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From: karn@allegra.UUCP
Newsgroups: net.audio,net.flame
Subject: Re: jj's Re: Thoughts on subjectivity and specifications
Message-ID: <2248@allegra.UUCP>
Date: Wed, 1-Feb-84 16:14:00 EST
Article-I.D.: allegra.2248
Posted: Wed Feb  1 16:14:00 1984
Date-Received: Tue, 7-Feb-84 14:01:26 EST
References: many, <779@drufl.UUCP>, <2387@rabbit.UUCP>, <782@drufl.UUCP> <2458@rabbit.UUCP>
Organization: AT&T Bell Laboratories, Murray Hill
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Regarding the "phase shift" complaint in CDs....again...

THIS IS AN UTTER RED HERRING!!!!!  The only people who complain about the
"inherent CD player phase shift problem" are those who  a) haven't looked
at many CD player lab tests  b) don't know the first thing about
signal theory, and c) can't find any other term to latch onto to give
their vague complaints some pseudo-scientific credibility.

Take a look at the square wave and impulse response tests of the various
CD players.  For example, the Marantz player reviewed in the current
issue of Audio.  Notice the ripples on each side of the impulse or
square wave edge. See how they're nice and symmetrical?  This, BY
DEFINITION, indicates linear phase, and many of the CD scope photos I've
seen are practically textbook examples! The existence of the ripples in the
first place is an inescapable result of the sharp (i.e., nearly ideal)
AMPLITUDE response cutoff.  Only if these ripples were asymmetrical would
they indicate phase nonlinearity, in which different signal frequencies
encounter differing delays in arriving at the output terminals.

Now it is true that SOME CD player manufacturers have elected to
simplify the design by using filters that do not provide linear phase. 
It is still doubtful that ANYONE can hear the difference at the high
frequencies involved, but even if some could it is totally wrong to
claim that "phase shift" is an inherent and unacceptable problem with
ALL CD players.  The fact that people are fighting major wars over such
insignificant squabbles indicates just how close to perfection CD players
really are.

Phil Karn