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From: rpw3@fortune.UUCP
Newsgroups: net.physics
Subject: Re: Re: Digital Vs. The Audiophile. - (nf)
Message-ID: <2017@fortune.UUCP>
Date: Fri, 16-Dec-83 04:05:16 EST
Article-I.D.: fortune.2017
Posted: Fri Dec 16 04:05:16 1983
Date-Received: Tue, 20-Dec-83 01:46:18 EST
Sender: notes@fortune.UUCP
Organization: Fortune Systems, Redwood City, CA
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#R:unc-c:-117000:fortune:8600003:000:1995
fortune!rpw3    Dec 15 23:15:00 1983

"WATCH MR. WIZARD" COMES TO USENET (See "Experiment:", below)

-------------

Not to worry about phase distortion due to sampling rate. There is
an interesting thing about the human ear:

	- At LOW frequencies (a few hundred Hertz and below), we use
	  phase information to locate things, while

	- At HIGH frequencies (a few kiloHertz and up), we use
	  amplitude (loudness) to locate things.

In between, we use a mixture, as one might expect. The cross-over
between the two occurs at frequencies whose wavelengths are roughly
equal to the width of your head (surprise!), since making use of
phase information implies that the signal diffracts (not scatters)
around your head. (Sort of over-the-hairline sonar)

Experiment: You can prove this to yourself by putting a tone-generator
on to your amp + one speaker in a "soft" or "quiet" room. Set for a
single sine wave, and turn up the volume a bit. For very low ( <200 )
and very high ( >6000 ) freqs, you will think the sound is coming from
the speaker, but for certain middle frequencies, as you turn your head
(maybe eyes closed, to help), the sound will appear to "jump" around
the room. Try it. Fun.

[As an exercise for the reader, measure your head, divide by the
speed of sound, take the reciprocal, and listen to Andy Devine
saying "No, no, Froggie!"]

Don't use a "hard" room, or your head will wander in and out of
standing waves of the high frequencies, making you think phase is
important there too. It is, in a "hard" room, but only because the
standing waves actually modulate the amplitude at your ear.

So don't worry about your digital disks. The main problem with
sampling is aliasing harmonics back into lower frequencies "growls",
and (if they are AT ALL competent), the raw audio will have gone
through an anti-aliasing filter before being digitized.

Rob Warnock

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