Remove Background Hum in Kdenlive with Gate Filter

This article provides a step-by-step guide on how to use the “Gate” audio filter in Kdenlive to eliminate constant background hum, hiss, or ambient noise from your audio tracks. You will learn how to locate the filter, apply it to your timeline, and configure its key parameters—such as threshold, attack, and decay—to achieve clean, professional-sounding audio.

Understanding the Gate Filter

An audio gate (or noise gate) works by muting or lowering the volume of signals that fall below a specific volume threshold. When a person is speaking, the audio is loud enough to open the “gate.” When they stop speaking, the background hum falls below the threshold, and the gate closes, silencing the background noise.

Step-by-Step Guide to Applying the Gate Filter

1. Add Your Footage to the Timeline

Import your video or audio clip into Kdenlive and drag it onto the timeline. If your audio is embedded in a video clip, you can edit it directly or right-click the clip and select Split Audio to view the waveform more clearly on a separate audio track.

2. Locate and Apply the Gate Effect

1. Open the Effects tab (usually located in the bottom-left or top-left panel of the default workspace).
2. Use the search bar in the Effects panel and type “Gate”.
3. Under the Audio or Audio channels category, locate the Gate filter.
4. Drag and drop the Gate effect directly onto your audio clip in the timeline.

3. Configure the Filter Settings

Once applied, select the audio clip to view the Gate settings in the Properties or Effect/Composition Stack panel. Adjust the following key parameters to clean up your audio:

• Threshold (dB): This is the most critical setting. It determines the volume level at which the gate closes. Play your audio and find a section where there is only background hum (no talking). Note its volume level on the audio meter, then set the Threshold just above that level. If your voice gets cut off, lower the threshold.
• Attack (ms): This controls how quickly the gate opens when you start speaking. Set this to a low value (between 1ms and 10ms) so that the first syllables of your words are not accidentally cut off.
• Hold (ms): This keeps the gate open for a short duration after the audio drops below the threshold. A setting of 50ms to 100ms helps prevent the gate from stuttering during brief natural pauses in speech.
• Decay / Release (ms): This controls how gradually the gate closes. A longer release time (around 100ms to 300ms) creates a smooth transition into silence, preventing the audio from sounding artificially chopped or abrupt.
• Range / Reduction (dB): This determines how much the background noise is reduced when the gate is closed. Setting this to maximum will completely silence the hum, while a moderate setting will just lower the hum, which can sometimes sound more natural.

4. Preview and Fine-Tune

Play back your timeline to test the results. Listen closely to the transitions between speech and silence. If the speaker’s voice sounds unnatural or clipped at the beginning or end of sentences, slightly lower the Threshold or increase the Decay time until the voice sounds natural while the background hum remains silent during pauses.