@audio/shift-delay

Delay-line (harmonizer) pitch shift — dual crossfading taps sweeping a modulated delay window

npm install @audio/shift-delay

import delay from '@audio/shift-delay'

Canonical delay-line (harmonizer) pitch shift — the method behind hardware harmonizers (Eventide H910 lineage, Lexicon "rotating tape head"). Two read taps sweep a modulated delay window at rate ratio, alternating through a Hann crossfade a half-cycle apart. Each time a tap wraps, it splices at whichever lag offset in the search window best correlates with the still-live tap ("intelligent splicing"), which is what keeps the join from phase-slipping the carrier.

delay(audio, { ratio: 1.5 })
delay(audio, { ratio: 1.5, window: 1024, tolerance: 128 })

| Param | Default | | |---|---|---| | window | 2048 | Delay-line length (samples); trades flutter rate against transient smear | | tolerance | window/4 | Splice search radius (±samples) |

Preserves duration, pitch accuracy — no grain or frame to quantize the shift against; state is bounded by window samples, the shape a real-time implementation needs. Destroys clean sustain on wideband or polyphonic material — the two taps share one delay line, so simultaneous partials all splice through the same wrap points and beat against each other; audible as mild flutter at the crossfade rate.

| f0 err | THD% | alias | attack corr | formant dist | phase coh | shift | |-------:|-----:|------:|------------:|-------------:|----------:|------:| | 1.10 | 0.1 | 0.028 | 0.995 | 2.445 | 0.940 | 1.610 |

f0 err 1.10 Hz sits at the measurement floor — nothing here to quantize pitch against. Formant dist 2.445 is unremarkable: the shared delay line resamples the envelope exactly like a time-domain stretch does, no better.

The streaming write/flush wrapper shipped here buffers the whole input like hpss/hybrid — the algorithm's own state is bounded by window samples, but nothing yet exposes that as incremental output.

Use when: Real-time-shaped, lowest-latency time-domain shifting, or the hardware-harmonizer flutter is the wanted character. Not for: Dense chords or polyphony (the splice artifacts stack per partial).

Stream

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

delay buffers the whole input; write(chunk) accumulates and the batch algorithm runs once on write() (flush, no argument), returning everything at once.

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