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task-39: HiFi capture is silent; the DMIC needs the Q6 voice session

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92133 frames at peak 0. Codec routing is correct and forcing the call profile's
TX7 decimator changes nothing, so it is neither the decimator nor the front end
- what is left in the 11-control diff is VoiceMMode1. Voice Call (Mic, Speaker)
gives working mic plus speakerphone and is the workaround. Capture gain is UCM's
to set; runtime amixer does not survive profile activation.
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Fimeg 2026-08-02 08:20:58 -04:00
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docs/tasks/39-audio-levels-as-state.md
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@ -135,3 +135,40 @@ that **native PulseAudio owns the phone audio stack** and `conflicts`/`replaces`
pipewire, pipewire-audio and wireplumber — while the device is in fact running
pipewire, pipewire-pulse and wireplumber. Reconcile which is true before
building policy on either.
## The HiFi profile captures pure silence (measured 2026-08-02)
**`HiFi` capture is dead, and not subtly: 92133 frames, peak `0`.** Exactly
zero, not a low level — the stream runs and the ADC delivers nothing. This is
why STT on the keyboard has no microphone.
The codec routing in `HiFi` is *correct*, which is what makes it a real bug
rather than a missing mixer line:
DMIC MUX5 = DMIC4 CDC_IF TX5 MUX = DEC5 ADC MUX5 = DMIC
DEC5 Volume = 84 AIF1_CAP Mixer SLIM TX5 = on
MultiMedia2 Mixer SLIMBUS_0_TX = on (front end, on in both profiles)
Forcing the capture onto the **TX7** decimator — the exact chain the call
profile uses (`DMIC MUX7=5`, `CDC_IF TX7 MUX=2`, `DEC7 Volume=124`,
`AIF1_CAP Mixer SLIM TX7=on`) — still yields peak `0`. So it is **not** the
decimator, and not the front-end mixer.
Only **11** mixer controls differ between `HiFi` and `Voice Call (Mic, Speaker)`.
After eliminating the TX5/TX7 pairs, what remains is
`QUAT_TDM_RX_0 Voice Mixer VoiceMMode1` and
`VoiceMMode1 Capture Mixer SLIMBUS_0_TX` — i.e. the DMIC only produces data
while the **Q6 voice session** is up. That is the thing to chase; do not
re-litigate the decimator, it is measured and ruled out.
**Working configuration today: `Voice Call (Mic, Speaker)`.** It carries the
`Both CS35L36 amps, speakerphone` output *and* a live DMIC4 capture, and it
survives a wireplumber restart. That is a workaround, not the answer — it holds
the modem voice path open (`VoiceMMode1`) for ordinary media use, whose power
and call-interaction cost is unmeasured.
**Capture gain belongs in the UCM.** The voice verb sets `DEC7 Volume=124`,
which gives a flat noise floor at rms ~14000 with no speech variation at all;
84 drops it to ~6200. A runtime `amixer cset` does **not** persist — activating
the profile reapplies the UCM value, verified. Whatever gain STT wants has to
land in `souveraine-ucm-blueline`.