Tech Flashback: The Microcasette – Part 1: The Tapes

Just the other day, I was talking to a random stranger about floppy disks and VHS cassettes, and how another generation has already been born not knowing the frustrations and wonderment of simple old-fashioned technology. It’s interesting how such old man topics seem to bubble up to the surface, and despite the fact that many “old” media types are represented by some posts on this blog (be it VHS, floppy disks, Syquest cartridges, ZIP disks or optical disks), it’s been a while since my last “tech flashback” post, and a while since I’ve looked at a (mostly) defunct media format. As usual, despite good intentions, the lists of things to post about still keeps growing.

So lets take a trip down memory lane, by looking at Compact Cassette’s less successful cousin – the Microcassette.

History

A very condensed history of mainstream audio recording technology would probably read something like ‘wax cylinder, leads to phonograph, leads to wire recorder, leads to reel to reel tape, leads to compact cassette, and then digital CDs’. All of this is documented elsewhere.

What is most fascinating to me is the time-frame in which audio cassettes ruled. The Compact Cassette (which you probably know as a regular cassette) was invented by Philips in 1962 and licensed free of charge, initially as a format for recording voice in dictation and portable situations. It wasn’t until 1971 that Compact Cassette was taken seriously, with Chrome Dioxide tape formulations and better transports leading to improved quality, finally leading to the demise of reel to reel in consumer applications by the mid 80’s, only to then slowly die out by the early 2000’s.

The microcassette was competing with the Compact Cassette in some way, by making things even more compact. The format was invented by Olympus in 1969, which was a surprise to me as Olympus is best known for their imaging and optical equipment. The format found some use in dictation and answering machines (areas where Compact Cassette were also used), and in 1982, a Metal (type IV) formulation microcassette and stereo recorder was introduced for a short period to try and capture the higher fidelity market. Despite being the most-successful of the smaller-than-compact-cassette market, it was not as commonplace. This led me on an interesting journey of looking at the medium itself and trying to understand its technical aspects.

The Microcassette Tapes

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Microcassettes, as the name implies, are smaller than Compact Cassettes. Side by side, the difference in size is quite obvious. The plastic shell they are built from is somewhat thinner, and feels slightly less robust, although robust enough for casual handling. The tape runs in the opposite direction for compact cassettes – from the right spool to the left.

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Despite the difference in shell size, the width of the tape used in both types of cassettes are the same, about 3.81mm. Two pressure pads are employed in the microcassette design, with the capstan/pinch roller in the centre.

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They were available in a variety of running durations that overlapped with those commonly used in Compact Cassettes as well. Common brands included Olympus, Sanyo, TDK and Sony.

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A small write protect tab was featured in the side corner of the cassette, with an arrow indication given by the label on the face. This is as opposed to the write protection tab on the spine of Compact Cassettes.

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The spine of compact cassettes features a batch code, and is curved, with the other edges square.

Technical Details

So, how did Olympus shrink the Compact Cassette? Well, the devil is in the details.

Compact Cassettes have a tape speed of 1 and 7/8th inches per second, or 4.7625cm/s. Olympus had defined the microcassette tape speed as 2.4cm/s or 1.2cm/s (for double the listed run-time). As a result, the microcassette speed is 50.39% and 25.20% of the speed of the Compact Cassette. A slower tape speed means less tape is required for the same duration of recording. A rudimentary calculation of common cassette durations and required tape lengths are provided in the following table.

cassette-tape-lengthsAs we can see, the longest microcassette runs for 90 minutes, and requires 64.8m of tape to be spooled into the shell.

This is somewhere between the length of tape in a 40 or 46 minute Compact Cassette. The longest Compact Cassette commonly encountered today is a C-120, which has over 2.5 times the length of the longest microcassette.

A slower tape speed doesn’t come without consequences, namely in the frequency response of the recording medium being lower, as well as increased effect from magnetic oxide drop-outs or irregularities.

In fact, in an experiment I did, I tested the recording quality of microcassettes at 2.4cm/s and 1.2cm/s.

24cm-recordanalyz

At 2.4cm/s, we can see that frequency response generally extends only to 5khz, and then rolls off to noise by about 8khz.

12cm-recordanalyz

At 1.2cm/s, the frequency response is strong only to about 3khz, and is mostly in the noise by 4.5khz. Both of these frequency responses are suitable for voice, but not so much for music, sounding similar to an AM radio.

I tried to improve the frequency response, in case that the fault is in the recorder through further experiments.

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At first, I decided to record audio played at half-speed, using the 1.2cm/s setting on the recorder, and then play it back at 2.4cm/s. If the frequency response limitation is due to the electronics in the recorder filtering the recorded frequencies, we should see an improvement by doing this. A slight improvement is had, with strong signal response up to about 5.5khz, and going into the noise by about 8.5khz. Not too significant.

I then did the same thing, but instead artificially boosting frequencies above 5.5khz by 12dB through equalization before recording. This is essentially trying to apply “pre-distortion” to the system. It was able to get good frequency response up to 6.5khz, with it falling through to noise by about 9.5khz. There was some improvement, although limited.

This is relatively expected, as the best decks using Compact Cassette generally achieve about 16khz frequency response on Type I (ferric oxide) media. With a tape speed that is halved, we expect to see a frequency response that is halved – and indeed, this is the case.

