Pressing and holding the footswitch will engage the Brake control, which will eventually stop the LFO.

A short press of the footswitch will toggle between Fast/Slow. The LFO for Fast mode is the value determined by the Rotor/Horn speed parameters. When Slow mode is engaged the LFOs will slow down by a predetermined factor, simulating a physical Leslie cabinet slowing down.

The Hz display will not change when you toggle between Fast/Slow.

Let me know if you have any other questions.