FFT library in android Sdk [closed]

Answer 1

Unfortunately the top answer only works for Array that its size is a power of 2, which is very limiting.

I used the Jtransforms library and it works perfectly, you can compare it to the function used by Matlab.

here is my code with comments referencing how matlab transforms any signal and gets the frequency amplitudes (https://la.mathworks.com/help/matlab/ref/fft.html)

first, add the following in the build.gradle (app)

implementation 'com.github.wendykierp:JTransforms:3.1'

and here it is the code for for transforming a simple sine wave, works like a charm

    double Fs = 8000;
    double T = 1/Fs;
    int L = 1600;

    double freq = 338;

    double sinValue_re_im[] = new double[L*2]; // because FFT takes an array where its positions alternate between real and imaginary
    for( int i = 0; i < L; i++)
    {
        sinValue_re_im[2*i] = Math.sin( 2*Math.PI*freq*(i * T) ); // real part
        sinValue_re_im[2*i+1] = 0; //imaginary part
    }

    // matlab
    // tf = fft(y1);

    DoubleFFT_1D fft = new DoubleFFT_1D(L);
    fft.complexForward(sinValue_re_im);
    double[] tf = sinValue_re_im.clone();

    // matlab
    // P2 = abs(tf/L);
    double[] P2 = new double[L];
    for(int i=0; i