Android mic audio, not getting expected frequency

Question

I have a code which detects Android mic audio and calculates frequency. Though, the frequency what I'm getting is not the same as tested. E.g. sound 260Hz is outputted as 62Hz.
I have no clue why I'm not getting the expected frequency.
FFT I'm using is from the website http://jfftpack.sourceforge.net/
Please help me solve this problem.

/**
 * 
 * @reference 
 *            http://stackoverflow.com/questions/5511250/capturing-sound-for-
 *            analysis -and-visualizing-frequencies-in-android
 * 
 */
public class RecordAudio extends AsyncTask<Void, Double, Void> {

    @Override
    protected Void doInBackground(Void... arg0) {

        try {
            int bufferSize = AudioRecord.getMinBufferSize(sampleRate,
                    channelConfiguration, audioEncoding);

            AudioRecord audioRecord = new AudioRecord(
                    MediaRecorder.AudioSource.MIC, sampleRate,
                    channelConfiguration, audioEncoding, bufferSize);

            short[] buffer = new short[blockSize];
            double[] toTransform = new double[blockSize];

            audioRecord.startRecording();

            while (started) {
                double peakFreq = 0;
                int bufferReadResult = audioRecord.read(buffer, 0,
                        blockSize);
                int elementSize = blockSize / numSplit;
                double max = 0;

                for (int i = 0; i < blockSize && i < bufferReadResult; i++) {
                    toTransform[i] = (double) buffer[i] / 32768.0;
                }

                for (int i = 0; i < numSplit; i++) {
                    double[] chunk = new double[elementSize];

                    System.arraycopy(toTransform, i * elementSize, chunk,
                            0, elementSize);

                    HanningWindow(chunk, 0, chunk.length);

                    transformer.ft(chunk);

                    max = getMaxFrequency(chunk);

                    if (max > peakFreq)
                        peakFreq = max;
                }

                publishProgress(peakFreq);
            }

            audioRecord.stop();

        } catch (Throwable t) {
            t.printStackTrace();
            Log.e("AudioRecord", "Recording Failed");
        }
        return null;
    }

    @Override
    protected void onProgressUpdate(Double... frequency) {
        if (frequency[0] > 25d)
            textView.setText(Double.toString(frequency[0]));
    }

    private double getMaxFrequency(double[] fft) {
        int i, mgIndex = 0, size = fft.length / 2;
        double[] re = new double[size];
        double[] im = new double[size];
        double[] mg = new double[size];

        i = 0;
        re[i] = fft[i];
        im[i] = 0;
        mg[i] = Math.sqrt(re[i] * re[i]);

        for (i = 1; i < size - 1; i++) {
            // set real part
            re[i] = fft[i * 2 - 1];
            // set imaginary part
            im[i] = fft[i * 2 - 2];
            // Calculate magnitude
            mg[i] = Math.sqrt(re[i] * re[i] + im[i] * im[i]);
        }

        re[i] = fft[fft.length - 1];
        im[i] = 0;
        mg[i] = Math.sqrt(re[i] * re[i]);

        for (i = 1; i < mg.length; i++) {
            if (mg[i] > mg[mgIndex])
                mgIndex = i;
        }

        return mgIndex * sampleRate / blockSize;
    }

    /**
     * 
     * @reference 
     *            http://stackoverflow.com/questions/11600515/hanning-von-hann
     *            -window
     * @param signal_in
     * @param pos
     * @param size
     */
    public void HanningWindow(double[] signal_in, int pos, int size) {
        for (int i = pos; i < pos + size; i++) {
            int j = i - pos; // j = index into Hann window function
            signal_in[i] = signal_in[i] * 0.5
                    * (1.0 - Math.cos(2.0 * Math.PI * j / size));
        }
    }
}

Android mic audio, not getting expected frequency

0 Answers0