[linux-audio-user] Re: Sample Rates /Sample Sizes

[Greg Murphy]

On Sat, Jun 19, 2004 at 04:30:26 -0400, Chris Pickett
wrote:
> At first glance that seems fairly honest.  It does
also suggest that 
you 
> wouldn't appreciate the benefits with a normal audio
CD, so in that 
> respect it seems pointless, but maybe I'm missing
something.  As for 
the 
> Nyquist frequency I read some discussion that some
people can hear up 
to 
> 23 kHz, and that there may even be psychoacoustic
effects up to 30 
kHz, 
> but I didn't try to find any references on this.

I think that there has been quite a lot of work done
on the optimal theoretical sampling rate for audio and
as I remember it was somewhere around 60kHz (I may be
wrong). There are good reasons why it's not as simple
as saying that the limit of hearing is, say, 23kHz so
we need a max sample rate of 46 (as per Nyquist).
Unfortunately, the A/D/A process uses filters (e.g.
decimation filters) which can introduce distortion at
frequencies which may be audible. Thus, one benefit of
higher sampling rates is that these distortions are
pushed up to higher frequencies well outside the range
of our ears. Thus, while a system running at 44.1 may
introduce distortions at, say, 20kHZ, a system running
at 96kHz would produce analogous distortions at, say,
44kHz which is way above the audible range. Thus 44.1
is probably not as transparent as 88, 96, etc.

I'm away from my desk at the moment so I can't list
any references but I do know that Dan Lavry has
recently written an AES paper about this subject.
While it's mainly about the reasons why 192kHz is bad
(limits of engineering), it provides an excellent
background in sample rates, etc. I think the web site
is lavryengineering.com

Psychoacoustics is just a bit too frightening for me
I'm afraid. Although I would urge everybody to read
Yost's book and if they like this stuff try Moore's
psychoacoustics book. Prepare to be amazed though!

Greg





	
	
		
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