Newsgroups: rec.audio

> 	YES!  New and amazing Music Lite!   All the
> 	profit margin with only 80% of the sound!
> 

Sigh.  I don't know why I'm dignifying this with a response, but there's
obviously some folks out there who are going to respond to the word
"compression" even more irrationally than a similar crowd responded to
"quantization."  (And first, a disclaimer: I'm not a digital audio expert,
nor do I play one in real life.  JJ oughta be writing this, and who knows?
- maybe he'll follow up with a better explanation.  But right now, "the
spirit has moved me," which means you all gotta suffer while I take a crack
at it. :-))

Yes, DCC and MD use compression algorithms which are "lossy."  Does this
necessarily mean *bad* sound?  Not at all - as has been pointed out and
demonstrated, these media will provide very good sound quality in all but the
most demanding of situations; they're ideal, for example, for portable or
automotive applications, where the listening environment isn't dead quiet
and there are concerns over shock and vibration that could be a problem for,
say, CDs.  In short, I think that they will have their place.

But the problem seems to be with the idea of compression, and further, with
this absolutely terrible notion of "lossy" compression.  Where, though,
did anyone get the idea that we'd only get "80% of the sound"?  What exactly
does "80% of the sound" MEAN, anyway?  It's going to only produce 80% of
full volume?  The string section will be missing?  What the hell are you 
talking about?

Again, I don't deal with this in audio, at least nor professionally.  But I
am working right now in some digital video areas, and can draw an analogy
here.  Does it shock you to think that we're going to be stuffing a full
HDTV signal (at God-knows-what resolution, but probably around 2k x 1k) into
a measly little 6 MHz channel?  Gee, doesn't that mean we're gonna hafta
(shudder!) *compress* the information?  Sure does!  Is said compression
gonna be LOSSLESS?  Nope, doesn't look like it - unless somebody can come
up with a really amazing compression trick, really soon.  Does that have the
entire industry quaking in its boots?  Nope!  Well, gee, don't you guys worry
about what this is gonna look like?  Of course - in fact, some of the people
working on the new digital TV standards are *producers* of programs, and you
can bet that they're the FIRST to worry about how their work is going to appear
to the consumer.  I have yet to hear ANY big concerns from these folks over
the proposed compression schemes.  We've argued color, refresh rates, 
resolution, etc., etc., etc., but not word one about "goddamit, we just CAN'T
compress this stuff!"  Why?  Because they realize that "lossy compression"
does NOT equate to "bad picture."  Yes, there are cases which can be 
demonstrated where the compression result in visible artifacts - especially
in still shots, where the eye has time to pick them out.  But in actual
viewing of the image, the "lossy compression" scheme results in a very, very
nice picture.  (And if you really want a shock, figure the uncompressed
bandwidth of a 2048x1152, 24 bits/pixel image at just 60 frames/second.  Then
recall that I said we're gonna stuff it into a 6 MHz channel.)

The problem is that people here numbers like "80%" and react to it without
really understanding what this number means.  In both audio and video, there
is typically a LOT of completely redundant data.  (I use the word "data" as
distinct from "information", here - information being "usable, meaningful
data.")  You can whack this out, and no one will be the wiser.  There's also
a fair amount of data which actually has meaning, but can safely be ignored
because the information it conveys will be overwhelmed by other information
in the system, or is below the threshold of perception, or the limits imposed
by the final output device, or otherwise is really UNusable information.
A technique which gets rid of such data is said to be "lossy" - which ONLY
means that you CANNOT recover the original data exactly.  It does NOT
necessarily imply a change in the perceived result.  Not that you can't wind
up with a perceivable artifact in the final result, but just saying "this is
a lossy system" doesn't directly translate to "you WILL always hear a problem
with this."

As it turns out, MD and DCC DO suffer a slight degradation in the sound,
which is undeniably audible under certain conditions of both listening
environment and source material.  But to say that "it's only 80% of the sound"
is a completely meaningless statement.


Bob Myers            | "One man's theology is another man's belly laugh." 
myers@fc.hp.com      |                     - Lazarus Long/Robert A. Heinlein
                     |