designPeakingEq() mapped the RBJ cookbook's a1/a2 straight into the
ADAU1701 Param EQ cell's A0/A1 registers. The cookbook's difference
equation subtracts the feedback terms; the ADAU1701 cell adds them. Any
nonzero band gain therefore applied positive instead of negative
feedback at the target frequency, so the biquad's state diverged and
railed to a constant (inaudible DC) value -- the "any EQ/enhancement
change goes completely silent, even the beep test tone" bug.
Confirmed live: SigmaStudio's own direct safeload writes to the same
registers (correctly signed by its own tool) only distorted, never
silenced, which pointed at this driver's own coefficient math rather
than the DSP chain or the safeload mechanism itself.
Adds a host test asserting Jury stability for the ADD-convention
denominator across the actual bass/stereo-enhance gain values and the
GainDb range extremes, so a regression trips ctest instead of requiring
a live listening test to notice.
Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
micheleandClaude Sonnet 5
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