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From: kimr@azure.UUCP (Kim Rochat)
Newsgroups: net.audio
Subject: Re: CD player differences - did you control for absolute phase?
Message-ID: <424@azure.UUCP>
Date: Tue, 20-Aug-85 13:47:23 EDT
Article-I.D.: azure.424
Posted: Tue Aug 20 13:47:23 1985
Date-Received: Sat, 24-Aug-85 03:29:38 EDT
References: <456@olivee.UUCP> <4150@alice.UUCP>
Organization: Tektronix, Beaverton OR
Lines: 32

> Hearing differences and not being able to agree on what they are
> is a typical result of very slight level differences.  Since you didn't
> match levels, how do you know that mismatches don't account for
> the differences you think you heard?

I've been hearing a lot from alice!ark about level matching to with .01db
(at what frequency?) for CD player comparisons.  What I haven't been hearing 
anything about is how he controls for absolute phase differences between 
players.  We all know from looking at Len Feldman's tests in Audio magazine 
that CD players in general tend to be haphazard about observing correct 
polarity for the output signal.

There is an excellent discussion of absolute phase in "On the Audibility
of Midrange Phase Distortion in Audio Systems" (Lipshitz, Pocock, and 
Vanderkooy, JAES Vol 30, #9, Sept. 1982), which includes the observation
that "(absolute phase) is an audible factor, and should be taken into
account when performing comparisons of audio components."

Just as ark discounts all CD comparisons which do not control for amplitude,
I discount his comparisons until he shows that he controlled for absolute
phase.

(Of course, another popular position is that the differences between CD
players are so gross that you can hear them without controlling for either)

I submit that the differences reported heard between CD players 
in this forum (soundstage, image placement, hardness) more closely 
correspond with the effects of different absolute phasing than the effects of 
different amplitudes.

Kim Rochat
tektronix!azure!kimr