BlitSaw.h

#ifndef STK_BLITSAW_H
#define STK_BLITSAW_H
 
#include "Generator.h"
#include <cmath>
#include <limits>
 
namespace stk {
 
/***************************************************/
/***************************************************/
 
class BlitSaw: public Generator
{
 public:
  BlitSaw( StkFloat frequency = 220.0 );
 
  ~BlitSaw();
 
  void reset();
 
  void setFrequency( StkFloat frequency );
 
 
  void setHarmonics( unsigned int nHarmonics = 0 );
 
  StkFloat lastOut( void ) const { return lastFrame_[0]; };
 
  StkFloat tick( void );
 
 
  StkFrames& tick( StkFrames& frames, unsigned int channel = 0 );
 
 protected:
 
  void updateHarmonics( void );
 
  unsigned int nHarmonics_;
  unsigned int m_;
  StkFloat rate_;
  StkFloat phase_;
  StkFloat p_;
  StkFloat C2_;
  StkFloat a_;
  StkFloat state_;
 
};
 
inline StkFloat BlitSaw :: tick( void )
{
  // The code below implements the BLIT algorithm of Stilson and
  // Smith, followed by a summation and filtering operation to produce
  // a sawtooth waveform.  After experimenting with various approaches
  // to calculate the average value of the BLIT over one period, I
  // found that an estimate of C2_ = 1.0 / period (in samples) worked
  // most consistently.  A "leaky integrator" is then applied to the
  // difference of the BLIT output and C2_. (GPS - 1 October 2005)
 
  // A fully  optimized version of this code would replace the two sin 
  // calls with a pair of fast sin oscillators, for which stable fast 
  // two-multiply algorithms are well known. In the spirit of STK,
  // which favors clarity over performance, the optimization has 
  // not been made here.
 
  // Avoid a divide by zero, or use of a denormalized divisor 
  // at the sinc peak, which has a limiting value of m_ / p_.
  StkFloat tmp, denominator = sin( phase_ );
  if ( fabs(denominator) <= std::numeric_limits<StkFloat>::epsilon() )
    tmp = a_;
  else {
    tmp =  sin( m_ * phase_ );
    tmp /= p_ * denominator;
  }
 
  tmp += state_ - C2_;
  state_ = tmp * 0.995;
 
  phase_ += rate_;
  if ( phase_ >= PI ) phase_ -= PI;
    
  lastFrame_[0] = tmp;
         return lastFrame_[0];
}
 
inline StkFrames& BlitSaw :: tick( StkFrames& frames, unsigned int channel )
{
#if defined(_STK_DEBUG_)
  if ( channel >= frames.channels() ) {
    oStream_ << "BlitSaw::tick(): channel and StkFrames arguments are incompatible!";
    handleError( StkError::FUNCTION_ARGUMENT );
  }
#endif
 
 
  StkFloat *samples = &frames[channel];
  unsigned int hop = frames.channels();
  for ( unsigned int i=0; i<frames.frames(); i++, samples += hop )
    *samples = BlitSaw::tick();
 
  return frames;
}
 
} // stk namespace
 
#endif