Re: [PATCH] ALSA: usb-audio: Rename the Audient iD14 monitor mix volume control

[Takashi Iwai]

On Thu, 13 Aug 2026 22:41:24 +0200,
Neil Andrews wrote:
> 
> On the Audient iD14 (2708:0008), feature unit 12 is traced through to
> the Speaker output terminal and is therefore exported as "Speaker
> Playback Volume".  The name fits it badly.  It advertises Volume on
> only four of its six logical channels, which the driver records as
> cmask=0xf, channels=4 on a 6-channel playback stream, and it sits on
> the monitor mixer branch rather than in the direct playback path:
> 
>   INPUT_TERMINAL 2 (USB streaming, 6ch) -> EXTENSION_UNIT 51 ->
>     FEATURE_UNIT 10 (no controls) -> OUTPUT_TERMINAL 20 (Speaker)
> 
> while FU 12 hangs off MIXER_UNIT 60 and feeds back into
> EXTENSION_UNIT 51.
> 
> Userspace adopts the control as the stream's hardware playback volume,
> so any setting below 0 dB attenuates part of the stream and not the
> rest.  Measured over the device's own digital loopback, with one
> -12 dBFS tone per channel played straight to hw:, PCM channel 0 is
> unaffected while channel 1 tracks the control: at 107/127 (-20 dB) the
> two read -15.89 and -35.89 dBFS, a 20.00 dB imbalance, and at 127/127
> both read -15.89 dBFS.
> 
> Give the unit a non-standard name so that it is no longer taken for
> the stream's master volume.  Dropping the control instead also fixes
> the imbalance, but FU 12 keeps its value across a module reload, so
> dropping it strands a device that is already attenuated with nothing
> able to reset it.  Renaming leaves the monitor gain reachable and that
> recovery path intact.
> 
> The mapped name ends in "Playback" because a name from the map
> suppresses the automatic " Playback" but still gets " Volume"
> appended; the control comes out as "Monitor Mix Playback Volume".
> 
> Tested on the ACP path with PipeWire, which is where the problem
> reproduces: the control now stays at 127 at every volume setting and
> the imbalance is 0.00 dB, and setting it by hand to 107 and back to
> 127 gives 20.00 dB and 0.00 dB as before.
> 
> Link: https://lore.kernel.org/linux-sound/0102019fed22f9d3-fa294ec5-02f1-4fd3-b3fa-76efc14331cc-000000@xxxxxxxxxxxxxxxxxxxxxxx/T/#u
> Signed-off-by: Neil Andrews <neil@xxxxxxxxxx>

Applied to for-next branch.  Thanks.


Takashi