You know, the older authentic blues harp players that were around when i was younger would often play with a pulsing effect that i had always mistakenly thought was throat vibrato. It's not--it's actually throat tremolo. Much more subtle than vibrato.
Took me a long time to learn how to do it. I use it every now and then these days. Don't really see this technique discussed very much, though.
The way harp players define tremolo and vibrato is something I've been confused about for a long time. This is a thread I started about it some years back (I took the sound files down, but if anyone is interested, I can re-host them somewhere). There's some good discussion on that old post, and it would be great if we could get some more started on this one!
