[pulseaudio-discuss] pavucontrol : input device listed, but no signal

[Sean Greenslade]

On Fri, May 06, 2022 at 11:33:55AM +0000, Pieter J Voet wrote:
> Hi all,
> 
> I'm running Fedora 35 which has pipewire. Next, I have an external USB DAC ( Behringer Firepower FCA610 ).
> My speakers are connected to the USB DAC, and it's configured as the default output sink.
> This all works fine, audio on my laptop plays thru the USB DAC.
> I have three userspace processes running : 'pipewire', 'pipewire-pulse' and 'wireplumber'.

In that case, this is probably not the right place to ask for help.
Pipewire bills itself as a replacement for pulseaudio. If you are
running pipewire, you should probably find a pipewire support list
instead.

> Now, I have a keyboard plugged in the USB DAC analog input, and can hear it's sound on my speakers.
> I can  play audio on my laptop, play something on the keyboard simultaneously, and it all plays fine
> with audio output on my speakers.
> 
> So far, so good. But what I want is to record from the USB DAC analog input.
> Unfortunately that's not working. Using Audacity, I can click 'Start Monitoring' , but there's no sound.
> 
> To simplify things and rule out Audacity, I see that 'pavucontrol' ( GUI ) lists the UDB DAC both as an Output and an
> Input Device. But the 'Input Devices' tab does not show output signal level upon pressing the
> keys on the keyboard...
> Again, I can hear the keyboard on the USB DAC attached speakers. This means that the input stream
> is somehow redirected to the output-sink right ?

Based on my limited skim of the pipewire docs, it seems that pipewire
just presents a pulseaudio-compatible API for the purpose of allowing
existing pulse client software to work as-is. They may not have gone to
the trouble of exposing all the APIs that pavucontrol needs. Using
pavucontrol with pipewire may not work as expected.

If you're looking for GUI tools to control pipewire, maybe check these
out:

https://wiki.archlinux.org/title/PipeWire#GUI

> I'm a long-time Linux user, but Pipewire/Pulseaudio really confuses me. I don't know what to do..
> 
> To make the story even weirder : sometimes after a reboot the USB DAC 'Input Device' actually has
> a signal !! And I can then record in Audacity.
> But that's 'sometimes'..  My latests attempts by rebooting do not  give me inputsignal level anymore.
> 
> This all probably is caused by my lack of knowledge of pipewire/pulseaudio..  but hopefully somebody
> can educate me a bit on this.

Pipewire and pulseaudio are two different sound servers, and it's
unlikely that they will coexist cleanly on the same machine. If you want
to stick with pipewire, then seek help on a pipewire forum. If you want
to try pulseaudio, you will need to figure out how to disable pipewire
and install / enable pulseaudio.

--Sean