Key Change Experiments
Progression of experiments toward Ableton-quality key changes (+6…-5 semitones) in the browser, for SongSelect Rehearse and lyric videos.
Step 01Formant compensation on the vocal stem
Signalsmith Stretch, vocal stem A/B: formant compensation OFF (current product behaviour) vs ON. Instruments shifted as-is; drums never shifted.
Verdict: noticeably better vocals at extreme shifts — but not yet Ableton-level.
Step 02Engine shoot-out: Signalsmith vs Rubber Band R3
Same graph and stems; the vocal-stem variable is now the engine itself — Signalsmith + formant compensation (Step 01 winner) vs Rubber Band R3 real-time WASM with formant preservation. GPL build, evaluation only.
Verdict: no better — Signalsmith more open, R3 more muted. Engine swap isn't the fix.
Step 03Signalsmith tuning lab
Four arms on the vocal stem — clean (no formant comp, today's product), baseline (+ formant comp), a frozen hand-tuned preset, and fully tunable (block size, tonality, HF "air" bypass, shelf, formant base). Plus a second axis: vocal source bitrate from 96 kbps up to 320, all encoded from the lossless master.
Verdict: pending listening.