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From: mat@hou5d.UUCP (M Terribile)
Newsgroups: net.audio
Subject: Re: CDs: why no square waves?
Message-ID: <990@hou5d.UUCP>
Date: Tue, 19-Jun-84 08:43:43 EDT
Article-I.D.: hou5d.990
Posted: Tue Jun 19 08:43:43 1984
Date-Received: Thu, 21-Jun-84 01:00:29 EDT
References: <28@sunybcs.UUCP>
Organization: AT&T Information Systems Laboratories, Holmdel, NJ
Lines: 32

Here we go again:

	But you missed the point...
	If the CD logic is sound it must reproduce a perfectly square wave
	given a properly generated square wave test disk.

	The sinusoidal properties that the square wave on CDs display
	is the perfect example of how the CD theory is either improperly
	executed or has a basic fault.

	They ring, and you know it.

If you put in a 1 Khz square wave, run the output through a filter with
perfect phase characteristics which cuts off sharply at 21 kHz, and view the
result, you will see a square wave with sinusoidal type ripples on it.  That's
all there is to it -- the 21st, 23rd, etc, harmonics of a 1kHz square wave are
large enough to be visible, less than 15 db down, and over 21 kHz.

It's true, some (but not all) of the filters used exhibit ringing.  Oversampled
players with combination digital and analog fiters do better than straight
analog filters.  The oversampling allows the corner frequences to be up
over 40hKz (hence less phase muck-up) and move much of their increased
quantitization up to the 176kHz area.  The digital filtering spreads the
reconstruction distortion both backwards and forwards in time, so that
the result looks more like what they showed you when you learned about
Fourier transforms.
-- 

					from Mole End
					Mark Terribile
		     (scrape..dig)	hou5d!mat
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