From: Rick.Moen@f207.n914.z8.rbbs-net.ORG (Rick Moen)
Newsgroups: sci.skeptic
Subject: Re: Sampling and human hea
Date: 29 Sep 92 06:13:31 GMT

In message <1992Sep26.091859.17640@u.washington.edu> mpark@milton.u
.washington.edu (Michael Park) wrote as follows:

> Isn't oversampling supposed to address the excessively sharp LP filter
> problem (i.e. by making the effective sample rate 8x higher, much
> less roll-off is needed)?  Shouldn't it then be relatively easy to
> ensure that any filtering artifacts will only occur above 22kHz?
> If audible artifacts remain, might that be taken as evidence that
> the limits of human hearing ought to be re-examined?

As I understand it, oversampling amounts to a kind of digital filtering
at the D/A conversion step (playback).  By no means does this make the
effective sample rate _any_ times higher.  The standard for storage in
the CD medium is absolutely fixed at 44.1 kHz, by definition.  However,
a correspondent from the Netherlands kindly reminded me of a remedy
for this _particular_ problem that is possible on the _recording_ end,
where the damage from excessively sharp anti-aliasing filters occurs:
Record at a multiple of 44.1 kHz, allowing use of a reasonably linear
low-pass analogue filter, then digitally convert the signal down to 44.1
kHz time-domain resolution.  That should help a great deal in this _one
area_, but to my knowledge none of the studios are doing it.

Some may remember that the CD format was largely invented by Sony.
Well, at the recent Summer Consumer Electronics Show in Chicago, who
should appear but a rather contrite-looking Sony VP Marketing, a
producer, a remastering engineer, and a corporate spokesman, to give ar
rather curious press-conference.  It seems that Sony/CBS, which has
been producing avowedly perfect recordings & players for some time
(remember the "perfect sound forever" original players, which were
surpassed only by the better-than-perfect ones of a couple of years
later?), is coming out with new "MasterSound" reissues, made from 20-bit
recorders, which they claim have "better sound" on account of "better
lower-level resolution".  Imagine that!  Will wonders never cease!

It gets better:  For commercial release, they have to drop four bits per
sample, such that the resulting CDs "have never realized the full sonic
potential of these master recordings", but that their bit-dropping
technique "enables the 16-bit [really 15 bits, net of a parity bit] CD
format to provide sonic performance that is very nearly the equal of the
original 20-bit recordings." Then, it seems that they had _listening
tests_! "Much richer.... Instrumental and vocal soloists seemed to image
more accurately; spatial relationships were more convincingly rendered.
High string instruments were preceived as sounding mellower and more
fluid, while the lower strings were more full-bodied.  A concert grand
piano was reproduced with a greater sense of scale, with the resonance
of its sounding board more clearly audible."  Do you perceive a party
line starting to crumble, here?  Further, Amy Herot, the remastering
engineer, said Sony/CBS would be obtaining early-generation analogue LPs
of the original version to listen to for sonic differences during the
remastering process.  (It wasn't even April 1st!)

Sample size and sample rate are not the only areas of technical
difficulty for the CD standard, either.  There's also a severe and
acknowledged jitter problem in most players (caused by hunting of the
servo mechanism as it attempts to stay locked onto the recording's clock
rate), modulation between digital and analogue and digital sections via
poorly engineered ground and power circuits, mechanically-induced read
errors sloppily covered over by error-correction circuits, and grossly
non-linear, cheap analogue-section components.  There's also amplitude
modulation of the original signal, during A/D conversion, by the
sampling frequency, creating sidebands well down in the audible range
as artifacts inserted into the recording.

LPs are dead, and it's long past time.  The problem is that we haven't
yet been offered anything better at the consumer level.

Cheers,
Rick M.

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