[net.audio] Digital Vs. The Audiophile.

pd (12/16/82)

I have some comments on the The Audiophile vs. Digital Recording debate.

The audiophile's position, that I have heard often, is "It doesn't sound
right, so there's something wrong with it." To which the Digital enthusiast
retorts : "All audio signals can be expressed as a sum of sine waves with
frequencies up to 20 Khz; and Digital techniques can accurately reproduce 
sine waves up to 20 Khz. So Digital recordings can accurately reproduce
all Audio signals."  At which point the audiophile retreats, baffled and
beaten.

However.

Fourier Transforms attempt to MODEL a REALITY. There are merely a way of
mathematically representing a REAL phenomenon. Fourier never claimed 
(like the good Scientist he was) that his frequency domain representation
of an audio signal (for example) was a complete explanation of reality.

A real scientist attitude would be not to reject the audiophiles perception
of poor quality of Digital recordings because it didn't fit within Fourier-
and z-transform models, but to devise repeatable, comprehensive experiments
to gather data on the Audiophiles' dislike of digital recordings, and then
attempt to explain it!

Who knows. We might actually learn something!

Prem Devanbu

ark (12/17/82)

I have yet to see documentation of a carefully constructed double-blind
experiment in which a panel of "experienced listeners" consistently found
a well-made digital recording to sound inferior to the best analog recordings.

karn (12/17/82)

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

burris (12/17/82)

#R:eisx:-47100:ihlpb:4000026:  0:1432
ihlpb!burris    Dec 16 21:28:00 1982


With only a very few exceptions, any audio signal CAN be reproduced
via the Fourier transform. The Fourier transform will accurately
represent any PERIODIC function. This is the key to the whole
argument. Most audio signals change in frequency and amplitude very
slowly with respect to even the lowest frequency to be reproduced.
Therefore, with the proper sampling and filtering, an audio signal
for all practical purposes is a periodic function.

The problem of a 20 Khz. square wave is a valid one. In order to reproduce
a 20 Khz. which is a REASONABLE representation of a square wave, at
least the first three odd order harmonics should be present at the
correct amplitude. This would require a response of 180 Khz. if
trying to use sine waves to reconstruct a square wave of 20 Khz.

There IS a perceptable difference between a 20 Khz. sine wave and
square wave but I'm not sure if there would be a perceptable difference
between a if even the first odd harmonic were present. However, This
would still require a response of 60 Khz. 

A digital format which has the capability to vary the slope rate
would stand a better chance, especially if the clock rate were high
enough. The main question is what would the audible waveshape of a
square wave look like after it passed through the amplifier,
recorder, reproduction chain and your ears, even using the best of
analog equipment.

Dave Burris 
ihlpb!burris
BTL - Naperville

FtG (12/17/82)

This digital discussion reminds me of the great hi-fi debate of so many
years ago. It seems the "experts" knew that there was no point
in reproducing high frequencies since human beans couldn't hear them.
Well... somebody performed an experiment using live musicians (as 
opposed to dead ones?) separated by a system of baffles from the
listeners. By adjusting the baffles, high frequencies could be
damped out. The listeners noticed a significant loss of fidelity.
The experts hadn't taken into account the huge difference between
detecting a single tone and "sensing" a full range of harmonics.
Thus hi-fi was born. (Coming next week, Uncle Ferd will tell you
the story of stereo!!!)
It seems that the digital people should know about these experiments
and taken into account the complex nature of hearing. In any case, I
can easily imagine the experts to be wrong again.
				FtG

thomas (12/17/82)

At the risk of being flamed off the net (watch out for the Geisthounds!), I
will add my two cents to this debate.

1.  How many of you can hear 20kHz anyway?  Can you hear the whine of a TV
    set (15.75kHz)?  If so, can you hear the ultrasonic burglar alarms in
    some retail stores (K-Mart has them around here) (about 18kHz)?  If you
    answer no to either of these questions, then you have nothing to worry
    about when it comes to 20kHz signals (whether sine or square).

2.  You certainly can't record a 20kHz square wave on most analog recording
    media, either.  Most serious listeners have cassette decks these days.
    How many cassette tapes have a frequency response above 20kHz?   How
    can you say "digital is inferior because it won't reproduce a 20kHz
    square wave" when your current medium won't either?  If somebody can
    show that the human ear can distinguish between a sine wave and a
    square wave at the upper limit of hearing, then this is a motivation
    to improve things.  Note that feeding a sine wave and a square wave
    into a speaker and listening for the difference doesn't count as a
    proper comparison (as somebody pointed out), because of non-linearities
    in the reproduction system, a square wave can actually cause some
    lower frequencies to be generated by the speaker.  A valid comparison
    would involve generating sine and square pressure waves in the air.

3.  Even listening comparisons must be done carefully.  I used to work for
    a small digital audio firm, and we got one of a competitor's recorders
    in once (a large recording firm had a large backlog because editing
    using this competitor's system was very difficult, and they asked for
    help in getting a couple recordings edited).  The converters in this
    recorder were so badly adjusted that they were introducing about 20dB
    worth of noise into the recording and reproduction!  Although the
    theoretical S/N ratio was 96dB, the actual measured S/N was 70dB.
    Needless to say, this made music played on this system not sound as
    good as it could have.  It would be a shame if sloppy manufacturing
    practices ruined the potential of digital recording.

4.  For those of you who claim that listening is the real test, I have done
    a lot of listening to REAL digital recordings (not the record pressings,
    but the actual bits themselves).  They have been, in general, the best
    reproductions of music I have ever heard.  Instruments such as trumpets
    and drums, which suffer badly in most traditional recording media,
    sound just like trumpets and drums.  The imaging is fantastic (arguing
    against those who claim that digital recording will necessarily
    introduce huge phase shifts).  When I closed my eyes, I could imagine
    that I was sitting in the ideal seat in an otherwise empty concert hall,
    listening to a flawless performance (since mistakes can be edited out).
    It was the best listening experience I have ever had.

I for one, can't wait for home digital (but when I get mine, I'm going to take
it to my friendly local digital music company and get those D/A converters
adjusted, that's for sure).

Digitally yours,
Spencer

mat (12/18/82)

I for one CAN hear TV raster, though I don't know if it is the 17+ kHz signal
or some lower frequency that is being generated.  In any case it is one of the
most offensive sounds that I know.  Yes, my terminal bothers me a little too!
I can also hear SOME of the ultrasonic store alarms, and can 'feel' some
others.  This notwithstanding, I find most digital recordings just fine.  Some
of them seem a bit on the bright side after listening to 10 or 15 year old
recordings ... but is that the fault of the digital process or of the older,
less accurate recordings ?  Every medium introduces SOME effects, either as
a result of the medium itself or as a result of the paraphenalia that
accompanies the medium.  There are some people who feel that Avery Fischer
Hall is too 'bright' and prefer Carnagie hall.  There are some who find the
visible delay in sound propagation in Carnagie Hall to be disconcerting and
prefer the more 'accurate' Avery Fischer.  Are recordings made in anechoic
chambers with perfect mikes? What about reflections from the recording
artists body, the mike stands, etc?  And how many of us listen at the
ideal locations for proper phasing relative to our speakers ... in an
anechoic chamber.

Yes, there ARE bad things that can happen to the HiFi signal ... but not
all things that happen must be bad, and some of these can thoroughly mask
many of the 'distortions' that get introduced.       --NEXT PLEASE!