@audio/shift-sms

Spectral Modeling Synthesis (Serra/Smith) sinusoidal+residual pitch shift

npm install @audio/shift-sms

import sms from '@audio/shift-sms'

Spectral Modeling Synthesis. Parabolic-interpolated peak picking builds sinusoidal tracks (freq, mag, phase); each peak's lobe is copied intact to round(f·ratio). Stochastic residual shifts to ratio-scaled bins with analysis phase.

sms(audio, { ratio: 2 })
sms(audio, { ratio: 1.5, maxTracks: 40 })

| Param | Default | | |---|---|---| | maxTracks | Infinity | Max simultaneous sinusoidal tracks | | minMag | 1e-4 | Peak detection threshold (linear) |

Preserves formant envelope (lobes scale freely with peaks), harmonic structure, tonal clarity. Destroys transients, noise-like textures (absorbed into residual), polyphony beyond maxTracks.

| f0 err | THD% | alias | attack corr | formant dist | phase coh | shift | |-------:|-----:|------:|------------:|-------------:|----------:|------:| | 0.00 | 0.0 | 0.002 | 0.963 | 1.845 | 0.929 | 1.701 |

Lower attack corr (0.963) because sinusoidal modeling smooths onset transients into the residual.

Use when: Sustained tonal / harmonic instruments, vowels. Not for: Percussion, noise-heavy material.

Stream

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

sms 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