Another "What instrument is this?"

Cafe Society
1

In the song Apostrophe by Frank Zappa there is a instrument playing “lead” from 0:18 to 1:18. You can’t miss it; it’s right out front. (After 1:18 you can still hear it, but it’s more in the background.)

I used to think it was just a distorted guitar. But lately I’ve been thinking it’s some kind of horn. Or I suppose it could be a heavily distorted bass guitar. Or keyboard. Hell, I dunno.

2

It’s Jack Bruce playing bass guitar.

3

Thanks! Never heard a bass sound like that. I wonder what he was playing through?

4

Sounds like an Envelope Filter to me.