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    kernowpete
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  • FIR Band Pass filtering in processing
    Hi and thanks,

    I am a DSP beginner, so this question will be reflective of that.

    I am trying to work my way through the implementation of band pass filtering with convolution.

    My question is this. 

    I have gone through the process of using AudioPlayer to import a wav file, do FFT of this and use the sinc(PI*x/PI*x) function to create a filter fft.

    with these I can point wise multiply the FFT of the input with the filter FFT and get a resultant FFT, this is then Inverse FFT'd and the resulting array should contained the filter data?

    Is there a set way to take an Array of floats and make them into an Audio output. So rather than data it comes full circle back to outputting a time based buffer that minim can play back as a filtered version of the original?

    I have definatly got the FFT drawing out, I am wary of my sinc() function as when i draw this it doesnt seem to be what I expected.

    Any pointer would be appreciated, or even just some suggested Tutorial. I am at college and I have to implement the process, rather than use minim's own band pass. 

    Here is my dodgy code.

    import ddf.minim.analysis.*;
    import ddf.minim.*;
    import ddf.minim.AudioSnippet;

    Minim minim;
    AudioPlayer jingle;
    FFT fftAudioLeft, fftAudioRight, filterfft, fftResultLeft;
    float[] filterData, resultLeft, resultFilter, finalArray, filtered;
    int mySize;
    float sampRate;
    AudioSnippet[] sample = new AudioSnippet[mySize];

    void setup() { 
      minim = new Minim(this);
      jingle = minim.loadFile("nuecut.wav", 2048);
      jingle.loop();
      mySize = jingle.bufferSize();
      sampRate = jingle.sampleRate();
      fftAudioLeft = new FFT(mySize, sampRate);
      fftAudioRight = new FFT(mySize, sampRate);
      fftResultLeft = new FFT(mySize, sampRate);
      filterData = new float[mySize];
      resultLeft = new float[mySize];
      resultFilter = new float[mySize];
      filtered = new float[mySize];
      finalArray = new float[mySize];
      size(fftAudioLeft.specSize(), 200, P3D);
      textMode(SCREEN);
      for (int i = 0; i<mySize;i++) {

        filterData[i] = sinc(i);
      }
      filterfft =new FFT(mySize, mySize);
    }

    void draw()
    {
      background(0);
      stroke(255);
      float[] left = jingle.left.toArray();
      float[] right = jingle.right.toArray();
      fftAudioLeft.forward(left);
      fftAudioRight.forward(right);
      filterfft.forward(filterData);

      for (int i = 0;i<mySize;i++) {

        resultLeft[i] = fftAudioLeft.getFreq(i);
        resultFilter[i] = filterfft.getFreq(i);

        finalArray[i] = resultLeft[i]*resultFilter[i];
      }
      fftResultLeft.inverse(finalArray);

      for ( int i = 0;i<mySize;i++) {

        filtered[i] = fftResultLeft.getFreq(i);
      }

      for (int i = 0; i < fftAudioLeft.specSize(); i++)
      {
        stroke(125, 125, 125, 100);
        line(i, height, i, height - fftAudioLeft.getBand(i)*4);
      }
      for ( int i = 0; i < left.length - 1; i++ )
      {
        float x1 = map(i, 0, jingle.bufferSize(), 0, width);
        float x2 = map(i+1, 0, jingle.bufferSize(), 0, width);
        // we multiply the values returned by get by 50 so we can see the waveform
        stroke(255, 0, 255, 60);
        line(x1, height/4 - left[i]*50, x2, height/4 - left[i+1]*50);
        line(x1, 3*height/4 - right[i]*50, x2, 3*height/4 - right[i+1]*50);
      }
    }

    float sinc(float x) { //Design the filter using the sinc(x) function.

      if (x == 0.f) {
        return 1.f;
      }

      return sin((PI*x)/PI*x);
    }

    void stop()
    {
      jingle.close();
      minim.stop();

      super.stop();
    }







  • Beginner question? Jbox2d. How do you texture/fill colour polygons/rect/circle?
    I am at college doing very basic stuff, currently experimenting with basic games.

    I was trying to use Jbox2d to structure all the gravity and collisions. As a beginner I had presumed that you would be able to texture/colour the objects like vertex shapes etc in processing? 

    Is it a much more complex process, to if you like, colour and texture for design and look over the gravity model?
    or is there a simple' ish way for a beginner to add colour and texture in the jbox2d scene?

    Thank you. 

    Pete.