feat: adjustable filter slopes (12/24/48 dB/oct)#33
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Shelves + HP/LP bands gain a selectable slope. 12 dB/oct is the original single biquad (bit-exact regression); 24/48 dB/oct cascade Butterworth sections using the exact per-section pole-Q tables, keeping the -3 dB point at Fc and splitting shelf gain across sections. Peaking/Notch/BandPass/ AllPass are single-biquad and ignore the slope. - ApoFilter keeps its head biquad + an 'extra' section cascade (empty at 12 dB/oct, so the common path is byte-identical). New builder .slope_db_oct + ApoFilter::set_slope. - Wired through IPC (BandState.slope_db_oct + Command::SetBandSlope), the daemon (AudioCommand::SetBandSlope, handler, snapshot, Profile toml persistence) and the Windows APO FilterSnapshot. - Tests: 12 dB bit-exact vs single biquad; LP/HP rejection ~12/24/48 dB one octave past Fc; -3 dB at Fc for all orders; shelf reaches full gain; slope ignored for peaking.
add BandType::uses_slope() (true for shelves + HP/LP) and next_slope_db_oct() (12->24->48->12) so the front-ends gate and cycle the per-band filter slope consistently.
add `resonance band-slope <index> <12|24|48>` -> SetBandSlope (1-based index, value validated). status now prints the slope for shelf/HP/LP bands (e.g. `24 dB/oct`); single-biquad types omit it.
add a 12/24/48 db/oct slope dropdown in the bands table next to the type badge. shown only for shelf/hp/lp bands (single-biquad types get a dim placeholder); sends SetBandSlope on change. new Slope column collapses one width tier before the Type combo.
add `S` to cycle the selected band's filter slope 12->24->48 (shelf/ hp/lp only; single-biquad types get a status hint). the Type column now shows the slope for those bands (e.g. `LS 24`); help overlay + footer document the key.
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Adjustable filter slopes (12/24/48 dB/oct)
Shelf + high/low-pass bands gain a selectable slope (roadmap "Adjustable filter slopes"). Peaking/Notch/BandPass/AllPass stay single-biquad and ignore it.
DSP
ApoFilterkeeps its head biquad + anextra: Vec<BiquadFilter>cascade (empty at 12 dB/oct, so the common path is byte-identical to before). 24/48 dB/oct cascade Butterworth sections using the exact per-section pole-Q tables — the −3 dB point stays exactly at Fc, and shelves split their gain across sections so the pass-band gain is unchanged. New.slope_db_oct()builder +ApoFilter::set_slope.Reach
BandState.slope_db_oct+Command::SetBandSlope+BandType::uses_slope()+next_slope_db_oct().AudioCommand::SetBandSlope, handler, snapshot, Profile toml persistence.FilterSnapshot.slope_db_oct.band-slope <index> <12|24|48>+ slope instatus; GUI per-band Slope dropdown (gated to shelf/HP/LP); TUISkey cycles slope + Type column shows it.Tests
12 dB bit-exact vs the single biquad (regression); LP/HP rejection ≈ −12/−24/−48 dB one octave past Fc; −3 dB at Fc for all orders; shelf reaches full gain; slope ignored for peaking. Native profile round-trips the slope through TOML; APO
.txthas no portable slope token (documented — native-profile only).Verification (all three surfaces)
make check(fmt + clippy-D warnings+test --all) EXIT=0. Live daemon smoke on real PipeWire: loaded a 3-band APO,band-slope 1 24→ shelf shows "24 dB/oct",band-slope 2 48→ "48 dB/oct", peaking band shows no slope (gated).cargo test --all+cargo clippy --all-targetsclean.resonance-apoFFI harness passes single-threaded (22/22, as designed).12 dB/oct is the default, so existing presets/profiles are unchanged.