If AUTO is chosen the first MIDI channel used by the audio tracks, and not used by any of the MIDI tracks, will be used.
Default is 1 (MIDI > CHANNELS)
But :
If an audio track and a MIDI track share the same MIDI channel, the MIDI track will block the audio track from sending out data while the audio track will block the MIDI track from receiving data.
Still with default settings, if a midi track is set to ch1, AUTO becomes 2!
3 if another midi track is set to ch2, etc…
If midi tracks are set to ch 1-8, or if audio tracks channels are off, nothing is sent.