It's possible to specify what each of the 1-8 knobs below the display will control from the main menu in the GT-100. From the factory, these knobs are already set to control various parameters like "Patch Select," "Channels A/B," and "Patch Level" etc.. Reassigning the knobs makes it convenient so you can quickly control your own desired parameters that you use most often.  For example, maybe you'd prefer to have knob 1 control the Compressor Level instead of it changing patches.    

Here's how assign them. 

1. Press SYSTEM. 

2. Turn knob 4 to highlight the "KNOB SETTING" icon. 

3. Use knobs 5-8 to set the parameters that  you'll want to control with the 1-4 knobs.

4. Press PAGE right (>) to select tab 2.

5. Use knobs 5-8 to set the parameters that  you'll want to control with the 5-8 knobs.   

6. When you're finished, press EXIT. The new settings are saved automatically. You'll now notice your new knob control assignments in the main menu.