Re: [TCLUG:12668] [OT] 4-channel MP3/CD-audio?

[Philip C Mendelsohn <mend0070@tc.umn.edu>]

On Thu, 20 Jan 2000, Mike Hicks wrote:

> After seeing the recent post that showed a couple of the flags available
> for CD audio (DATA, 4_CHANNEL, COPY_PERMITTED, PRE_EMPHASIS), I began
> wondering about 4-channel audio.  Has anyone ever come across a CD that
> actually has 4-channel audio?  

No, and you won't either.  This is an unsupported spec in the Red Book
spec for CD-DA.  If you were to set the flag, you would never get the disc
through manufacturing -- it would be rejected in incoming inspection, if
memory serves.  AFAIK, there has never been a CD player sold that supports
it.  I would say there has never been one built, but I don't know for a
fact that they didn't kludge something together at the lab in
Eindhoven.  This is really just a reminder that much of the work on CD was
done in the 70's, before Quad died completely (thank god!), and was a
"hey, it's easy to include a flag, just in-case" kind of decision.

> I'm kind of guessing that radio stations
> at least occasionally broadcast 4-channel audio, but then I'm not
> sure..  That would make sense, since a lot of people listen in their
> cars, but I don't know if FM can even do 4 channels.

Nope, not on one carrier, in that band with any sort of fidelity.  Cars
aren't true four channel -- they're stereo with two sets of speakers.

> Anyway, if I ever actually came across a CD with 4-channel audio, would
> I be able to play back a ripped track through anything I have?

Not without the right software.  You can put anything you want on a CD,
but it won't be any officially recognized data spec.

> Could I
> make an MP3 out of that and play it back ?

If you had a way to deal with 4 discrete audio files, sure.

Phil M
Chief Engineer
Hotdish Mastering 

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