Adventures In Audio

The cassette revival? This is just so wrong on many levels.

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People are buying cassettes again. What? Has there been an outbreak of mass insanity?

"Just so wrong on many levels". That's a stock phrase used by nay-sayers who generally can only think of one level to complain about. But cassettes - there's a whole multi-storey car park here.

Firstly, a bit of personal temporal perspective. Most people can remember the first album they bought. I bought two on the same day - Please Please Me and With The Beatles, by the Beatles. Their third album (in the UK), A Hard Day's Night, was yet to be released. I bought both albums on five-inch reel-to-reel tape, and yes that was a thing in those days.

And so yes I do remember when the cassette, or Compact Cassette to give it its full title, was invented. And I also remember my surprise when the so-called Musicassette came out. I remember that from reading a review in Tape Recorder magazine of Pink Floyd's The Piper at the Gates of Dawn - their first album.

And so, fast-forwarding through history, I bought my first 'proper' cassette machine, an Akai GXC-510D which had the best specification I could find and afford. Owning a hi-fi stereo cassette deck was popular and common, particularly among students.

What did people do with their cassette decks? Well from today's perspective one might assume that they used them as the centre-piece of their home recording studio. But no, they copied music from the radio (preferably FM stereo with a decent aerial) or an obliging friend's records. Totally illegally of course, and if I ever did this, my memory of this topic has unfortunately been long-since erased.

But to be honest the cassette was, is, and always will be a rubbish format. Which is why the cassette revival is wrong, and on so many levels.

Cassette revival?

Yes apparently. Sparked by Star-Lord's Sony TPS-L2 Walkman in Marvel's Guardians of the Galaxy Vol. 2, people want to buy cassettes, and presumably cassette decks or Walkman-type devices to play them on. Apparently the UK is on track for 100,000 cassettes to be bought by the end of this year. I'm presuming that this time they will be pre-recorded cassettes rather than blank, and you can choose from artists such as Robbie Williams, The Who, Coldplay, Beck and more.

So many levels

So on how many levels is this an insane idea? Quite a few. Cassettes have many problems that should have sealed their death in a lead coffin six feet under for eternity rather than rising zombie-like from the grave.

Level 1 - Frequency response

The cassette format has an inherently poor frequency response. Consider that professional reel-to-reel tape is normally run at 15 inches per second (ips), or 30 ips for superior high-frequency response. Cassettes run at one and seven-eighths inches per second. There's no way they are going to have a decent HF response. Actually there is, by using chrome or metal tape rather than the standard iron oxide (often known more simply as rust). But the poor HF performance was baked into the format at its inception and the remedy of inventing different tape formulations led to other issues.

Level 2 - Noise

Going back once again to reel-to-reel tape, professionally the tape is a quarter of an inch wide, divided into two for the two channels of a stereo signal (there are also guard bands at the edges and centre that reduce the width slightly). The cassette format uses tape that is a mere one eighth of an inch wide, and that is for two stereo tracks so that you can turn the tape over and play it in the other direction. So each track is one quarter the width of pro tape.

This leads to noise. Noise is troublesome enough in a pro recorder, and in the cassette format it is - to my ears - intolerable. Once again though, there came a remedy, but the cure didn't come without significant undesirable side effects.

Level 3 - Wow and flutter

To be honest, wow and flutter didn't trouble me too much with the cassette. If you're not aware already wow and flutter is an instability in the speed of the tape that leads to pitch variations. Wow is a longer term variation, flutter is faster.

But having said that, digital audio suffers no wow and flutter at all, and it is with digital audio that surely cassettes must now be compared.

Level 4 - Tape tangling

Anyone who ever had a cassette deck will remember this. At worst the tape will tangle around the mechanism and has to be cut free. A milder tangle can be teased out, but the tape will be creased and the sound will be mangled during this portion of the audio.

