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FFT Java

I used this tutorial that uses DFT http://jvalentino2.tripod.com/dft/index.html but the algorithm is too slow. Does anyone knows any similar tutorials explaining step by step of trasnforming audio into frequency domain using FFT? I wanted to use jtransforms library http://sites.google.com/site/piotrwendykier/software/jtransforms but can't find any examples how to use it. What method use, what input does it take? It is not specified. Anybody can help me with that?
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chudyksg
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chudyksg
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1 Solution
 
garypfirstechCommented:
I am no expert on this stuff but since no one else has answered, I'll give it a shot.

Try this (I haven't tested it but it should be close):

First, change "int x[] = new int[n];" to "double x[] = new double[n];"

Then, replace the last box with the following:
DoubleFFT_1D f = new DoubleFFT_1D(n/2);
f.realForwardFull(x);
for (int j = 0; j < n; j += 2) {
	double amplitude = 2 * x[j]/n;
	double frequency =(j/2) * h / T * sample_rate;
	System.out.println("frequency = "+frequency+", amp = "+amplitude);
}

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Be sure to check these results against your existing algorithm to determine if this method is correct.

Also, since the transform only uses the first half of x, you can save time in the loop populating x by changing "for (int i = 0; i < n*2; i+=2) {" to "for (int i = 0; i < n; i+=2) {".  There's no sense populating values that you're not using.
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Jose ParrotGraphics ExpertCommented:
There is a complete package, including Java source code at
http://sites.google.com/site/piotrwendykier/software/jtransforms

It covers 1D, 2D and 3D. You should select what algorithm is the right for your needs, but most common is DFT.  The author claims it as the fastest FFT around and a benchmark is shown, to compare it against other packages.

It was developed in Unix environment, but compiles without problems in Windows or Linux, providing the right Java libraries.

Jose
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Jose ParrotGraphics ExpertCommented:
oops, sent uncompleted answer...

Please note that you should select if you need 1D, 2D or 3D functions.
Let use single precision (faster) if it is enough for your case. If you need the best precision, then use the doubleFFT functions. As noticed by garypfirstech about work with just half of the matrix, due its symmetry, this package has such approach too..

You must first create the instance, by calling FloatFFT_2D (or 1D or 3D).
Must populate the matrix, with random numbers by calling fillMatrix_2D or filling it by yourself.
Use showReal_2D to watch the results and
writeToFileReal_2D to save it.

If you have difficulty with this package, you can also try the fft pacjkage at sourceforge: http://sourceforge.net/projects/jfftpack/ , but the Piotr's one is faster.
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