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More digital audio



Chris Bacon of DuArt wrote the following to me... though it is not
directly a telecine issue, many of us may benefit from his
perspective... lengthy discussions on audio issues probably will not
server the TIG well, but certainly we should all be informed on these
issues.

--Rob Lingelbach
TIG admin                           

--- Forwarded mail from KA2IQB <KA2IQB at aol.com>

Hi Rob,

Given our e-mail exchange on digital audio a couple of weeks ago, you
might be interested to hear about a joint SMPTE/AES meeting held here
in New York last night.  The theme of it was 5.1 audio and AC/3
compression.  It was a panel discussion hosted by a local audio
manufacturer's rep, with a Dolby rep, a speaker manufacturer rep, and
a mixer from Sony pictures who basically got up, showed us some music
videos on DVD, and said, "yeah, I mixed this and that."

I know you may think it's just my typical New York cynicism, but if
you think CD audio leaves something to be desired, you're just gonna
love AC/3.  Side- by-side comparisons were run between original and
compressed versions of solo singing, rock, and classical.  I was
underwhelmed.  AC/3 works on the principle of masking, that is, quiet
sounds underneath louder ones aren't noticed, so no bits are wasted on
them.  The result is voices that hiss and pop like somebody forgot the
"de-esser," and certain musical instruments (such as violins and
pianos) that lose their high frequency "zing."  I think the masking
theory has been misapplied: while it is true that the ear generally
tunes out steady-state quiet sounds under louder ones, it is still
detects subtle changes and transients in them.  In other words,
hearing is both a differential process as well as a linear one.  Lose
the differential information and sound becomes unnatural and processed
-- like AC/3!  Perhaps it stands for "Almost Complete, 3rd try."

Of course, the Dolby folks were quick to defend all this on the basis
of being constrained to the bandwidth that was allotted by the ATTC.
And it is pretty remarkable when one considers that on an ordinary CD,
16 bits x 2 channels x 44,100 samples per second = 1.411 Mbits/sec,
while in AC/3, 5.1 channels are fit into 428 Kbits/sec.  I know I'm
being overly critical; it is one hell of an improvement over the 4"
speaker in the old Zenith TV I'm using now.  On the other hand, a lot
of people have been saying that the audio portion of digital
television is going to be CD-quality.  I trust my own ears, and what
they told me is that they're in for a big disappointment when they
spend thousands of dollars on home theaters and end up with sound that
doesn't even measure up to a good quality CD ghetto blaster!

I also wasn't terribly impressed with the 5.1 audio, but that's
nothing new.  Contrary to what Dolby tells you, on most material that
is allegedly surround encoded, I find it hard to hear any difference
between 5.1 and ordinary stereo unless I am precisely in the "sweet
spot."  That's been the case both at this demo and in Dolby's own
permanent screening room.  I wasn't the only one in the audience who
noted this either.  To think that any normal person setting up a
television set in their living room is going to get all the speaker
placements exactly right for surround to work is utterly ludicrous.

Aside from that, in both their screening room and the meeting, Dolby's
subwoofers operate at levels that I find excruciating.  If this is
really what 5.1 is supposed to sound like, it will probably have to be
outlawed due to all the shootings that are going to be committed in
apartment houses!  Even in all the new wave dance places I attended in
my misspent youth (I was the one standing a short distance from the
ladies room hitting on the women while they waited on line!), I never
heard bass that was so entirely disproportionate to the rest of the
sound.  Maybe that's their answer to the poor transient response of
their compression?  If so, it's like dumping a bottle of ketchup onto
a plate of rotten food so you won't notice how bad it tastes!

All in all, I think Dolby may be headed the way of DBX.  They've done
us a real disservice and I won't be surprised if the industry
ultimately scraps 5.1 and AC/3 in favor of a simpler stereo system
that delivers better sound.

I did not post this to the main TIG because it obviously doesn't have
much to do with telecine, and it's highly opinionated besides.  If you
think it is suitable for the main group, please be my guest!

Best regards,
Chris

--- End of forwarded message from KA2IQB <KA2IQB at aol.com>



---
Thanks to CB Gaines for support in 1998..
No product marketing allowed on the main TIG.  Contact rob at alegria.com
944 subscribers in 36 countries on Wed Mar 11 10:42:49 PST 1998 
complete information on the TIG website http://www.alegria.com/tig3/