Drag to set speed directly, −100 to +100. Sends at 10 Hz while dragging and always sends the value you released on, so the robot cannot be left running at a speed the slider is not showing.
Pick a side to start pulsing it at its stored null; the slider is dead until you do, because a servo that is not being driven cannot be judged. Then drag and watch that flipper arm: below the true null it creeps one way, above it the other, and at the null it sits still. Land on the middle of the still range, save, and release.
Release when finished. A held servo keeps pulsing, and pulsing at neutral is the single loudest thing on the microphone — about 17 dB above 8 kHz. Normal operation ceases pulses within 120 ms of stopping for exactly that reason.
span µs is a different quantity and is not set here: it is
the deflection meaning full speed, where a speed mismatch between the
two physical servos gets corrected. Judge it by driving both at the
same speed, then set it from the custom box with
servo.calibrate.
Speak while it records. Peak and RMS come back with the result: speech at a normal distance lands near −30 dBFS RMS with peaks around −10. Below −60 means the mic is not hearing you, which is a mixer problem rather than a code one.
Playback is normalised to −3 dBFS so you can hear it — a good recording peaks near −14, and the small speaker at 0 dB makes that barely audible. The file on disk stays raw, and the gain applied is reported, so a loud playback is never mistaken for a hot recording. Play back raw skips it.
Volume attenuates the analogue output, leaving the DAC at full scale,
so 100% is 0 dB rather than the amplifier's ceiling. Add
{"persist":true} in the custom box to keep a level across
restarts; the CYD knob does not persist, since turning a dial is not
the same as choosing a setting. Mute never persists — a robot
that booted silent would give you nothing to go on. Mic off disconnects
the input in hardware.
Capture is fixed at 48 kHz stereo — asking ALSA for 16k directly warbles on this driver. The wire rate is reached by integer decimation, which also removes the aliased converter tones above 6 kHz.
Gain belongs in the analogue boost ahead of the ADC, not in the digital Capture control behind it. Boost lifts signal relative to the noise floor; Capture lifts both equally.
Changes apply immediately but are forgotten on restart until you press keep these settings, which writes them to the robot. Reset throws them away and restores the recipe the robot shipped with — the way back from a tuning session that went wrong.