula into the 1990s, but even they moved over to substitutes eventually.
The early 1980s saw chrome and high bias Type II cassettes storm the mass market. In my opinion, the primary reason for this was that technology finally reached the point where it allowed consumers to appreciate the advantages offered by chrome. ‘Record players’, ‘tape recorders’ and ‘stereos’ were out, and ‘hi-fis’ had arrived in their wake. Speaker systems were now incorporating separate tweeters as standard – even on portable devices, so consumers could actually hear the full frequency range of a music track in something like its original form.
Music production was also getting more definition-focused, and commercial tracks were incorporating higher trebles as electronic instrumentation and early digital recording techniques came to the fore. Suddenly, that sizzling high treble mattered in a recording, and the chrome audio cassette came into its own.
For the owner of a contemporary ghetto blaster, with an interest in the then modern, electronic music, a tape was no longer a tape. There were Type Is, and Type IIs – and Type IIs were definitely where it was at. There were of course, by the early 1980s, also Type IV metal cassettes, and the remnants of the ferrochrome Type IIIs. But on the high street shelves, in Woolworths, WHSmith – the places ordinary consumers went to buy their tapes – the clear choice was Type I or Type II.
To this day, Type II cassettes, and in particular real chrome Type IIs, have remained a favourite with many tape enthusiasts. Type IV Metal tapes offered stronger bass, better level and a very impressive frequency response across the treble spectrum. But for some, they still didn’t capture the transparency of a great chrome cassette. Certainly, playing back some of my early to mid 1980s BASF chromes, I can see why they gained such an eminent rep. I do prefer a great metal tape, but in the golden age of hi-fi, chrome Type IIs were undoubtedly the real craze.