Configure FFmpeg Flanger Delay Feedback and LFO

This guide explains how to customize the flanger audio filter in FFmpeg by configuring its key parameters: delay, feedback, and LFO (Low-Frequency Oscillator) depth. You will learn the exact syntax, parameter definitions, and practical command-line examples to achieve the perfect sweeping flanger effect for your audio files.

Understanding the Flanger Parameters

The FFmpeg flanger filter accepts several options to shape the audio sweep. The specific parameters used to control delay, feedback, and LFO depth are defined as follows:

delay (Delay): Sets the base delay in milliseconds. This determines the starting point of the flanging effect. The allowed range is 0 to 30 ms, with a default of 0 ms.
regen (Feedback): Sets the regeneration (feedback) percentage. This dictates how much of the delayed signal is fed back into the filter. Higher values create a more intense, metallic, resonant sound. The allowed range is -95 to 95 percent, with a default of 12%.
depth (LFO Depth): Controls the sweep depth in milliseconds. This defines how far the LFO modulates the delay time away from the base delay setting. The allowed range is 0 to 10 ms, with a default of 0.9 ms.
speed (LFO Speed): While not explicitly requested, configuring depth often requires adjusting the LFO sweep speed. This is set in Hz. The allowed range is 0.1 to 10 Hz, with a default of 0.5 Hz.

Command Syntax

To apply these settings, use the -af (audio filter) flag in your FFmpeg command. The parameters are passed as key-value pairs separated by colons.

ffmpeg -i input.mp3 -af "flanger=delay=[value]:regen=[value]:depth=[value]" output.mp3

Practical Examples

1. Subtle, Spacey Flange To create a mild, slow-moving effect, keep the delay and feedback low, with a moderate sweep depth:

ffmpeg -i input.wav -af "flanger=delay=2:depth=1.5:regen=20:speed=0.25" output.wav

2. Intense, Jet-Plane Flange To achieve the classic dramatic “jet-plane” sweep, increase both the base delay, the feedback (regen), and the LFO sweep depth:

ffmpeg -i input.wav -af "flanger=delay=10:depth=8:regen=75:speed=0.5" output.wav

3. Vibrato/Chorusing Effect By setting a higher speed and moderate depth with low feedback, you can transition the flanger into a chorus-style effect:

ffmpeg -i input.wav -af "flanger=delay=5:depth=3:regen=10:speed=2.0" output.wav