Contra dancers rely on the music for three things:

• To tell them when to take steps (108-120 times per minute)
• To tell them when to start figures (every eight steps)
• To tell them where they are in the dance (including that after 64 steps they need to start it over)

Sounding good, managing dynamics, even being in tune; these are not strictly required. The dancers aren't relying on the musicians for those things, just enjoying them.

What kind of music has these properties? There are a huge variety of musical traditions that can give you tunes with a steady 108-120 beat per minute tempo. It's really the second and third requirements that start excluding genres. What traditional contra dance music provides that many genres do not is phrasing. Think of the song "oh susanna". It's 64 beats long and has the structure AABB. That means it has an A part which takes 16 beats (8 measures) and is played twice. Then there's a B part which also has 16 beats, and that B part is also played twice. The verses of the song are each a pair of A parts (AA) and then the chorus is a pair of B parts (BB). Together, the verse and chorus make up the whole song (AABB).

Both of the 16 beat A and B parts are made up of two 8 beat phrases. It is these phrases that the dancers are using to tell them when to start figures, and it is these phrases most drum solos lack. It is possible to beat out a rhythm that indicates phrasing, but many drummers don't know how. An experienced group can continue without phrasing cues for 16 counts pretty easily, but by the time it gets up to 32 counts (half a dance) people are going to be making mistakes.

One interesting thing in this is that there is not yet any mention of meter. Jigs and reels are common, but not the only option. Broadly, the simplest thing you could do would be to play one note on every downbeat, perhaps a walking bass line. The whole tune would be 64 notes. No one really does this. The next simplest thing would be to play one note on the downbeat and one on the upbeat. Easy tunes often like this, including "mary had a little lamb" and "ba ba black sheep". Easy reels are often mostly like this, "sandy boys", for example. Add another beat any you have a jig: each down beat is followed by two other beats. A non-dance tune would be "99 bottles of beer", a dance tune would be "hundred pipers". When we add another beat, we get to a reel consisting entirely of eighth notes. Each down beat is followed by three other beats. I'm not thinking of any popular songs like this, but some tunes that are mostly eighth notes would be "evit gabriel" and the A part of "flying home to shelly".

This is as far as tunes usually go. Perhaps there'll be a triplet or other ornamentation, but a beat is usually divided into two, three, or four even pieces. Why not five? This would be a tune in 10/8 meter, with five notes per beat. This has been on my "look into this" list since 2007, and I think I can now play fast enough to think about it in more depth. Hmm.