What is a Patch
A "Patch" is a mapping between a control "Source" (Src) and a "Destination" parameter (Dst). A Patch allows a Source to control a Destination.
Source ===> Destination
Sources can be internal (LFO, A/B, etc..) or external (Pedal, MIDI).
Destination parameters are different depending on what effects are part of the current program. Each effect has parameters that can be use as Patch Destinations (Mix, Level, Time, etc..).
Sources and Destinations
Sources always have a range of 0-127 but Destinations can vary. The real job of the Patch is to scale the Source value to the scale of the Destination parameter's range. By default, a new Patch uses the full range of the Source (0-127) and the full range of the Destination (i.e. 0-100%) but the Patching system allows you to adjust the range of both the Sources and the Destinations.
For example, a typical gas pedal has a range of 0-127. You could create a Patch that would translate the pedal's 0-127 to 0-100% on a Delay effect's Mix parameter. Moving the pedal would then change the value of the Mix parameter.
Select "Pedal" as the Source (Src)
Select Delay "Mix" as the Destination (Dst)
If you only wanted the Mix to go from 0-50%, the patching system allows you to adjust a Destination Min and a Destination Max value (there is also a Mid). By default the Max would be 100%. If it was adjusted to 50%, the gas pedal's 0-127 would only change the Mix parameter from 0-50%.
Things really start getting interesting when you start scaling the value of the Source. Like the Destination, a Min, Mid and Max are provided for the Source. By default they are set to 0, 63 and 127 respectively. If you change the Source "Max" value to 100, then moving the pedal from 0-100 would change the Mix from 0-50.
If you then create another Patch that uses the gas pedal as a Source but something like Feedback as the Destination, you can use part of the range of the pedal to control the Mix and the rest to control the Feedback. The Source Min on the second Patch would be set to 100 with the Max left at 127. Now 100 is mapped to the Min of the Destination (0% Feedback) and 127 is mapped to the Max of the Destination (100% Feedback). The Mins and Maxs of both the Sources and the Destinations can be tweaked for some really amazing controls from just a single Source.
I created a program at one point that had a similar mapping as described above but I put a volume control effect in front of the delay and fed the dry signal on a parallel routing. The Patch to the Volume effect turned the input to the delay off when the pedal was fully forward. With the Feedback at 100%, it basically turns into a looper. There is an overview of it with graphics here. Cool stuff.
In most cases, separate Patches are created for separate Sources and Destinations. I typically use 2 gas pedals with a Patch for one always mapped to the master output level (Post Level under EDIT/Mix).
Create A Patch
To create a Patch, you select a source and a destination, then, optionally, adjust the range of either the source or the destination. Easy.
Consult the users guide section 4.2 for additional options and menu navigation.