@audio/shift-pvoc

Canonical phase vocoder (Bernsee/SMB) pitch shift

npm install @audio/shift-pvoc

import vocoder from '@audio/shift-pvoc'

SMB/Bernsee bin-shift. Computes true instantaneous frequency per bin from consecutive-frame phase advance, scatters peaks to shifted bins, accumulates synthesis phase at the shifted frequency.

vocoder(audio, { ratio: 1.5 })

Preserves dominant-partial pitch, long-horizon phase per bin. Destroys transients, vertical phase coherence ("phasiness"), formants.

| f0 err | THD% | alias | attack corr | formant dist | phase coh | shift | |-------:|-----:|------:|------------:|-------------:|----------:|------:| | 0.00 | 0.0 | 0.000 | 0.981 | 1.158 | 0.928 | 1.553 |

Phase coh 0.928 from independent per-bin phase accumulation — no inter-bin locking. Best shift score among the general phase vocoders — the simpler scatter avoids the peak-locked family's own assignment overhead on these fixtures.

Use when: Simple tonal material, educational baseline. Not for: Music with percussion, voice.

Stream

let write = vocoder({ ratio: 1.5 })
let out = write(inputBlock)
let tail = write()  // flush

vocoder streams per-frame: each write(chunk) call renormalizes and emits audio as soon as a frame completes, and re-chunking the same input differently reproduces the batch output byte for byte.

Data

Input is a Float32Array (mono) or an array of Float32Array channels ([left, right, ...]) — anything else throws TypeError. ratio also accepts a function t => ratio (seconds from stream start) or a Float32Array breakpoint envelope (resampled across the input via ratioDuration, default the input's own duration) for time-varying pitch.

Part of @audio/shift — the shift family umbrella. This README is generated from the umbrella docs.

MIT © audiojs