Open Source Commercial-Grade Time Stretching/Pitch Shifting Project
ClearScale is an open source GPL-based project to bring high quality
time stretching and pitch shifting to the Linux platform. The goal is
to create an open standard for a commercial grade algorithm that allows
changing the pitch and speed of music and sound independently of each
other. It should achieve this in an artifact-free, sonically pleasing
manner, comparable to commercial algorithms on the MacOS and Windows
platform available today.
The algorithm should work equally well with musically monophonic and
polyphonic material over a wide range of scaling ratios, and it should
encompass a way to compensate for the formant shifts ("Mickey-Mouse
effect") that occur during pitch shifting.
It is hoped that an open standard for such an immensely important
integral part of audio processing will make Linux-based audio
processing both easier and more popular. The algorithm should be
designed to serve as a quality reference for other algorithms in the
field, and a suite of audio files and test signals will be provided
with it to serve as a testbed for other future algorithm designs.
The project is initiated by Stephan M. Bernsee (formerly Stephan M.
Sprenger) who maintains a highly popular educational web site about
time stretching and pitch shifting and related topics at
http://www.dspdimension.com. He has authored several commercial
solutions on the MacOS and Windows platform and his papers and
algorithms are part of lectures on DSP at several universities and
The project has initially been funded by a private research grant and
its running costs will be financed through PayPal donations to its
maintainer. More information on its current status, design goals and a
FAQ can be found on the project web site, http://www.clearscale.org