Microtonal music is my primary conservatory music passion.

My earlier posting Musical Equal Temperament Ain't dealt sufficiently with the ontology of the 12-tone system of western classical music so I won't repeat that here.

The term "microtonal music" is a western music theory pormanteau category for modern explorations of ideas laboriously weeded out of our standard tonal system over the centuries.

Microtonal music means, roughly, one or both of two things:

1. use of scales composed of Just Intonation intervals, that is, intervals represented by rational numbers
2. use of equal temperament scales having more than 12 steps

A number of composers exercise point 1 above in various JI schemes.

A good example of point 2 above is  Concerto For Double Bass No 2 by Edgar Meyer, which is written for accompaniment by a 24-step scale instrument composed of lengths of PVC tubing and struck with mallets.

Both Arabic classical music and Sangeet Madras are good examples of both of the above: they are in modern times essentially tempered systems (possessing 24 and 72 intervals respectively) which veer exotically compared with a straightforward western-style extension of our 12-tone system to 24-step equal temperament.

The  two great difficulties for the microtonal buff are:

1. Finding musicians who want to play along
2. Notation

Point 1 is self-explanatory: this sort of stuff is outside many an instrumentalist's ear, experience and/or comfort zone.

 Point 2 arises from the eurocentricity of both our notation system and our music theory. Intervals are often described in relation to equal temperatment intervals using the horrid concept of "cents", 100th's of a half-tone, which is sort of like describing a smooth blues rythm in terms of a beer garden oompahpah waltz beat.

Fortunately, I've located a few musicians interested in microtonality. I'll try to post links to some of our work soon.