When a jazz group is playing and improvising, how do they communicate so as not to produce cacophony? Somehow, one player's choices and intuition need to guide the other players so that they can change keys/tempos/sounds in concert. I've heard whispered commands in a Miles Davis recording (presumably from Mr. Davis), but what if the leader's mouth is occupied producing the music? Do they make eye contact, wave their instruments, nudge each other, or set off a flare? Or do they communicate solely through the music itself?
Collective improvisation doesn't mean "everyone plays at the same time". Playing jazz is as much about listening as it is being able to play your instrument. In that kind of situation, a player isn't thinking about "what should I play next", but rather "what is the music, at this moment in time, missing that I can provide?"
Cacophony is more likely to happen with less experienced players who haven't fully grasped this concept, and need to be reminded that not playing is equally valid as playing in one of these sections (particularly in big bands with a lot of players!).
The vast majority of communication that does occur is musical, and even when playing notated music, happens in the spaces around the notation. In a traditional big band, the entire rhythm section is usually given a lot of freedom, and is typically very good at this. The piano and bass will be listening to each other for harmonic material, and the drums obviously have immense influence over the rhythmic groove. It is very common for the drums to respond to rhythmic figures improvised by one of the other instruments. When a soloist is improvising, they are included into this feedback loop, and the most exciting soloists you see will have a constant line of communication open to the rhythm section. You should be able to hear them respond to each other when one of them improvises a lick or rhythm that stands out.
There is some nominal visual communication that occurs in this context, usually to direct traffic during solo sections. One thing you will probably start seeing everywhere now that I've mentioned it is when a soloist is playing his last chorus, he'll give a look to the bandleader or next soloist to indicate that he's about to be finished. Sometimes solo lengths are predetermined, and sometimes the music the soloist is playing is so strongly formulated that the ending chorus is completely obvious to everyone based entirely on the content. Again, with less experienced ensembles, a bandleader with a more active role will usually direct traffic more obviously; pointing to the next soloist a few bars before the next chorus where they should come in.
Same way a string quartet does, or for that matter A Far Cry does: body motion and eye contact. Further, even a free-form jazz ensemble rehearses a lot, and the members have a pretty good idea who's next up for a solo, and how many choruses are going to be taken, etc.
Miles Davis' famous "play it and I'll tell you what it is later" doesn't really count as a command :-) . OTOH, if you listen to the famous 1938 Goodman Carnegie Hall recordings, there's a place or two when you can hear him tell a soloist to "take another chorus."
I recommend going to see a live performance, preferably by renowned musicians, and looking for clues. You will see people tremendously listening to each other. You will see glances exchanged, smiles, frowns, astonished faces (if they are good, mostly good astonishment). Keep in mind that the tunes have been reheased before hand, that some groups have been playing together for many years and musicians know each other very well.
Example: http://www.dailymotion.com/video/x121uc2_avishai-cohen-jazz-a-vienne-2013_music for the tune starting round 1:35:00 see 1:36:04 (glances), 1:36:26 (piano drums synchronous break) 1:37:18 (pianist gesturing the sax player to enter) 1:37:27 (bassist glaring smile encouraging the drummer) 1:37:31 (bassist nod to get back to the theme). The whole concert is worth watching, both for the music itself and if you're looking for how the 4tet interacts.
You may also see, especially in a jam session where the structure of tunes has not been rehearsed, some codified signs which are well know to (jazz) musicians (such as pointing to one's head, telling every one to get back to the beginning of the harmonic grid).
In the vast majority of jazz music, there is far more form and structure than inexperienced ears are likely to hear. In fact, I believe this is why people who don't like jazz typically dislike it in the first place - they don't understand what they are hearing, so it sounds like cacophony to them. The truth is that jazz is (generally) highly organized while allowing for stylistically-appropriate improvisation.
Typically, these things are understood by all of the players ahead of time:
- Time signature
- Style (Bebop, cool jazz, bossa, etc.)
- Form (AABA, ABA, etc.)
- Solo form (if different than melody form)
The style is very important and typically provides a reference for the types of improvisations that are appropriate. An experienced player would take very different liberties with a bossa nova than he/she would with a bebop tune. Understanding these styles, and being able to improvise appropriately within them is essentially the definition of a good jazz musician, and is what allows complex interactions and improvisations to take place in a tune without leading to what is affectionately known as a "train wreck."
An in-depth knowledge of a style of jazz is similar to an in-depth understanding of a language. When one becomes fluent in a language, holding a conversation with another person who is fluent in that same language becomes effortless. Similarly, when one becomes fluent in a style of jazz, holding conversations with other musicians within the context of that style becomes effortless. Yes, there are (mostly) nonverbal cues that are being exchanged, but far fewer than some might think. Most of what is being communicated between players is done through what they are playing.
All that being said, once you begin to push style boundaries or get into the free jazz arena, nearly all bets are off, and the method of communication is usually established before-hand, either through the establishment a specific cue, e.g., "When you see me do X, it means Y", or just through familiarity between players.
Be attentive and mindful of your band-mates in the same way you would be attentive and contribute to a group discussion. In conversation you become aware of: the content and meaning of their message, their body language, the dynamic with which they speak, the sentence structure, rhythm and rhyme and all other types of literary devices.
These elements are all present in Jazz - you need to know who you're playing with, their background, what type of personalities you're working with. Seek first to understand what your friends are trying to convey, and then respond. Just like a conversation, sometimes you reiterate what is being said with your own perspective, perhaps verbatim (a "quote"), or even with absolute (and golden) silence, the importance of which can never be understated.
As far as keys are concerned, a player may use fingers to tell the fellow players which key he's in, or going to play the next tune in. As in 3 fingers held upwards denotes 3#, thus A maj. 2 held down,2 flats, Bb maj, etc. This has always worked, but I brought up this subject a couple of years ago on this site, and was asked "did you make it up by yourself?". I've always thought it was universal, and, if not, why not? It works in a noisy environment (stages!) and is unequivocal.
Otherwise, eye contact for most other communications works well, as in other walks of life.Moral - don't close your eyes for too long when soloing...
Since I am in a Jazz Band myself, my main way of communicating would be to tap my foot lightly near the bassists. This is a signal for him to either change the tempo or to get on track without taking my hands of the guitar. As a bassist and guitarist I know to follow the pianist. Whereas for the bass I have been telling our bassist is to use the bass drum as inspiration. " The Drum is your Friend." So continue to listen to recordings for ideas but here are the main signals as a guitarist to the rhythm section: Drums: shake head, Mouth Piano: Smile, Eyebrows Bassist: Tap foot, Smile