Configure OBS Expander Filter to Block Room Noise

Eliminating distracting background sounds like PC fans, air conditioning, or distant traffic is crucial for creating professional broadcasts and recordings. This guide provides a step-by-step walkthrough on how to configure the Expander filter in OBS Studio to completely silence ambient room noise, ensuring your microphone only captures your voice when you speak.

What is an Expander?

Unlike a Noise Gate, which abruptly cuts off all audio below a certain volume, an Expander acts like a gentle volume controller. It reduces the volume of sounds that fall below a specific threshold, making ambient noise quiet or completely silent, while preserving the natural fade-out of your voice.

Step 1: Add the Expander Filter in OBS

1. Open OBS Studio.
2. Locate your microphone source in the Audio Mixer dock.
3. Click the three vertical dots (or gear icon) next to your microphone name and select Filters.
4. In the Filters window, click the + (plus) icon in the bottom-left corner.
5. Select Expander from the list, name it (e.g., “Room Noise Expander”), and click OK.

Step 2: Set the Detection Method and Style

At the top of the Expander settings, you will see options for Presets and Detection:

• Preset: Set this to Expander (do not select “Gate”).
• Detection: Set this to RMS. RMS measures average audio levels, which creates a smoother, more natural sounding transition for human speech than the “Peak” setting.

Step 3: Configure the Expander Settings

To completely silence your room’s ambient noise, adjust the sliders using the following guidelines:

• Ratio: Set this between 2.0:1 and 4.0:1. A ratio of 4.0:1 means that for every 1 dB the background noise goes below your threshold, the Expander will reduce it by 4 dB. This is aggressive enough to silence most ambient noises without sounding artificial.
• Threshold: This is the most critical setting.
  1. Stop speaking and look at the green bar moving in your OBS Audio Mixer. Note the decibel (dB) level where the background noise sits (e.g., -50 dB).
  2. Set your Threshold slider to about 3 to 5 dB higher than that background noise level (e.g., if noise is at -50 dB, set the threshold to -45 dB). This tells OBS to quiet down any audio lower than -45 dB.
• Attack: Set this to 2ms or 3ms. A fast attack time ensures the filter opens instantly when you start talking, preventing the first syllable of your words from being cut off.
• Release: Set this to 100ms to 150ms. This control dictates how quickly the volume drops after you stop speaking. A value in this range allows your words to fade out naturally.
• Output Gain: Leave this at 0 dB unless your overall microphone volume became too quiet after applying the filter.

Step 4: Test Your Audio

With the filter configured, look at your Audio Mixer while remaining completely silent. The green bar for your microphone should drop all the way to the left (infinity), indicating total silence. Next, speak at a normal volume and then whisper; your voice should sound clear, full, and uninterrupted, while the room noise vanishes the moment you stop speaking.