How to Use FFmpeg Rubberband for Audio Pitch Shifting

This guide explains how to use the rubberband filter in FFmpeg to perform high-quality audio pitch shifting without changing the audio’s tempo. You will learn the basic command structure, how to calculate pitch shifts using semitones, and how to adjust pitch and tempo independently using the Rubber Band library integration.

Prerequisites

To use this filter, your FFmpeg build must be compiled with support for the Rubber Band library. You can verify this by running ffmpeg -filters in your terminal and checking if rubberband is listed. If it is missing, you must install the librubberband package and compile FFmpeg with the --enable-librubberband flag.

Basic Pitch Shifting Syntax

The rubberband filter uses a scale factor to shift the pitch. A value of 1.0 represents the original pitch.

To shift the pitch up or down, use the following syntax:

ffmpeg -i input.mp3 -af "rubberband=pitch=1.5" output.mp3

• pitch=1.5: Increases the pitch. A factor of 2.0 shifts the pitch up by one octave.
• pitch=0.5: Decreases the pitch. A factor of 0.5 shifts the pitch down by one octave.

Pitch Shifting by Semitones

Because the pitch parameter requires a multiplier rather than a semitone value, you must calculate the ratio. The formula to shift pitch by \(n\) semitones is:

\[\text{Pitch Factor} = 2^{(n/12)}\]

Here are the pitch factor values for common semitone shifts:

Example Command (+2 Semitones):

ffmpeg -i input.wav -af "rubberband=pitch=1.12246" output.wav

Adjusting Pitch and Tempo Independently

The primary benefit of the rubberband filter over options like atempo or asetrate is its ability to adjust pitch and tempo independently with minimal transients and phasing artifacts.

To speed up the audio while keeping the pitch higher, use both the pitch and tempo options:

ffmpeg -i input.mp3 -af "rubberband=pitch=1.2:tempo=1.5" output.mp3

To change only the tempo while preserving the original pitch, set pitch to 1.0 and adjust the tempo:

ffmpeg -i input.mp3 -af "rubberband=pitch=1.0:tempo=0.85" output.mp3