Behringer UMC404HD Line A/B volume too low when used in "Pro Audio" mode

[GitHub issues - opened <github@alsa-project.org>]

alsa-project/alsa-ucm-conf issue #662 was opened from mrbumpy409:

The Behringer UMC404HD shows five volume faders in alsamixer:
* **Line A** and **UMC404HD 192k Output Front**: These faders are linked (changing one changes the other) and control the level of **L & R MAIN OUT** and **PLAYBACK OUTPUT A 1/L & 2/R** on the back of the unit.
* **Line B** and **UMC404HD 192k Output Back**: These faders are linked and control the level of **PLAYBACK OUTPUT B 3/L & 4/R**.
* **UMC404HD 192k Output 1**: The primary volume control for the unit.

How these sliders are used by Pipewire depends on the mode selected for the Behringer:
* **Default**: Two output devices are presented to the user:
  - **UMC404HD 192k Line A**: Controls the "Line A" volume in alsamixer.
  - **UMC404HD 192k Line B**: Controls the "Line B" volume in alsamixer.
  - The "UMC404HD 192k Output 1" slider in alsamixer appears to be unused.
* **Direct UMC404HD 192k**: One output device is presented to the user:
  - **Direct UMC404HD 192k**: Doesn't seem to be manipulating any of the hardware output levels in alsamixer.
  - The "Line A" and "Line B" channels are not available via Pipewire in this mode.
* **Pro Audio**: One output device is presented to the user:
  - **UMC404HD 192k Pro**: Controls the "UMC404HD 192k Output 1" output level in alsamixer.
  - The "Line A" and "Line B" channels are not available via Pipewire in this mode.

I would imagine most people are using a Behringer UMC404HD for recording purposes, and therefore would likely be using it in "Pro Audio" mode (or at least they should be if they care about latency).

Since a recent update (Fedora 43 KDE), the levels of the "Line A" and "Line B" channels (and their linked pairs) are being set by default to **41**, which results in audio that is far too quiet when using the line outputs (headphone output is unaffected). Furthermore, these low levels throw off the balance between the computer's output and the UMC404HD's live input monitoring. "Line A" and "Line B" channels should both be at **100** by default to match the Windows driver (and previous ALSA version?) and provide correct balance with the live monitoring feature.

Currently, I have to run alsamixer on every boot to adjust "Line A" and "Line B" to **100**. Am I right to report this to ALSA, or is this something Pipewire should be handling? Pipewire doesn't appear to touch the "Line A" or "Line B" levels at all when in "Pro Audio" mode, so I'd assume this is ALSA's doing, but I don't really know.

Issue URL     : https://github.com/alsa-project/alsa-ucm-conf/issues/662
Repository URL: https://github.com/alsa-project/alsa-ucm-conf