Development [LWN.net]

Stretching and squishing audio files with rubberband

By Forrest Cook
March 18, 2009

The Rubber Band Library and the associated rubberband audio processing utility have been developed by Breakfast Quay, creators of the dssi-vst VST audio plugin adapter. The software is dual-licensed, with GPLv2-licensed source code and a commercially licensed edition. The Rubber Band description states:

Rubber Band Library is a high quality software library for audio time-stretching and pitch-shifting. It permits you to change the tempo and pitch of an audio recording or stream dynamically and independently of one another. Rubber Band Library is intended for use by developers creating their own application programs rather than directly by end users, although it does also include a simple command-line utility program of its own that you can use for simple adjustments to the speed and pitch of existing audio files.

The features document discusses the capabilities of the library in more detail and the Rubber Band Technical notes explains some of the underlying software methods:

Rubber Band Library is a block-based phase vocoder with phase resets on percussive transients, an adaptive stretch ratio between phase reset points, and a "lamination" method to improve vertical phase coherence. It is implemented in portable C++, and it requires separate library support for the FFT and resampling implementations: for the Free Software edition, this means FFTW and libsamplerate (the proprietary edition supports other options as well).

See the Rubber Band API documentation for more information on the library's components. Version 1.3 of Rubber Band Library was announced on March 16, 2009, no new features were added but a number of build and runtime bugs were fixed.

The source code for rubberband can be downloaded and built, or a pre-compiled executable is available for the curious (and trusting). The Usage document explains the various options available for rubberband. A simple example batch run such as: rubberband -T1.5 infile.wav outfile.wav takes infile.wav and produces outfile.wav with a tempo that's 1.5 times faster, but with the same pitch. There are a number of additional options that can be used to select the other types of audio conversions and to fine-tune the processing methods. For the curious, a number of example audio files are available for listening to.

A number of interesting uses for rubberband come to mind. The software could be used in radio production for making those annoying compressed legalese notices that show up at the end of pharmaceutical ads. It could be used to greatly speed up the time it takes to listen to audio books and podcasts, or the producers of those files could use it for compressing their sound files to reduce bandwidth usage. Recordings can be pitch-shifted to correct the speed problems that can be caused by older analog recording equipment. Those who are learning a new language could use the software to slow down the speed of the foreign speech. The software could be useful for producing musical sound effects or amusing answering machine messages.

Rubberband addresses a fairly narrow range of audio processing needs, but gives the user more control when compared to built-in pitch-shifting and/or tempo-shifting functions found in software such as the popular Audacity and Ardour audio editors. It makes a useful addition to a collection of open-source audio processing utilities.

Comments (11 posted)

System Applications

Database Software

PostgreSQL 2009-03-16 security update

Security updates dated 2009-03-16 for the PostgreSQL DBMS have been announced. "The PostgreSQL Project today released minor versions updating all active branches of the PostgreSQL object-relational database system, including versions 8.3.7, 8.2.13, 8.1.17, 8.0.21 and 7.4.25. This release fixes a denial of service issue with encoding conversion, and all users should update their installations at the next reasonable opportunity."