audioJS

@audio/tune-snap

Status calibrated

npm2.0.2licenseMIT

Pitch correction to a scale: each note's centre moved onto its note, its slow drift flattened, the voice's own cycles re-spaced along one pitch curve (Auto-Tune / Melodyne class)

Overview

Install
Updated
Family
tune, 3 packages under it
import snap from '@audio/tune-snap'

snap(voice, { fs })                                  // chromatic, natural: centres on their notes, vibrato kept
snap(voice, { fs, scale: 'major', root: 2 })         // to D major
snap(voice, { fs, speed: 0 })                        // every moment on its note: the hard, stepped sound
snap(voice, { fs, strength: .5 })                    // half way there
snap([left, right], { fs })                          // a stereo voice, on one pitch and one set of cycles

The voice's pitch is pYIN's Viterbi path (Mauch & Dixon, ICASSP 2014) every 5 ms. The note each moment means is a Viterbi path over the scale's notes: a frame costs its squared distance from a note, a change of note costs what 40 ms a semitone away does, so a vibrato swinging past the midpoint between two notes stays on its note and a sung step moves to the next. Each note's centre, the median of its middle half, is moved onto its note; the part of its pitch slower than speed (drift, a held note sagging) is taken away and the faster part (vibrato, a scoop, a slide) kept. Between notes the shift crosses over a raised cosine, inside the gap between them, or speed long across a legato step. Then the voice's own glottal cycles are re-spaced along that curve, found on the same pitch (@audio/tune-curve, TD-PSOLA): formants, consonants and breath kept.

Nothing is cut out, shifted apart and crossfaded back over the dry voice, so no note comes in or out with a jump in pitch or a dip where two pitches cancel. Unvoiced audio passes as it is; a note already in tune is left as sung, and a take all in tune comes out sample for sample.

options default
fs 44100 Hz (sampleRate is read too)
scale 'chromatic' 'major', 'minor', 'harmonic-minor', 'melodic-minor', 'pentatonic-major', 'pentatonic-minor', 'blues', 'dorian', 'mixolydian', 'whole', or the degrees as semitones above the root
root 0 the scale's root, semitones above C (2 is D, 9 is A)
a4 440 Hz, the tuning of A4
strength 1 how much of the correction is applied: 1 all, .5 half way, 0 none
speed 80 ms: how slow a motion within a note must be to be corrected away. 0 sets every moment on its note; 20 keeps 40% of a 5.5 Hz vibrato, 50 keeps 80%, 80 keeps 90% and takes away drift; 400 moves the notes' centres alone
tolerance 8 cents: a note whose centre, and its motion slower than speed, stay this close to its note is left as sung
minFreq, maxFreq 60, 1000 Hz, the pitch looked for

pitchOf(channels, opts) and correction(midi, opts) are the two halves before the retune: the pitch every 5 ms (MIDI, NaN unvoiced), and the shift in semitones that tunes it.

Measured

Eight solo singers of Vocadito (tracks 1, 5, 10, 14, 20, 27, 33, 38: 158 s, 2021, CC BY 4.0), chromatic. A note's pitch is the median of the corrected voice's pYIN pitch over the middle of each annotated note of 150 ms or more; periodicity is 1 less YIN's least normalized difference over 30 ms, its loss counted where the sung voice's exceeds 0.8.

notes within 10 cents of a semitone mean distance periodicity lost, 1% worst frames time per second of audio
as sung 26% 23.7 cents
tune-snap 1 (per-note PSOLA, crossfaded over dry) 64% 10.4 cents 0.17 97 ms
speed: 80 71% 8.4 cents 0.07 19 ms
speed: 0 96% 2.6 cents 0.17 (the steps between notes) 19 ms

On a synthetic voice gliding from A3 30 cents sharp to C#4 40 cents flat in 80 ms, the glide kept its level within 1.2 dB and moved no faster than it was sung; tune-snap 1 dropped 3.2 dB where its shifted note crossed back into the dry glide, and YIN found no period there.

Use when: one voice, sung or played on a monophonic instrument, tuned to a scale: natural correction or the hard-tuned effect.
Not for: chords, mixes, a choir (one pitch per moment); retuning to a written melody, use @audio/tune-midi.

Part of @audio/tune, the tune family umbrella.

MIT © audiojs