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From: gregr@tekig1.UUCP (Greg Rogers)
Newsgroups: net.audio
Subject: Re: cd playback sampling delays
Message-ID: <1653@tekig1.UUCP>
Date: Thu, 17-May-84 02:52:16 EDT
Article-I.D.: tekig1.1653
Posted: Thu May 17 02:52:16 1984
Date-Received: Mon, 21-May-84 05:28:05 EDT
References: <415@houxa.UUCP>
Organization: Tektronix, Beaverton OR
Lines: 43


While it is true that many CD players have an 11.34 uS time delay between
channels for the reason you cited this has ABSOLUTELY NO EFFECT during
normal stereo reproduction!  During stereo reproduction through speakers the
11.34 uS time delay is exactly the same effect as moving the left or right 
speaker forward by 0.15 inch.  (Sound travels approx. 1130 ft/sec.  Hence
1130 ft/sec x 11.34 uS x 12 inches/ft = 0.15 inches.)  Since I am quite 
certain you haven't measured the distance from your ear to the left and right
speaker to this accuracy, and installed a head restraint to prevent you from
moving your ears less than 0.15 inches while you listen, you are already 
listening to far more interchannel time delay than this with your ANALOG 
record playing system.  So if this problem is really bothering you so much
while listening to your speakers you don't have to buy a "good" CD player
to fix it, simply move one of your D#!% speakers.

Please note: This is an entirely different issue than nonlinear phase response
in a single channel caused by anti-aliasing filters which we have spent so
much time on in the past.

I also don't believe there is any evidence to support the ability of interear
time delay perception anywhere near 11 uS.  This would be the case when 
listening to stereo headphones.  With stereo headphones the path delay between
ears is pretty tightly matched.  But since each ear gets a single channel
exclusively there is no opportunity for phase cancellation.  

The only case where a problem can exist is with mono signals electronically
mixed together by putting a preamp in the mono mode.  Even here it is necessary
to use headphones to detect the effect, since with speakers each ear will
hear both speakers and a path difference larger than 0.15 inch will result
unless the abnormal (and perhaps kinky?) precautions mentioned above are taken.
Hence you will hear both the effect from the CD player and the effect from
using two speakers to reproduce mono present with any ANALOG media.  For my own
listening I could care less what happens in mono through headphones and wouldn't
spend a dime more to get a player that corrects a problem in a mode that 99%
of the user's would never use.  To me this is GOOD engineering not bad as
implied.  Radio station's that broadcast in mono may be well advised to buy
a unit prepared for this purpose however.

				Once more into the breach,
				Greg Rogers
				Tektronix