Use FFmpeg Tremolo for Rapid Amplitude Modulation

This guide explains how to apply rapid amplitude modulation to audio tracks using FFmpeg's built-in tremolo audio filter. You will learn the underlying mechanics of the filter, its primary parameters, and practical command-line examples ranging from subtle, fast pulsations to extreme stutter effects.

The Tremolo Filter Syntax

The tremolo filter in FFmpeg modulates the volume of an audio signal using a low-frequency oscillator (LFO). The basic syntax within the audio filter graph (-af) is:

ffmpeg -i input.mp3 -af "tremolo=f=FREQUENCY:d=DEPTH" output.mp3

Key Parameters

The tremolo filter accepts two primary arguments:

  1. Frequency (f): Specifies the modulation speed in Hertz (Hz). The default value is 5.0. To achieve a rapid amplitude modulation, increase this value beyond the default. Standard rapid musical tremolo usually falls between 8.0 and 16.0 Hz.
  2. Depth (d): Specifies the modulation depth as a percentage between 0.0 and 1.0. The default is 0.5. A depth of 0.0 results in no modulation, while 1.0 causes the audio volume to drop to complete silence at the lowest point of each cycle.

Practical Examples

1. Fast, Pronounced Tremolo

To create a standard, rapid fluttering effect where the volume distinctly pulses 12 times per second:

ffmpeg -i input.wav -af "tremolo=f=12.0:d=0.8" output.wav

2. Rapid Chopping or Stutter Effect

For an aggressive, machine-like stutter where the sound rapidly cuts completely in and out at 16 Hz:

ffmpeg -i input.wav -af "tremolo=f=16.0:d=1.0" output.wav

3. Applying Tremolo to a Video's Audio Track

To apply rapid modulation to the audio of a video file while copying the video stream without re-encoding:

ffmpeg -i input.mp4 -c:v copy -af "tremolo=f=10.0:d=0.7" -c:a aac output.mp4

Frequency Threshold Considerations

While the frequency parameter supports values up to 20000.0 Hz, setting f above 20.0 Hz crosses from rhythmic amplitude modulation into the audible frequency spectrum. Frequencies above this threshold produce ring modulation effects—generating metallic, robotic sideband tones rather than discernible volume pulses. For pure amplitude flutter, keep the frequency between 8.0 and 20.0 Hz.