Speech Overlap Detection I’m trying to figure out how to go about differentiating between a single-voice speech and a multiple-voice conversation in which voices overlap. In other words – the moment of overlap is what I’m interested in. I want to be able to listen to a vocal conversation between two people, and detect when voices collide/overlap.

I guess that spectrum-wise there’s a major difference between a speech-based conversation with no overlaps compared with a conversation with speech overlaps, so perhaps one direction to look at is detecting sudden spectral changes?
Most human vowels produces a series of harmonic spectral peaks that resolve to a single F0 pitch (plus some broad spectrum noise).  If you can't fit a single F0 pitch to the series of the spectral peaks, then you might try testing the hypothesis that the spectrum resolves to 2 or more f0 pitches, which would imply more than one speaker talking with an overlap of vowel sounds in their words.

Detecting an overlap between a vowel and someone else's consonant, without lots of false positives, seems like it might be far more difficult.