A short explanation as to how this works: The voice can be modeled using two main components. The vocal chords are a periodic source of sound, which is then fi

A short explanation as to how this works: The voice can be modeled using two main components. The vocal chords are a periodic source of sound, which is then filtered by the mouth and tongue to produce vowel sounds [0]. The filter can be modeled as a set of band-pass filters, each of which let through a specific band of frequencies — these are called ‘formants’ in acoustic phonetics. Different vowel sounds are produced by combining formants at different pitches in a systematic way [1]. You can hear this yourself by very slowly moving your mouth from saying an ‘eeeee’ sound to an ‘ooooo’ sound: if you listen carefully, you can hear one formant changing pitch while the others stay the same. (I like [2] as an intro to this kind of stuff.) The ‘voder’ works by having one key for each possible frequency band-pass filter. Pressing multiple keys adds the resulting sounds, producing an output sound with distinct formants. If you use the right formants, the resulting sound is very similar to that produced by a human mouth saying a specific vowel! Software such as the vowel editor in Praat [3] take it further, by allowing selection of formants from a standard vowel chart. [0] Consonantal sounds are a bit more complicated, since they tend to involve various different noise sources and transient disturbances of the sound. For instance, /ʃ/ (the ‘sh’ sound) is noise of a lower frequency than /s/. I can’t work out how Harper produced the difference between those two sounds in the video — it seems to be impossible to do this with the live demo. In fact, any sort of pitch control seems to be impossible in the demo. [1] This is how overtone singing and throat singing works! Selectively amplifying one formant gives the impression that you’re singing that note as the same time as the ‘base’ pitch. In fact, if you do that, your vocal cords are producing a pitch plus all its overtones, while your mouth is enhancing one overtone while filtering out all the others. [2] https://newt.phys.unsw.edu.au/jw/voice.html https://newt.phys.unsw.edu.au/jw/voice.html [3] https://www.fon.hum.uva.nl/praat/ https://www.fon.hum.uva.nl/praat/ — probably also available from your favourite Linux distro!