It just occurred to me that a pitch tracking oscillator may fit the bill, it tracks (follows) the pitch so isn’t monotonous …
“mda tracker” available from here … http://wiki.audacityteam.org/wiki/VST_Plug-ins [Windows only]
That does it. There’s no intelligibility left. What’s the third version? Koz
the third take is the “mda tracker” in “sine mode” and restricting the sound to a narrow frequency range , (second take is on square-wave mode, without restricting the range).
The third version reminds me of the children’s animation the Clangers (who had swannee-whistle voices).
There was some intelligibility in the Clanger voices : they got in trouble for swearing … Clangers - Wikipedia
The “mda tracker in sine mode” output is improved by adding harmonics …
Free Kazoo plugin http://www.g200kg.com/en/software/mykazoo.html [Windows only]
Any better than the (all platforms) Nyquist effect Kazoo effect ?
“MyKazoo” VST looks like another frequency-tracker , so the result is unintelligible.
Whereas I can still understand speech after applying your kazoo effect …
The VST is more kazoo-ish …
To complete the set, the scat-singing with each effect:
as you can with a real kazoo:
“MyKazoo” VST adds a glissando which doesn’t occur in a real Kazoo , or via your Kazoo effect.
Other trackers like “AlienSolo” have a similar frequency-glide …
[ “AlienSolo” is Windows-only VST plugin , and the free version is crippleware ].