The Type IV Metal Audio Cassette

1986 Sony Metal-ES 60 Type IV Metal Audio Cassette

The metal-formulated audio cassette hit the scene near the end of the 1970s, as the answer to a number of problems with previous tape formulations. The standard ferric-oxide (Type I) tape had typically rendered poor high frequency definition, with pervasive noise, meaning a woolly sound without much presence or zing… except where you didn’t want it – in the hiss.

Two subsequent solutions had been developed – the first (Type II) being a chrome (CrO2) formulation, which rendered much better frequency reproduction and very low noise (hiss) at the expense of some output level and low frequency solidity. The second solution, ferro-chrome (Type III), was an attempt to restore some low frequency firmness to the bright and airy sound of chrome, by adding a second coating layer (ferric) to the existing chrome formulation. Whilst the Type III cassette worked as a concept, it was not well accomodated in the market or well catered for on recording equipment. Fundamentally, it was a technically-imperfect innovation, and it wasn’t significant enough an improvement over standard chrome to be worth the hassle of ‘re-jigging’ the market. Indeed it could be said that Type II chrome’s light and airy feel was actually preferable to the slightly stodgier fullness of a Type III ferro-chrome.

Enter the Type IV tape, with a completely new formulation, of metal particles. The advantages were quickly recognised. This was a very hard-wearing tape, which could take much higher sound levels than a chrome, whilst reproducing equal or better high frequency definition, and a firmer bass – but, without losing the spacious midrange in the way ferro-chromes could.

Sadly, the disadvantages were quickly recognised too – excess wear on the tape heads, and excess expense in the retail price being the most significant. The metal audio tape was, however, considered worth persevering with. Efforts were made to solve the problem of wear, and in the course of the early 1980s the Type IV cassette did start to catch on. By the mid 1980s, when the Sony Metal-ES 60 depicted in this post was made, metal tapes had been adopted by a lot of enthusiasts. They remained too expensive to be bought in bulk by the average consumer, but if you wanted to record something special – and particularly if you produced music yourself – you’d probably be highly attracted by the exceptional recording quality of a good metal cassette.

I should just quickly mention, for reference, that the Metal-ES 60 in this photo is the 1986 version – slightly different from the 1987 Metal-ES 60 I covered in an earlier post.

Perhaps the most obvious defining visual feature on a metal tape is the run of indentations along the top of the cartridge. The indentations on the top of a cassette were read by the recording/playback equipment, so as to automatically determine the correct electronic settings for each tape type without the need for the user to adjust anything. The cassette photographed for this article has not had its write-protect dips opened up – the break-off tabs on the far left and right of the line of notches are still in place, meaning the tape will accept recordings. Bodge those tabs out with a screwdriver and you have a ‘safe’ tape. If you hit the record button by accident, you won’t erase or record anything.

Right next to those write-protect tabs, moving inward, are the indentations which reset the recording/playback equipment from the standard 120 micro-second EQ setting, to the chrome/metal tape’s 70 micro-second setting, and raise the bias in keeping with a Type II tape. In the centre, a metal tape has two further notches which raise the bias even higher. Metal cassettes had the highest bias of all the four types. When you see those two indentations in the centre on the top of the casing, you know you’re looking at a metal tape.

A really good metal bias audio cassette, such as this one by Sony, offered superb sound reproduction which was, technically at least, the epitome of compact cassette audio recording. The sophisticated treble, the solid bass, and the transparent midrange were all there – coupled with the desirable capacity to take extremely high levels of volume before distortion set in. Some people do still prefer chrome tapes to metals, but for me, metal at its best, was the ultimate.

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