1. A method for free rhythm musical input, the method comprising: receiving musical input comprising a sequence of notes; determining an optimal metrical grid corresponding to the sequence of notes, wherein the optimal metrical grid is defined as the metrical grid that optimally represents the sequence of notes, and wherein determining the optimal metrical grid is based in part on an a priori probability of the occurrence of the optimal metrical grid, wherein the a priori probability is independent of the sequence of notes; annotating the musical input with the optimal metrical grid; and storing a representation of the annotated musical input.