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A Brief History


Understanding Digital Audio

We all take it for granted these days - the fact that we can fit thousands of tracks on a music player that will fit in our pockets. But it wasn't always this way. There was a time when the only way to carry your tunes around with you was to fill a knapsack full of cassettes.

If you wanted a playlist, you spent hours creating compilation tapes. And if you wanted quality on the move to match that which you could experience at home you could forget it. I remember spending huge amounts of cash on special, high quality blank tapes and fiddling around with Dolby noise reduction to get the best listening experience possible, but it was still far from perfect and not particularly portable either.

These days it's easy. Just stick a CD in your computer, rip it and you've got a damned good copy without even thinking about it. And thanks to audio compression technology you now carry around your entire music collection on something that will fit in your pocket.

But there's a whole lot more to digital audio compression than meets the eye.

Music compression effectively began with the CD. Most people think of CDs as being the perfect solution - a faithful copy of the original signal - but that's actually a long way from the truth. Unlike vinyl before it, the audio information stored on a CD doesn't actually represent the whole of the audio spectrum.

In order to squeeze everything onto a 648MB disc some information had to be ignored. All you get on a CD are sounds above 20Hz and below 20kHz. Everything else is excluded from the recording, the theory being that, due to physical limits in the make-up of the human ear, sounds from outside this range can't physically be heard.

But a CD is still pretty big, even by today's cheap storage standards, and in order for portable music to evolve, some other way of making music tracks smaller needed to be found.

It finally emerged in 1991. In the search for a convenient and portable recordable format - a successor to the analogue cassette tape - Sony introduced the MiniDisc format. Although MP3 was also born around this time, this was the first mainstream music format to use data compression and managed to squeeze the whole of a 648MB CD onto a single, 140MB magneto optical read/writable disc. To do it, it used Sony's in-house developed ATRAC (Adaptive Transform Acoustic Coding) compression algorithm to squeeze a CD's worth of audio data onto a much smaller disc and it was a revelation.


Sony's MiniDisc technology was the first commercially successful implementation of lossy audio compression technology.


At a data rate of 292kbits, Sony claimed the new format was transparent to most users (indistinguishable from the original CD) and for the most part it was right. I remember comparing digital recordings made on my early MiniDisc deck with the CD the recording it was made from and finding it hard to tell the difference between the two.

Though few could have anticipated its eventual impact, it was a watershed moment for the music industry. It paved the way for computer-based music compression file formats and heralded, further down the line, a revolution in the way many of us now listen to, and buy, our music.

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