The difference in how to make Human Voice Sounds of A4 and OT is oscillator sync.
I made human voice patches with reference to this article.
A popular technique was to turn oscillator sync on and use ADSR to apply FM to VCO2. If oscillator sync is being applied, you don’t need to use a tuner to set the VCO2 COARSE position. VCO2 is functioning as an overtone, so you can move it freely. The trick is that it has to be at a higher pitch than VCO1 when applying modulation. This will produce a more sparkling effect. Set the ADSR to a fairly low sustain and a long decay. Once you hear this sound, you’ll understand for yourself the originality of the ARP Odyssey, and how it took an entirely different path than its rival models. Depending on the settings, it’s possible to create sounds that are as expressive as a human voice, letting the instrument behave like a living creature.
Ryota Hayashida (2015)Arp Odyssey-TUTORIAL: VCO