[sdiy] OTish - CDDA bandwidth

[Nicholas Gregorich]

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?  I've looked on Wikipedia and tried some Googling,  
but I can't find any hard facts.  I found an AES paper on the  
development of CDs but it doesn't talk about the analog front end  
conversion.

Does it even make sense?  Are harmonics over 11kHz not valuable?  I  
don't have the greatest hearing but I definitely hear over 11kHz.  If  
the signal was band limited to around 22kHz, lots of harmonics would  
be gained as well as high frequency fundamentals.  Don't you gain  
phase information of the ~11kHz signal by going multiples of Nyquist  
(and not limiting the signal in the analog domain)?  The harmonics of  
the frequencies between 10kHz and 20kHz aren't audible and thus  
unimportant [or are they?...but that's a topic for another day].

So my basic question is are CDs band limited to 11kHz and uselessly  
sampled at twice Nyquist?

[Anything to avoid studying].  Thanks.

Nick.