Some MIDI files are "multi-track", essentially several simple MIDI files in one. And each MIDI file can contain MIDI on one or more channels.
I think you will always be prompted if the file is a Multi-track file. I always explode it onto multiple Reaper tracks.
If you set this option you will always be prompted when loading a file with MIDI on multiple channels for how to explode them:
As for playing them,
(a) single-track file, single channel
-- put an instrument plug-in on the Reaper track
(b) single-track file, multiple channels
-- explode the channels onto multiple Reaper tracks,
-- then put an instrument plug-in on each Reaper track
or
-- do not explode the channels onto multiple Reaper tracks
-- add a multi-timbral instrument plug-in (e.g Kontakt, SampleTank. Falcon, TX16Wx) to the track
-- within the plug-in load instruments for each channel
(c) multi-track file, single channel
-- explode the tracks onto multiple Reaper tracks,
-- then put an instrument plug-in on each Reaper track
(d) multi-track file, multiple channels
-- explode the tracks onto multiple Reaper tracks,
-- explode the channels onto multiple Reaper tracks,
-- then put an instrument plug-in on each Reaper track
or
-- explode the tracks onto multiple Reaper tracks,
-- do not explode the channels onto multiple Reaper tracks
-- add a multi-timbral instrument plug-in (e.g Kontakt, SampleTank. Falcon, TX16Wx) to each Reaper track
-- within the plug-in load instruments for each channel.
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Here I have imported a multi-track, multi-channel MIDI file and exploded everything. Look at the clip-names to see the content of each one:
And, if I chose not to explode theMIDI channels: