Notch Filter

A notch filter (also called a band-stop filter) removes a narrow frequency band from the signal, most commonly used to eliminate 50 or 60 Hz power-line noise from neural recordings.

Why it matters: Electromagnetic interference from AC power lines is one of the most common artifacts in electrophysiology recordings. Notch filtering removes this interference without significantly affecting the neural signal.

Application: Applied during curation or real-time by the DAQ system. May need to target harmonics (120 Hz, 180 Hz) in addition to the fundamental frequency.

Considerations: Notch filters can introduce ringing artifacts near the notch frequency. Narrow notch width minimizes signal distortion. Proper grounding and shielding can reduce the need for notch filtering.