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An Introduction to Compression: Basic Compression - A free download from Audio Masterclass

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Three things that are tragically wrong with CDs

Pure perfect sound forever? The original CD slogan wears thin in the face of three major defects in the format

There are many good things about the CD format. It is better than vinyl for one thing, except of course for vinyl's hands-on features for certain styles of music.

And if you look after your CD collection, you will hardly ever find a disc that develops defects of its own accord.

However, the originators of the CD format, Philips and Sony, made three major errors in its design. Errors that are locked into the format and can never be rectified.

Firstly and most majorly, CDs are prone to damage. They are highly resistant on the side from which the date is read. Even severely scratched discs will play perfectly, although occasionally a scratch that follows the path of the spiral data track can be problematical. CDs are also affected by fingerprints, but fingerprints can easily be cleaned - they shouldn't be allowed to get onto the disc in the first place.

But CDs are prone to damage on the label side. The reflective aluminium layer is protected by only 10 to 30 microns of lacquer. Scratch this side and your CD is ruined.

More modern formats such as DVD use two layers of plastic, sandwiching the data very securely in between.

The second problem with CDs is one of lack of foresight. The development of CD followed the Quadraphonics craze of the 1970's by only a couple of years. So there can be such a thing as a 4-channel CD. Really.

Personally I have never seen one, nor have I come across a 4-channel CD player. But it can be done.

What can't be done however is to create a mono CD. No-one realized back in the early 1980's that one of the most significant applications of CD would be the reissuing of old recordings, many of which were made in mono.

Also, spoken word has been a great application for CD. Many spoken word productions can work perfectly well in mono.

If there had been a mono option in the CD format, then it would have been possible to double the standard maximum duration from 74 minutes to 148 minutes.

But it can't be done since there is no mono option, and no CD player would recognize a mono disc.

The third problem is astounding - there is no provision in the CD-Audio format for the CD to contain track title information!

How crazy is this - you can't store the title of the CD nor the titles of the tracks actually on the disc itself? (This facility is available in the CD-Text format. Unfortunately it came too late and its use is some way from universal.)

There is a workaround when a CD is played on a computer - the audio player software queries a central database that can return track titles based on timings read from the disc's table of contents. But standalone CD players can't do that.

There is in fact quite a lot of data space available on a CD that isn't used. The CD format allows for eight subcode areas, of which only two have a function - the P and Q codes.

The other six - R, S, T, U, V and W - are left blank because no-one ever managed to standardize any useful purpose for them. That is a potential data rate of 44,100 bits/second going to waste (the figure of 44,100 bits per second compared to the sampling rate of CD of 44,100 samples per second is coincidental).

And this unused data capacity could easily have been used for track titles.

The unused subcodes could also have been used for level control info, so that for instance a car CD player could lift the levels of quiet sections so that they could be clearly heard over the engine noise. Shame.

In conclusion, well done Philips and Sony because the CD is a very good format and continues to serve us well. But if we could turn back the clock...

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By David Mellor Friday December 16, 2005
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