Improved Metrical Alignment of Midi Performance Based on a Repetition-aware Online-adapted Grammar

This paper presents an improvement on an existing grammar-based method for metrical structure detection and alignment, a task which involves aligning a repeated tree structure with an input stream of musical notes. The previous method achieves state-of-the-art results, but performs poorly when it lacks training data. Data annotated as it requires is not widely available, making this drawback of the method significant. We present a novel online learning technique to improve the grammar’s performance on unseen rhythmic patterns using a dynamically learned piece-specific grammar. The piece-specific grammar can measure the musical well-formedness of the underlying alignment without requiring any training data. It instead relies on musical repetition and self-similarity, enabling the model to recognize repeated rhythmic patterns, even when a similar pattern was never seen in the training data. Using it, we see improved performance on a corpus containing only Bach compositions, as well as a second corpus containing works from a variety of composers, indicating that the online-learned grammar helps the model generalize to unseen rhythms and styles.