fix(audio): ES7210 mic PGA gain 21dB->12dB (ADC saturation)

[torlando-tech]

The ES7210 mic PGA initialized at the default micGain=7 (21 dB), which saturated the ADC: 0x8000 negative-rail spikes, an rms-7003 noise floor in silence, and a spectral-peak shift that masqueraded as a +17–25% pitch "warp". Drops it to GAIN_12DB (a pre-existing es7210.h enum) — a clean middle level: real signal, well below saturation.

Capture rate stays at main's 8 kHz. Part of the LXST voice investigation.

🤖 Generated with Claude Code

https://claude.ai/code/session_01UWZuYkHBRqNb6BZHV8sTG5

[greptile-apps]

Greptile Summary

Fixes ADC saturation on the ES7210 mic array by replacing the raw micGain cast with the hardcoded constant GAIN_12DB, dropping the PGA from 21 dB to 12 dB. The root cause (0x8000 negative-rail spikes, rms-7003 noise floor, and pitch warp) is well-diagnosed and the gain level chosen is reasonable.

• es7210_adc_set_gain() now always uses GAIN_12DB regardless of the micGain argument passed to init(), silently breaking the caller-visible API contract — any code that passes a specific gain value will have it ignored without error.
• The lxst_audio.h header still documents micGain with the old default of 7 (21 dB) and presents the parameter as functional, which is now inaccurate.

Confidence Score: 3/5

The gain fix resolves a real hardware symptom, but the micGain parameter is now dead code — any caller passing a value other than the default will have it silently overridden by 12 dB.

The diagnostic reasoning and chosen gain level are sound, but the implementation discards the caller-supplied micGain argument with no warning, and the header still advertises the parameter as functional with the old 21 dB default. A downstream caller or test that relies on configurable gain will receive wrong behavior without any indication.

lib/lxst_audio/lxst_audio.cpp (hardcoded gain ignores parameter) and lib/lxst_audio/lxst_audio.h (stale default and doc comment for micGain)

Important Files Changed

Filename	Overview
lib/lxst_audio/lxst_audio.cpp	Hardcodes GAIN_12DB in es7210_adc_set_gain(), fixing ADC saturation, but silently drops the micGain parameter — callers supplying a non-default gain will have it ignored.

Sequence Diagram

%%{init: {'theme': 'neutral'}}%%
sequenceDiagram
    participant Caller
    participant LXSTAudio
    participant ES7210

    Caller->>LXSTAudio: "init(codec2Mode, micGain=7)"
    Note over LXSTAudio: micGain parameter received but NOT used
    LXSTAudio->>ES7210: es7210_adc_init()
    LXSTAudio->>ES7210: es7210_adc_config_i2s()
    LXSTAudio->>ES7210: "es7210_adc_set_gain(MIC1|MIC2|MIC3|MIC4, GAIN_12DB)"
    Note over ES7210: Hardcoded 12 dB — micGain ignored
    LXSTAudio->>ES7210: es7210_adc_ctrl_state(START)
    LXSTAudio-->>Caller: init returns true

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sequenceDiagram
    participant Caller
    participant LXSTAudio
    participant ES7210

    Caller->>LXSTAudio: "init(codec2Mode, micGain=7)"
    Note over LXSTAudio: micGain parameter received but NOT used
    LXSTAudio->>ES7210: es7210_adc_init()
    LXSTAudio->>ES7210: es7210_adc_config_i2s()
    LXSTAudio->>ES7210: "es7210_adc_set_gain(MIC1|MIC2|MIC3|MIC4, GAIN_12DB)"
    Note over ES7210: Hardcoded 12 dB — micGain ignored
    LXSTAudio->>ES7210: es7210_adc_ctrl_state(START)
    LXSTAudio-->>Caller: init returns true

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Prompt To Fix All With AI

Fix the following 1 code review issue. Work through them one at a time, proposing concise fixes.

---

### Issue 1 of 1
lib/lxst_audio/lxst_audio.cpp:61
**`micGain` parameter silently ignored**

`GAIN_12DB` is now hardcoded, so any caller that passes a non-default `micGain` to `init()` will always get 12 dB, silently. For example, `audio.init(CODEC2_MODE_1600, 3)` (9 dB) or any diagnostic path that tries to sweep gain levels will have the value discarded with no warning. The `init()` signature and its `@param micGain` doc in `lxst_audio.h` still advertise the parameter as functional (`0-14, default 7 = 21dB`), making this a silent API contract break. Either remove/default-away the parameter in the header, or apply the enum cast back: `(es7210_gain_value_t)micGain` with `micGain`'s default changed to `4` (i.e., `GAIN_12DB`) in `lxst_audio.h`.

_{Reviews (1): Last reviewed commit: "fix(audio): ES7210 mic PGA gain 21dB->12..." | Re-trigger Greptile}

[greptile-apps]

micGain parameter silently ignored

GAIN_12DB is now hardcoded, so any caller that passes a non-default micGain to init() will always get 12 dB, silently. For example, audio.init(CODEC2_MODE_1600, 3) (9 dB) or any diagnostic path that tries to sweep gain levels will have the value discarded with no warning. The init() signature and its @param micGain doc in lxst_audio.h still advertise the parameter as functional (0-14, default 7 = 21dB), making this a silent API contract break. Either remove/default-away the parameter in the header, or apply the enum cast back: (es7210_gain_value_t)micGain with micGain's default changed to 4 (i.e., GAIN_12DB) in lxst_audio.h.

Prompt To Fix With AI

This is a comment left during a code review.
Path: lib/lxst_audio/lxst_audio.cpp
Line: 61

Comment:
**`micGain` parameter silently ignored**

`GAIN_12DB` is now hardcoded, so any caller that passes a non-default `micGain` to `init()` will always get 12 dB, silently. For example, `audio.init(CODEC2_MODE_1600, 3)` (9 dB) or any diagnostic path that tries to sweep gain levels will have the value discarded with no warning. The `init()` signature and its `@param micGain` doc in `lxst_audio.h` still advertise the parameter as functional (`0-14, default 7 = 21dB`), making this a silent API contract break. Either remove/default-away the parameter in the header, or apply the enum cast back: `(es7210_gain_value_t)micGain` with `micGain`'s default changed to `4` (i.e., `GAIN_12DB`) in `lxst_audio.h`.

How can I resolve this? If you propose a fix, please make it concise.