[sdiy] OTish - CDDA bandwidth

[Eric Brombaugh]

On Dec 14, 2006, at 9:33 PM, Nicholas Gregorich wrote:

> Kind of off topic.  I am studying for a communications exam and it 
> mentions CDs as an example of PCM application.
>
> 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.
>
> Is this correct?

No. As you note, CDDA sample rate is 44.1kHz and the bandwidth is 
~22kHz (probably a bit less to allow for the filter transition bands).

Sounds like the 'material' you have is a bit confused. That's fairly 
common since there are a lot of definitions of Nyquist out there. Just 
remember this: To prevent aliasing, sample at 2x the highest frequency 
present in the signal you're sampling.

Eric