Audio mixer and mixer control

[O'Connor, Daniel]

> On 11 Apr 2020, at 03:55, Harry Schmalzbauer <freebsd at 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.
> 
> 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?
> 
> Or is it possible to interconnect different dsp channels? (ugh, I don't really know anything about contemporary audio hardware :-( )
> 
> 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".
> 
> 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