From Ruth Hogan Poulsen
http://www.ruthhoganpoulsen.com/news/6-tips-9-8-09.html
Know your horses ideal BPM (beats per minute)
The average horse has BPM as follows.
Walk 90-106 BPM
Trot 138-160 BPM
Canter 96-108 BPM
Pick music that matches your horses BPM within 4-6 BPM range. (For example if your horse has a canter of 104 BPM, choose music that is between 100 BPM and 108 BPM)
Choose music that has a very clear down beat. (The down beat is the beat that you would tap your toe to.)
If you CAN'T tap you toe to the music or clap your hands easily to the beat of the music… it's not great riding music!!
Choose music that will help you achieve your horse's ideal tempo. For example: if your horse is a bit on the lazy side, choose an upbeat and energetic piece of music that will help YOU continue to strive for more energy. If your horse is more on hot or nervous side, choose music that will feel calmer, steadier and will help you with rhythm and relaxation.Choose music that has dynamic changes. Dynamic changes are audible changes within the music (either volume or intensity) where you can make transitions. (for example, the music should FEEL or SOUND like there is a transition to an extended trot) When you are riding a freestyle for competition, the dynamic changes of the music need to match your transitions both within the gait and from gait to gait. Meaning, when you begin and end a half-pass, the observer should see and hear the transition and hear the change in the music occurring together. When riding a transition from gait to gait, such as the canter to walk for example, the observer should hear and see the transition to the walk occur with the change in the music.
Choose music that has appropriate back ground music. Even when a selection of music has the correct BPM for a trot; for example, the music that is in the back ground has an impact on the FEEL of the music. If you have a hot nervous horse, a high pitched frantic violin in the back ground will NOT help you or your horse maintain rhythm and relaxation. On the other hand, if your horse is always lacking impulsion or is lazy, more upbeat and forward moving back ground music will help you increase his energy level. For example, a soft and slower piece of jazz music might be appropriate for a nervous horse, but would allow the quiet or lazy horse to have even less energy.
Choose music that tells a story. Pick a piece of music that has a clear melody. Music that does not have a clear melody is sometimes described as "back ground" or "elevator" music. Music that has a great melody also helps the listener predict and feel what is coming next.
Choose music that has clear phrases. A phrase in music is like a sentence. It has a clear beginning and ending. The beginning and ending of phrases are instinctive places to begin and end movements within a gait. For example, if you are a first Level rider, at the beginning of a phrase you might start a 10 meter circle or leg yield. At the end of the phrase, you would be ending that same movement. The length of a phrase should match the length of a movement. If one phrase is not long enough to complete a movement, then you can ride a complete movement to 2 or 3 phrases together as long as you begin and end at the end of any given phrase.