How to Use the FFmpeg asubboost Filter

The asubboost filter in FFmpeg is a specialized audio filter designed to enhance the low-frequency (sub-bass) components of an audio stream. This article provides a clear, practical guide on how to use the asubboost filter, explaining its core parameters and demonstrating how to apply it to your audio and video files using command-line examples.

Understanding the asubboost Filter

The asubboost (Audio Subwoofer Boost) filter works by isolating low frequencies, boosting them, and mixing them back into the original audio signal. It is particularly useful for adding depth to music tracks, emphasizing explosions or low rumbles in movie soundtracks, or optimizing audio for subwoofer playback.

Key Parameters

You can customize the filter using several key parameters. Each parameter is configured in a key=value format, separated by colons:

  • dry: Sets the gain level of the original, unprocessed input signal. The default value is 1.0.
  • wet: Sets the gain level of the boosted sub-bass signal. The default value is 1.0.
  • boost: Controls the amplification factor of the sub-bass frequencies. The default value is 2.0 (range: 1.0 to 12.0).
  • decay: Sets the decay time for the boosted bass, which can make the bass sound longer or more sustained. The default value is 0.0 (range: 0.0 to 1.0).
  • feedback: Adjusts the feedback level of the low-frequency generator. The default value is 0.0 (range: 0.0 to 1.0).
  • cutoff: Determines the upper frequency limit (in Hz) for the sub-bass boost. Frequencies below this limit will be amplified. The default is 80 Hz (range: 50 to 900 Hz).
  • slope: Sets the filter slope for the cutoff frequency. The default is 0.5 (range: 0.1 to 1.0).

Practical Examples

To use this filter, apply the -af (audio filter) flag followed by asubboost and your desired parameters.

1. Default Subwoofer Boost

If you want to apply a standard bass boost using FFmpeg's default settings, run the following command:

ffmpeg -i input.mp3 -af asubboost output.mp3

2. Increasing the Bass Boost and Cutoff Frequency

If you want a more noticeable bass boost and want to capture slightly higher low-end frequencies, you can increase the boost and set the cutoff frequency to 120 Hz:

ffmpeg -i input.mp3 -af "asubboost=boost=4.0:cutoff=120" output.mp3

3. Creating a Sustained, Boomy Bass (Using Decay)

To make the bass rumble linger longer (ideal for electronic music or cinematic sound effects), increase the decay and feedback parameters:

ffmpeg -i input.wav -af "asubboost=boost=3.5:decay=0.4:feedback=0.2" output.wav

4. Adjusting Dry and Wet Mix

If the bass boost is too overwhelming, you can lower the wet (processed) signal while keeping the dry (original) signal at full volume:

ffmpeg -i input.m4a -af "asubboost=dry=1.0:wet=0.5:boost=5.0" output.m4a