When you listen to music you may notice yourself tapping your foot or hand on something along to the beat. You may also notice that there's certain accented points where you tap harder or a point where everything seems to start over again. You are in the meter of the song; the underlying number of rhythmic pulses that drive the song. The pulse is a unit of time that is followed by more pulses that are connected in a group, such as a four pulse (or beat) song that is usually the mainstay of popular music. Jazz innovates in this area as composers have created songs with three beats, five beats and even some with eleven beats within the musical bar. The bar is another term for a set of beats or pulses that is repeated one after the other until the song is over. Jazz music also particularly accents beat two and four of a four beat musical bar.
The most important part of jazz rhythms is the so-called "Swing Feel" that players must learn how to execute correctly. This feel implies that the off beat or up beat, which will be explained shortly, is accented and also shorter than the downbeat. This up beat conveys the idea that musical pulse or beats can be subdivided and turned into smaller, more numerous notes. This is where the swing feel comes in. In this example there is the downbeat, right on the pulse, and the upbeat which is sounded half way through the whole first beat. Therefore you can listen to Miles Davis and hear him playing the first note of his solo soft and a little held over the middle of the beat, as is practiced by jazz players, and then a surprising accented upbeat which has more volume and is shorter in length.
The elements of a good jazz band always depend on the drummer and the bass player. The bass player is playing quarter notes throughout the musical bar. A quarter note equals one pulse or beat. The bass player does this to make sure the harmony of any song in question is supported and whatever is played over it is mellifluous. The drummer takes the job of accenting the upbeat with a ride cymbal so another player who is soloing can mesh with it. Also, the drummer uses his set to somehow accent beat two and four of a four beat bar to convey the feel Jazz music has.