Calibration¶

When an alarm is active, serial output prints:

cal: f0=XXX.X Hz h2=X.XX h3=X.XX snr=XX.X nf=X.XXeXX conf_ema=X.XX rms=X.XXXXX

Record these values with and without a drone present (or play rotor audio through a speaker).

Tuning Parameters¶

Key parameters in main/audio_task.c and main/audio_processor.c:

Symbol	Default	File	Description
`SAMPLE_RATE_HZ`	`16000`	`audio_processor.h`	Sample rate (Hz)
`FRAME_SAMPLES`	`1024`	`audio_processor.h`	FFT size (samples per frame)
`HOP_MS`	`100`	`audio_task.c`	Frame hop interval (ms)
`HARM_F0_MIN_HZ`	`180`	`audio_task.c`	Fundamental search lower bound (Hz)
`HARM_F0_MAX_HZ`	`2400`	`audio_task.c`	Fundamental search upper bound (Hz); 3×f₀ must stay < Nyquist
`CONF_ON`	`0.30`	`audio_task.c`	Smoothed confidence threshold to trigger alarm
`CONF_OFF`	`0.18`	`audio_task.c`	Smoothed confidence threshold to clear alarm
`SUSTAIN_FRAMES_ON`	`2`	`audio_task.c`	Consecutive frames above CONF_ON to trigger
`SUSTAIN_FRAMES_OFF`	`8`	`audio_task.c`	Consecutive frames below CONF_OFF to clear
`RMS_MIN`	`0.0004`	`audio_task.c`	Minimum windowed RMS — frames below this are skipped
`EMA_ALPHA`	`0.25`	`audio_task.c`	Exponential moving average factor for confidence
`AUDIO_PROC_HARM_PEAK_MIN_SNR`	`4.0`	`audio_processor.c`	Minimum f₀ peak SNR vs noise floor
`AUDIO_PROC_HARM_MIN_H2`	`0.07`	`audio_processor.c`	Minimum P(2f₀)/P(f₀) ratio
`AUDIO_PROC_HARM_MIN_H3`	`0.035`	`audio_processor.c`	Minimum P(3f₀)/P(f₀) ratio

Tip

Enable BATEAR_AUDIO_PERF_LOG in menuconfig for per-frame DSP timing.