Fast Gabor spectral transforms in Java. Using a JNI bridge with the gaborator C++ library.
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This library calculates fine grained constant-Q spectral representations of audio signals quickly from Java. The calculation of a Gabor transform is done by a C++ library named Gaborator. A Java native interface (JNI) bridge to the C++ Gaborator is provided here. A combination of Gaborator and a fast FFT library (such as pfft) allows fine grained constant-Q transforms at a rate of about 200 times real-time on moderate hardware. It can serve as a front-end for several audio processing or MIR applications.

For more information on the Gaborator C++ library by Andreas Gustafsson, please see the website or a talk by the author on the library called Exploring time-frequency space with the Gaborator

While the gaborator allows reversible transforms, only a forward transform (from time domain to the spectral domain) is currently supported from java.

A spectral visualization tool for sprectral information is part of this package. See below for a screenshot:


Getting started

Assuming Apache Ant, a c++ compiler and Java are correctly installed on your system the following set of commands should get you started:

cd gaborator #Go to the jni bridge director
make # compiles the JNI bridge, call make mac on Mac OS X
cd ../build # go to the java build directory
ant clean # Make sure no compiled files are remaining
ant # Compiles and  packages the library
cp ../gaborator/ . #Copy the jni bridge
java -Djava.library.path=. -jar JGaboratorBrowser.jar #Start the jar file making sure the JNI brige is in the java library path

To visualize a spectrogram drag and drop an audio file to the graph. The visualizer decodes and resamples encoded audio of almost any kind using ffmpeg. Make sure a recent version is available on your path. If not, install it using your packet manager for example apt-get install ffmpeg or brew install ffmpeg.

Folder structure

  • src contains the java source files
  • gaborator contains the c++ JNI bridge and a makefile
    • gaborator\gaborator-1.2 The gaborator C++ library, licensed under AGPL
    • gaborator\pfft the pfft C++ library, licensed under a BSD type license
  • build ant build files
  • lib a Java dependency: the TarsosDSP audio processing library.

Compilation on different platforms

For convenience and to ensure compatibility, both pfft and gaborator code is included in this repository. The pfft library has a BSD license while gaborator has an AGPL license.

On Linux the use of the pfft library is advised. Compilation of the JNI bride on a Linux system with a JDK installed and a correctly set JAVA_HOME can take the following form:

cc -c -O3 -ffast-math -fPIC pffft/pffft.c -o pffft/pffft.o
cc -c -O3 -ffast-math -fPIC -DFFTPACK_DOUBLE_PRECISION pffft/fftpack.c -o pffft/fftpack.o
c++ -std=c++11 -I"gaborator-1.2" -I"pffft" -I"$(JAVA_HOME)/include" -I"$(JAVA_HOME)/include/linux" -fPIC -shared -O3 -ffast-math -DGABORATOR_USE_PFFFT  -o pffft/pffft.o pffft/fftpack.o	

On Mac OS X the Apple's vDSP library can be used by defining GABORATOR_USE_VDSP and linking with the Accelerate framework. The following should suffice:

c++ -std=c++11 -I"gaborator-1.2"  -I"$(JAVA_HOME)/include" -I"$(JAVA_HOME)/include/mac" -O3 -ffast-math -DGABORATOR_USE_VDSP  -o  -framework Accelerate

Gabor transform from Java

The following code snippet shows how to calculate a spectral Gabor transform from Java. Remember to set your java.library.path to include the JNI library. For context of this code see the JGaboratorBrowser.

JGaborator zsazsa = new JGaborator(stepSize, sampleRate, bandsPerOctave, minFrequency,maxFrequency,refFrequency,resolution);
AudioDispatcher ad = AudioDispatcherFactory.fromPipe(path, sampleRate, stepSize, 0);
float[][] coefficients = zsazsa.getCoefficents()

## License
In the spirit of the packaged gaborator library this code is also licensed under an AGPL license.