CS411X - Lecture 4

Lecture Topic:

• Digital Signal Processing in Java
• What is DSP ?
• Why do we need it ?
• How do we do it ?
• Sample Quiz

<DT>
 

Conversion of a continuous signal into a quantized sample data stream.

Conversion of sampled voltage into digital values.

DSP is a kind of data processing which operates on digitized signals.

1-D DSP Sound and Noise processing V(X)

2-D DSP Image processing I(X,Y)

3-D DSP Image Sequence processing I(X,Y,K)

4-D DSP Range Image Sequence processing I(X,Y,Z,K)

currently does not support 1-D DSP. well... especially Sound processing

1-D DSP addresses any signal stream

How do we do it?

• Java support the playing of sound files
• These techniques extends to other Data Domains
• we can hear the results
• It is fun !

• Reading
• Playing
• Graphing

Reading Audio files in Java :

AudioFrame.java

import java.awt.*;
import java.io.*;
import sun.audio.*;
import java.applet.*;
        
public class AudioFrame extends Frame {
 
    private    Panel readoutPanel = new Panel();
 
     private     AudioStream audioStream;
     private            AudioDataStream audioDataStream;
 
    private       byte ulawData[] = null;
    private     double doubleData[] = null;
 
    AudioPlayer audioPlayer = AudioPlayer.player;
    private     String fileName;
    
    private     ObservableInt endPositionOfSamplesToGraph;
    private     ObservableInt startPositionOfSamplesToGraph;
    private final double pi_2 = Math.PI * 2;
    private    final double pi = Math.PI;
    private final double samplingRate = 8000.0;
    private final double frequency = 440.0;
    
    private Scrollbar horizontalScrollbar;
    Menu m = new Menu("Audio Menu");
    
    MenuItem openAu_mi        = addItem("[o] Open Au");
    MenuItem graph_mi        = addItem("[u] ulaw graph ");
    MenuItem graphSound_mi   = addItem("[g] graph sound");
    MenuItem decodeUlaw_mi   = addItem("[d] decode ulaw ");
 

.....
.....

public AudioFrame() {
        // openAudioStream will set the fileName 
        // and audioStream variables.           
        openAudioStream();
        
        // Init_menu requires that the fileName be set
        // for the frame title. 
        init_menu();
        endPositionOfSamplesToGraph = 
            new ObservableInt(audioStream.getLength());
        startPositionOfSamplesToGraph = 
            new ObservableInt(0);
            
        buildReadoutPanel();
        
    }
    public void openAudioStream() {
    fileName = futil.openFile();
    
    try {         
          audioStream = new AudioStream(new FileInputStream(fileName));
          if ( audioStream.getLength() < 1 ) {
            System.err.println("AudioFrame: Length negative");
            return;
                }
          ulawData = new byte[audioStream.getLength()];
          audioStream.read(ulawData, 0, audioStream.getLength()-1);
          }
    catch (IOException ioe)
      {System.err.println(ioe);}
    doubleData = Audio.decodeUlaw(ulawData); 
 
    play();
  }

called ulaw.

sampled logarithmicallly encoded.
Voice Grade Audio

The audio file can be stored in an array of doubles E [0..1]

Playing the Audio :

    public void play() {
        audioPlayer.start(new AudioDataStream(new AudioData(ulawData)));
        waitTillDone();
    }

Graphing the Audio :

The Audio data you read is ulaw format.

The graph of ulaw data is not meaningful !

so graph linear data ( ie decode ulaw first ! )

     // Waveform display.
     public void paint(Graphics g) {
        doubleData = Audio.decodeUlaw(ulawData);
        int limit = doubleData.length;
        Dimension dim = this.size();
        int height = dim.height;
        int width = dim.width;
        update();    
        // just plot first 100 points
        // keep in mind that the origin is
        // in the upper left corner
        // and so y = height - y 
        // Are we having fun yet?
        if (limit > width) limit = width;
        
        int x = (width / horizontalScrollbar.getMaximum()) * 
                    horizontalScrollbar.getValue();
        int upper_limit = limit - horizontalScrollbar.getVisible();
        for (int i = 0 ; i < upper_limit ; i++) {
            g.drawLine(
                i, 
                (int)(height -(doubleData[x+i] * height/4+height/2)), 
 
                i + 1, 
 
                (int)(height -(doubleData[x+i+1] * height/4+height/2)));
        }
       }
 

Wavetable Generation :

N = #of samples
i = sample index

Sample Quiz

• 8bit - 4khz
• 8bit - 8khz
• 16bit - 16khz
• 32bit- 32 khz
   

Last Update: 04/09/97
Copyright © 1997- Douglas Lyon
Lyon@cse.bridgeport.edu