charles@sunybcs.UUCP (Charles E. Pearson) (06/11/84)
<|->
With all this talk about CD and the like, how come nobody has started
either praising or flaming PCM???
Well? How 'bout it?
What are its problems? What about the sample rate?
What are its joys? (besides quiet background)
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.
Charles E. Pearson
UUCP: {allegra, seismo}!rochester!rocksvax!sunybcs!charles
decvax!watmath!sunybcs!charles
ARPA & CSNET: charles.buffalo@rand-relay
Physical: University Computing Services
4250 Ridge Lea Road
room 28
SUNY Center at Buffalo
Amherst, NY 14226fish@ihu1g.UUCP (Bob Fishell) (06/12/84)
Square wave response in CD players varies with the type of filtering
used. In general, those with digital filters tend to produce square
wave responses that are less ragged on top. However, it has to be
pointed out that musical instruments don't produce square waves, and
that square wave response is, at best, a very rough measure of the
frequency response of a system.
If you want to see some ugly square waves, hook up a function generator
to your amplifier, put some low-amplitude square waves through your
system, and hook the 'scope up to a microphone placed at any convenient
distance from your speakers. That's right, *your* speakers; I don't
care what kind they are or how much you paid for them. You will see
"square" waves that are considerably more distorted and ragged on top
than any CD player produces. Does this mean your speakers are no good?
Of course not, for the very reasons mentioned in the preceding
paragraph.
I don't know why you digiphobes don't appreciate CD technology, but I
do know that none of you has yet come up with solid technical evidence
for the abberations you purport to hear. Yes, there's a phase shift
with multipole Butterworth filters, and yes, there's a sharp rolloff
above 22 Khz. However, the fact remains that most people can't hear
whatever effects these phenomena produce. Now, I believe that you
really don't like what you hear from CDs, but you'll have to do a
little better than citing poor square wave response as a reason.
--
Bob Fishell
ihnp4!ihu1g!fishmike@brl-tgr.ARPA (Michael John Muuss <mike>) (06/18/84)
Charles Pearson asserts If they are sooooo good, them how come they naver can produce a square square wave? My NEC 803 produces a marvelous square wave. While 44.1 khz is woefully inadequate in my opinion, the NEC's technique of replicating the samples and then dong digital filtering, and running the DACs at a much higher rate with the (digitally) filtered result avoids all of the high frequency problems that most CD players are guilty of. The Philips machine uses this technique too, although I have heard tht they had to use 14 bit DACs instead of 16 due to the higher data rates needed... It is difficult to see how a test disk written by computer is likely to NOT have a perfect square wave on it -- my test CD does. As for the validity of testing auudio equipment with 20 khzsquare waves, Charles is RIGHT ON. *I* can hear the difference between a 20 Khz square wave, and a 20 Khz sine wave. The only difference is due to sine wave components at frequencies > 20 Khz. Therefore, extended frequency range is VITAL to accurate reproduction of very high frequency sounds, esp. percussion. This includes having speakers that are capable of reproducing the high frequencies, too. (My Infinity Quantum-2's are flat to 30 Khz, and gradually roll off beyond that. My Kenwood High Speed amp is flat to > 100 Khz. Even my Ortofon MC-20FL cartridge is fairly flat to about 25 Khz.) -Mike Muuss
karn@mouton.UUCP (06/19/84)
I find it rather doubtful that any member of the species Homo Sapiens (as opposed to members of the Canis family) can hear the difference between 20 khz sine and square waves. As any high school physics text will tell you, the next harmonic present above the fundamental in a square wave is the third. This means that the difference between a 20 khz sine wave and a 20 khz square wave starts at 60 khz! Any difference you hear is certainly due to audio frequency components generated by imperfections in your amplifer and/or speakers. I suggest that those who have a real fetish for perfect-looking square waves from your CD players simply bypass the D/A reconstruction low pass filters. You will then see transitions that are limited solely by the slew rate of the D/A converter and associated analog circuitry. Of course, those of you with perfect hearing will be bothered by all of the "image" spectrums centered around 44.1 khz, 88.2 khz, etc, on up to infinity, while those unfortunates such as myself who are afflicted with abysmally defective hearing (cutting off at only 20 khz) would still have to fight off all the neighborhood dogs (at least until the tweeters go up in smoke.) But wouldn't it be worth it just to get those lovely square waves without even a trace of ripple or phase distortion? Phil
5121cdd@houxm.UUCP (C.DORY) (06/19/84)
It would be a day that went down in history when you heard the difference between a 20kHz square wave and a 20kHz sine wave!! The first frequency component above the 20kHz fundemental is the 3rd harmmonic, 60kHz. The only thing you might be hearing are distortion products from your tweaters breaking up. Craig Dory AT&T Bell Laboratories Holmdel, NJ
charles@sunybcs.UUCP (Charles E. Pearson) (06/20/84)
make up your minds... Various re-flames on the subject alternate between the first harmonic from a 20Khz wave being 40K and 60K Well??? Which is it?
crandell@ut-sally.UUCP (Jim Crandell) (06/21/84)
> make up your minds... > Various re-flames on the subject alternate between > the first harmonic from a 20Khz wave being 40K and 60K > Well??? Which is it? Measure the duty cycle of your favorite 20-kHz square wave to an infinite number of decimal places, and I'll tell you. -- Jim Crandell, C. S. Dept., The University of Texas at Austin {ihnp4,seismo,ctvax}!ut-sally!crandell