Notch Audio Filter

Removes a very narrow range of frequencies centered around a selected frequency while leaving the rest of the spectrum largely unchanged.
This filter is designed to eliminate specific, unwanted tones such as hum, buzz, or ringing.

Notch is a frequency-domain filter evaluated continuously over time.

Parameters

Center frequency (5 - 21 600 Hz)

Sets the exact frequency that will be removed.

• Low values (≈50 - 120 Hz)
  Useful for removing electrical hum or low-frequency rumble.

• Mid values (≈300 - 3 000 Hz)
  Target problematic resonances in voices or instruments.

• High values (>3 000 Hz)
  Remove high-pitched whines or ringing.

Note:

This is the frequency you want to suppress.

Bandwidth (5 - 21 600 Hz)

Controls how wide the removed frequency range is around the center frequency.

• Low values
  Very narrow notch; removes a specific tone.

• High values
  Wider removal; affects more surrounding frequencies.

Important note:
Although expressed in Hz, this controls width, not position.

Rolloff rate (1 - 10)

Controls how steeply frequencies transition into and out of the notch.

• Low values (1 - 3)
  Gentle slopes; smoother, less obvious filtering.

• High values (8 - 10)
  Steep slopes; precise removal with minimal side effects.

Higher rolloff values make the notch more focused.

Dry → Wet (0.0 - 100.0%)

Controls the mix between the original signal and the notched signal.

• 0.0%
  Original audio only.

• 50.0%
  Partial removal of the target frequency.

• 100.0%
  Full notch effect.

Allows subtle correction when full removal sounds unnatural.

Keyframes

All four sliders are keyframeable.

Keyframes allow the notch filter to change over time, enabling:

• Sweeping the notch frequency to track a moving hum or whistle
• Gradually reducing or restoring a problematic tone
• Applying the notch only during specific sections of a clip
• Creating automated resonance suppression

Behavior note:
Because the filter operates in the frequency domain, keyframed changes are best evaluated during playback rather than on a single frame.

Channel selection

Determines which audio channels the filter is applied to. Buttons are toggle switches.

Available buttons depend on the project’s audio channel configuration: Settings > Audio Channels

• L — Front Left
• R — Front Right
• C — Center
• LF — Low-Frequency Effects (LFE)
• Ls — Surround Left
• Rs — Surround Right

Note:

Independent filtering per channel requires adding separate instances of the filter.

Auditory characteristics

• Removes a specific tone or resonance
• Minimal impact on overall sound when set narrowly
• Wide settings can make audio sound hollow
• Overuse may reduce naturalness

Recommended use cases

• Removing electrical hum (50/60 Hz)
• Eliminating microphone feedback
• Reducing ringing or resonant tones
• Cleaning up dialogue recordings
• Fixing tonal artifacts without affecting the full mix

Example settings

• 50 Hz hum removal

  • Center frequency: 50 Hz
  • Bandwidth: narrow
  • Rolloff rate: high
  • Dry → Wet: 100%

• Voice resonance reduction

  • Center frequency: 500 - 1 000 Hz
  • Bandwidth: narrow to medium
  • Rolloff rate: medium
  • Dry → Wet: 50 - 100%

• High-pitched whine

  • Center frequency: 4 - 8 kHz
  • Bandwidth: narrow
  • Rolloff rate: high

Usage notes and tips

• Sweep the Center frequency while listening to locate the problem tone.
• Use the narrowest Bandwidth that solves the issue.
• Prefer high Rolloff rate for surgical removal.
• Use Dry → Wet to soften the effect if needed.

Limitations

• Not suitable for broad tonal shaping
• Cannot remove multiple tones at once
• Extreme settings can cause audible artifacts