ion ichn, inum, ivel ioff ichn, inum, ivel iondur ichn, inum, ivel, idur iondur2 ichn, inum, ivel, idur
inum - note number (0-127)
ivel - velocity (0-127)
iondur and iondur2 (i-rate note on with duration) send a noteon and a noteoff MIDI message both with the same channel, number and velocity. Noteoff message is sent after idur seconds are elapsed by the time iondur was actived.
iondur differs from iondur2 in that iondur truncates note duration when current instrument is deactivated by score or by realtime playing, while iondur2 will extend performance time of current instrument until idur seconds have elapsed. In realtime playing it is suggested to use iondur also for undefined durations, giving a large idur value.
Any number of iondur or iondur2 opcodes can appear in the same Csound instrument, allowing chords to be played by a single instr.