Vowel Filter

Three resonant bandpass filters tuned to the formants of the human voice, turning any sound into something that sings, talks, or moans. Sweep between five vowels — ah, eh, ee, oh, oo — to lend pads, basses, and drums a vocal-tract character.

How it works

Each vowel is defined by three formant peaks, the resonances of the mouth and throat. The filter runs three parallel bandpasses at those frequencies and sums them, so the input takes on the spectral shape of that vowel. Vowel morphs the formant frequencies continuously between adjacent shapes, so the sound glides from one vowel to the next rather than switching abruptly. Left and right are filtered independently for a full stereo image.

Controls

  • Vowel — selects the vowel, morphing smoothly through Ah, Eh, Ee, Oh, Oo as you turn it.
  • Res — formant sharpness (Q 1–30); higher values narrow the peaks for a more pinched, pronounced vowel and stronger resonance.
  • Mix — wet/dry blend, from the untouched input to the fully filtered signal.
  • Shift — formant shift, scaling the whole vocal tract up or down (0.5x–2.0x) without changing which vowel you hear. Turn it down for a bigger, deeper, throatier voice; turn it up for a smaller, child- or chipmunk-like one. Centered, it leaves the formants where they sit.
  • Tilt — formant balance from dark to bright. Lower it to favor the low formant for a full, rounded body; raise it to favor the high formant for a brighter, more nasal, buzzy sheen. Centered, the formants sit in even balance.

Inputs & outputs

  • In L / In R — the audio to process; each channel is filtered on its own.
  • Vowel / Res / Shift / Tilt / Mix CV — voltage control over each knob; patch an LFO or envelope here to make the filter speak, morph the vowel, shift the formant register, or tilt its color in motion.
  • Out L / Out R — the filtered stereo result.

Tips

  • A slow LFO into Vowel CV gives the classic talking-synth "wah" sweep.
  • High Res on a static vowel adds a strong formant resonance — great for thin sounds that need body.
  • Drive Vowel CV from an envelope so each note articulates a vowel as it sounds.
  • Pull Shift down for a monstrous, oversized voice or push it up for a chipmunk register — it resizes the whole tract without touching the vowel itself.