Path: utzoo!mnetor!uunet!lll-winken!lll-lcc!lll-tis!ames!hao!gatech!bloom-beacon!mit-eddie!mit-amt!dlleigh
From: dlleigh@mit-amt.MEDIA.MIT.EDU (Darren L. Leigh)
Newsgroups: comp.sys.amiga
Subject: Re: Sonic Tomfoolery
Message-ID: <2078@mit-amt.MEDIA.MIT.EDU>
Date: 29 Feb 88 16:48:05 GMT
References: <8802251858.AA21577@cory.Berkeley.EDU> <719@ur-cvsvax.UUCP> <7233@cisunx.UUCP> <4292@xanth.cs.odu.edu>
Reply-To: dlleigh@media-lab.MEDIA.MIT.EDU (Darren L. Leigh)
Organization: Arakeen Sewage Authority
Lines: 47
Keywords: phase frequency audiophiles
Summary: phase -- do math and don't read audiophile magazines

In article <4292@xanth.cs.odu.edu> kent@xanth.UUCP (Kent Paul Dolan) writes:
>In article <7233@cisunx.UUCP> ejkst@cisunx.UUCP (Eric J. Kennedy) writes:
>>In article <719@ur-cvsvax.UUCP>, jea@ur-cvsvax.UUCP (Joanne Albano) writes:
>>> In article <8802251858.AA21577@cory.Berkeley.EDU>, dillon@CORY.BERKELEY.EDU (Matt Dillon) writes:

[discussion of phase, frequency the ears and the mind]

>I don't think so!  I remember reading many years ago that although the
>human ear can only hear pitches up to about 20,000 Hz, that a stereo
>system, to maintain fidelity enough to allow a listener to pick out
>the second violinist playing half a tone flat in a symphony recording,
>had to keep the left and right channel phase relationship correct to
>the equivalent of 200,000Hz, because the human brain, processing the
>audio signals, is that sensitive to phase relationships.  I believe
>the math can be done to prove this with a pocket calculator and a back
>of the envelope diagram of a symphony hall and a schematic human head.

Aaaayyy!  This gets batted around all the time in rec.audio.  How
about a little back of the envelope calculation instead of reading
trashy audiophile magazines.

Sound travels at about 340 m/s.  At 200 KHz, that makes one wavelength
equal to 1.7 mm.  If phase were a problem, we would have to match the
path lengths from each speaker to the eardrum to within a small fraction
of that distance.  Even when wearing headphones, there are differences
in the ear canal which can easily amount to more than that.  At
reasonable frequencies, say about 10 KHz, the wavelength is still
too small (3.4 cm) to worry about.  Also, there are diffraction and
interference problems that can mess up the phase.

I know there are some good texts on psychoacoustics.  Can somebody
recommend any?

>Certainly, given a choice between believing I detect directions that
>closely by the amplitude difference or by the phase difference, I'll
>go for phase on intuition alone.

This is the problem with a lot of those audiophile magazines.  Belief,
but no fact.

>Comments?
>
>Kent, the man from xanth.

Sorry, Kent.  I hope your presidential candidacy goes better.

Please don't post flaming replies to comp.sys.amiga.  If anyone has
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