It's only recently that I found that the "scenes" on the Line 6 M9 (and M13, come to that) can be swapped very rapidly using MIDI. If you don't know these pedals, a scene is a configuration of the DSP channels (3 on the M9, 4 on the M13) that can be saved and selected. On the M9 you can choose between two effects or none on each DSP channel. For example, my scene for "Boulevard of Broken Dreams" includes two different depths of reverb on channel 1, Tremolo/Octave on channel 2 and two types of distortion on channel 3. I'd bought the Cuvave/M-Vave Chocolate MIDI controller pedal so that I could send multiple MIDI commands, currently set up so that:
- stomp switch 1 selects trem and distortion 1 (stomping both of these on the M9 would put it into tuner mode)
- switch 2 selects octave and distortion 2
- switch 3 selects distortion 1 and turns off trem and octave
- switch 4 selects distortion 2 and turns off trem and octave
My scene for "Mind Eraser" is similar but with univibe instead of trem in position 2-A
To switch between scenes on the M9 without a MIDI controller requires you to stomp on the bottom right and tap tempo switches simultaneously, then choose one of scenes 1 to 6 by pressing one of the 6 effects stomp switches. (What's not so obvious is that the M9 has 4 scene folders of 6 scenes each - you can select which folder with the model select knob in scene select mode. The M13 has 4 folders each of 12 scenes.) This is a pain so I bought a second Chocolate MIDI controller - actually a Chocolate + because it has the capability to save and load configurations - to send the MIDI command to select the chosen scene. This speeded up switching between the scenes as we went from one song to another. Check this topic for how I connected two controllers to the M9 without buying a proper MIDI merge box.
What I didn't realise immediately was that the switch between scenes is as fast as the switch between effects, so you're not limited to one scene per song; I can have a clean, compressed and chorused setup in one scene and with the tap of a footswitch I can be in a completely different e.g. high-gain octaved deep reverb scene. ( I guess it's similar to switching between patches on a Pod, but you still have the ability to turn individual effects on and off.) It's like having multiple 3-effect loops (or 4-effect for the M13). This potentially makes my set-up for switching multiple effects within a scene irrelevant but hey, whatever.
Also: with MIDI if the scene you want is in a different folder you can send the command to change folder and scene instantly with no messing about with the model select knob.
If you're using a Behringer FCB1010, M9/M13 scene/folder selection is as simple as sending one Program change code. If you want to do something the FCB1010 can't do, you could get a Chocolate + on a deal and feed the MIDI into the FCB1010 input with the output configured in "through" mode.
Apologies if this is teaching grandmother to suck eggs.

