The "Pro Audio" profile in PipeWire for audio devices / sound cards

Question

After upgrading from PulseAudio to PipeWire my sound devices now feature the "Pro Audio" profile however I've Googled for it and haven't found anything interesting. You can find it by running PulseAudio Volume Control and see it under the Configuration tab for your devices.

Would be nice if someone could, I don't know, glance over PipeWire sources (I'm not a C programmer per se and I don't really understand digital audio aside from the very basics) and explain what it is and why the user may want to use it instead of e.g. something which is offered by default.

Answer 1

The Pro Audio profile provides "raw device access with the maximum number of channels and no mixer controls" (from the release notes with the feature).

Based on the code creating this profile, it looks like it adds direct mappings from each PCM device provided by ALSA to a corresponding input or output channel in PipeWire. This is in contrast with higher-level options such as the ALSA Use Case Manager, which would associate some of these channels to particular combination of verb and device type (e.g. "Voice Call" and "Mic", respectively).

The main reason someone might want to use the Pro Audio profile is to access all the channels of interfaces with more than a single stereo input/output; for example, a USB mixer with 8 channels, which may not all be usable through the default profile. By using Pro Audio, these extra channels could be connected to various other applications with PipeWire's graph architecture.

Here's an additional source describing the use of PipeWire for professional audio work, showing that not all channels are available by default.

Answer 2

Those Pro Audio slots are to pipe audio to other apps, thereby turning your OS into a digital audio workstation. This is the point of JACK/ JACK2, Carla, and to a certain degree, Pipewire as well.

Pulseaudio has the pipe functionality as well, but it is sort of hidden and much less intuitive. The modules in pulse are the same thing as the cards in other servers. They are shared memory slots with specific permissions/ purposes attached. Technically, you could run pulseaudio and pipewire alongside each other.