We use our ears to hear and our brains to listen.The problem this presents to the musician is that there is an assumption that what is heard is accurate. In music, particularly jazz music, the ability to hear accurately and quickly must be developed to the highest possible degree. This can be done in a number of ways. The first thing that is usually required of the student musician is to begin to accurately gauge intonation. Hearing pitch is never a simple cut and dried method due to the acoustic problems presented by each instrument. A saxophone must be inserted in the mouth and will create vibrations that are heard conductively through the teeth into the inner ear. This is in conjunction with perceiving the actual sound outside of the horn. Since the player is situated behind the instrument, accurately determining one's pitch is never a simple matter. Other instruments present similar yet individual problems.The accurate perception of pitch is one of the foundations of good musicianship.The use of modern tuners is a recent phenomenon that can be of assistance but we don't play music by eye, we play by ear. Using a visual aid can be of great assistance but it needs to be coordinated with the aural perception of what you are seeing.
The next important trait a musician must develop is the ability to hear intervals. An interval is the distance in pitch between two notes. Since there are only fifteen pitches, oops, just checking. Since there are only twelve pitches (not counting octave counterparts), this is not an infinite study. All melodies are based on intervals that take place in a rhythmic structure. Intervals are of a particular character : major, minor, augmented, diminished, perfect, not so perfect, all of the above. The key thing about an interval is that the improvising musician must be able to immediately, if not sooner, recognize it's precise character. Also, it is very important to be able to perceive the exact intonation of an interval because this is the key to playing in tune. We do not just tune our instruments and then forget about it. We tune as we go. The old "hunt and peck" system of learning songs had a lot going for it. Attempting to learn music "by ear" is, in fact, the only way to learn music because all music is played by ear. In other words, it filters through the ears and into the brain where the learning process takes place. Unfortunately, this process doesn't always happen. Those that believe they are really playing jazz by only reading tunes out of fake books are in for a rude surprise when they find themselves in the position of having to deal with musicians that are playing music that has been thoroughly internalized as all great jazz players do. In improvisation, a musical idea should be heard BEFORE it is played. This is conception. This is how music is composed.
Intervals are the basis of harmony. All chords are based on intervals, usually the same intervals used in corresponding melodies - but not necessarily. Rules are meant to be broken and many great composers and improvisers break those rules. Chords share many of the same characteristics of intervals. Major, minor, augmented, diminished and so forth. However, they take the concept of intervals further into the higher extensions known as ninths (sharped, flatted) elevenths (sharped) and thirteenths (sharped and flatted). Fortunately, we do not speak of a fourteenth or twenty second chord so this is also a finite study. The important point to remember is that these are sounds and sounds can be memorized. Many try to look at a chord sheet and are daunted at the prospect of attempting to learn a sequence visually. This will not work. If the chords can be recognized by their character, then it is not difficult to retain that knowledge with one requirement. That is that the root relationships of the chords must also be determined. Jazz players listen to the root movement as played by the bass and choose the harmonic character of the chords. This all must be perceived instantaneously in the context of the rhythmic form.
If the distance between notes (intervals) and chords (harmony) can be perceived and measured, then the distance between beats or pulses (meter) can be also be perceived. This is also known as "having good time." There are many more tempos than slow, medium and fast. Thelonious Monks was a master at finding tempos that were "in the cracks." Great jazz players can conceive of a tempo, maintain that tempo and execute it unshakably. The concept of swing is a gut level phenomenon but meter needs to be heard. This occurs in the brain.
The brain is a marvelous instrument of computation. It can handle all of the functions of music and still keep the body functioning (thank goodness!). In the computer world, this is known as multiprocessing. The brain, however, needs to be exercised and encouraged. It can handle all of these complicated tasks but it requires the owner's confidence. When using the brain to hear, the mind needs to be fully engaged. This requires much concentration but the more it is practiced the easier it becomes. "Use it or lose it" becomes the operative thought here. Learning songs is fine but they need to be played until the musician "owns" them. This requires performance, many performances until the song is so internalized that it becomes second nature.
Okay. I'm ready to start using my brain. What can I do to learn all of these neat tricks, you may query? There are many things. The first, oddly enough, is known as ear training. This starts with the ability to hear basic intervals in a blind situation. In other words, someone or something (computer, tape recorder) plays an interval to be identified.This process goes on until the musician can easily pick out any interval played. On a basic level, this can be done by humming the bottom note and counting steps up to the top note.The next step would be to hear more than one interval at a time in a blind situation. These would be triads and then four part chords. In classical theory, three and four part Bach Chorales are used in dictation. The theory of counterpoint and the rules of harmony are applied along with the ability to hear a bass line, a melody line, and all of the inner voices. This is how the dictation takes place, assigning Roman numerals to bass pitches for analysis.
One of the best ways to learn tunes is to transcribe them. This is the single most useful practice a musician can do other than practicing their instrument. But do not trust your "lying ears" at first until you get a second opinion. Have someone knowledgeable look at your work until you develop true proficiency. Just as many have lost friendships over differences in intonation perception, battles can break out between people transcribing the same tune. "No man. He played an F demented 57th in bar 23." "Oh yeah! That's not what I heard." Please, let cooler heads prevail.
When playing in an ensemble, always attempt to hear all of the parts simultaneously. This is kind of like walking around in New York City and hearing all of the sounds of the city at once. Clearly, this leads to insanity and a lot of talking to yourself. However, this is a priority in any kind of group situation. In order to respond to something, you would have to hear it, identify it, decide if you want to go with it or forget it and generally accommodate the circumstances. Then there is hearing things in your mind's eye (ear). This is also known as imagination and is the most creative part of making music. This is where all of the above mentioned techniques come into play.
The result of these types of discipline is that you become a better listener in all aspects of your waking hours. While driving and listening to the radio or tapes, keep an analytical ear open. In conversation, be still and really listen to what is being said so that you can get the entire message the first time. If you have difficulty with that, learn to ask questions. Remember that good relative pitch is the most important trait to develop. Retention is always a mental discipline. Start practicing it now.