  Lead sheets have become commonplace in generative music research, being used
as an initial compressed representation for downstream tasks like multitrack
music generation and automatic arrangement. Despite this, researchers have
often fallen back on deterministic reduction methods (such as the skyline
algorithm) to generate lead sheets when seeking paired lead sheets and full
scores, with little attention being paid toward the quality of the lead sheets
themselves and how they accurately reflect their orchestrated counterparts. To
address these issues, we propose the problem of conditional lead sheet
generation (i.e. generating a lead sheet given its full score version), and
show that this task can be formulated as an unsupervised music compression
task, where the lead sheet represents a compressed latent version of the score.
We introduce a novel model, called Lead-AE, that models the lead sheets as a
discrete subselection of the original sequence, using a differentiable top-k
operator to allow for controllable local sparsity constraints. Across both
automatic proxy tasks and direct human evaluations, we find that our method
improves upon the established deterministic baseline and produces coherent
reductions of large multitrack scores.
