Get frequency wav audio using FFT and Complex class

Question

It\'s been asked a lot, but I still stuck about implement FFT class on Android I need to process my audio data using FFT...

I already read the almost same question h

Answer 1

I already found the answer... :)

I create method to calculate array value from audio...

public double[] calculateFFT(byte[] signal)
    {           
        final int mNumberOfFFTPoints =1024;
        double mMaxFFTSample;

        double temp;
        Complex[] y;
        Complex[] complexSignal = new Complex[mNumberOfFFTPoints];
        double[] absSignal = new double[mNumberOfFFTPoints/2];

        for(int i = 0; i < mNumberOfFFTPoints; i++){
            temp = (double)((signal[2*i] & 0xFF) | (signal[2*i+1] << 8)) / 32768.0F;
            complexSignal[i] = new Complex(temp,0.0);
        }

        y = FFT.fft(complexSignal); // --> Here I use FFT class

        mMaxFFTSample = 0.0;
        mPeakPos = 0;
        for(int i = 0; i < (mNumberOfFFTPoints/2); i++)
        {
             absSignal[i] = Math.sqrt(Math.pow(y[i].re(), 2) + Math.pow(y[i].im(), 2));
             if(absSignal[i] > mMaxFFTSample)
             {
                 mMaxFFTSample = absSignal[i];
                 mPeakPos = i;
             } 
        }

        return absSignal;

    }

Then I called it in class Write Audio..

private void writeAudioDataToFile(){

        byte data[] = new byte[bufferSize];
        String filename = getTempFilename();
       FileOutputStream os = null;

        try {
                os = new FileOutputStream(filename);
        } catch (FileNotFoundException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
        }

        int read = 0;                
        if(null != os){
                while(isRecording){
                        read = recorder.read(data, 0, bufferSize);
                        if(read > 0){
                            absNormalizedSignal = calculateFFT(data); // --> HERE ^__^
                        }

                        if(AudioRecord.ERROR_INVALID_OPERATION != read){
                                try {
                                        os.write(data);
                                } catch (IOException e) {
                                        e.printStackTrace();
                                }
                        }
                }

                try {
                        os.close();
                } catch (IOException e) {
                        e.printStackTrace();
                }
        }
}

Answer 2

It sounds like your immediate problem is "N is not a power of 2." In this case, N is probably referring to the size of the data you are putting into your FFT. Most FFT algorithms only work on blocks of data that have a size that is a power of 2.

Are you trying to put the entire file into an FFT at once? If so, you may need to read more background material to understand what you are doing. Maybe start here: http://blog.bjornroche.com/2012/07/frequency-detection-using-fft-aka-pitch.html