This article is from the Grateful Dead FAQ, by John J. Wood, Eric Nay and Ihor Slabicky email@example.com with numerous contributions by others.
The Eleven is called that simply because it is in the time signature of
11/8. There are eleven beats to the bar with the eighth note as the beat.
It is subdivided as three groups of three(triplets) and one group of two.
It can be counted like this: 123 123 123 12, with each of the numbers
representing an eighth note. The last two eighths are usually emphasized,
often with two drum whacks or sometimes by Phil. The transition between
St. Stephen and The Eleven is basically in 12/8 with the 12th eighth note
being dropped at some point to create the basic structure for The Eleven.
12/8 is essentially the same as the common 4/4 except that triplets
predominate. Another example of a Grateful Dead song in 12/8 is Truckin'.
The Seven is essentially a variation of The Eleven. It is in 7/8 and the
main grouping is 123 12 12, although it switches around a good bit. There
are only four known performances of The Seven(according to Deadbase VII)
and two of those were Mickey and the Hartbeats shows.
Estimated Prophet has a 7 beat pattern. On some tapes, especially on early
versions, you can hear Bobby count to seven to start the song. It could
probably be written in either 7/8 or 7/4. However, alternating bars of 3/4
and 4/4 are easier for musicians to read and that is how it appears in the
published sheet music.
Playing in the Band is essentially in 10/4, hence its original name The
Main Ten. However, 10/4 measures would be difficult for musicians to read.
The most logical thing is to have two 4/4 bars followed by a 2/4 bar, which
is the way it appears in the published sheet music.
In time signatures where the quarter note gets the beat it is generally
common practice to not go over 5 beats a measure. 7 is used occasionally,
while 6 is better written as two 3/4 measures.
Other songs, such as the Other One, that might sound like they are in odd
meters are actually not. Their rhythmic complexity is derived from accents
on off beats. Unusual accents also add further to the complexity of
Playin'. [Thanks to Michael Bell firstname.lastname@example.org for the above