Well, not at all a vocoder, but it did sorta remind me of the way the Daleks sounded on Doctor Who.
During my years of isolation in deep East Texas in a tiny town with a population of 225, I had the only CoCo around. In fact, I may have had the only home computer that wasn’t at the school. I remember discovering (or maybe reading about this in Rainbow) how you could use the AUDIO command to create some weird effects as you played a tape through the cassette drive (I did not have a disk drive at this point).
Knowing what I now know about BASIC optimization, I present this bit of code:
0 AUDIOON:AUDIOOFF:GOTO
Stick a tape in the tape drive, press PLAY then type “MOTOR ON” to get the tape rolling, then RUN.
I learned I could open the tape door on my Sears (I think) cassette recorder and then hold down something inside and click REC-PLAY to put the tape player in RECORD mode. I could then speak into the microphone and it would send the output to the earphone jack into the CoCo, allowing me to use it like a microphone. I could turn up the volume and talk into the microphone and hear the distorted audio come out of my TV speaker.
Ever tried this?

Never even thought to try this. What a cool idea!
Did it sound like the bit “one of these days, I’m going to cut you into little pieces” that comes at 3:37 in Pink Floyd’s track ‘One of These Days’?
Ah, I don’t have that album, but PF has it officially on YouTube: https://www.youtube.com/watch?v=raV_A8YcBu0
I haven’t heard the CoCo effect since then, but yes — the on off sound (like talking through a fan, without the phasing). Interesting. I wonder what they used to do this effect back in 1971!