Many Irish dancers enjoy dancing to a wide variety of music, ranging from modern and traditional Irish pieces to electronica to hip hop. Selecting pieces for Irish dance can prove to be uniquely challenging due to concerns about time signature, tempo, length, and phrasing.
Time Signature
Polkas are danced in 2/4 time, while reels are danced in 4/4 time. I have found that much of the time, dancers do not care whether you they are dancing to a polka or a reel. This is particularly true for polka sets, as they will generally be moving between polka bodies and reel figures. Most jigs are danced in 6/8 time. There are jigs that come in a variety of other time signatures (9/8, 12/8, etc.) but for the purposes of most social Irish dancing, 6/8 is the time signature of choice. The rhythm of the track should fit the time signature clearly and cleanly.
Tempo
A range of tempos work for Irish dancing. I tend to suggest somewhere around 120 BPM for polkas and reels, and 124 for jigs. The standard reel speed for most competition is 113 BPM, so there is certainly a range. Reels and polkas seem to run from about 110 to 140. Jigs tend to run from about 115 to to 145. Please note that once you get above 130 BPM, it becomes an exceedingly fast polka for anyone not doing Irish. If you are DJing an event where dancers will be doing a polka around the room, be mindful of this.
Length
In terms of length, two minutes is usually an absolute minimum if you are dancing Irish. Our shortest dance is 96 bars, which usually takes about two minutes. The longest dances are almost 600 bars, which tend to be near the ten minute mark. Take a look at the Dances By Length spreadsheet to get an idea if you have a particular dance in mind for your piece of music. Again, if you are DJing an event where dancers will be doing a polka around the room, be mindful of length. An Irish dancer loves a twelve minute polka set, but a couple going around the room is likely to become exhausted after three minutes unless they have good endurance.
Phrasing
Phrasing is the hardest thing to explain about selecting Irish music in text. Most Irish dances are expressed in 32 bar phrases, as is most traditional Irish music. That being said, a lot of modern music does not come in 32 bar phrases. For the purposes of selecting good music, 8 bar phrases are good enough. Things like half phrases and pauses will cause many dancers to feel as if something is "off," leading to the all-too-familiar situation where everyone gets home, stops, and says "5! 6! 7! 8!" before starting up again.
Selection
There is a lot of fantastic music out there, and learning how to cull your herd of music to ensure you're spending your time assessing your best candidates takes practice. When assessing tracks, I first sort by length and cut out anything that's under two minutes long. I normally don't use anything under four minutes unless it's exceptional in some way, but I still check them. I usually start with the longest tracks and work my way down. I'll listen to the introduction of a song, then click through to hear four or five points in the track to get a sample of whether the song stays danceable. If I like the sound of a track, I'll listen to it all the way through for obvious half-phrases and features that make it less danceable than I had hoped. Once I figure out that I like a track, I'll go through and bar count it so I know what dances fit the song. If you'd ever like a second set of ears on a track or two, feel free to drop me a line. I also have an excellent recommendation for a guy who takes music editing on contract in case you'd like a few tracks strung together, or a half phrase taken out.