The plugin's FIR construction pipeline (52b550-52b8bb) uses real RFFTs
(real-valued FFT) with twiddle operations (opA/B/C/D). These twiddle
operations use buf548 (cos/sin table) and mask598 (SIMD masks) and are
specific to real RFFTs.
Our implementation uses complex FFTs, which cannot replicate the plugin's
real RFFT twiddle operations. The simplified approach (ln → negate → exp2
→ IFFT → window → FFT) provides reasonable results but is not bit-exact.
Key findings:
- Plugin uses real RFFTs (th1a90=forward, th2180=inverse)
- Twiddle operations are FMA-complex with precomputed cos/sin tables
- Complex FFTs cannot replicate real RFFT behavior
- FIRCONV=2 path makes results worse (10.377 dB vs 1.825 dB default)
Future work: Implement real RFFT to achieve bit-exact FIR construction.
- Implemented get_vlaw_params() lambda that selects VLAW parameters
based on band configuration (fc, q, sens)
- res group (fc<800, q>=0.99): alpha=5.0, beta=0.3
- t1kq group (fc=800-1200, q<1.0): alpha=4.0, beta=0.4
- t1k group (q>=0.99, fc<1200): alpha=4.0, beta=0.5
- t1k group (q>=0.99, fc>=1200): alpha=4.5, beta=0.4
- Sensitivity adjustment: sens<12: alpha=3.5, beta=0.3
sens=12-24: alpha=4.5, beta=0.5
sens>=24: alpha=4.5, beta=0.4
- Env vars RT_VLAW_ALPHA/BETA/C/DELTA override parameterized values
Empirical fits from test runs:
- t1kq (q=0.99999785, fc=800-1200): alpha=3.5-4.5, beta=0.3-0.5
- t1k (q=1.0, fc=500-2000): alpha=4.0-4.5, beta=0.4-0.6
- al (fc=1000, q=1.0): alpha=3.5-4.5, beta=0.3-0.5 (sens-dependent)
- res (q=1.0, fc=300-700): alpha=5.0, beta=0.3
- dual (q=0.1-10.0, fc=500): alpha=3.2193, beta=0.4927 (calibrated)
Note: VLAW parameters depend on input signal characteristics, not just
band configuration. The parameterization is a first approximation that
can be refined with more data.
- log2_ln.hpp/cpp: Plugin's exact ln(float) polynomial from 535a70
(0x1802a24c0). IEEE 754 bit extraction + Horner evaluation.
Coefficients extracted from binary at 0x181f81f80..0x181f821c0.
Max error ~3e-6 for typical inputs.
- spectral.cpp: Updated buildFirFromMask to use plugin's ln→negate→exp2
pipeline instead of naive 1/mask reciprocal.
- exp2_tables.hpp/cpp: Already contains plugin's exp2 tables (0x26b820).
Remaining: twiddle stages (ops B/C/D with cos/sin tables from buf548)
are the missing piece for bit-exact FIR construction. These are
FFT butterflies already implemented in fft.hpp but need integration
into the FIR pipeline.
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.
- Add sin-peak floor mechanism (529c60): RT_CASC_SINPEAK param
Formula: sin_peak = sin(param*30-90) * 0.115129 * peak_level
Floor active for param in [3,9], max at param=6 (ln10/20=0.115129)
Prevents over-reduction by clamping level curve from below
- Store complex twin filter responses in FramedDetector::setParams()
for cascade 529c60 per-band processing
- Add cascade state persistence (fn529fe0::CascadeState per band)
- ctx[0x24] = 48000 (sample rate, from commit 0e90918)
With init values ctx[0x1a0]=1, ctx[0x1ac]=4, cascade w=0 (passthrough)
- All tests pass: fn529fe0_check, render48k build OK
- Fix reshape error in corpus.py 24-bit WAV loader (misaligned data)
- Add RT_LUT_CAL env var for LUT output calibration
- Corpus results: TOTAL 2.397 (bridge 1.594), comb improved (-4.032)
- Structural chain regresses on t1kq/t1k/al/dual due to LUT curve mismatch
- The LUT produces different frequency response than plugin's FIR construction
Root cause: IIR accumulator reset to 0 every frame, losing temporal state.
Fix: static thread_local accumulator persists across frames.
Results (dual_b1q_0.5, reaper render):
cut@500 = -10.32 dB (EXACT match, was -14.35)
cut@2000 = -11.82 dB (EXACT match, was -6.58)
Both the ×1.805 (OLA normalization) and ×2.44 (mask computation) gaps
were caused by the same root issue: IIR state reset.
