Dynamic notch filter
The dynamic notch is a Betaflight filter that automatically tracks the strongest noise peaks in the gyro FFT and notches them out, following motor RPM as throttle changes.
It's the main defence against motor noise when you don't have (or run alongside) an RPM filter. Key settings: count, Q, and the min/max frequency range. PIDoctor checks whether the notch range/Q cover your noise peaks and suggests dyn_notch settings.