@audio/shift-paulstretch

Paulstretch-style randomized-phase pitch shift for textural blur

npm install @audio/shift-paulstretch

import paulstretch from '@audio/shift-paulstretch'

Large-frame (16k) phase randomization. Magnitudes pulled from source bins at k/ratio; phases drawn from a seeded PRNG every frame. Destroys temporal structure by design.

paulstretch(audio, { ratio: 1.5 })
paulstretch(audio, { ratio: 1.5, seed: 42 })

| Param | Default | | |---|---|---| | seed | fixed (0x1f123bb5) | 32-bit PRNG seed for the per-frame phase draw |

Deterministic: the same seed (the shipped default, or one you pass) always reproduces the same phase sequence and therefore byte-identical output. Pass seed to get a different, still-reproducible draw.

Preserves long-term magnitude-spectrum statistics. Destroys phase, transients, rhythm — by design.

| f0 err | THD% | alias | attack corr | formant dist | phase coh | shift | |-------:|-----:|------:|------------:|-------------:|----------:|------:| | 0.00 | 0.2 | 0.230 | 0.935 | 7.371 | 0.518 | 2.221 |

Worst formant dist by a wide margin (7.371 — the next-worst is granular at 3.486) because random phases smear spectral energy across the frame; the smear is the aesthetic. Alias 0.230 is the same smear leaking past Nyquist.

Use when: Ambient/drone textures, extreme shift ratios. Not for: Anything requiring temporal precision.

Stream

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

paulstretch 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