Utility patch that generates non-robotic vowel sounds, meaning sounds as close as possible to a real human voice.
It uses neither dedicated modules (like Pink Trombone or Squinky Labs Formants) nor samples. Only free modules from the library are used.
The patch is configured for the sound “O” pronounced by a bass voice.
The tables of formants values needed to configure it differently (other vowels for bass, tenor, alto…) are are available here.

https://www.classes.cs.uchicago.edu/archive/1999/spring/CS295/Computing_Resources/Csound/CsManual3.48b1.HTML/Appendices/table3.html

And you can find an example of its implementation in a choir patch that I built around this utility patch:
 https://www.youtube.com/watch?v=S80ckm7EGqQ