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From: ark@rabbit.UUCP (Andrew Koenig)
Newsgroups: net.audio
Subject: Unmeasurable differences?
Message-ID: <2389@rabbit.UUCP>
Date: Fri, 13-Jan-84 17:23:49 EST
Article-I.D.: rabbit.2389
Posted: Fri Jan 13 17:23:49 1984
Date-Received: Sat, 14-Jan-84 07:30:41 EST
Organization: AT&T Bell Laboratories, Murray Hill
Lines: 56

Quote from Phil Rastocny:


	Now if there is a set of technical parameters that will assist me
	in relating what can be heard to what can be measured, fine.  Specs
	are supposed to steer us in the direction of what equipment we want
	by correlating them to what we hear.  AND we should be able to measure
	literally anything that we hear.  Great!  No argument.

	But if I can hear something that any of the specifications supplied
	with a piece of equipment cannot be correlated to the observation, then
	where do we go?  We talk about what we hear (like the soundstage size
	or inner detail) and then poke around in the circuit until we realize
	exactly what causes the observation spec-wise.

	Amplifiers that have similar distortion, damping, power, bandwidth, etc.,
	should all sound about the same.  But when comparing two equivalent
	amplifiers (like an Acoustat TNT-200 to a Kenwood Basic M-2)
	on a suitably refined reference system, they still sound different.
	(Both amps are class B about 200W, < 0.01% THD and IM distortion, both
	slew > 100V/uS, and both are finely engineered.)  All of the specs are
	orders-of-magnitudes greater than the ear should be able to detect and
	essentially identical.  But yet they still do not sound insignificantly
	different.

I'll mention this again.  A number of years ago, Audio magazine did
a carefully controlled double-blind test.  Very briefly, they concluded:

	1.  If two amplifiers with reasonably low distortion
	    figures are made to match VERY accurately in
	    frequency response, and they are not driven into
	    clipping, it is not possible to tell the difference
	    between them by listening, even if the listener
	    is a "golden ear."

	2.  Two amplifiers that differ in frequency response
	    by a little tiny bit will be perceived by a careful
	    listener as different, but not in any way subjectively
	    related to frequency response.  Rather, the listener will
	    hear differences in "depth," "imaging," and so on.

	3.  We are talking about frequency response variations of
	    the order of 0.3 dB -- small enough that two samples of
	    the same make and model will be that far apart.  In fact,
	    a SINGLE amplifier will vary that much from one day to
	    the next, from changes in temperature and humidity.

One of these days, when I have the time, I will scare up the exact
reference.  I posted it the first time I mentioned this test.  In
any event, the description of the test conditions was detailed enough
that unless the author was lying outright there was no doubt in my
mind that the test was fair.

I have NEVER seen any documented evidence that it IS possible
to hear differences in amplifier behavior that cannot be accounted
for by objectively measurable parameters.