Some years ago I spent two weeks working with an experienced jazz pianist, a deeply intellectual man with great technical skills and enormous ability and inventiveness as a jazz soloist. During the course of our work, this musician had to call upon his broad background in order to function as a collaborative arranger, as a "lead voice player" in a piano trio (both of which roles he filled superbly), and as an ensemble pianist in the role of accompanist to a singer and various jazz instrumentalists. This last role was the one for which his background had least prepared him, and it took the most concentration and adjustment for us to arrive at a musical relationship that worked for everyone.
In exploring the possible choices of register, texture and dynamics available to a pianist in the accompanying role, we discovered several principles which we could apply. But, because of the amount of music we had to prepare and the limited amount of time in which we had to do it, the accompanying principles had a tendency to slip away as, in the heat of battle, old habits took over. It was a valiant effort and one which lacked no application of intelligence or generosity of spirit. None-the-less, the results were inconsistent.
At the end of our work together, at almost the last minute, this fine musician played me some obscure popular songs that he felt would make good vehicles for jazz improvisations. He started playing one and halfway through, decided to sing the melody. Instantly and intuitively his hands dropped an octave into the correct register for accompanying his voice, and the amount of textural activity was reduced by more than half. He had not been able to accomplish this kind of accompanying proportion consistently in the preceding weeks, and I didn't recognize that this was the moment to tell him, "That's it! That's how the rest of us need to be accompanied, just the way you're accompanying yourself!" (The French call these experiences "l’esprit d'escalier", thoughts in the stairwell, the "I shoulda saids" of life.)
There are many ways of making effective and beautiful accompaniments, but they all share one thing in common: The accompanist must apply fully 90% of his or her consciousness towards "living in the body" of whomever has the lead voice. This attention must be applied in such a way that the accompanist experiences every breath, every nuance of muscle tension and timing, and every dynamic change in the music of the "lead" musician. Only when this much energy is devoted to the empathetic experience can the best accompaniments be created. At the first moment that a part of the accompanist's attention is diverted to a question like, "What clever thing can I fit in now?", the intuitive thread to the lead voice will be broken, and something less than ideal will occur. The accompanist must be vigilant and learn to recognize these diversions until the posture of listening through the lead voice becomes second nature, and the process of "letting it happen intuitively" through the link to the lead voice replaces other processes.
These are habits of thinking and feeling which are subject to modification and training just as are the habits and techniques necessary for the creation of great jazz solos. These ensemble habits are explored and developed early in the training of string and wind players and ensemble singers. Pianists, organists and guitarists play alone so long in their early exposure to music that they risk incorporating unproductive habits that need to be overcome when they enter the social world of ensemble music.
Here are some guidelines that can help to create good accompaniments:
The most useful register for piano comping is centered below middle C, roughly from D below middle C to F or G above, for rootless voicings. (Occasional bass notes are useful in filling out the sound at climactic points, or when the movement of the bass line creates attractive counterpoint with the melody.) This "upper bass" register is the range of most effective ensemble impact, the "body" range that makes the band sound full and meaty, without being overbearing. Most of the "weight" needs to be on the notes below middle C. Whenever this range is exceeded in the upward direction, that means anytime!, that encroachment must be recognized as an intrusion into the acoustic territory in which the human ear is most sensitive. This means that that gesture must be deliberate and the moment for it carefully chosen so as not to compete with the dominance of the lead line. Sometimes colorful interjections in this higher register are useful and appropriate but they are useful in inverse proportion to the frequency of their use. In other words, less is more, and play three times more softly in that register unless there is need for an accompanying exclamation point, in which case, make the point and get out of the way.
Staying in the register above F or G above middle C for the lead line of accompanying piano chords can have multiple detrimental effects. It crowds the acoustic area that singers and instrumentalists need. Even if their notes are below that register, subliminal but colorful overtones need to "ring" in that space. Besides this, the ear's sensitivity in this range makes continued accompanying sounds wearing and monotonous, forcing the listener to divert energy to mentally "turning them down" in order to maintain attention on the primary voice.
