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From: gregr@tekig1.UUCP (Greg Rogers)
Newsgroups: net.audio
Subject: Re: differences in sounds of CD players
Message-ID: <1509@tekig1.UUCP>
Date: Thu, 12-Jan-84 04:51:36 EST
Article-I.D.: tekig1.1509
Posted: Thu Jan 12 04:51:36 1984
Date-Received: Sun, 15-Jan-84 00:28:52 EST
References: <773@drufl.UUCP>
Organization: Tektronix, Beaverton OR
Lines: 69

Phil, you seem to want to provoke a debate on the sound of CD's based only
on unsupported assertions of their sound quality.  Is it correct to assume
that you have no knowledge of, or respect for scientific method?  I have yet
to find a single person who has been able to demonstrate any significant
audible difference between CD players under a scientifically controlled
double-blind test.  If anyone is aware of any such test that supports your
assertion will they please provide a reference to the test.  This will 
really be of benefit to those of us who spend a great deal of time
discovering the physical, measurable differences between audio components
that do contribute to audible differences. 

It must be stressed EMPHATICALLY that any perception of differences between
audio components that is NOT the result of controlled double-blind testing
is simply worthless information given the performance levels of todays 
electronic components.  (It is likely that the audibly gross differences
between speakers and cartridges makes such rigorous testing unnecessary
to merely prove differences exist but continued improvements in these
components may make or already have made even this a dangerous exception.)
Note carefully the word CONTROLLED above.  This implies that all external
variables that can influence the sound of the units under test are removed.
I believe that we are all aware that when comparing two nearly identically
components if the sound levels are not precisely matched (0.2 dB has been
documented) that the louder observation will usually sound better and at 
the least different.  Hence I repeat any claims of sound differences between
CD players NOT made under controlled double-blind testing is WORTHLESS.

But maybe the real question should be, "Given the amazing measured performance
levels of even the very first CD players, could they still sound different?"
The answer to that is very simple - "Of course they could".  It seems unlikely
(even contradictory to many controlled tests) that the current set of parametersbeing measured would be responsible.  But the possibility exists that we are
not measuring some previously unconsidered parameter that does have an effect
at an audible level.  But it is clearly up to those that claim to hear a 
difference to prove through proper testing that a difference exists before
we need to search for some heretofore unknown parameter.  Until that day comes
the evidence suggests that even the first of the CD players are capable of
reproducing the recorded CD's with no significant degradations or differences.

(Ah yes, that word "significant" again, there is no question that measurable
differences exist between players, but our previous knowledge maintains
that they are not audible.)

For anyone not yet bored I should give an example of discovering a new 
parameter that affected sound quality but proved tough to discover.  It was
long believed by many (seemed obvious to most critical listeners) that
moving magnet input stages of phono preamps sounded different between
components.  Some "objective" reviewers who based their opinions only on
measurements claimed that differences didn't exist.  This was due to the fact
that they made measurements by driving the input of the preamp from signal
generators which didn't accurately simulate the complex interaction between
the output impedance of the cartridges and the input loading of the preamp.  
Hence their measurement technique was faulty.  (Their real sin here was not
trusting their ears to make them question the measurements).  Controlled 
double-blind testing provided ample evidence that differences did in fact exist.Having proven the existence of differences it was relatively straightforward to
isolate the cause and design better measurement techniques and in fact to
design better circuits to eliminate the interaction problem.  The difference
in this example to today is that testing did show audible differences between
components.  Critics of CD's should not take too much encouragement from this
example because the reverse has also proven true.  Despite the best efforts
of a rather famous amplifier designer he was unable after several attempts
to prove his amplifier to sound audibly different than another under such
rigorous testing.  If anyone would like further information on testing
methodology or any example I noted consult the back issues of the 
Audio Engineering Society Journal.

				Still working on REAL improvements,
				Greg Rogers