ftufc said
You know, I wrote my post before listening to your vid Barry, because I thought it was the Christmas clip you did the other day that I already watched.

Okay, so in this vid you've done a great job of describing/demonstrating how to "improvise" a song that you already know,,, and I do get that,,, but my post had to do with jamming on a new song that you don't know.  How do you just jump into a song that someone else is playing that you don't already know and accompany what they're playing?

Any ideas?

To sort of tag along with what Barry said, when you practice just "doing it" (improvising I mean) You'll get into the habit of forming interval patterns in your subconscious thoughts about scales and their different modes. Watch some of fiddlerman's blues series and you'll see what I mean when he mentions a "Secret weapon pattern."

(Theres actually a lot of different patterns that just naturally sound good together transposed to any key!)

Back when I played trombone, I improvised every day since I was in a jazz group with several other musicians that jammed together frequently, and you'll be surprised what you can commit to muscle memory if you practice scales often. It had gotten to the point that it didn't matter what key I was in, I didn't even subconsciously think about it or the name of the key.. it just sort of comes out!

It's similar to developing my sight reading ability, but with ears and no music. In sight reading's case it will get to the point where you don't even think about the names of notes or the logistics of the instrument, it will just automatically happen when you look at music, even for the first time.