Intone

Intone is a formant synthesis voice based on the CHANT project at IRCAM, described by Xavier Rodet, Yves Potard and Jean-Baptiste Barrière in 1984.

Intone produces a voice-like sound from five parallel formant cells. Each cell produces overlapping FOF (Formant Wave Function) grains, which are damped sine waves at that cell’s formant frequency. A vowel morph slider interpolates between presets for /a/, /e/, /i/, /o/ and /u/. The module is 16 HP and has one monophonic audio output.

How formant synthesis works

The vocal tract has resonances, called formants, which boost the voice’s harmonics near particular frequencies. Each vowel has its own pattern of formant frequencies, and that pattern is most of what lets a listener tell /a/ from /i/. Intone models this by summing five parallel cells, each producing sound at one formant frequency.

Each cell produces FOF grains, which are short bursts of a sine wave at the formant’s center frequency with a cosine-windowed attack and an exponential decay. The cell starts a new grain once per cycle of the fundamental frequency, and the grains overlap, so the output is a continuous tone at the fundamental pitch with a peak in its spectrum at the formant frequency.

Three excitation modes

Default (nothing patched): The internal F0 oscillator starts the FOF grains and V/Oct sets the pitch, so Intone works as a VCO with a vowel sound.

Audio mode (audio patched, switch up): The input passes through a bank of five parallel resonant bandpass filters tuned to the formant frequencies, so drums, oscillators and other sources come out with a vowel color. V/Oct transposes the formant pattern.

Trigger mode (clock patched, switch down): Each rising edge at EXC starts a new FOF grain, so each trigger produces a short burst with a vowel sound. V/Oct transposes the formant frequencies.

Controls

Per-Formant (x5)

Global

Inputs

Outputs

Vowel preset frequencies (Hz)

Spectrum display

The display shows the five formant peaks as colored bell curves on a logarithmic frequency axis from 50 Hz to 5 kHz, with the combined envelope drawn over them as a brighter line. It updates as the parameters change.

Patch ideas

Vowel Pad: Patch a slow LFO to Vowel CV, and the vowel changes continuously as the LFO moves.

Vocal Filter: Patch audio to EXC in Audio mode. Drum loops, oscillators or samples pass through the five formant resonances and take on the current vowel.

Triggered Vowels: Patch a clock to EXC in Trigger mode, and each pulse produces a short vocal burst. Modulate Vowel CV to change the vowel from one burst to the next.

Formant Sweep: Patch an LFO to one of the F1-F5 Freq CV inputs, and that formant peak moves up and down independently of the vowel preset.

Historical context

Intone uses the FOF technique from the IRCAM CHANT project (1979-1984), which was developed to synthesize the singing voice. The same technique was used in spectral music by composers including the Finnish composer Kaija Saariaho, the French composer Gérard Grisey and the Italian composer Marco Stroppa.