Line 6 M13 - Manual (Page 32)

Appendix A : Reference
A•4
Miscellaneous CC Commands
Command MIDI CC#
Bypass All + FX Loop 23 0 to 63 = Bypass 64 to 127 = Undo Byp.
Bypass All - FX Loop 24 0 to 63 = Bypass 64 to 127 = Undo Byp.
Tuner Mode 69 0 to 63 = Exit 64 to 127 = Enter
Looper Levels - Controlled via EXP pedal only -- not MIDI CC