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From: gwes@inmet.UUCP
Newsgroups: net.audio
Subject: Re: differences in sounds of CD players - (nf)
Message-ID: <749@inmet.UUCP>
Date: Thu, 19-Jan-84 23:45:31 EST
Article-I.D.: inmet.749
Posted: Thu Jan 19 23:45:31 1984
Date-Received: Mon, 23-Jan-84 02:49:32 EST
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#R:drufl:-77300:inmet:2600029:000:1716
inmet!gwes    Jan 16 14:00:00 1984

Re: distortion perceptions, time delays, and reviews

1) Up to 3% (or so) of CORRELATED 2nd harmonic distortion is often not perceived.
It is often first noticed as "warmth" in the sound.  HIGHER ORDER or
UNCORRELATED distortions (time domain) are much more easily perceived,
at the low levels of .05% or below.  In general, the higher order distortions
are much more unpleasant in smaller quantities.

2) The one area of time domain measurements I have done indicates extreme
sensitivity to time delays for ambience and placement information.  Movements
of speaker elements of approximately 1 inch (= 80 microseconds) can be
distinguished by comparisons.  Proper time correlation is recognized as an
"open window" effect, with instrument placement becoming definite.

Time delays in filters seem to generate the same type of effects.  I have not
been able to run controlled experiments to properly examine this, however,
the psychoacoustics folks often use Bessel filters for their experiments
because of the uniform delay characteristics.  They don't (often) care so
much about the amplitude ripple.

3) If you really want to get useful information from the advertising noise
in Audio, etc., read the reviews carefully.  Absence of praise and exact wording
is very important.  The classic example is the review that praises the
beautiful styling of the unit, and leaves performance to last.  The reviewer
is probably obligated to praise SOMETHING.  If he doesn't like the sound,
you will notice qualifiers or lack of definition in the review.  

The graphs and tables DO give you the objective data.  Read them.
The subjective data can be obtained by subtracting the hype offset.

Geoff Steckel (harpo!inmet!gwes)