BlitSquare.h

#ifndef STK_BLITSQUARE_H
#define STK_BLITSQUARE_H
 
#include "Generator.h"
#include <cmath>
#include <limits>
 
namespace stk {
 
/***************************************************/
/***************************************************/
 
class BlitSquare: public Generator
{
 public:
  BlitSquare( StkFloat frequency = 220.0 );
 
  ~BlitSquare();
 
  void reset();
 
 
  void setPhase( StkFloat phase ) { phase_ = STK_PI * phase; };
 
 
  StkFloat getPhase() const { return phase_ / STK_PI; };
 
  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 a_;
  StkFloat lastBlitOutput_;
  StkFloat dcbState_;
};
 
inline StkFloat BlitSquare :: tick( void )
{
  StkFloat temp = lastBlitOutput_;
 
  // A fully  optimized version of this 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 denomralized divisor
  // at the sinc peak, which has a limiting value of 1.0.
  StkFloat denominator = sin( phase_ );
  if ( fabs( denominator )  < std::numeric_limits<StkFloat>::epsilon() ) {
    // Inexact comparison safely distinguishes betwen *close to zero*, and *close to PI*.
    if ( phase_ < 0.1f || phase_ > STK_TWO_PI - 0.1f )
      lastBlitOutput_ = a_;
    else
      lastBlitOutput_ = -a_;
  }
  else {
    lastBlitOutput_ =  sin( m_ * phase_ );
    lastBlitOutput_ /= p_ * denominator;
  }
 
  lastBlitOutput_ += temp;
 
  // Now apply DC blocker.
  lastFrame_[0] = lastBlitOutput_ - dcbState_ + 0.999 * lastFrame_[0];
  dcbState_ = lastBlitOutput_;
 
  phase_ += rate_;
  if ( phase_ >= STK_TWO_PI ) phase_ -= STK_TWO_PI;
 
         return lastFrame_[0];
}
 
inline StkFrames& BlitSquare :: tick( StkFrames& frames, unsigned int channel )
{
#if defined(_STK_DEBUG_)
  if ( channel >= frames.channels() ) {
    oStream_ << "BlitSquare::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 = BlitSquare::tick();
 
  return frames;
}
 
} // stk namespace
 
#endif