One of the adjustments a listener must make during the progress of a conventional jazz performance is to understand the change from an accompanying role to a solo role in the same instrument. The accompanying sounds have been pushed to the background by the listener's involvement in following the lead line, so when the accompanying voice moves into a lead role, the listener must shift attention in order to maintain focus on the primary activity. This shift always takes a few seconds and there is communicative benefit in anything the performer/composers can do to improve the listener's chances of recognizing the changing roles quickly. To this end, it is useful if there is a noticeable change in dynamics, density of activity and register, when a pianist moves from an accompaniment into a solo. This is difficult to accomplish if the accompaniment has been as busy as, and nearly as loud as, the following piano solo, and it is made doubly difficult if the accompaniment has been in the same register as the solo.
Sometimes the same pianists who accompany their own solos wonderfully well with their left hands, feel that this kind of accompaniment is insufficient for other instruments. Why? Fuller participation in listening to the soloist, reaching out one's ears to include the complete experience of the soloist into the accompanist's consciousness, will go a long way towards the achievement of correct balances and textures. In other words, when in an accompanying role, put yourself on automatic pilot and concentrate on listening to the other guy. Listen to yourself only subliminally and play only when your ear, not your desire for kinetic activity, pulls you in. Make your body experience the soloist's activity as your own and your responses will be more likely to be empathetic. Listen for the level of left hand activity that usefully accompanies a "right hand" jazz piano solo. How many notes are in the chords? How often is a chord struck? Is the accompaniment a drone or a series of refreshing interjections? How long can a melodic line sustain harmonic interest without an accompanying chord? (A long time. See J.S. Bach.) Might not proportions which work well for a pianist accompanying himself also work for that same pianist accompanying another soloist?
Play commentary to the melody, not concerted rhythms. Play chords in answer to or anticipations of the expected rhythms of the bass notes or else the bass part is either duplicated or forced to a less successful position where too many bass notes will have to be played off the beat in order to be heard as separate from the piano.
It is a simple thing to say, "play less", but that is hardly the only issue. It is necessary to listen carefully to a lot of accompaniments in order to acquire a taste for what the individual accompanist feels might best compliment a particular solo style. The lead sheet full of chord symbols can be a trap, and smart musicians who recognize the elasticity of bar lines and harmonic side trips in their solos are often tricked by their eyes into ignoring their ears and playing every chord in the piece. The tradition of having the bass and drums delineate every beat and chord root is monotonous enough without adding insult to injury by including the piano.
Some chords are more important than others and welcome emphasis. The tension in a dominant chord needs more sound and force than the tonic chord which follows it. Chords which are out of the key of the moment or which indicate a change of tonality usually have more need to be sounded than chords which are diatonic in the tonality of the moment.
Within a given chord, some voices are more important than others in indicating harmonic direction or in delineating a secondary line. It's good to remember that "the piano is an orchestra", and a good orchestral accompaniment would not use all the instruments all of the time and they wouldn't necessarily play at the same dynamic level. Bill Evans played chorus after chorus of blues in F, accompanying himself with the five notes between middle C and the A flat below it, one at a time, of course. (I'm not even counting the choruses he performed before bringing his left hand into play at all.) This simple technique left him the option of increasing the density and power of the rhythm by adding two or three more notes to the accompaniment chords and striking them more often when he wanted to communicate an increase in musical energy. If a pianist enjoys the variety and shift in energy level achievable by this technique, might not other soloists also benefit?
