How to Use the FFmpeg Bandpass Filter

This article provides a quick and practical guide on how to use the bandpass audio filter in FFmpeg. You will learn the basic syntax, key parameters such as center frequency and bandwidth, and see concrete command-line examples to isolate specific frequency ranges in your audio files.

Understanding the Bandpass Filter

A bandpass filter allows frequencies within a certain range to pass through while attenuating (quieting) frequencies below and above this range. This is highly useful for isolating specific sounds, such as human speech, or removing low-frequency rumbles and high-frequency hisses simultaneously.

Filter Parameters

The bandpass filter in FFmpeg uses three primary parameters to control the audio output:

• frequency (or f): The center frequency of the band in Hz. The default is 3000 Hz.
• width_type (or t): The unit used to define the bandwidth. Options include:
  • h: Hz (default)
  • q: Q-factor (higher Q means a narrower, sharper band)
  • o: Octaves
• width (or w): The width of the band. The default is 200 Hz.

Basic Syntax

The basic syntax for applying the bandpass filter using the -af (audio filter) flag is:

ffmpeg -i input.wav -af "bandpass=f=CENTER_FREQUENCY:w=BANDWIDTH" output.wav

Practical Examples

1. Isolate a Specific Frequency (Standard Hz Width)

To isolate a frequency range centered at 1000 Hz with a width of 200 Hz (allowing frequencies roughly between 900 Hz and 1100 Hz to pass), use the following command:

ffmpeg -i input.mp3 -af "bandpass=f=1000:w=200" output.mp3

2. Isolate Human Speech

Human speech generally falls between 300 Hz and 3400 Hz. To target this range, you can set the center frequency to 1850 Hz and the width to 3100 Hz:

ffmpeg -i interview.mp4 -af "bandpass=f=1850:w=3100" cleared_speech.mp4

3. Using Q-Factor for a Narrow Band

If you want a very sharp, narrow band around 2000 Hz, you can define the width using the Q-factor. A higher Q-factor results in a narrower filter:

ffmpeg -i input.wav -af "bandpass=f=2000:t=q:w=2.0" output.wav

4. Combining Bandpass with Other Filters

You can chain the bandpass filter with other audio filters, such as volume adjustment, by separating them with a comma:

ffmpeg -i input.wav -af "bandpass=f=1500:w=500,volume=1.5" output.wav