Replace the static fir_taps parameter with auto_taps(cutoff_norm) which
computes ceil(3.32 / cutoff_norm).clamp(63, 16383). This ensures the
filter transition band equals one passband width regardless of SDR sample
rate, giving correct image rejection when the user sets audio_bandwidth_hz.
At 912 ksps with 3 kHz audio bandwidth this yields ~2018 taps instead
of the previous hardcoded 64, eliminating the 114 kHz stopband gap that
caused adjacent-band signals to alias into the audio output.
Co-authored-by: Claude Sonnet 4.6 <noreply@anthropic.com>
Signed-off-by: Stanislaw Grams <stanislawgrams@gmail.com>
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