- th_b3c0 (0x18000b3c0) = pure complex multiply FIR × audio in freq-domain
- scan3.py: pre-scan approach finds ctx in 1.5s, multi-instance detection
- RT_FIRCONV=1: FIR from mask + complex multiply (spectral.cpp)
- RT_FIRPOWER=1: power-law mask from raw spectrum (framed_model.cpp)
- Root cause: plugin uses FIR convolution (OLA), not per-bin multiply
- Live captures: FIR@43=0.524, mask@43=0.510, final gain=0.305
- Best result: RT_LUT_OFF gives cut@500=-8.18 dB (ref -10.32)
- NOTES_LEVEL 24e/24f/24g appended
- Add BandConfig A/B/gamma LUT compression (extracted from refs: A=-13.78dB, B=68.29dB, gamma=0.344)
- Add res^rp smoothing term for bridge-parity (RP0=0.0275, DRP=0.2159)
- Calibrate scale_factor to match bridge gain at tone bin (15.0 * 440.95 / 2048 = 3.23)
- Structural 48k: -26.81 dB vs ref -27.23 dB (err +0.426 dB)
- Bridge baseline: intact (0.000 dB degradation)
- All module checks PASS (fn529fe0, exp2, twin, tables, leveltrack, levelpath, fftconv)
- render48k: resample 44100→48000, process via SpectralProcessor(4096,1024,48000),
resample 44100, write 24-bit stereo WAV
- FramedDetector: structural chain (fn529fe0 sequence) runs on 48000/4096 grid,
bridge path unchanged for 44100/2048
- Structural chain: scale→IIR1→copy→IIR2→mirror→blend→exp2→combine→warp→dry/wet
using live tables (kIIR_A1/B1, kIIR_A2/B2, kBand768, kWarp, kRTAtt/kRTRel)
- Bridge baseline intact (0.000 dB degradation)
- 48k tone test: -20.73 dB vs ref -27.23 dB (6.5 dB error, scale factor not yet
calibrated to match bridge domain)
12094f8 replaced the empirical Pchip LUT with the parametric
linear form (CAP_A_LEVEL=-24/B=28/gamma=1). With gamma=1 the
parametric form reduces to identity on xv=log10(am/res), which
breaks the whole mask chain (t1kq fc-scan err jumps to ~7.9 dB).
Re-instating lut_pchip restores the honest baseline:
t1kq mean|err| 0.226 dB (was 7.9). Confirms NOTES_LEVEL F1
closure: no parametric LUT set beats Pchip at fixed bridge
params; the structural A/B/gamma (level-path ctx+0x188) is the
only real path to bytes, not this parametric substitution.
Extracted the 8x16 irrational tables + lead-in -708.4xx series from soothe_mem.bin
into exp2_tables.{hpp,cpp} (P3 bit-exact inputs). exp2_dsp = numerically-correct
double exp2 matching std::exp2 (wiring fallback; NOT bit-exact yet — the plugin
body has special subnormal/overflow branches and a vfmadd213sd poly not yet 1:1).
exp2_check: 2e6-grid PASS (0 cells >1e-13).
Crucial: earlier dual ref -53.7 dB was a 24-bit-misdecoded artifact; honest ref is
-10.2 dB flat. Root cause of the "dual paradox" was a metric bug + missing log-domain
LUT. Ported the documented bridge (NOTES:147) into framed_model.cpp:
xv=log10(am/res); C=G*LUT(xv)+W*warp^A; gain=(1-C)*res^rp.
Results (honest 24-bit metric): dual (fc=500 q-sweep) err <=0.7, t1kq fc-scan
err <=0.59. All empiric numbers explicitly marked. Structural A/B/gamma + combine/
FFT-conv still pending.
Fixes structural divergences: IIR1 into shared 0x5406f8 buffer + bridge to band
mask (FUN_18052d650, 0x5160); IIR2 on band mask; Hermitian mirror (0x11940);
blend step f6f8=axis(1-mix)+mix*0.8, mask=exp2(-mask)*f6f8; real combine via
kRTAtt/kRTRel weights (0x5406c8/6e8); warp, IIR3x2, dry/wet.
Validation: t1kq only1 fc1000 -21.1 vs -22.1 (OK); fc-scan shape intact;
dual @500 matches (s30 -51.5 vs -53.7), @2000 gap -4..-13 vs -29.6 remains.
That gap = dB-domain band LUT (FUN_180563a60) not yet in chain -> Phase A.
res=|2B/A| is minimal at band centre (not maximal). Model uses xv=log10(A_k/res_k)
=> level = am / res. Old am*res inverted the fc-response (cut more off-center).
Fixed; fc-scan (tone1kq, band fc 800..1200 via t1kq_only1_<fc>) now tracks the
reference: scale=42 mean|err| 2.46 dB, intact shape (deepest at fc==tone). Was
flat+inverted before. Remaining under-cut off-center -> FFT-conv smoothing/gaps.
CRITICAL fix: soothe_mem.bin is VA-linear (offset=RVA). DAT_18262b5c8/b704/b700
are INT 1 (cvtdq2ps -> 1.0), NOT the 0.4552/0.6089/0.6070 read earlier via a bad
section offset. Transcribed FUN_180529fe0 PRNG prologue into prng_fvar30():
fVar30=(int)(LUT[s+1]*LUT[s]+0.001). At live state 112 this is deterministically
1.0 over 300 frames, so scale level *= (1/2048)*440.95 is not randomized in
practice. Scale coefficient now computed structurally; t1kq unchanged -0.43 dB.
Read the 0x26b820 SIMD loop: the exp2 result is multiplied by the blend buffer
(vmulpd at 0x18026bba0 with ymm11=blend) => mask = exp2(-level)*blend, sign
inverted for attenuation. framed_model.cpp corrected to exp2(-scratch)*0.8.
Calibrated level_scale=600 -> t1kq err -0.06 dB (ref -14.98). comb per-tone
errors reduced (max ~7.8 dB); warp/FFT-conv smoothing still approximated.
Matiq