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Date:      Thu, 4 Apr 2002 15:03:03 -0500
From:      The Anarcat <anarcat@anarcat.dyndns.org>
To:        Lars Eggert <larse@ISI.EDU>
Cc:        John Utz <john@utzweb.net>, multimedia@FreeBSD.ORG
Subject:   Re: Soundblaster Live rear channels?
Message-ID:  <20020404200303.GF279@lenny.anarcat.dyndns.org>
In-Reply-To: <3CACAFC9.3060908@isi.edu>
References:  <3CAC8E70.3040700@isi.edu> <Pine.LNX.4.44.0204041147440.2292-100000@jupiter.linuxengine.net> <20020404193214.GD279@lenny.anarcat.dyndns.org> <3CACAC92.3040506@isi.edu> <20020404194937.GE279@lenny.anarcat.dyndns.org> <3CACAFC9.3060908@isi.edu>

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On Thu Apr 04, 2002 at 11:55:53AM -0800, Lars Eggert wrote:
> The Anarcat wrote:
> >> My understanding was that "virtual" channels act like virtual sound
> >> cards, i.e. each applications gets what looks like a separate
> >> sound device, and the kernel muxes the output. I'm not sure this
> >> has anything to do with the mixer channels, which is where I would
> >> expect the rear channel to show up.
> >
> >
> > And this is why I brought up the "mapping" issue. I think pcm can use
> > the multiple channels available (front and rear) through the virtual
> > channels technique.
> >
> > The kernel can mux the input from various apps into a single sound
> channel,
> > so it's likely that it can do the opposite: mux a single sound input
> > to multiple channels.
> >
> > I can't answer wether it is the case, but it's likely to be.
>=20
> It's not as simple as that. There's harware on the card that processes
> stereo input (from apps) and creates four separate signals for surround
> sound. (Otherwise you could simply hook up the rear speaker pair in=20
> parallel to the front one, using the same output signals.)

You're right, of course.

Then I guess the proper answer is in:

$FreeBSD: src/sys/dev/sound/pci/emu10k1.c,v 1.6.2.8 2001/12/22 16:17:02 cg =
Exp $

In particular line 1143.

Also note, as I said that this is dependant on the channel mapping:

	/* Routing - this will be configurable in later version */

So I guess it's for a future version. ;)

A.
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