Load Custom EQ Curves with FFmpeg Firequalizer

This article explains how to load custom equalizer (EQ) response curves into FFmpeg using the firequalizer audio filter. You will learn the syntax required to define custom frequency response curves, how to format configuration files, and how to apply these EQ curves to your audio files using command-line examples.

The firequalizer filter is a frequency-domain equalizer that uses finite impulse response (FIR) filtering. Unlike standard equalizers with fixed bands, it allows you to define a highly customized, continuous frequency response curve.

Method 1: Specifying EQ Points Directly in the Command

The simplest way to load a custom curve is to define specific frequency-to-gain coordinate points directly in the FFmpeg command using the gain_entry parameter.

The syntax for an entry is entry(f, g), where f is the frequency in Hertz and g is the gain in decibels (dB).

Command Example:

ffmpeg -i input.mp3 -af "firequalizer=gain_entry='entry(0, -20); entry(100, 0); entry(1000, 3); entry(15000, -6)'" output.mp3

In this example: * 0 Hz (sub-bass/DC offset) is cut by -20 dB. * 100 Hz is set to 0 dB (neutral). * 1000 Hz (mid-range) is boosted by +3 dB. * 15000 Hz (high treble) is cut by -6 dB.

By default, FFmpeg uses cubic interpolation (gain='cubic(f)') to smoothly connect the points you define.

Method 2: Loading an EQ Curve from an External File

If you have a complex curve with many points, writing them directly in the command line can become impractical. You can save your EQ curve in a plain text file and load it using shell interpolation.

Step 1: Create the EQ Profile File

Create a text file named my_curve.txt and define your custom curve using entry(f, g) points separated by semicolons or newlines:

entry(0, -10);
entry(50, -5);
entry(100, 0);
entry(500, 1.5);
entry(1000, 3);
entry(4000, -2);
entry(16000, -5);
entry(20000, -12);

Step 2: Run FFmpeg to Load the File

Use your operating system’s command-line syntax to inject the contents of the text file into the gain_entry parameter.

For Linux and macOS (Bash/Zsh):

ffmpeg -i input.wav -af "firequalizer=gain_entry='$(cat my_curve.txt)'" output.wav

For Windows (PowerShell):

ffmpeg -i input.wav -af "firequalizer=gain_entry='$(Get-Content my_curve.txt -Raw)'" output.wav

Advanced Interpolation and Custom Functions

The firequalizer filter uses the gain parameter to determine how the curve is drawn between your specified points. You can change this behavior by altering the mathematical evaluation method: