What You Need To Know
-There are common forms composers use in all musical genres. AABA is the most common forms in jazz
-AABA consists of a section of music repeated twice (AA), followed by differing musical content called the Bridge (or "B" section). After the bridge we hear the A section one more time and then the performer returns to the top of the form.
-Because this form is so common and well known amongst musicians, it makes improvising easier.
AABA FORM
This aspect of jazz is so fundamental that everyone who listens to it should be able to hear it. So today we will talk about it a bit. Like an essay, there are common forms that are used in different musical genres. These forms give the composer some kind of structure to work with and the listener something familiar to hold on to when listening to something new.
One of jazz' most popular forms is AABA. It is the 5 paragraph essay of jazz. It is exactly what it looks like: You hear an A section, then hear the A section repeated, then a contrasting B section, and then right right back to the A section again. This format is a big part of what allows for improvisation: while every song is new and different, at some point as you get more experienced you don't have to worry so much about what chords you are on and you don't get lost as easily. After performing so many songs in this format you know what an AABA format and feels like and you can feel where you are at in the form as you are improvising (even if you are soloing on this song for the first time). You still have to keep track of the different chords and phrases in each tune, but internalizing AABA form makes that easier.
Here are some good examples of AABA (I marked what times each section occurs, try to listen to how that form repeats regardless of whether the singer is singing or instruments are soloing). Jazz is like a carousel: The rhythm section keeps the same form going round and round and the instrumentalists and singers jump on based on where they are told to in the arrangement. Note that some times there are conventions: at an open jam everyone solos once or twice on the whole form and then lets someone else solo until everyone has soloed. On a slower tune, each musician might take just a section of the form so the song does not drag on. This is often decided in advance. Sometimes jazz musicians will just decide on the fly, but because everyone knows the form it is not that mysterious a process.
Girl From Ipanema
A: 0:13 , A: 0:28 B: 0:43 A: 1:14
https://www.youtube.com/watch?v=UJkxFhFRFDA
Take the A Train
A: 0:18 A: 0:29 B: 0:42 A: 0:54
https://www.youtube.com/watch?v=cb2w2m1JmCY