Simulate Small Room Reverb with FFmpeg

This article explains how to simulate a realistic small room reverb effect on an audio file using FFmpeg's built-in freeverb filter. You will learn the precise command-line syntax and how to adjust key parameters—such as room size, damping, and the wet/dry mix—to achieve a natural-sounding, tight room acoustic for your voiceovers, music, or sound effects.

The FFmpeg Freeverb Command

To apply a small room reverb, you will use FFmpeg's freeverb audio filter (-af). Below is the standard command-line template to process your audio:

ffmpeg -i input.wav -af "freeverb=roomsize=0.2:damp=0.5:wetg=0.3:dryg=0.8:width=0.5" output.wav

Parameter Breakdown for a Small Room

To make the reverb sound like a small room (such as a bedroom, office, or small studio), you must configure the parameters to limit the decay time and high-frequency reflections:

  • roomsize=0.2: Controls the size of the simulated room (range: 0.0 to 1.0). A low value like 0.2 or 0.3 creates rapid reflections, simulating a small physical space.
  • damp=0.5: Controls the high-frequency damping (range: 0.0 to 1.0). A value of 0.5 simulates standard wall materials (like drywall, wood, or carpet) that absorb treble frequencies, preventing the reverb from sounding too metallic or bright.
  • wetg=0.3: Sets the wet gain, which is the volume of the reverb effect (range: 0.0 to 1.0). For a natural small room, keep this relatively low (0.2 to 0.4) so the effect remains subtle.
  • dryg=0.8: Sets the dry gain, which is the volume of the original, unprocessed audio (range: 0.0 to 1.0). Keeping this high ensures the original sound remains clear and upfront.
  • width=0.5: Controls the stereo width of the reverb effect (range: 0.0 to 1.0). A value of 0.5 provides a realistic stereo spread suitable for a small space.

Customizing the Room Sound

You can easily tweak these parameters to simulate different types of small rooms:

  • For a "Dead" Room (closet/booth): Lower the room size and increase the damping. freeverb=roomsize=0.1:damp=0.8:wetg=0.15:dryg=0.9
  • For a "Live" Room (bathroom/tiled space): Keep the room size small but lower the damping to allow higher frequencies to bounce. freeverb=roomsize=0.25:damp=0.2:wetg=0.4:dryg=0.7