Piano score rearrangement into multiple difficulty levels via notation-to-notation approach

Musical score rearrangement is an emerging area in symbolic music processing, which aims to transform a musical score into a different style. This study focuses on the task of changing the playing difficulty of piano scores, addressing two challenges in musical score rearrangement. First, we address the challenge of handling musical notation on scores. While symbolic music research often relies on note-level (MIDI-equivalent) information, musical scores contain notation that cannot be adequately represented at the note level. We propose an end-to-end framework that utilizes tokenized representations of notation to directly rearrange musical scores at the notation level. We also propose the ST+ representation, which includes a novel structure and token types for better score rearrangement. Second, we address the challenge of rearranging musical scores across multiple difficulty levels. We introduce a difficulty conditioning scheme to train a single sequence model capable of handling various difficulty levels, while leveraging scores from various levels in model training. We collect commercial-quality pop piano scores at four difficulty levels and train a MEGA model (with 0.3M parameters) to rearrange between these levels. Objective evaluation shows that our method successfully rearranges piano scores into other three difficulty levels, achieving comparable difficulty to human-made scores. Additionally, our method successfully generates musical notation including articulations. Subjective evaluation (by score experts and musicians) also reveals that our generated scores generally surpass the quality of previous rule-based or note-level methods on several criteria. Our framework enables novel notation-to-notation processing of scores and can be applied to various score rearrangement tasks.