Perform Hamming window and FFT with Java

Question

Hi all,
I am trying to apply Hamming window on my lengthy sound data soundSample[1000] with window length 100. Then proceed with FFT.
And i found that java does have the package for Hamming window and FFT. As below,
http://code.compartmental.net/minim/javadoc/ddf/minim/analysis/FFT.html
http://marf.sourceforge.net/api/marf/math/Algorithms.Hamming.html
But i hardly find an example that illustrate how to use the package in a java program. So no idea how should i use the method in package.
Please advise and appreciate if reference is provided.
Thank you.

Answer 1

Hi,
I have spent sometimes to study and do the coding for FFT on audio samples.
My project is to study the FFT working by performing the FFT on audio sampled data.
After this is done, then only proceed to extract the pitch value in the audio data.
Below is the coding that i have done by referring to the provided steps:
In my main, i call this method and past the retrieved sampled sound data to this method.
public static void Analyze(int[] soundSample,float sample_rate ) {
        int N = (int)sample_rate/5;
        int Number_Sample = soundSample.length;
        Complex[] fftBuffer = new Complex [2*N];
        Complex[] fftResult = new Complex [2*N];
        Complex [] lastN = new Complex [N];   // The array to save the last N sample
        int delay = 0;
        double delta = 2*Math.PI/(2*N);
        // I have no idea how can i convert my sample array to double so that it will be in the range of [-1,+1]
        while(delay <=soundSample.length){
            //Extract the 2N sample for FFT analysis and convert the data to complex number.
            for (int z=0; z<2*N; z++){
                fftBuffer[z] = new Complex(soundSample[z+delay],0) ;                
            for (int i=N-1;i>=N/2; i-- ){
                lastN[N-1-i] = fftBuffer;
for (int z=0; z<2*N; z++){
fftBuffer[z] = fftBuffer[z].times(0.54-0.46*Math.cos(z*delta));
fftResult = FFT1.fft(fftBuffer);
delay = 2*N + delay;
1) I was trying to perform FFT with 2N samples then keep on looping the FFT method until 2N reaches the ends of sampled data.
But the FFT that i am working with is radix 2... It doesn't work with my 2N samples... Please teach me how should i work out FFT regardless the number of sample?
2) The hamming window coefficient i m using is based on http://www.mathworks.com/help/toolbox/signal/hamming.html . I am working on index [0:2N] ..
Is it appropriate?
3) According to your No1 steps, the acceptable frequency resolution is 5Hz. May i know what is this representing? And is it application for most of the FFT application? How can i determine the frequency resolution that i should used in my project?
Sorry for late reply as i was trying to work out the thing..
Hereby attach to your the my coding.. and hopes to have your guidance and tutorial how to extract the pitch for recording audio file with Java.
I have done the pitch extraction with MATLAB.. but Matlab as built-in FFT function... 
So i m now get stucked how to perform FFT on audio sound sample regardless the N value of sound sample for FFT buffer.
Many thanks for your former advise... and
Looking forward for your replies again.
Happy New Year 2011 :)
Edited by: 诸葛 on Dec 31, 2010 9:29 AM