There is another implication of the hierarchy of "voice importance" that's particularly applicable to the piano. When chordal passages are played by choirs of instruments, the players, according to their sensitivity and training, control the dynamics and pitch nuances of each voice in the chord. More important voices get special emphasis while secondary "coloristic" notes in the lines get more subtle treatment. There are pianists who use the sensitivity of the piano keyboard with considerable expressivity during their solo passages. Some of these same musicians have a tendency to forget variety of touch when creating a chordal accompaniment. All the fingers strike the keys with the same intensity. Sometimes that's appropriate and sometimes not. If the notes A flat/G sharp below middle C along with D and E above it constitute a B flat chord, then the E welcomes special emphasis, and the A flat probably needs a legato connection to the G or G flat that is likely to follow in that voice in the next chord. If those notes are functioning as an E7, then the D is more important and the G sharp may be crossing over the A above it, landing on a coloristic ninth (B natural perhaps) on the following chord. This creates a different set of articulation and dynamic tendencies, just one example of the variety of possibilities that exist every time the harmony moves in a jazz accompaniment.
There is a long history of the development of rhythm section styles that has led to the selection and refinement of these practices. Bill Evans, John Lewis, Ellis Larkins, Hank Jones, Wynton Kelly, Tommy Flanagan, and Sonny Clark are just a few examples of great piano accompanists whose accomplishments in this area come quickly to mind.
The role of a piano in a big band is somewhat different. It is dramatically less powerful in relation to the full band than it is to a small group, and that sets up another set of conventions. Extremes of register are sometimes necessary just in order to be heard. Basie set a classic example by his impeccably timed minimalist approach, and Ellington made occasional great use of cascading romantic figures which were set in remarkable textural contrast to the prevailing ensemble sound. Both of these masters, "wrote themselves out" for long periods when there was a competing ensemble texture to which the piano could only add confusion.
The existence of successful "band choir" accompaniments in the octave above middle C does not change the situation for the piano. The trumpets, flutes and clarinets that sometimes provide accompanying lines in this register, have acoustic properties that are markedly different from those of the piano. For one thing, when you stop blowing into a wind instrument, the sound stops. When you lift your hands and feet from a piano, it continues to ring, perhaps softly but still perceptibly. This is a wonderfully useful characteristic of the piano sound, but it does tend to swamp the harmonic space of instruments and voices that the piano may be accompanying. Besides this element of the piano's sound envelope, there is the obvious fact that a piano must be struck repeatedly in order to maintain even a quiet level of sound over a period of a few measures, whereas wind instruments can sustain a series of notes over a similar period without re-articulation. This is a significant difference, and it gives the piano the edge in the percussive attack department rendering its lines particularly rhythmically incisive, but the advantage goes to the winds when smoothness and neutrality are required. It can be interesting to orchestrate against these tendencies, but that does not negate the fact of their existence or effect.
I can think of two examples of players who sometimes disregard these guidelines to good effect. Bob James and Mike Abene are two fine musicians who have made more of their reputation in commercial music than in jazz. I've played with Bob James when he has used the register above the main body of the chord to extend the color of the tonalities into a series of "poly-chords". The range below middle C held the thirds, sevenths and an occasional fifth, ninth or thirteenth, while the octave above that was used for notes more closely related to other tonalities. This device didn't seem to interfere as much with the sound of the soloist as the doubling of basic chord tones in this register would have done. The new notes occupied another psycho-acoustic environment that seemed to expand the available space instead of obliterating the soloist. I found this style to be fascinating and refreshing and I regret that more jazz musicians haven't had the opportunity to experience it. Mike Abene has achieved a similarly interesting effect by using some high register "out" notes in order to punctuate things in his recordings as the pianist with Grover Mitchell's band.
Maybe there are no rules except the one against monotony, (and Phillip Glass has made a career of flying in the face of that one).
Accompanying rubato passages is a subject for a "whole 'nother" discussion.
One other thing: it's impractical to try to substitute for missing instruments. Better leave them to our imagination. If there's no bass player, just play the piano part as beautifully as possible, adding roots when they are convenient or necessary. The piano makes a poor substitute for a "walking" string bass. The attack and decay are different, and few pianists can control the effect without a lot of practice. Trying to imitate Ray Brown's propulsive energy by anticipating the bass notes only makes the music edgy. Besides, even as loud as Ray can be, the bass register of the piano is twice too loud if the same force is applied. Would a pianist attempt to play the drum part if the drummer were missing?