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 ___________________________________________________________ALL-NEW Yahoo! Messenger - sooooo many all-new ways to express yourself http://uk.messenger.yahoo.com
