From: utzoo!decvax!harpo!eagle!karn
Newsgroups: net.audio,net.physics
Title: Re: Digital Vs. The Audiophile.
Article-I.D.: eagle.694
Posted: Thu Dec 16 18:47:37 1982
Received: Sun Dec 19 08:59:36 1982
References: eisx.471

A properly designed digital audio system records waveforms in the time
domain by sampling them at a rate greater than twice the highest
frequency component in the input signal.  It doesn't matter what the
sampling rate is, so long as it is at least the Nyquist rate (2x f) and
the anti-aliasing input filter doesn't distort or roll off the highest
frequency desired input signal.  A 200 khz sampling rate would be a
complete waste of bits.

The human ear CANNOT distinguish between a 20 khz sine wave and a 20 khz
non-sinusoidal wave, unless your hearing extends to at least 40 khz.
This is an established fact.  For this reason, a digital audio system's
inablility to reproduce 20 khz square waves means nothing.

As far as phase balance errors between channels are concerned, I find
this hard to accept as a real problem.  If both channels are not sampled
simultaneously, this is fine so long as the D/A converters
reconstructing the output signals update their outputs with the same
timing.  If not, this would be an inexcusable design error which could
have been easily avoided.

I'm sure that analog tape heads introduce more phase balance errors simply
by being out of azimuth alignment than any production digital recording
system.  To show the effect of azimuth alignment on channel-to-chanell
phase delay, try this experiment:

Play a high frequency tone (a head alignment tape always has this) with
the output channels combined (mono).  Adjust the head azimuth.  You will
hear "beats" as the adjustment is made; this is the result of the two
tracks going alternately in and out of phase as the angle of the
playback head is adjusted. The proper adjustment is to peak the tone in
the "center" beat; I usually find that I can get to the proper point by
adjusting azimuth first on music known to have been recorded by a
well-aligned deck, peaking the high frequencies by ear,
then making the fine adjustment with the high frequency alignment tape.
Only a small change in azimuth would be sufficient to cause a 10 degree
phase imbalance between channels at 10-15 khz.

Back to digital audio, my point is that almost any shortcoming of
digital audio, imagined or otherwise, is far more likely to actually occur in
conventional analog recorders.  Try aligning even a good quality analog deck at
high speed with good tape, and you'll be amazed at how imprecise they
really are compared with digital's known performance.  Again, I
challenge anybody to produce a properly controlled, double-blind study that
shows 50 khz, 16 bit digital audio to be inferior to the best possible
analog recording techniques.

Phil Karn