  We propose the Multi-Track Music Machine (MMM), a generative system based on
the Transformer architecture that is capable of generating multi-track music.
In contrast to previous work, which represents musical material as a single
time-ordered sequence, where the musical events corresponding to different
tracks are interleaved, we create a time-ordered sequence of musical events for
each track and concatenate several tracks into a single sequence. This takes
advantage of the Transformer's attention-mechanism, which can adeptly handle
long-term dependencies. We explore how various representations can offer the
user a high degree of control at generation time, providing an interactive demo
that accommodates track-level and bar-level inpainting, and offers control over
track instrumentation and note density.
