You’re prepared. The time comes for downbeat and, horror of horrors, your keyboardist has car trouble and your guitar player is in jail. It’s bass, drums, and horn staring down a deep, dark 2-hour tunnel.
Well, Mr. or Ms. horn player (or singer), I hope you’ve been hitting the treadmill, because you’re in for the Iron Musician endurance challenge. The bass might take a couple solos–though if your drummer is also missing, that’ll be tough sledding. You won’t be able to improv as freely as usual. Granted, with no chord it’s hard to hit a wrong note, but that’s far different from hitting right notes. How can you make the audience hear what isn’t there?
I wind up playing a lot of arpeggios, avoiding suspensions (suspend against what?), and not going outside very much (again, outside what?). The bass player is more likely (but not guaranteed) to play the root on each chord change, so I’m hitting a lot of chord changes on the third and doing small scalar figures right around the color tones (like b9 or #9). I’m also playing lots of long notes and looking for interesting through-lines.
If you have two horns, you’re still walking without a net, but at least you have a balance pole. Now you have melody, the implications of chords from the bass, and a one-note chord instrument. (I just got home from playing this gig.) So I look at the melody note, listen very carefully to the bass, and pick the other note that most defines the chord. The instrumentation is an awfully thin sound, so I do a lot of long notes even though just harmonizing key notes in the melody would suffice to indicate the harmony. For the same reason, I do a lot of fills, again favoring arpeggios. As for the melody on the head, it’s useful to do a lot of re-articulation (instead of a long note, play several short hits on the same note) to keep the rhythm going. Beyond that, I hope the other guy plays it pretty straight because I’m doing a lot of guesswork on every note he’s going to play.
The best hope, however, is to play songs the audience knows well and let them fill in the missing chords. Hopefully they know something other than Jimmy Buffet.