Digital Notch Filters improve performance in applications containing resonant mechanical elements such as couplers or belts.
The digital notch filters can improve response by reducing system gain over the same frequencies that contain resonances. You can then increase the gain for the frequencies outside this range, without exciting the resonance causing instability.
The Gemini drive has two cascaded notch filters labeled "A" and "B". Both filters operate exactly the same way.
Consult the Gemini hardware installation guide and the command reference for filter adjustments and command syntax.