How to Use FFmpeg asubboost Filter Cutoff and Decay

The asubboost filter in FFmpeg is a specialized audio filter used to boost subwoofer frequencies, giving your audio a richer, deeper bass response. This article provides a direct, step-by-step guide on how to configure the filter’s two essential parameters—cutoff frequency (cutoff) and decay (decay)—to fine-tune your audio’s low-end performance.

Understanding the Parameters

To configure the asubboost filter, you need to understand how the cutoff and decay parameters alter the sound:

• cutoff: This parameter sets the cutoff frequency in Hertz (Hz) for the subwoofer boost. Only frequencies below this threshold are targeted for amplification.
  • Default value: 80 Hz
  • Typical range: 50 to 200 Hz
• decay: This parameter controls the decay time of the sub-bass frequencies. It dictates how long the boosted bass sound lingers after the initial hit.
  • Default value: 0 (no added decay, resulting in a tighter sound)
  • Range: 0 to 1 (higher values create a longer, booming sustain)

Basic Command Syntax

The basic syntax for applying the asubboost filter with custom cutoff and decay values in FFmpeg is as follows:

ffmpeg -i input.mp3 -af "asubboost=cutoff=VALUE:decay=VALUE" output.mp3

Step-by-Step Configuration Examples

1. Creating a Tight, Punchy Bass (Low Decay)

If you want to boost only the ultra-low frequencies while keeping the bass hits fast and precise (ideal for kick drums in electronic music or rock), set a lower cutoff and keep the decay low:

ffmpeg -i input.wav -af "asubboost=cutoff=60:decay=0.1" output.wav

• Cutoff (60 Hz): Focuses the boost only on the deepest sub-bass range.
• Decay (0.1): Ensures the bass notes stop quickly without muddiness.

2. Creating a Heavy, Booming Bass (High Decay)

If you are working with cinematic audio or hip-hop tracks where you want a long, rumbling bass tail, increase both the cutoff limit and the decay:

ffmpeg -i input.wav -af "asubboost=cutoff=100:decay=0.6" output.wav

• Cutoff (100 Hz): Allows the boost to extend into the upper bass frequencies.
• Decay (0.6): Causes the sub-bass frequencies to ring out longer, creating a sustained “rumble” effect.

Combining with Other asubboost Parameters

For complete control, you can combine cutoff and decay with the dry/wet mix parameters of the filter:

• dry_gain: Volume of the original, unaltered audio (default is 1.0).
• wet_gain: Volume of the boosted sub-bass signal (default is 1.0).

To boost the bass heavily, keep the decay moderate, and blend it with the original track:

ffmpeg -i input.mp3 -af "asubboost=cutoff=90:decay=0.3:dry_gain=1.0:wet_gain=1.5" output.mp3