[sdiy] OTish - CDDA bandwidth

[Byron G. Jacquot]

>Now we all know the sampling rate is 44.1kHz.  However, the material  
>I have says that CDs are sampled at twice Nyquist.  They say since  
>Nyquist is 2x, then twice Nyquist is 4x, so the analog signal to be  
>sampled must be band limited to 11.025kHz.

You say Nyquist, do you mean Nyquist frequency, or Nyquist rate?

There are two frequencies here: the Nyquist frequency is the highest frequency you want to sample.  The Nyquist rate is the lowest sampling rate needed to capture that frequency.  The rate is generally 2x the frequency.

Human hearing is usually accepted as being something like 20 Hz to 20 kHz.  20 kHz X2 = 40 kHz ~= 44.1 kHz.  The band-limiting should pass a 20kHz signal, but stop anything at 22.05 kHz...and the design of such steep filters leads to another batch of problems.

Byron Jacquot