Rubber Band
===========
An audio time-stretching and pitch-shifting library and utility program.
Copyright 2007 Chris Cannam, cannam@all-day-breakfast.com.
Distributed under the GNU General Public License.
Rubber Band is a library and utility program that permits you to
change the tempo and pitch of an audio recording independently of one
another.
Attractive features
~~~~~~~~~~~~~~~~~~~
* High quality results suitable for musical use
Rubber Band is a phase-vocoder-based frequency domain time
stretcher with partial phase locking to peak frequencies and phase
resynchronisation at noisy transients. It is suitable for most
musical uses with its default settings, and has a range of options
for fine tuning.
* Real-time capable
In addition to the offline mode (for use in situations where all
audio data is available beforehand), Rubber Band supports a true
real-time, lock-free streaming mode, in which the time and pitch
scaling ratios may be dynamically adjusted during use.
* Sample-accurate duration adjustment
In offline mode, Rubber Band ensures that the output has exactly
the right number of samples for the given stretch ratio. (In
real-time mode Rubber Band aims to keep as closely as possible to
the exact ratio, although this depends on the audio material
itself.)
* Multiprocessor/multi-core support
Rubber Band's offline mode can take advantage of more than one
processor core if available, when processing data with two or more
audio channels.
* No job too big, or too small
Rubber Band is tuned so as to work well with the default settings
for any stretch ratio, from tiny deviations from the original
speed to very extreme stretches.
* Handy utilities included
The Rubber Band code includes a useful command-line time-stretch
and pitch shift utility (called simply rubberband), two LADSPA
pitch shifter plugins (Rubber Band Mono Pitch Shifter and Rubber
Band Stereo Pitch Shifter), and a Vamp audio analysis plugin which
may be used to inspect the stretch profile decisions Rubber Band
is taking.
* Free Software
Rubber Band is Free Software published under the GNU General
Public License.
Limitations
~~~~~~~~~~~
* Not especially fast
The algorithm used by Rubber Band is very processor intensive, and
Rubber Band is not the fastest implementation on earth.
* Not especially state of the art
Rubber Band employs well known algorithms which work well in many
situations, but it isn't "cutting edge" in any interesting sense.
* Relatively complex
While the fundamental algorithms in Rubber Band are not especially
complex, the implementation is complicated by the support for
multiple processing modes, exact sample precision, threading, and
other features that add to the flexibility of the API.
Compiling Rubber Band
---------------------
Rubber Band is supplied with build scripts that have been tested on
Linux platforms. It is also possible to build Rubber Band on other
platforms, including both POSIX platforms such as OS/X and non-POSIX
platforms such as Win32. There are some example Makefiles in the misc
directory, but if you're using a proprietary platform and you get
stuck I'm afraid you're on your own, unless you want to pay us...
To build Rubber Band you will also need libsndfile, libsamplerate,
FFTW3, the Vamp plugin SDK, the LADSPA plugin header, the pthread
library (except on Win32), and a C++ compiler. The code has been
tested with GCC 4.x and with the Intel C++ compiler.
Rubber Band comes with a simple autoconf script. Run
$ ./configure
$ make
to compile, and optionally
# make install
to install.
Using the Rubber Band utility
-----------------------------
The Rubber Band command-line utility builds as bin/rubberband. The
basic incantation is
$ rubberband -t <timeratio> -p <pitchratio> <infile.wav> <outfile.wav>
For example,
$ rubberband -t 1.5 -p 2.0 test.wav output.wav
stretches the file test.wav to 50% longer than its original duration,
shifts it up in pitch by one octave, and writes the output to output.wav.
Several further options are available: run "rubberband -h" for help.
In particular, different types of music may benefit from different
"crispness" options (-c <n> where <n> is from 0 to 5).
Using the Rubber Band library
-----------------------------
The Rubber Band library has a public API that consists of one C++
class, called RubberBandStretcher in the RubberBand namespace. You
should #include <rubberband/RubberBandStretcher.h> to use this class.
There is extensive documentation in the class header.
The source code for the command-line utility (src/main.cpp) provides a
good example of how to use Rubber Band in offline mode; the LADSPA
pitch shifter plugin (src/ladspa/RubberBandPitchShifter.cpp) may be
used as an example of Rubber Band in real-time mode.
IMPORTANT: Please ensure you have read and understood the licensing
terms for Rubber Band before using it in another application. This
library is provided under the GNU General Public License, which means
that any application that uses it must also be published under the GPL
or a compatible license (i.e. with its full source code also available
for modification and redistribution). See the file COPYING for more
details. Alternative commercial and proprietary licensing terms are
available; please contact the author if you are interested.
Paul Davis
c8cc2d1dd6