Sixteenth-note index from the start of the figure.
Loudness as a factor of the passage's base velocity.
OptionalvoiceThe voice this onset is played on, where the material has more than one. A figure written for a single voice — a bass lick — leaves it out.
OptionallimbThe limb that plays it, where the material names one. It outranks GridEvent.voice as the stream an onset belongs to, since what crowds a player is one limb rather than one drum.
An onset on the shared sixteenth grid.
Both kinds of material are lists of these with their own extra fields, so a transform is generic over the record and only ever reads the fields named here.