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From: jbm@eos.arc.nasa.gov (Jeffrey Mulligan)
Newsgroups: sci.electronics
Subject: Re: ..but what about _output_ filtering for D/A's?
Message-ID: <7520@eos.arc.nasa.gov>
Date: 27 Oct 90 00:17:51 GMT
References: <1319@beguine.UUCP> <17660121@hpfcdj.HP.COM> <5877@munnari.oz.au>
Organization: NASA Ames Research Center, California
Lines: 30

gja@mullian.ee.mu.oz.au (Grenville Armitage) writes:

>In article <17660121@hpfcdj.HP.COM> myers@hpfcdj.HP.COM (Bob Myers) writes:
>>Wait just a minute, John.  As SOUND, the answer to this question is *no*.
>>You will not, for example, hear a 1000 Hz tone when exposed to *sound sources*
>>of, say, 20 kHz and 21 kHz.  The ear doesn't work that way.

>Hmmm. Try telling that to guitar players who
>tune their instruments by ear. At least one technique
>I know of (and use) involves listening for the 'beat' notes
>as you tune each higher string to a harmonic of the previous
>string.

There seems to be a lot of confusion about this.  Sure a guitarist
can hear the beat; but he can because he can hear the carrier,
not because the beat itself might be at an audible frequency.
There has to be a nonlinearity before there will be any spectral
energy at the beat frequency.

Another poster mentioned the psychological phenomenon of
"periodicity pitch", where a complex of tones having frequencies
1000, 1100, 1200 will have a subjective pitch of 100 Hz.
This is fine, but again the tones in the complex have to
get into the auditory system first.  Ultrasonic tones don't.

-- 

	Jeff Mulligan (jbm@eos.arc.nasa.gov)
	NASA/Ames Research Ctr., Mail Stop 262-2, Moffett Field CA, 94035
	(415) 604-3745