Orinj version 3.0.0
There are 128 instruments and a percussion section (see MIDI Program Change message). The percussion section is not a separate instrument, but a reserved MIDI channel (channel 9 if counting from 0). In Orinj, you can use this channel as if it is a separate instrument.
The instrument that is selected in this control panel is the instrument that will be chosen for the piano roll in the MIDI roll view. It does not change the instruments that will be played by your MIDI file. The instruments that will be played by your MIDI file are determined by the MIDI events that you will create separately (see Orinj MIDI control line).
If you click on an instrument in this list, this instrument will be played in the piano roll. You can then click on the piano keys to hear the instrument. If you click on Percussion at the end of the instrument list, the piano roll will change to show you available percussion instruments. Use the Find button () at the top to search for specific instruments by name.
The sound of each instrument depends on your MIDI devices (e.g., your computer). The same MIDI instrument may sound differently on different computers. MIDI devices may or may not support some instruments or notes. Also, you should expect that some instruments will not cover all of the piano roll and that some piano keys may not produce any sound for some instruments.