Michael K. Sanders said:
> In message <19980925074913.A23859@reilly.home>, "Andrew Reilly" writes:
>>On Thu, Sep 24, 1998 at 07:44:04PM +0200, Lennart Augustsson wrote:
>>
>>Is it reasonable to configure a USB sound system for more than
>>two channels?  Would DVD-style five-or-six channels work?  Would
>>eight be possible?
> 
> Are you asking about 6 channels in general, or 6 channels specifically
> from a DVD source?

In general, really.  Fiddling around with six high-quality audio
connectors on the back pannel of a PC doesn't really sound plausible
to me, so if USB can do the job, that would be wonderful.

> The Dolby Digital (aka AC-3) encoding found on most DVD-Video discs
> does not necessarily imply all 6 channels.  It's just an encoding
> format, which can be anything from 1 channel Mono to the full 5.1
> L/R/C/RL/RR/Sub.

True, but there are other formats on DVD now, and there will probably
be others in the future.  There can already be Dolby ProLogic in the
stereo tracks, or DTS (which is six full bandwidth channels, I think), 
and now MLP (Meridian Lossless Packing) has been admitted, and that
can manage up to 64 channels (well, I'll believe that when I see more
of the specs, but I've seen channel allocation lists for up to eight.)
I believe that MPEG is available on some DVDs, at least in Europe, and 
we know that software decoders for that are available.

The most likely scenario for the free software community that I can
think of, though, is either raw PCM or an as-yet unknown free
compression scheme, onto CD-ROM or DVD-ROM (or hard-disk or internet).

> It would be Really Cool to be able to pop a DVD into a NetBSD box with
> a DVD-ROM drive and get 5.1 Dolby Digital out of USB speakers.  But
> assuming everything else were in place, having a software DD decoder
> would be the kicker.  Somehow I doubt that's feasible.  I don't know
> of any sound cards offhand that do DD either, but we can dream... :)

I think you'll find that many DVD-supporting video cards also have the
audio decode, but perhaps they do a mix-down to two channels.
Software decode is certainly possible, but making it happen for NetBSD
could be difficult (to manage), since Dolby wants a licence fee per DD
decoder.

-- 
Andrew