Since the early 20th century, jazz and popular musicians in the US have utilized a particular style of musical organization or ritual known as a jam session. This format also extends to the gigging world, where bands of jazz musicians will come together for a gig and play songs from a standard repertoire of tunes. The repertoire is based primarily on the classic recordings of jazz tunes which make up the canon of jazz repertoire.
The format and etiquette of jazz combo playing is not set in stone, but knowing a bit about it can help you feel much more comfortable in a jam session or small group jazz situation.
Part 1 - Terms
It is helpful to start with some terminology so we can look at how various parts of a song might be organized in a jam session.
Head - “the Head” is a term which refers to the melody of the song being performed.
Solos - This is the portion of the performance where people in the ensemble improvise solos. This is usually done using the same chord progression that was used for the head. Some tunes have a different chord progression for the solos, examples include Red Clay, Four on Six, and Stolen Moments.
Vamp - A short, repeated chord progression, sometimes a single chord which can be played repeatedly to fill time or extend the beginning or end of a song. An example might be “Just play a I, VI-, II-, V, vamp as an intro.” which would mean to repeat that chord progression until the head starts.
Tag - A repetition, or two, of the final phrase of a song. This is often the last four measures, but it depends on the song. Tags are often used as de facto endings if an ending has not been discussed and the song has a final melodic statement that is able to be repeated.
Intro/Outro - A musical section which is added to the beginning or ending of a song as a way to create a vamp, set up a melody, or jam on an extended ending. Intros and outros are often created spontaneously in the moment or discussed right before beginning the song.
Both versions have an intro, head, solos, head, outro structure. There are many differences in the two interpretations, but in terms of the arrangement, the two performances are the same.
Part 2 - The Default Arrangement
The first thing to know is how song performances are usually structured in jam session settings. At most jam sessions, and some gigs, song selection happens in the moment and there is little time to talk about an arrangement. The music is played unrehearsed and without much discussion. For this reason, a default arrangement has been developed over the years to facilitate these kinds of sessions.
Unless otherwise discussed prior to the count off, the default jazz arrangement is as follows.
- Head: Listen or watch for indications, often the head is played twice.
- Solos: Order is often decided in the moment using eye contact or initiative on the part of the players. A typical order for solos is first any horns or melodic instruments, then piano and/or guitar, then bass, and finally drums, which will often trade fours.
- Head: The “head out” is usually played twice on shorter tunes, once on longer tunes, or may start at the B section on ballads and exceptionally long tunes. Often, the melody player will signal the arrival at the head by lightly patting their head to signal the head out.
- Ending: If the ending has not been discussed, one of several possible endings could play out depending on the song and the people playing. There are standard jazz endings like the “Basie ending” and the “Ellington ending” to choose from, and some songs have built-in endings which are associated with the tune. The best policy is to keep your ears open and over time, develop your experience and ability to spontaneously end a tune.