If you're lucky, then the tape won't be tangled at all - there's just a loop sticking out of the cassette when you remove it from the machine. You can use a ball-point pen to turn one of the spindles and take up the slack. Note that some modern-day cassette enthusiasts seem to think of this as a positive 'hands-on' feature. You will probably know by now that I disagree.

Level 5 - Dirty heads

Whoever cleaned the heads of their cassette deck? Ever? Hardly anyone. Yet the heads of a professional tape recorder would be cleaned at least once a day. And how much dirty brown stuff should you expect to come off onto your Q-Tip when you clean the heads with isopropyl alcohol? None - the heads should already be so clean that any residue is invisible.

So - a cassette deck with dirty heads. What's the problem? Well firstly high-frequency response suffers. High-frequency response drops rapidly if the tape is spaced away from the record/playback head by dirt. There's a formula that involves d (the spacing from the head), lambda (the wavelength of the signal) and the constant of 55, but I forget the mathematical arrangement. It was a long time ago.

Secondly - see I haven't finished yet - is that dirty heads make tangling more likely. Oh dear.

Level 6 - The infamous Dolby button

Ray Dolby helped invent the video recorder. Yes really. And he invented the Dolby button too, which nearly all hi-fi cassette decks had.

What the Dolby Type B noise reduction system does is boost low-level, high-frequency signals on record, and cut them back again on replay. It's a little more complex that that, but that's the gist.

The wonderful thing is that cutting back low-level signals on replay also cuts back the noise - by as much as 10 dB, which is very well worth having.

But there's a problem. Well two. Firstly, the Dolby system, in all of its types, only works properly if the level that comes off the tape on playback is the same as the level that when on during record. This is why the pro Dolby systems have line-up tones so that engineers can check.

But having 'unity gain', as we call it, depends on the tape recorder or cassette deck being correctly aligned to the tape that is in use. In pro studios, line-up is a vital part of daily analog tape routine. Whoever aligned their cassette deck? (Er, I did.)

So the result of the tape not being aligned correctly was that the Dolby system could play back with too much or too little high frequency energy.

And of course dirty heads would make this worse.

The upshot was that many casual users didn't like the Dolby button and left it switched out. They thought it sounded better that way.

Level I've lost count - Incompatible tapes

This relates to some of the topics above, but it was an issue that there were different types of tape - iron oxide, chromium dioxide and metal, which required the deck to have different alignments electronically. In theory either the deck itself could detect which type of tape was inserted, or the user could push a button. In practice it caused a lot of confusion. Furthermore, different brands of the same type could require different alignments. Incorrect alignment would lead to incorrect frequency response, particularly at high frequencies, and incorrect operation of the Dolby noise reduction system.

Level Just one more...

I nearly forgot about this one, but azimuth. Azimuth is the orientation of the tape head with respect to the tape. The gap in the magnet of the tape head must be at 90 degrees to the direction of travel of the tape. In any one cassette deck, correct azimuth wouldn't matter much because the same head is used for both recording and playback. But record a cassette on a machine with incorrect azimuth and play it back on one with correct (or simply different) azimuth and there would be frequency response issues galore.

Phew

OK, I'm exhausted, and there are most likely other problems that I've forgotten about. But surely any potential cassette revivalist will realise by now that they should be listening to Spotify, Apple Music, or any of the other wonderful outlets for digital music with NONE of the faults listed above.

One more thing however... It wouldn't be right to leave this topic without paying respect to design engineers who worked incredibly hard and put in an enormous degree of creativity to make some cassette decks that really could challenge pro reel-to-reel. I'm thinking primarily of Nakamichi. If you want to treat yourself to views of some amazing audio engineering, head over to YouTube and take a look...

P.S. Thanks to Guardian writers Zoe Wood and Ben Beaumont-Thomas for inspiring this article.

Saturday November 9, 2019

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David Mellor

David Mellor

David Mellor is CEO and Course Director of Audio Masterclass. David has designed courses in audio education and training since 1986 and is the publisher and principal writer of Adventures In Audio.

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