How to Use the FFmpeg Phaser Filter

This article provides a quick, practical guide on how to use the phaser audio filter in FFmpeg to create a sweeping, spacey sound effect. You will learn the syntax of the filter, the meaning of its key parameters—such as delay, decay, and speed—and see real-world command examples to help you apply this classic effect to your audio and video files.

The phaser filter in FFmpeg simulates an analog phaser effect by splitting the audio signal, modulating the phase of one part using a Low-Frequency Oscillator (LFO), and mixing it back with the original input.

The Basic Syntax

To apply the phaser filter, use the audio filter flag (-af or -filter:a) followed by phaser and its parameters:

ffmpeg -i input.wav -af "phaser=parameter1:parameter2:..." output.wav

If you want to use the default settings, you can run the command with just the filter name:

ffmpeg -i input.wav -af phaser output.wav

Phaser Filter Parameters

You can customize the phaser effect by passing specific values in the following order, separated by colons:

phaser=in_gain:out_gain:delay:decay:speed:type

• in_gain: Sets the input gain (volume). The default value is 0.89.
• out_gain: Sets the output gain (volume). The default value is 0.74.
• delay: Sets the delay in milliseconds. The range is 0.0 to 5.0. The default is 3.0.
• decay: Sets the decay parameter (feedback), which controls how intense or “resonant” the sweep sounds. The range is 0.0 to 0.99. The default is 0.4.
• speed: Sets the modulation speed in Hertz (Hz) of the LFO sweep. The range is 0.1 to 2.0. The default is 0.5.
• type: Sets the modulation LFO wave type. You can choose either triangular (or t) or sinusoidal (or s). The default is triangular.

Practical Examples

1. Slow and Deep Phaser Effect To create a slow, dramatic sweep, lower the speed to 0.2 Hz and increase the decay to 0.6 using a sinusoidal wave:

ffmpeg -i input.mp3 -af "phaser=0.9:0.8:2.0:0.6:0.2:s" output.mp3

2. Fast, Shimmering Phaser Effect To achieve a fast, fluttering effect, increase the speed to 1.5 Hz and reduce the delay:

ffmpeg -i input.mp3 -af "phaser=0.8:0.74:1.0:0.5:1.5:t" output.mp3

3. Heavy Resonance Phaser Effect For a highly pronounced, metallic sweeping sound, push the decay close to its limit:

ffmpeg -i input.mp3 -af "phaser=0.89:0.74:4.0:0.9:0.4:t" output.mp3