When you strum the Jamsik 7, the guitar sends MIDI "NOTE ON" messages which make sounds come from the speakers. If you want to stop the notes manually (using MIDI "NOTE OFF" messages), use the Choke Mute.
Simply compress 4 or more strings at the same time with your picking hand.
In this example, we're using the Choke Mute feature to silence the guitar. Also, you will notice the LED will blink red very briefly, indicating that the function executed successfully.