There are only few buttons on foot controllers and number of looper commands is much bigger. To deal with it multi-tapping is used. If delay between taps is less than 0.5 seconds they belong to one series and produce MIDI note as explained below.
Assume button A sends note ON message for note 60. Multiple tapping will send one additional note ON for note 60 with changed velocity. Original note velocity we assign to be 100. Additional note velocity = number of taps + 5 for a hold in the end.
For this example:
Using multi-taps one button sends different MIDI messages. Multiple taps use 0.5 seconds delay to decide if there will be next tap. Because of this it should not be used for time critical commands – start playing or recording. Use it for other commands like changing volume, scrolling song list, etc.
Notes from MIDI IN are converted to looper commands by menu configuration files. Example is below.
A100 : command1: command2
A2 : command3: command4
A3 : command5
Here velocity 100 is velocity assigned to original MIDI notes from controller. Velocity 1, 2, 3, ... 10 is velocity of counted notes in multi-tapping mode.
If foot controller sends control change (CC) messages from expression pedal the looper can convert them into notes. As example CC 12 will be converted to note 12 ON/OFF.
As an example in iRig Blue Board MIDI foot controller there are two expression pedal inputs. Plugging ON/OFF momentarily switches into these inputs will send CC messages converted into note messages.