Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Posting-Version: version B 2.10.1 6/24/83; site mordor.UUCP
Path: utzoo!watmath!clyde!burl!ulysses!mhuxl!houxm!houxz!vax135!floyd!cmcl2!seismo!ut-sally!mordor!sjc
From: sjc@mordor.UUCP
Newsgroups: net.audio
Subject: CDs: why no square waves?
Message-ID: <3821@mordor.UUCP>
Date: Tue, 12-Jun-84 04:34:34 EDT
Article-I.D.: mordor.3821
Posted: Tue Jun 12 04:34:34 1984
Date-Received: Wed, 13-Jun-84 00:12:48 EDT
Organization: S-1 Project, LLNL
Lines: 37

>now, back to my favorite passtime of flaming CD's....
> 
>If they are sooooo good, them how come they naver can produce a 
>square square wave?
>All of you out there who insist on seeing measurements and alike
>before evaluating something never seem to notice that a CD has
>never produced a (nearly) square wave.  Either they cannot produce one
>or the test disk was not properly written (and nobody is even trying
>to make a proper one)[test disk that is].
>Whay you all seem to miss is that the CD square wave has a decaying 
>sine wave across the top and bottom of the square where it is supposed
>to be flat.
>Even the SHURE V15 type II can produce a more square wave.

A square wave is equivalent to an infinite series of sinusoids. No
matter how perfectly a CD reproduces the components below 22kHz, it
cannot reproduce the components above 22kHz, so its square wave is
doomed.  The Shure V15 type II reproduces the components below 22kHz
more poorly than does the CD, but since it reproduces some components
above 22kHz (albeit even more poorly), its square wave looks "squarer".

I suggest, Mr. Pearson, that you perform two experiments, using a high
quality audio system. Find a signal generator which produces square
waves and sine waves of the same RMS amplitude. First, record a 10kHz
square wave at 0dB on a cassette and play it back, using a dual-trace
scope to compare the original with the copy. Then connect the signal
generator to the auxiliary input of your preamp, and alternately listen
to a 10kHz square wave and a 10kHz sine wave. In the first case, I find
the difference horrifying; in the second, it's almost imperceptible.

Analog tape recorders have a rough time of it: not only do they have
trouble reproducing high frequencies at full amplitude due to tape and
head saturation, they have phase-shift problems considerably messier
than those which have generated so much controversy with respect to CDs.

                                                           --Steve Correll
sjc@s1-c.ARPA, ...!decvax!decwrl!mordor!sjc, or ...!ucbvax!dual!mordor!sjc