SmartMusic is an excellent computer/iPad program for preparing solos that require piano accompaniment. Most (although not all) major repertoire is available for study in the program. SmartMusic features include adjustable tempos, optional metronome click, the ability to start in any measure of the piece, and recording play-back. For students preparing for a Horn & Piano performance, this is invaluable. The current rate is $40/year for a student subscription.