spliff.vst3 — adaptive transient processor, a downspout-style approximation of
Oeksound Spiff.
Unlike a conventional transient shaper (attack/sustain gain envelope), Spliff detects transients per frequency band and applies dynamic cuts or boosts only where transient energy exists, leaving non-transient material intact. Input level barely matters: Depth behaves the same regardless of gain staging.
Cut or boost first. Mode selects Cut (tame clicks, mouth noise, harsh sticks) or Boost (bring drums, piano attacks forward). Spiff manual advice holds: cut last in the chain, boost early before compressors and saturators.
Workflow (from the manual): Delta on, raise Depth, tune Sensitivity and Decay, sculpt the band splits, optionally Sharpness and Decay LF/HF, then Delta off, re-tune Depth, Bypass to compare, Mix to taste, Trim to compensate.
| Parameter | Range | Default | Notes |
|---|---|---|---|
| Mode | Cut, Boost | Cut | Pink = boost, blue = cut in the manual's graph |
| Depth | 0–100 % | 50 % | Amount of cut/boost; CC 1 |
| Sensitivity | 0–100 % | 50 % | Higher catches more transients; CC 2 |
| Sharpness | 0–100 % | 30 % | Per-band independence; low = natural on drums |
| Decay | 0–100 % | 25 % | Recovery time; 0 = onset only; CC 3 |
| Decay LF/HF | LF … equal … HF | equal | Which end of the spectrum decays longer |
| Split Low / High | 20 Hz–12 kHz | 250 Hz / 4 kHz | Detector band crossovers (sidechain weighting, not EQ) |
| Mix | 0–100 % | 100 % | Dry/wet blend; CC 4 |
| Trim | −12 to +12 dB | 0 dB | Wet-only makeup gain |
| Bypass | active/bypassed | active | Soft in intent; DSP keeps running |
| Delta | off/on | off | Monitor wet−dry: what is removed or added |
| CC Depth/Sens/Decay/Mix | 0–127 | 1/2/3/4 | 0 = off; Drift lane defaults |
| CC Channel | 1–16 | 1 | MIDI channel for the four CCs |
Route Drift's MIDI output to Spliff's MIDI input: CC 1 → Depth, CC 2 → Sensitivity, CC 3 → Decay, CC 4 → Mix.
Stereo. The detector is mono (fixed full link — transients never shift the image); both channels share the decision and keep their own band content. M/S operation from the manual is not implemented in v1.
cmake -S . -B build -DCMAKE_BUILD_TYPE=Release -DDOWNSPOUT_BUILD_SPLIFF=ON
cmake --build build --target downspout_spliff_core_tests spliff-vst3 --parallel "$(nproc)"
ctest --test-dir build -R downspout_spliff_core_tests --output-on-failureCore tests cover silence, dry passthrough at Mix 0, bypass, Depth-0 transparency, cut reduction and boost lift on an onset burst, the sensitivity gate, decay-tail behaviour and tilt direction, Delta polarity, Trim gain, block-split determinism, clamping, and state round trip.
Core DSP, deterministic tests, the VST3 target, the panel and the catalogue screenshot are complete. Host validation in REAPER remains. Deliberately deferred to follow-ups: M/S stereo modes, parametric sensitivity-curve bands, resolution / oversample / window / phase controls, and live gain-reduction metering in the panel.