The above stated method can also be applied to the multiphonic case.
Projecting the onset timings of all notes in a multiphonic music score
onto a one-dimensional time axis, we obtain a ``rhythm score'' from
which the 
-gram ``grammar'' can be defined in the same way. After
preprocessing for grouping nearly simultaneous onsets, the rhythm score
is recognized from the input sequence of IOIs across multiple voices in
the observed MIDI signal, followed by postprocessing for assigning note
length to each of recognized note onsets.