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feat: add tempo-synced stereo delay and coupled room reverb

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Johannes Findeisen 2026-11-05 23:53:03 +01:00
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docs/BUILTIN_DEVICES.md
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@ -121,3 +121,34 @@ license/provenance in SAMPLE_LICENSE.md. Both are installed with the examples.
Tests cover source-rate conversion, one-shot endpoint, looping, release,
partitioning, preset references, missing assets, GUI relinking/undo/reload and
preparation-allocation/callback guards.
## Phase 43 stereo effects
**File → Add stereo delay/reverb** and **Edit → Insert stereo delay/reverb on
wire** add new devices (indices 5/6). Original Delay/Reverb (indices 2/3) retain
their original algorithms, values and saved identities. Existing control and
automation editors, undo and persistence support both generations.
Stereo Delay adds integer **Sync**: 0 milliseconds, 1 quarter, 2 eighth,
3 dotted eighth, 4 eighth triplet. Nonzero sync follows project tempo; changing
tempo uses ordinary stopped project preparation. Time changes crossfade two
fractional read heads for 5 ms. A crossfade finishes before adopting the latest
automated target, bounding transition work and avoiding read-head jumps.
Feedback cross-couples channels (80% same, 20% opposite), with a 0.95 bound.
Delay storage covers four seconds, sufficient for all divisions at 20..300 BPM.
Stereo Reverb adds **Room** (0..1, scales comb spacing) and **Diffusion** (0..1,
cross-couples damped feedback). The right comb timings differ from the left.
Decay/damping retain 0..0.95 bounds. This is a simple algorithmic reverb, without
physical room simulation or a measured RT60. Room automation can alter coloration.
The graph evaluates both channels' inputs before calling a coupled internal
processor. Each stereo device has one prepared state, with no callback allocation.
Mono processing excites both sides and folds the wet output to mono. External
plugins and the original effects retain independent mono instances.
Tests compare whole/split blocks, tempo-synced impulse placement, left-to-right
energy, bounded extreme feedback/diffusion and graph/direct stereo output
(including the engine's subnormal-to-zero policy). GUI tests save/reopen both
identities; callback guards and ASan/UBSan cover processing. `make builtin-preview`
also writes files 5/6 for repeatable listening; human listening remains pending.