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This has to be one of the most off-beat subjects I have seen on TV this year. There I was watching Discovery on a cold Japan winters day, while others were out trying to photograph something for the next Photo Hunt competition, when a program started and explained the birth of the Compact Disc.

So the story goes that it became a 74-minute medium because the then-president of Sony, Norio Ohga, wanted to be able to hear all of Beethoven’s 9th symphony,a popular piece in Japan, without interruption. I would venture to say that I can totally believe this story as I have been in enough Japanese meetings to understand how irrational some of the requirements can be, so this is not an extreme requirement at all.

However, having watched intently I began to question the validity of all this so I decided to turn to everybody’s friend, Google, and I uncovered an article which I found very interest.

Apparently, the story regarding the Sony President’s desires was not the case at all, at least not according to an engineer who worked on the CD. Instead it was Philips, not Sony, who were pushing, and they were pushing for the CD to be close in size to the “compact cassette tape”. Now, it turns out that a CD is slightly wider than that—120mm instead of 115mm, but the basic premise holds.

Also in the article it explains why CDs are 16 bit and 44.1khz. Not as arbitrary as we are usually told. The BBC in the UK was one of the first to adopt digital sound, and they were working with a 13-bit distribution system for the transmitter network, sampled at 32 kHz. Stockham’s experiments in 1972-3 with the Soundstream system involved sample rates averaging around 40 kHz, and he used computer tape as the means of storage, which made it practical to store data at 16 bit resolution because of the byte-orientated nature of computer data storage. 8 bits would have been too few, and 14 bits would have meant inefficient use of the storage space, so 16 bits seemed logical.

Sony and Philips worked under the following constraints:

• The bits to be etched the CD had to be 0.83 microns long and 1.6 microns apart. Hence about 750,000 bits fit in 1 sq. mm
• CD uses 16-bit audio with 2 (stereo) channels.
• Sound is sampled at at 44.1 KHz for historical reasons. So 1 sq mm translates to about 750,000 bits / 44,100 Hz / 32 = 0.53 seconds of music.

To read the full story select this link.

This story clearly is not as sexy or as cult-of-personality as the “We did it for the Pres” version but eminently interesting in its own right.

This post is tagged Why does the Compact Disc hold 74 minutes