Android Open Source - APSK Spectrum Thread

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License

The source code is released under:

GNU General Public License

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Java Source Code

/*
 * This file is part of znudigi./*from  ww w .ja  v a  2  s  . c o  m*/
 * Released under GNU GENERAL PUBLIC LICENSE Version 2
 * See file COPYING.
 * Copyright (C) 2007-2008 Leigh L. Klotz, Jr. <Leigh@WA5ZNU.org>
 */

package org.wa5znu.znuradio.receiver;

import org.wa5znu.znuradio.dsp.Complex;
import org.wa5znu.znuradio.dsp.FFT;
import org.wa5znu.znuradio.dsp.Window;

public class SpectrumThread extends Thread
    implements WaveHandler
{

  double waveDataIn[]=null;
  int dataLengthIn=0;
  int dataFrameIn=0;
  double window[];
  SpectrumHandler spectrumHandler;
  private final Object lock = new Object();
  double alcMax = 3.0;
  double alcMin = -2.0;

  public SpectrumThread(SpectrumHandler spectrumHandler) {
    this.spectrumHandler = spectrumHandler;
  }

  public void run() {
    Complex x[]=null;
    double powerSpectrum[]=null;
    while(true) {
      int dataLength=0;
      int dataFrame=0;
      double waveData[]=null;
      synchronized(lock) {
  try {
    lock.wait();
    dataLength=dataLengthIn;
    dataFrame=dataFrameIn;
    waveData=waveDataIn;
  } catch(InterruptedException e) { }
      }

      if (waveData != null) {
  synchronized (lock) {
  // Set the window function and convolve the real signal with it
  // and produce a Complex signal with a zero imaginary component.
  if (window == null || window.length != dataLength) {
    window = new double[dataLength];
    Window.hammingWindow(window);
  }

  if (x==null || x.length != dataLength) {
    x = new Complex[dataLength];
  }

  for(int n = 0; n < dataLength; n++) {
    x[n] = new Complex(waveData[n] * window[n], 0.0);
  }

  // Perform the Complex FFT
  Complex X[] = FFT.fft(x);

  int outputLength = dataLength/2;

  // Calculate the log power spectrum of the Complex FFT
  if (powerSpectrum == null || powerSpectrum.length != outputLength) 
    powerSpectrum = new double[outputLength];

  for(int n = 0; n < outputLength; n++) {
    double d = X[n].norm();
    powerSpectrum[n] = (d == 0.0) ? alcMin : Math.log10(d)/2.0;
  }

  double max = alcMax;
  double min = alcMin;

  // Normalize spectrum to max-min and truncate to [0,1]
  max -= min;
  for(int n = 0; n < outputLength; n++) {
    powerSpectrum[n] -= min;
    powerSpectrum[n] /= max;
    if (powerSpectrum[n]<0) powerSpectrum[n]=0;
    else if (powerSpectrum[n]>1) powerSpectrum[n]=1;
  }

  // Dispatch spectrum data
  spectrumHandler.handleSpectrum(dataFrame, powerSpectrum, outputLength);
  }
      }
    }
  }

  // Accept the incoming data
  public void handleWave(int frame, double data[], int length) {
    // Just drop samples of the wave data if it's not ready.
    synchronized(lock) {
      waveDataIn = data;
    dataLengthIn = length;
    dataFrameIn = frame;
    lock.notifyAll();
    }
  }
}

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