Expert: Cleggsan - 9/10/2010

Question
I am an old man trying to come to grips with new technology. I understand that CD spins 200-400 times per minute to deliver a constant rate of data. Can you tell me how this compares with the delivery or amount of data contained in the old vinyl records? Just a rough answer would be good enough. Thank you very much.

Answer
CD does not spin at a constant rate; it spins at a linear rate so at the center of the disc it spins faster than at the outside of the disc.

The data rate of a CD is easy to think about.  The sampling rate is 44.1 KHz and the sample size is 14 bits.  That gives around 700 bits per second.  Another way of looking at it is the full play of a cd is 70 minutes and it contains about 700 MB of data.  Or about 1.4 MB/Sec (which includes all kinds of support data in addition to the music).

Since audio in analog form is a totally different format it is difficult to compare with digital, but as you know the bandwidth is 20 Hz to 20,000 Hz and in a vinyl recording it occupies an area much greater than a cd due to its diameter of 12 inches whereas the diameter of the CD is 12cm.  So, on that basis, comparing real estate used for the same music piece the cd is 2.54 times more dense.  This comparison does not take into consideration the digital music is much better in dynamic range and has a much better signal to noise ratio.

You can google around and find out lots of basic information.  See here;

http://www.mediatechnics.com/cdaudio.htm