Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Posting-Version: version B 2.10.1 6/24/83 v7 ucbtopaz-1.8; site ucbtopaz.CC.Berkeley.ARPA Path: utzoo!linus!decvax!ucbvax!ucbtopaz!newton2 From: newton2@ucbtopaz.CC.Berkeley.ARPA Newsgroups: net.audio Subject: Re: Re CDs and square waves Message-ID: <502@ucbtopaz.CC.Berkeley.ARPA> Date: Sat, 23-Jun-84 03:41:09 EDT Article-I.D.: ucbtopaz.502 Posted: Sat Jun 23 03:41:09 1984 Date-Received: Sat, 23-Jun-84 23:44:03 EDT References: <3979@mordor.UUCP> Organization: Univ. of Calif., Berkeley CA USA Lines: 41 Here's another contribution to the discussion of square-wave response that seems evergreen among audiophiles. First, in comparing the perceived sound from reproducing 20 kHz sine and square waves, it seems to me that equal rms amplitudes is precisely what you *don't* want- you want the audible components equal (a little question- begging here, I'm afraid). If the rms values are equal, then 10% or so of the energy of the square wave is in higher harmonics, versus 100% of the sine wave concentrated at 20 kHz. You're trying to demonstrate that the so-called ultrasonic components are audible, so shouldn't they be present *in addition* to the 20 kHz component? Second, as someone earlier pointed out, for a symmetrical waveform, the first higher harmonic present is at 60 kHz, not 40 kHz. We're talking BATS here, forget about Fido. Only tiny flying rodents (and golden-eared audiophiles unconstrained by double-blind experiments) can hear this stuff; only hunter-killer submarines and Polaroid cameras can emit it. The Nyquist argument seems definitive to me-- the whole point of the anti- imaging or reconstruction filter is to eliminate the ambiguity inherent in the sampled data. Just asserting that alternating maxes and mins are written "by a computer" on the disk doesn't show that a "square" was written-- *every* sinusoidal component of the audio spectrum recorded on a CD could be interpreted as a poorly-reproduced squarewave, and images-without-end (within the slewrate limit of the DAC) would be reproduced absent the smoothing filter. Speaking as an erstwhile audio designer (and only for myself), I find squarewave testing the world's most wonderful shortcut in *quickly* assessing what's going on phase/amplitude wise *in those well-behaved circuits where it's useful*. Examples of such are DC-coupled amplifiers and such, equalizers that are alleged to have "flat" positions and so on. Examples of circuits that everyone either puts up with, assumes are "perfect" or simple doesn't realize are ubiquitous are transformer- coupled mic preamps, transformer-output mics, virtually all FM exciters, "classic" tube amps, crossover networks (active or passive) and so on-- square wave testing is often uninformative for these circuits, which nevertheless seem to perform sufficiently transparently (when well-designed) to allow golden-earniks to hear right through to the special beeswax Georg Neumann used to coat the capacitors in those priceless prewar tube mics...:-)