The disadvantages don’t end there, as the smaller shell size and spool also necessitate using thinner media. Thinner media has a greater tendency to stretch, making the cassette less durable. Thinner media also often means thinner oxide coatings, which have less magnetism, thus resulting in a weaker signal and poorer signal to noise ratio. Another side effect is that the magnetic material is “layered” onto the next layer of tape much more closely on the spool, thus increasing the chance of print-through distortion (where magnetism is transferred across adjacent layers of tape) causing pre and post-echo. Indeed, when you put the XD60 next to the XB80, the difference in the oxide thickness and film thickness are immediately apparent.

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For one of my experiments, I decided to take apart a cassette, remove all the tape, and re-wind tape from a C-120 Compact Cassette (the longest regular length cassette available). Once I had reached the maximum limit which the microcassette spools could hold, the tape counter said I only had about 62.3 minutes of tape wound onto the spool.

Thus it can be inferred that the MC-60 cassettes contain tape of a similar thickness to a C-120, and that the MC-80 and MC-90 cassettes must contain tape thinner than a C-120. It is important to note that the Compact Cassette C-180 was briefly available and then discontinued as it was considered too thin and fragile.

Unboxing/Unwrapping Olympus Cassettes

Cassettes were available at retail, often in hanging tab cellophane packages – either individually, or in 3-packs, with a barcode for easy stock management. This particular cassette is the XB80, 80-minute cassette. Olympus offered a one-year warranty on their cassettes – an interesting offer which I doubt many people ever took-up.

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Each cassette would be housed in its own case – in the case of Olympus cassettes, instead of having a vertically-opening case like the Compact Cassettes, the cases opened horizontally.

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The rear of the package included a paper insert, with some space to annotate your recording details on and care instructions provided. The label on the cassettes generally do not have space for you to do so due to their small size.

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Rarely, did you find microcassettes available in bulk. It seems that this is a pretty interesting find, as the cassettes were available in 10-pack boxes, similarly to Compact Cassettes.

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It seems that these were not destined for retail sales, due to its very simple drab colouration and as there wasn’t even a barcode on the box. Instead, these would have been supplied by office supply companies for institutional usage. Each of the tapes inside was wrapped in cellophane with a quick-peel tab.

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Teardown

What’s a good flash-back without some looking inside. The first step is to remove the label from the microcassette – a thing that is much easier said than done. Adhesive residues were left everywhere, which took a lot of work to clean, and that resulted in little balls of gum which stuck to everything! Yikes.

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Here, we can see the cassette shell itself. Interestingly, the tape capacity viewing window is clear, but most of the body is frosted in anticipation of receiving an adhesive label. Despite this, it didn’t stop them from putting some clear sections in the mould – namely the logo and the tape side indicators.

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The cassette itself is held together at four points by having glued lugs. In order to open it, I had to use a 2.5mm drill bit and drill through these lugs to free the halves of the shell. Inside, we can see the “v-shaped” spring and pad system, as well as the clear plastic guide sheets to help keep the tape packed well. The hubs are more clearly visible, and they have a spoked arrangement to them and a thin plastic clip bar to hold the tape ends. No leader or special tape is placed at the end – the tape base is directly clipped into the hub.

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Conclusion

The microcasette format was pioneered by Olympus, but did not achieve the same level of success as the Compact Cassette. Despite being much smaller, it has tradeoffs in the recording quality achieved due to the reduced tape speed and quality of the deck transports. The thinner tape employed, along with thinner oxide coating reduces durability and also limits the signal to noise ratio and increases the risk of print-through distortions. Its lack of popularity may have been the reason why microcassette tapes were more expensive to purchase. The microcassette format has hence remained mostly used for voice and dictation purposes in mono, and has since given way to even more compact digital flash-memory based recorders.

In the upcoming part, I will be looking at microcassette recorders.

About lui_gough

I'm a bit of a nut for electronics, computing, photography, radio, satellite and other technical hobbies. Click for more about me!
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3 Responses to Tech Flashback: The Microcasette – Part 1: The Tapes

  1. Brent says:

    If you use a Compact Cassette repair kit (called a C-Zero) and wind the tape from the MC-90 Ninety Minute Microcassette tapes into a compact cassette you can make a 192 minute standard audio cassette. It’s nice for holding an 1800 foot 3-3/4 ips reel to reel for your Walkman. The best sound quality comes from the TDK microcassettes.

    • Will says:

      Interesting. I wonder if transferring chrome or metal tape in the opposite direction could increase the audio quality on a standard Microcassette recorder (albeit with a short duration).

      • lui_gough says:

        I think the issue is that metal and chrome tape have a 70uS bias and different coercivity, so using the microcassette recorder itself to record such media is unlikely to achieve a full erase and record resulting in poor quality. If it was pre-recorded before spooling into a microcassette shell, it will probably play but at the wrong speed (regular compact cassette is 1 and 7/8th inches per second, or about twice as fast). If you doubled the speed of the audio before recording it onto the tape with a regular compact cassette machine, then you would have a recording that would play back at regular speed on the 2.4cm/s setting, but then you might run into frequency response issues as the compact cassette recorder is unlikely to record with a frequency response better than about 20kHz in optimal conditions, and playing that back at half speed leaves you with a 10khz frequency response at best.

        I suppose if you were lucky and have one of the rare chrome/metal capable microcassette recorders, which were quite shortlived on the market, then this could be a viable way of producing appropriate cartridges for those recorders, but I found from my disassembly of the cassettes that clipping the end of the tape onto the hub is a royal pain … so your mileage may vary.

        Good thought though …

        – Gough

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