STK Filters

• STK provides a variety of classes for digital filtering, all inheriting from the Filter abstract base class.

• The class Iir provides generalized infinite impulse response filtering functionality similar to that of the filter function in Matlab.

• The class Fir provides generalized finite impulse response filtering functionality and is slightly more efficient than using the Iir class when only a feedforward structure is needed.

• All filter classes in STK inherit from the Filter class, including Fir, Iir, OneZero, OnePole, PoleZero, TwoZero, TwoPole, BiQuad, Delay, ...

• The BiQuad class provides functionality for resonance filtering, as used below.

  #include "FileWvIn.h"
  #include "FileWvOut.h"
  #include "BiQuad.h"
  using namespace stk;
  
  int main( int argc, char *argv[] )
  {
    FileWvIn  input;
    FileWvOut output;
  
    if ( argc != 2 ) {
      std::cout << "usage: " << argv[0] << " file" << std::endl;
      std::cout << "    where 'file' is an input soundfile to process" << std::endl;
      exit(0);
    }
  
    try {
      // Load the input file
      input.openFile( argv[1] );
    }
    catch ( StkError & ) {
      exit(0);
    }
  
    // Set the global STK sample rate to the input file sample rate.
    Stk::setSampleRate( input.getFileRate() );
  
    // Reset the input file reader increment to 1.0
    input.setRate( 1.0 );
  
    try {
      // Define and open a 16-bit, one-channel WAV formatted output file
      output.openFile( "filter2", 2, FileWrite::FILE_AIF, Stk::STK_SINT16 );
    }
    catch ( StkError & ) {
      input.closeFile();
      exit(0);
    }
  
    BiQuad filter;
    filter.setResonance( 1000.0, 0.999, true );  // set resonance to 1000 Hz, pole radius = 0.999, and normalize gain
    StkFrames frame( 1, 2 );                     // one frame of 2 channels
  
    int i;
    i = input.getSize();  // in sample frames
    while ( i-- >= 0 ) {
  
      try { // single frame computations
        frame[0] = input.tick();
        frame[1] = filter.tick( frame[0] );
        output.tick( frame );
      }
      catch ( StkError & ) {
        goto cleanup;
      }
    }
  
   cleanup:
    input.closeFile();
    output.closeFile();
  
    return 0;
  }