FFT library in android Sdk [closed]

Answer 1

Use this class (the one that EricLarch's answer is derived from).

Usage Notes

This function replaces your inputs arrays with the FFT output.

Input

• N = the number of data points (the size of your input array, must be a power of 2)
• X = the real part of your data to be transformed
• Y = the imaginary part of the data to be transformed

i.e. if your input is (1+8i, 2+3j, 7-i, -10-3i)

• N = 4
• X = (1, 2, 7, -10)
• Y = (8, 3, -1, -3)

Output

• X = the real part of the FFT output
• Y = the imaginary part of the FFT output

To get your classic FFT graph, you will want to calculate the magnitude of the real and imaginary parts.

Something like:

public double[] fftCalculator(double[] re, double[] im) {
    if (re.length != im.length) return null;
    FFT fft = new FFT(re.length);
    fft.fft(re, im);
    double[] fftMag = new double[re.length];
    for (int i = 0; i < re.length; i++) {
       fftMag[i] = Math.pow(re[i], 2) + Math.pow(im[i], 2);
    }
    return fftMag;
}

Also see this StackOverflow answer for how to get frequencies if your original input was magnitude vs. time.