I loved Jack Mercer, and I got him. I understood him. And what helped me understand that Popeye voice -- it's a high voice and a low voice at the same time -- cause when I was a kid, we all used to try to do that and we all stunk. It didn't sound right. So one day, I see this film -- it was an independent film called Genghis Blues. And it was about this blind singer in San Francisco who wrote a hit for Steve Miller. ... And he was listening to a world-band radio one night, and he heard this strange noise. And it was a program about Tuvan singers. And Tuvans had a way of singing where they could do one and two voices. And I realized, 'Oh man, that's how this guy did it. Jack Mercer.' [He imitates both voices.] There'd be two voices, an octave apart. And he'd put them together."It's worth listening to the whole segment (it's 28 minutes long), but the Popeye bit starts at about 17:05.
Billy West: The Many (Cartoon) Voices In His Head [Fresh Air]