NetNews Usenet Archive 1993 #3/NN_1993_3.iso/spool/rec/audio/19504

Text File | 1993-01-28 | 7.4 KB | 144 lines

Newsgroups: rec.audio
Path: sparky!uunet!destroyer!gatech!rpi!scott.skidmore.edu!jreiser
From: [e-mail] (Jason Reiser... Asleep)
Subject: Re: Digital vs Analogue, Yet Again!
Message-ID: <[e-mail]>
Organization: Skidmore College, Saratoga Springs NY
References: <[e-mail]>
Distribution: na
Date: Thu, 28 Jan 1993 01:23:37 GMT
Lines: 132

[e-mail] (Frank Ferguson x3584) writes:
>
>
> As long as we're going 'round yet again on the digital vs analogue
> question, I thought I'd raise a point that I've pondered, off an
> on, for some time.  My initial reaction to criticisms of digital sound
> was that people were simply unused to hearing recorded music reproduce
> sound with a "flat" response from dc to 20khz (and with 95db dynamic
> range!).  I still think this it true (at least for those of us who've
> been into hifi long enough to have "grown up" on LPs.

Wouldn't it be nice if CD players were actually capable of anything
approaching 95dB dynamic range!  But, sadly they fall quite short of
this, and the numbers quoted throughout the industry are strictly
bogus!  The following is an excerpt from The Absolute Sound,
July/August '92 by Gerard Rejskind.

"DYNAMIC RANGE PROBLEMS:
    Digital's biggest selling point is its wide dynamic range.
Certainly it is true that most CD's do not suffer from ticks and pops
(unless they are mistracking, a common phenomenon that usually comes
as a shock to new CD owners).  In fact, digital systems have quite
poor dynamic range.  The usual claim of over 90 dB of dynamic range is
based on a common mathematical blunder, coupled with what may be
outright fraud.
    The formula for calculating the theoretical maximum dynamic
range of a digital system is well known.  It is:
    20 log (2^b - 1)
where b is the number of bits in the system.  Since the CD uses 16
bits, we can calculate the dynamic range:
    20 log (2^16 - 1) = 96.33 dB
    This is a very attractive figure, but the fact that some CD
player manufacturers actually claim dynamic range _greater_ than this
theoretical maximum should make us suspicious!  In any case, even this
value is unattainable.  The calculation ignores the fact that all 16
bits are not used for signal data.  The last bit is used as a parity
check (which alerts the error correction circuit that something is
wrong with the data), and so we should do the calculation with only 15
bits:
    20 log (2^15 - 1) = 90.3 dB
    This is still very good, but there is a problem: It expresses
the peak-to-peak value of the noise.  The usual way we measure noise
is by its root mean square value.  To convert, we need to subtract:
    20 log (2 x SQR(2)) = 9.03 dB
    We are now down to about 81 dB, not all of which is usable,
because digital has a "hard ceiling" that you can't cross without
disastrous distortion.  If we leave an extra 8 dB of headroom, we are
now down to 73 dB, considerably less than we can obtain with a modern
analogue recorder using Dolby SR noise reduction.  Even so, the bottom
part of the dynamic band is not usable because low level signals
suffer, in nearly all players, from severe distortion.  This can be
reduced considerably by the proper use of dithering (the deliberate
addition of abalogue noise to the signal), but a simple instrument
test confirms that only the best players can reproduce a sine wave at
a level of -60 dB as anything but a caricature of the original.
    So why do CD players seem dynamic range of over 90 dB?  This
figure is based on the (deliberate?) confusion of two concepts.  Turn
off the signal in an analogue system, and you can read the system's
actual noise.  Do the same in a digital system, and you are left with
nothing at all.  Noise measurements of CD players usually express
nothing more than the residual noise of the analogue section.  Not
surprisingly, it is usually terrific.
ANALOGUE PROBLEMS:
    This is the problem that most player designers attack first,
because most of them know analogue better than digital.  Because of
price pressure, most companies cut corners wherever they can.  Their
analogue sections usually contain inexpensive amplifier chips,
including the venerable (and horribly slow) 741.  Such chips will
spoil anything, including the sound of players that were none too good
to start with.  Most players also have inadequate power supplies, and
those are targets for improvement by nearly all designers.
    I am not much cheered by the direction in which digital is
moving, and every time I hear an audio executive talk about "The
Future of Digital" I get chills.  There is some cause for optimism, I
suppose.  The very finest players (one of which I get to hear almost
daily) are astonishing in their ability to reproduce emotionally
satisfying music from the best disks.  However, there seems to be a
growing acceptation, even in certain audiophile circles, of common
digital flaws as a normal part of electronic music reproduction.  A
lot of supposedly critical people find that certain mediocre players
"don't sound so bad after you listen for a while."  Some of these same
people go on to design and market unlistenable players, sometimes at
great cost.
    Well, what is to be done?  I think we need to speak up, to
keep demanding something better.  If we do not, we will be like those
who have seen all the great movies only on video, and who are unaware
that once upon a time, there was Cinerama.
    Think about it."


> I couldn't figure, however, whu anyone would react negatively to
> hearing the full range of music reproduced, until I reflected on
> the way most music is recorded.  Seems to me most studio recording
> is done with several mikes placed very close to the performer or
> instrument (much live recording is done the same way).  Few of us,
> I expect, have spent much time listening to various instruments with
> our ears positioned a half inch from the strings or bells, or within
> an inch of a singer's mouth--yet that's the way recordings seems to be
> made.  I expect that a medium like analogue which is a bit rolled off
> in its preproduction capability would soften some of the sibilants and
> stridency which would seem to naturally arise from such an unusual
> listening position, and present a sound which more closely approximated
> what one might hear from a normal listening venue--more suitably
> removed from the performer or instrument.  Digital, however, could
> well reproduce the fairly intense and unrealistic "up close" experience
> with ruthless fidelity, giving in process the appearance of harshness
> and stridency.  Does this seem reasonable?

I suppose that it makes some sense that the problems of digital are
compounded by the close mic'd recordings, but the idea of that is to
eliminate the sound of the recording room itself, as best as possible
(as I understand it anyway).  If we mic'd farther away, you would then
have to listen to two rooms... the recording one and the listening
one... doesn't sound like a healthy prospect to me.

> Just another victim of the audiophile disease.

I envy my musicial suitemate who listens to and really enjoys his Sony
box (nothing wrong with it inherently, just not overly impressive).
My taste tends to keep my wallet empty too.

>
> Francis Ferguson
> [e-mail]

                - Jason

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