The Power of Fragmentation: A Hierarchical Transformer Model for Structural Segmentation in Symbolic Music Generation

Symbolic Music Generation relies on the contextual representation capabilities of the generative model, where the most prevalent approach is the Transformer-based model. The learning of musical context is also related to the structural elements in music, i.e. intro, verse, and chorus, which are currently overlooked by the research community. In this paper, we propose a hierarchical Transformer model to learn multi-scale contexts in music. In the encoding phase, we first designed a Fragment Scope Localization layer to syncopate the music into chords and sections. Then, we use a multi-scale attention mechanism to learn note-, chord-, and section-level contexts. In the decoding phase, we proposed a hierarchical Transformer model that uses fine-decoders to generate sections in parallel and a coarse-decoder to decode the combined music. We also designed a Music Style Normalization layer to achieve a consistent music style between the generated sections. Our model is evaluated on two open MIDI datasets, and experiments show that our model outperforms the best contemporary music generative models. More excitingly, the visual evaluation shows that our model is superior in melody reuse, resulting in more realistic music.