feat(binaural): reverb size and per-band decay, live up to Studio (S2-15) - #351
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S2-15. The late tail had one decay time for every band and one set of
line lengths. Two more handles shape it the way a room's tail is shaped:
- `reverb.size` (0.5–2) scales every delay line together, allocated for
the maximum: shorter lines make a small, dense room, longer ones a
sparser, larger one. The feedback gains are recomputed with the lengths
so the RT60 stays what was asked at any size, and a running network
stretches its lines at no more than 0.02 samples per sample — a
second-long ±2 % pitch drift rather than a splice (a fresh or cleared
network snaps).
- `reverb.rt60_low_ratio` and `reverb.rt60_high_ratio` (0.25–4): the
decay time below ~250 Hz and above ~4 kHz as ratios of the broadband
RT60. Each line's loop gain becomes the broadband value plus two
first-order shelves — trapezoidal one-poles, exact complements, so the
shelf reaches its band's gain (the `exp` one-pole reached ~60 % of it) —
whose gains are what the band's own RT60 adds to the broadband gain.
At a ratio of 1 both terms are exactly zero: the default tail is
arithmetically the one before the shelves existed. The fixed one-pole
wall damping stays underneath; the high ratio acts on top of it.
`Fdn::set_params` takes the `BinauralReverb` block. Wired through
config (`render.binaural.reverb.{size,rt60_low_ratio,rt60_high_ratio}`),
engine build, persistence, OSC (`…/reverb/size`, `…/reverb/rt60_low_ratio`,
`…/reverb/rt60_high_ratio`), the state snapshot, BINAURAL.md, and Studio:
three sliders in the Late reverb block (the ratios on log2 sliders so ×0.5
and ×2 sit symmetrically about ×1), three Tauri commands, i18n ×8.
Tests: first output of a fresh network lands after the pre-delay plus the
shortest line at each size and the decay slope is size-invariant; a size
change on a running network slews at the bound and gets there; bass ×4
lengthens the 40–150 Hz tail more than tenfold and treble ×¼ shortens the
4–8 kHz tail more than tenfold, each leaving the other band within 3 dB
(band energies off a Hann-windowed FFT).
Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>
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Summary
Series 2, lot 3, S2-15 — reverb size and per-band RT60, three settings wired from YAML to Studio.
reverb.size(0.5–2, default 1): scales every FDN delay line together (allocated for the maximum). Feedback gains follow the lengths so the RT60 is unchanged at any size. A running network stretches its lines at ≤ 0.02 samples/sample (a second-long ±2 % pitch drift, not a splice); a fresh or cleared network snaps.reverb.rt60_low_ratio/reverb.rt60_high_ratio(0.25–4, default 1): decay time below ~250 Hz / above ~4 kHz as ratios of the broadband RT60. Per line, the loop gain becomes the broadband value plus two first-order shelves (trapezoidal one-poles — exact complements; theexpform only reached ~60 % of the band's gain) carrying what the band's own RT60 adds. At ratio 1 both terms are exactly zero: the default tail is arithmetically unchanged. The fixed wall damping stays underneath.Wiring
live_params→config(render.binaural.reverb.{size,rt60_low_ratio,rt60_high_ratio}) →renderer_build→persist→osc_contract+osc(…/reverb/size,…/reverb/rt60_low_ratio,…/reverb/rt60_high_ratio) →snapshot(size,rt60LowRatio,rt60HighRatio) → BINAURAL.md (table, OSC table, a Tail character tip) → Studio: three sliders in the Late reverb block (ratios on log2 sliders), three Tauri commands, i18n ×8 (npm run i18n:check: parity).Tests
size_scales_the_lines_and_keeps_the_decay,size_changes_are_slewed,band_ratios_shape_the_decay_by_band(bass ×4 → >10× longer 40–150 Hz tail; treble ×¼ → >10× shorter 4–8 kHz tail; each leaves the other band within 3 dB; band energies off a Hann-windowed FFT).cargo test -p renderer --lib: 384 passed, 2 ignored.cargo test -p runtime_control: green (contract conformance included).cargo checkonorender_engineand Studio'ssrc-tauri: clean.npx vite build: OK. Golden unchanged.Listening
Size 0.5 vs 2 at the same RT60; bass ×1.5 + treble ×0.5 against a flat decay on dialogue and on a held note.
🤖 Generated with Claude Code