OBS Studio Sidechain Ducking Source Explained

The “Sidechain/Ducking Source” dropdown inside the OBS Studio compressor filter is a powerful tool used to automatically lower (or “duck”) the volume of one audio source when another source becomes active. This feature is most commonly used by streamers and content creators to automatically quiet background music or game audio whenever they speak into their microphone, ensuring their voice always remains clear and audible.

How the Sidechain/Ducking Source Works

In traditional compression, a compressor lowers the volume of an audio source based on that same source’s volume (e.g., quietening loud peaks in your voice).

With sidechaining, the compressor on one audio source is triggered by a completely different audio source.

When you select a microphone as the Sidechain/Ducking Source on your desktop audio compressor: 1. OBS monitors your microphone input. 2. The moment you start speaking, the compressor activates on your desktop/music audio. 3. The desktop/music volume is instantly lowered by a set amount. 4. When you stop speaking, the desktop/music volume smoothly returns to its original level.

How to Set Up Sidechain Ducking in OBS

To use this feature, you must apply the compressor filter to the audio source that you want to quiet down (usually your Desktop Audio, Game Audio, or Music), not your microphone.

1. Locate the source you want to quiet down (e.g., Desktop Audio) in the OBS Audio Mixer.
2. Click the three dots (options icon) next to it and select Filters.
3. Click the + icon in the bottom left, select Compressor, and name it (e.g., “Ducking”).
4. In the filter properties, find the Sidechain/Ducking Source dropdown.
5. Select your primary microphone from the list.

Tuning the Compressor Settings for Smooth Ducking

Once the sidechain source is selected, you need to adjust the compressor settings to make the volume transition sound natural:

• Threshold: This controls how loud you need to speak to trigger the ducking. Start around -30 dB to -35 dB and adjust until the music ducks only when you speak at a normal volume.
• Ratio: This determines how much the music volume is reduced. A ratio of 2.5:1 to 4:1 is usually sufficient for background music. Higher ratios will quiet the music even further.
• Attack Time: How fast the music volume drops when you start speaking. Keep this fast (around 1 ms to 10 ms) so the music drops instantly as soon as you say your first word.
• Release Time: How fast the music returns to normal volume after you stop speaking. Set this between 500 ms and 1000 ms (1 second) so the music fades back in smoothly during natural pauses in your speech.
• Output Gain: Leave this at 0 dB. Increasing this will boost the overall volume of the music, defeating the purpose of the compressor.