Path: utzoo!attcan!uunet!lll-winken!lll-lcc!ames!eos!phil
From: phil@eos.UUCP (Phil Stone)
Newsgroups: comp.sys.amiga
Subject: Re: Sampling at 29KHz (long)
Summary: Followup to EMAIL please
Message-ID: <736@eos.UUCP>
Date: 19 May 88 16:45:29 GMT
References: <2845@polya.STANFORD.EDU> <734@eos.UUCP> <53788@sun.uucp>
Reply-To: phil@eos.UUCP (Phil Stone)
Organization: NASA Ames Research Center, Calif.
Lines: 39

In article <53788@sun.uucp> cmcmanis@sun.UUCP (Chuck McManis) writes:
<In article <734@eos.UUCP> phil@eos.UUCP (Phil Stone) writes:
<<Compute a 256-point sine wave and put it in memory (32-byte sine waves
<<don't cut it in my book - even a tin ear can hear the interpolation
<<noise in fixed, jagged steps that big).
<
<Phil you still don't get it do you? If take a 32 sample sine wave
<and run it through a spectrum analyzer, you will find that it has
<a big fundamental at the frequency of interest, and a bunch of 
<higher order frequencies that are caused by the 'interpolation' noise.
<The key feature is that *all* of these frequencies are above the
<'nyquist' frequency. The Amigas low pass filters start cutting of 
<frequencies above 7Khz and pretty much eliminate everything above
<14Khz.....etc.
<--Chuck McManis

Wow - now the 7Khz cutoff of the filter on the Amiga sound channels is
being touted as an advantage!  The reason the cutoff is so low (and
therefore has inspired hacks and now a 500/2000 option to bypass it 
in order to get any decent high frequency response) is precisely because
of the low sampling rate.  Saying that the low sampling rate is not a
problem because the absurdly low cutoff frequency of the filter "fixes"
it, is like equating not swimming with solving the problem of shark
attacks.  Damn, I'm not saying scrap the Amiga sound driver, just
suggesting some areas where it could be improved.  I am amazed at how
many people (not all of whom even program the sound device) have reacted
with "That's not a problem!"

I've taken the original discusion to email, as I sense that its welcome
is about to wear out here.  Please feel free to write.

>uucp: {anywhere}!sun!cmcmanis   BIX: cmcmanis  ARPAnet: cmcmanis@sun.com
>These opinions are my own and no one elses, but you knew that didn't you.

			Phil Stone

phil@eos.arc.nasa.gov
phil@eos.UUCP
{ uunet, hplabs, hao, ihnp4, decwrl, allegra, tektronix } ames!eos!phil
I'm sneaking these opinions out without my employer's knowledge.