Voice and Formant

Changing a voice well means separating two things that naive pitch shifting smears together: the note being sung and the character of the voice.

That character lives in the formants.

This page grounds voice editing in libsonare's VoiceChanger and FormantWarp; for the vocabulary, read Editing Basics.

What a formant is

A formant is a peak of acoustic energy at a fixed frequency range. In a voice, those peaks come from resonances of the vocal tract: mouth, throat, and nasal cavity.

Formants define two things:

Formants affect	Example
Vowel identity	The difference between "ee" and "oh"
Perceived voice character	Whether a voice feels smaller, larger, brighter, or darker

The important point is that formants stay in roughly the same frequency regions regardless of the note. A soprano and a bass singing the same vowel have very different pitches, but their formants can sit in similar regions.

Why pitch shifting alone sounds wrong

A plain pitch shift moves everything up, formants included. Shift a voice up several semitones and the formants rise too, shrinking the apparent size of the singer — the "chipmunk" effect. Shift down and you get an unnatural, oversized voice. The problem is that pitch and formants were never meant to move together.

PARAM SWEEP · PITCH SHIFTIDLE

Pitch shift — moving the whole harmonic comb

Pitch shifting transposes a sound without changing its length. Drag the semitones and watch the spectrum: every harmonic scales together and the fundamental marker tracks the new pitch. Because this shift is not formant-preserving, the formant bumps move too — the "chipmunk" effect. Press play to hear it.

Pitch

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Pitch and formant on separate controls

Good voice editing exposes the two independently:

• Change pitch alone → the same person sounds like they are singing a higher or lower note.
• Change formant alone → the voice sounds smaller/brighter or larger/darker at the same pitch.
• Change both → from subtle character tweaks to dramatic voice design.

That independence is what makes natural transposition (shift pitch, hold formants) and creative voice design (warp formants freely) both possible from one tool. As always, small moves stay natural; large moves are an effect.

PARAM SWEEP · FORMANTIDLE

Formant shift — changing character, not pitch

Formant shifting is pitch shift's counterpart: it moves the spectral envelope — the formant peaks that make a voice feel small and bright or large and dark — while leaving the note alone. Drag the factor and watch the harmonic comb and the fundamental marker hold their place as the envelope slides. Above 1.0 the voice brightens and shrinks; below 1.0 it darkens and enlarges; the pitch never changes. Press play to hear the character shift with no retuning.

Formant

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Compare this with the pitch shift above: there the harmonic comb slides and the formants ride along; here the comb and the fundamental hold still while only the envelope moves. Those are the two independent axes voiceChange exposes.

How libsonare changes a voice

voiceChange takes pitchSemitones and formantFactor as separate arguments. The pitch path reuses the phase-vocoder/resampling backend from Time Stretch and Pitch Shift, while FormantWarp (FormantWarpConfig) shifts the spectral envelope independently of the harmonic structure — so the vocal-tract character moves without retuning the note. Lowering the formant factor makes a voice larger and darker; raising it makes it smaller and brighter; the pitch stays where pitchSemitones puts it. It operates on decoded mono samples like the other editing helpers.

Related: Editing Basics, Time Stretch and Pitch Shift, Pitch Correction, Editing DSP