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9c0564fcc2
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@eu-west-1.amazonses.com/T/#u
Signed-off-by: Neil Andrews <neil@androos.io>
Link: https://patch.msgid.link/0102019ffcdbb1e6-9b59d3cc-ef05-4df1-8f9f-fb2f425bcda2-000000@eu-west-1.amazonses.com
Signed-off-by: Takashi Iwai <tiwai@suse.de>
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