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Date:      Sat, 11 Apr 2020 14:27:55 +0930
From:      "O'Connor, Daniel" <darius@dons.net.au>
To:        Harry Schmalzbauer <freebsd@omnilan.de>
Cc:        freebsd-stable@freebsd.org
Subject:   Re: Audio mixer and mixer control
Message-ID:  <AF5EFF09-34E3-444E-B1D6-FE0315C4025B@dons.net.au>
In-Reply-To: <426353fd-bb39-5bba-5ca1-af00a8b8ff4e@omnilan.de>
References:  <426353fd-bb39-5bba-5ca1-af00a8b8ff4e@omnilan.de>

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> On 11 Apr 2020, at 03:55, Harry Schmalzbauer <freebsd@omnilan.de> =
wrote:
> today I wanted to utilize my optical S/PDIF out with an external D/A =
converter to empower my garden radio.
> Unfortunately, it seems mixer(8) isn't really doing what I understand =
a mixer's job is.
>=20
> As far as I understood, mixer(8) is just controlling/pushing settings =
to the dsp's specific hardware mixer (if that's true, mixctl(8) was more =
clear e.g.).

mixer is purely to control mixer devices which the hardware provides, =
you can set various levels in the final input and output mix.

In the old days there were actually a number of things it could =
meaningfully do (eg control CD volume level or line in) but these days =
everything is digital so it's pretty vestigial IMO.

> So if I have dsp0 with line-in and line-out, and dsp3 with a S/PDIF =
out, there's no way to get the dsp0-"mix" over to dsp3?

You can't use mixer to do what you want, but you can probably do =
something with a sox pipe line that would read from one input and feed =
to another if that is indeed what you need.

> What I'm looking for is a mixer which processes various input sources =
and sends them to arbitrary output devices.
> Does anybody know if there's such kind of mixer available?
>=20
> Or is it possible to interconnect different dsp channels? (ugh, I =
don't really know anything about contemporary audio hardware :-( )
>=20
> I also have problems understanding the mixer(8) channels.  Hard to =
find the corresponding dsp channel... The relation of "speaker", "mix", =
the invible "monitor" and "rec" is completely unclear to me, likewise =
the difference of "vol" and "pcm".
>=20
> Is it common that S/PDIF out is a separate dsp?  I never had to =
investigate on other OS, where I get the same signal on analog and =
digital outputs simultaniously.

I don't think it's very uncommon, although I haven't used FreeBSD on a =
desktop for quite a while..

What does this output?
cat /dev/sndstat

If you just want to play some audio out to the S/PDIF you can tell your =
audio program to use that particular device (eg /dev/dsp1 or whatever it =
is)

--
Daniel O'Connor
"The nice thing about standards is that there
are so many of them to choose from."
 -- Andrew Tanenbaum





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