Configure Reverb Wet and Dry Levels in FFmpeg

This article explains how to configure the wet and dry levels of the reverb filter in FFmpeg using the freeverb audio filter. You will learn the exact command-line syntax, parameter ranges, and practical examples to control the balance between your original dry audio and the wet, reverberated sound effect.

Understanding the Freeverb Filter Parameters

FFmpeg uses the freeverb filter to apply studio-quality reverberation to audio streams. To control the mix of the original sound and the reverb effect, you must adjust the dry and wet parameters:

  • dry: Determines the level of the original, unaltered input signal. The value ranges from 0.0 (completely silent/muted dry signal) to 1.0 (maximum dry signal volume). The default value is approximately 0.66 (or 2/3).
  • wet: Determines the level of the processed, reverberated signal. The value ranges from 0.0 (no reverb effect) to 1.0 (maximum reverb volume). The default value is approximately 0.33 (or 1/3).

Basic Command Syntax

To configure these levels, use the -af (audio filter) flag followed by the freeverb filter name and your desired values separated by colons.

ffmpeg -i input.mp3 -af "freeverb=wet=0.5:dry=0.5" output.mp3

In this example, both the original dry signal and the wet reverb signal are set to equal strengths (0.5), creating an even balance.

Advanced Examples

You can combine the wet and dry levels with other freeverb parameters like roomsize (size of the virtual room) and damp (high-frequency absorption) to customize the environment.

1. Large, Spacious Hall (High Wet, Low Dry)

If you want a highly ambient sound where the reverb dominates the original signal, increase the wet level and decrease the dry level:

ffmpeg -i input.wav -af "freeverb=roomsize=0.85:damp=0.4:wet=0.7:dry=0.3" output.wav

2. Subtle Ambience (Low Wet, High Dry)

For a subtle acoustic spacing where the original voice or instrument remains prominent, lower the wet level and keep the dry level high:

ffmpeg -i input.wav -af "freeverb=roomsize=0.4:damp=0.5:wet=0.15:dry=0.85" output.wav

Key Considerations

  • Clipping Prevention: If the sum of wet and dry exceeds 1.0, the output audio may exceed maximum digital headroom and cause digital clipping (distortion). To prevent this, ensure your combined levels do not exceed 1.0, or apply the volume filter afterward to scale down the signal (e.g., -af "freeverb=wet=0.6:dry=0.6,volume=0.8").
  • Channel Width: You can also add the width parameter (range 0.0 to 1.0) to adjust the stereo spread of the wet reverb signal.