Problem solved but I don't know what I did - can anyone explain?

[George Kiagiadakis]

Hi Chris,

On Friday, 6 September 2024 at 08:55, Chris Angelico <rosuav at gmail.com> wrote:

> 

> 

> Hi! Sorry if this is the wrong place to ask this; I didn't find a
> matching -users mailing list.
> 

> What I'm about to lay out is my struggles with audio over the past
> week. But now suddenly the problem is solved... and I don't know how.
> Which means, if I run into the problem again, I won't know how to fix
> it! Please, can anyone tell me what happened here?
> 

> I have a number of audio devices in this computer, including a
> headset, a set of speakers for alerts, and a set of high quality
> speakers connected via S/PDIF (TOSLINK) to a breakout off the
> motherboard. I recently did a fresh install of Debian onto a new SSD;
> the previous install drive is still available so if there's any config
> files to compare against, I can fetch them.
> 

> The S/PDIF works fine in ALSA. To get audio routed to that output in
> ALSA, I send it to "USB Audio, USB Audio #2 Hardware device with all
> software conversions" in VLC, or with "aplay -D
> plughw:CARD=Audio,DEV=2". No problems at all.
> 

> But in Pipewire or Pulse, that device didn't show up. There are a
> number of profiles available to me, as shown in pavucontrol or any
> other place that lists device profiles, but none specify this device,
> and playing audio through all of them leaves the speakers silent.
> 

> On the previous installation, I would use the sink
> "alsa_output.usb-Generic_USB_Audio-00.HiFi_7_1__hw_Audio_2__sink" to
> send audio to the S/PDIF. Nothing I've done has made any such device
> name appear.

These profiles are made available by the ALSA UCM configuration files, which are being installed by some ALSA package. Perhaps you are missing those, or this new installation has a different version of those files (or something like that). These files describe how the various ALSA devices, subdevices and controls map to real inputs/outputs and use cases.

> As of now, though, I have a new profile available in pavucontrol,
> which hadn't previously been there: "Pro Audio". This makes available
> four sinks called "alsa_output.usb-Generic_USB_Audio-00.pro-output-0"
> to "pro-output-3", and output-2 results in the S/PDIF lighting up!
> Yay! But what made it appear?

The "Pro Audio" profile is a PipeWire-specific profile that PipeWire makes available to allow exposing all the devices & subdevices of an ALSA card. That makes it possible to work, as it would work with "aplay", without requiring the UCM config files.

Not sure what "as of now" means. These profile has been available for a long time. Unless you had a really old version of PipeWire running previously (or you were even using PulseAudio) and you just upgraded to a more recent one.

> My best guess is that installing OBS Studio build dependencies may
> have done something. I'd previously been running OBS as installed from
> Debian's repos, and now am about to start building from source,
> although I hadn't actually done the build yet - just installed the
> build deps and cloned the repo.

OBS has nothing to do with this.

Best regards,
George
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