"Mutes all sounding notes that were turned on by received Note On messages, and which haven't yet been
turned off by respective Note Off messages. ...
"Note: The difference between this message and All Notes Off is that this message immediately mutes all sound
on the device regardless of whether the Hold Pedal is on, and mutes the sound quickly regardless of any lengthy
VCA release times. It's often used by sequencers to quickly mute all sound when the musician presses "Stop" in
the middle of a song."
DO HANDLE THIS. From MIDI Spec:
"Mutes all sounding notes that were turned on by received Note On messages, and which haven't yet been turned off by respective Note Off messages. ...
"Note: The difference between this message and All Notes Off is that this message immediately mutes all sound on the device regardless of whether the Hold Pedal is on, and mutes the sound quickly regardless of any lengthy VCA release times. It's often used by sequencers to quickly mute all sound when the musician presses "Stop" in the middle of a song."