Implement minimum-phase FIR design from BLOCKMAP:
- buildFirFromMask: mask → 1/mask (reciprocal via log→negate→exp) →
IFFT → causal window → FFT → normalize → complex multiply
- RT_FIRCONV=2 activates the new path
- RT_FIRCONV=1 preserved as simple mask × audio (legacy)
Results (tone1kq single band):
default (pointwise): 500Hz=-25.35 dB, 1kHz=-50.60 dB
FIRCONV=1 (mask mul): 500Hz=-1.31 dB, 1kHz=-25.92 dB
FIRCONV=2 (min-phase): same as FIRCONV=1
The twiddle stages (ops B/C/D with cos/sin tables) are the missing
piece for bit-exact FIR construction. They perform FMA operations
with twiddle factors that modify the mask shape.
Note: dual_b1q_0.5.wav reference is empty (0 bytes) — corpus can't run.
Needs regeneration.
Matiq
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