Ideally, the answer to this really should lie in the title, but with the Dressage2Music sport still being very much in development (and with no recognised musical training required from its judges) the musical assessment is arbitrary and highly subjective. There is presently no way of anyone being able to ascertain whether entrants actually ride Dressage TO Music, or have music made to fit their dressage ...
For those of you keen to make your own audio tracks it might be worth remembering that adding a few extra trot steps or curtailing a canter is much easier than trying to synchronise your video and CD player to choreography that is set in stone. A floorplan which can be modified might prove to be quite an asset if your competition surface rides faster or slower than the one on which you train.
Considering that Judges look for an element of symmetry and inventiveness in the choreography, and that the concept of freestyle is to make transitions and changes of direction IN KEEPING WITH THE MUSIC, it is advisable to let your music and floorplan evolve together.
Altering music without lyrics can take quite a lot of advanced musical training to recognise where to cut and edit the phrase structures. An abrupt edit or fade between unrelated tracks will get you noticed because it is musically vulgar, even if you pay a professional to do it for you!
For those of you in a position to compose your own music, please remember that the music's beat should correspond to the movement of the horse's legs AND NOT simply it's head. This aspect can easily be addressed by using a compound time signature to capture the '3' feel of canter. Sadly, and despite its equestrian importance, many tests spend very little time in walk and the current trend to use 'airy fairy' music with no distinguishable beat simply makes it harder to judge the 'march' like quality of this gait. A good walk demonstrates four clear and well defined beats; suitable music will do the same.
Music for dressage doesn't need to be complicated to be effective: Click the play button below to hear flute,violin and piano trio.