Automatic alignment of music performances with structural differences

Both in interactive music listening, and in music performance research, there is a need for automatic alignment of different recordings of the same musical piece. This task is challenging, because musical pieces often contain parts that may or may not be repeated by the performer, possibly leading to structural differences between performances (or between performance and score). The most common alignment method, dynamic time warping (DTW), cannot handle structural differences adequately, and existing approaches to deal with structural differences explicitly rely on the annotation of ``break points'' in one of the sequences. We propose a simple extension of the Needleman-Wunsch algorithm to deal effectively with structural differences, without relying on annotations. We evaluate several audio features for alignment, and show how an optimal value can be found for the cost-parameter of the alignment algorithm. A single cost value is demonstrated to be valid across different types of music. We demonstrate that our approach yields roughly equal alignment accuracies compared to DTW in the absence of structural differences, and superior accuracies when structural differences occur.