How to Use FFmpeg Lowpass Filter to Cut High Frequencies

This guide explains how to use the lowpass audio filter in FFmpeg to eliminate unwanted high-frequency sounds from your audio files. You will learn the basic command-line syntax, how to specify the cutoff frequency, and how to adjust the filter’s steepness to achieve cleaner audio results.

The lowpass filter in FFmpeg allows high frequencies to be attenuated (reduced in volume) while allowing frequencies below a certain cutoff point to pass through unchanged. This is highly useful for removing high-pitched hiss, wind noise, or sibilance from voice recordings and audio tracks.

Basic Syntax

To apply the lowpass filter, use the audio filter flag (-af or -filter:a) followed by the filter name and its parameters. The most important parameter is frequency (or simply f), which defines the cutoff frequency in Hertz (Hz).

Here is the basic command structure:

ffmpeg -i input.mp3 -af "lowpass=f=3000" output.mp3

In this example, FFmpeg will cut off frequencies above 3000 Hz (3 kHz) from the input file.

Key Parameters

You can customize the filter behavior using the following parameters:

• frequency (or f): Sets the cutoff frequency in Hz. Frequencies above this limit are attenuated. The default value is 3000 Hz.
• poles (or p): Controls the steepness of the filter roll-off. It must be an even integer between 2 and 48 (the default is 2). A higher number of poles results in a steeper cut above the cutoff frequency.
• width_type (or t): Defines the band-width unit.
• width (or w): Sets the band-width of the filter.

Practical Examples

1. Applying a Standard Lowpass Filter at 8 kHz

To preserve human speech while cutting out high-frequency background hiss, an 8000 Hz cutoff is often ideal:

ffmpeg -i interview.wav -af "lowpass=f=8000" cleaned_interview.wav

2. Using a Steeper Roll-Off (More Poles)

If you want a sharper, more aggressive cut at the cutoff point, increase the number of poles. This command cuts frequencies above 4000 Hz with a steep 4-pole filter:

ffmpeg -i audio.wav -af "lowpass=f=4000:p=4" output.wav

3. Processing Audio within a Video File

If you want to apply the filter to a video file without re-encoding the video stream, use the -c:v copy option to save time and preserve video quality:

ffmpeg -i input.mp4 -af "lowpass=f=5000" -c:v copy output.mp4