SimpString.cpp

/******************************************/  
/* Simplified string model                */
/* Compatible with STK version 4.2.1.     */
/* Julius Smith, 2000-2005                */
/******************************************/

#include "SimpString.h"
#include <iostream>
using namespace std;

SimpString :: SimpString(StkFloat lowestFreq)
{
  length = (long) (SRATE / lowestFreq + 1);
  lastLength = length;
  lastFreq = lowestFreq;
  loopGain = (StkFloat) 0.999;
  delayLine = new DelayA(length,length);
  combDelay = new Delay(length,length);
  pluckAmp = (StkFloat) 0.3;
  pluckPos = (StkFloat) 0.25;
  combDelay->setDelay((int) (pluckPos * lastLength + 0.5));

  loopFilter = new Filter;
  StkFloat bCoeffs[3] = {0.25,0.5,0.25}; 
  std::vector<StkFloat> b(bCoeffs, bCoeffs+3); 
  loopFilter->setNumerator(b);
}

SimpString :: ~SimpString()
{
  delete delayLine;
  delete combDelay;
  delete loopFilter;
}

void SimpString :: clear()
{
  delayLine->clear();
  combDelay->clear();
  loopFilter->clear();
}

void SimpString :: setFreq(StkFloat frequency)
{
  StkFloat loopFilterDelay = 0.5; /* just a guess */
  lastFreq = frequency;
  lastLength = ((StkFloat) SRATE / lastFreq); /* length - delays */
  delayLine->setDelay(lastLength - loopFilterDelay);
}

void SimpString :: setPluckPos(StkFloat position)
{ /* Set Pick Position  */
  pluckPos = position;
  combDelay->setDelay((int) (pluckPos * lastLength + 0.5));
}

void SimpString :: noteOff(StkFloat amp)
{
  loopGain = (StkFloat) (1.0 - amp) * 0.5; // Accelerate decay
#if defined(_debug_)        
  printf("SimpString : NoteOff: Amp=%lf\n",amp);
#endif    
}

void SimpString :: pluck(StkFloat amplitude)
{
  pluckAmp = amplitude; /* actual excitation is by tick(input) */
}

void SimpString :: pluck(StkFloat amplitude, StkFloat position)
{ 
  pluckPos = ((position<0) ? 0.0 : ((position>1) ? 1.0 : position));
  combDelay->setDelay((int) (pluckPos * lastLength + 0.5)); 
  this->pluck(amplitude);
}

void SimpString :: noteOn(StkFloat freq, StkFloat amp)
{
  this->setFreq(freq);
  this->pluck(amp);
#if defined(_debug_)        
  printf("SimpString : NoteOn: Freq=%lf Amp=%lf\n",freq,amp);
#endif    
}

void SimpString :: noteOn(StkFloat freq, StkFloat amp, StkFloat position)
{
  this->setFreq(freq);
  this->pluck(amp,position);
#if defined(_debug_)        
  printf("SimpString : NoteOn: Freq=%lf Amp=%lf Pos=%lf\n",
         freq,amp,position);
#endif    
}

StkFloat SimpString :: computeSample(StkFloat stringInput)
{
  /* pluck-position comb filtering: */
  stringInput -= combDelay->tick(stringInput);
  lastOutput_ = delayLine->tick(loopFilter->tick( stringInput 
                                                 + (delayLine->lastOut() 
                                                    * loopGain)));   
  return lastOutput_;
}

StkFloat SimpString :: tick(StkFloat stringInput)
{
  return computeSample(stringInput);
}

StkFloat SimpString :: computeSample(void)
{
  return this->tick(0);
}

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written by Julius Orion Smith III
Julius Smith's background is in electrical engineering (BS Rice 1975, PhD Stanford 1983). He is presently Professor of Music and Associate Professor (by courtesy) of Electrical Engineering at Stanford's Center for Computer Research in Music and Acoustics (CCRMA), teaching courses and pursuing research related to signal processing applied to music and audio systems. See http://ccrma.stanford.edu/~jos/ for details.