Thank you for your reply. I really admire that talent. Maybe in my next life I will have that gift.
Al Stewart and Dave Nachmanoff doing Year of the Cat.
Al likes to take off on these little flights of fancy every now and then, and Dave just matches him perfectly.
Oh yeah, Bruce Hornsby and his band are kind of famous for this. They will ask the audience to call out songs and musical styles, and then they’ll put two together and make up a song on the spot and play it – like Stairway to Heaven as a reggae number.
I’m a working jazz singer (come hear me in DC on March 6!). Lots of good info here; particularly, everything velvetjones said.
My first paid jazz gig was at a private birthday party, and none of us in the band knew each other prior to the event. Afterwards, while mingling with some of the guests, I was frequently asked “How long have you guys been playing with each other?” Everyone was shocked to learn that we’d just met.
Jazz standards also have standard keys, which tend to be the default when no singer is present. Not that an instrumentalist couldn’t call a key, but if you hear someone call a tune but no key and yet everyone seems to magically know it, they’re probably playing in the default/standard key.
I disagree: a bad note (one that doesn’t fit the chord) will stand out in jazz just like in any other genre. Otherwise, jazz improv would equal “play/sing whatever you want.” 
True story (names withheld to protect the guilty party).
Back in the 70’s I had a short gig w/ a lounge/standards trio. The leader/drummer was a bit of a ‘player’ and on the afternoon of a scheduled 9 pm gig called to tell me that he and the guitar player couldn’t make the date and that in order to not screw over the club I (that would be me) needed to put together a replacement. By 9:00, remember.
Turns out he had booked a high-paying gig elsewhere, told the club owner I had it covered and was just dropping me in it. My week in the barrel, I guess.:smack:
Anyhow, not wanting to get a bad rep, I phoned a piano player pal, got him to phone two friends (Guitarist/Drummer) from another band and we agreed to meet at “The Palms” in Blaine, WA.
I’d gigged w/ my piano player friend and knew the guitarist and drummer but had only heard them play. Since we all came from country/blues/rock backgrounds, after we set up the stage we sat down over beers to work out some sets. It was the typical " Okay, we all should know songs X, Y and Z, right?" “Yeah, what key and who kicks off X- piano intro, maybe?” “If they are dancing, let’s stretch it out a bit to save songs but not too much” " Something a little jazzy, maybe - you know the changes to “Bag’s Groove”?".
Like that we came up with a set, figuring we could work out another on our break.
Sticking to well known material served us well and we played a pretty good set that got us settled down and the house seemed to be enjoying it right enough.
Second verse, same as the first - we dug into our common song list and came up with another set, getting a bit more adventurous as we felt out what we might be able to pull off without embarrassment.
The crowd seemed to be digging the music quite a bit, the dance floor was consistently full and we felt like we had kept the energy in the house at a high level.
Last set, goin’ down the home stretch we were all feeling it ( those beers didn’t hurt) and we tore up some rock numbers and then finished up with a barrel-house “Sweet Little Sixteen” that had them jumping. We probably played a couple of encores, but that was a great ending. Always leave 'em asking for more.
The embarrassing part came after, when folks came over and said “You guys are the best band they’ve had in here for months! How long have you been together?” Didn’t have the heart to say “Uh, well… about 6 hours, now”.
N.B.
Thanks again to Kerry, Oren & Robbie. You guys hit the note that night.
What a great story!
Classic Victor Borge piece of improvisation here. During Borge’s 80th birthday (!) celebration concert, the audience reaction was so good that the violinist Anton Kontra suggested an encore. None had been planned, but Kontra suggested Czardas – which Borge had heard before, but had never played. Nevertheless he said yes.
The expression on his face, as he starts just having pure fun, is wonderful.