krajeski_flt.h

#pragma once

#ifndef KRAJESKI_LADDER_H
#define KRAJESKI_LADDER_H



/*
This class implements Tim Stilson's MoogVCF filter
using 'compromise' poles at z = -0.3

Several improments are built in, such as corrections
for cutoff and resonance parameters, removal of the
necessity of the separation table, audio rate update
of cutoff and resonance and a smoothly saturating
tanh() function, clamping output and creating inherent
nonlinearities.

This code is Unlicensed (i.e. public domain); in an email exchange on
4.21.2018 Aaron Krajeski stated: "That work is under no copyright. 
You may use it however you might like."

Source: http://song-swap.com/MUMT618/aaron/Presentation/demo.html
*/

class KrajeskiMoog 
{
	
public:
  KrajeskiMoog() {}
  KrajeskiMoog(float sampleRate)  
	{
		
    
	  for (int i = 0; i < 5; i++) {
	    state[i] = delay[i] = 0;  
	  }
		
		gComp = 1.0;
		
    SetDrive(0.0f);
		SetCutoff(1000.0f);
		SetResonance(0.1f);
	}
 
	
	virtual ~KrajeskiMoog() { }
	
	inline float Process(float sample) ;
	
 	inline void Init(float samplerate) {
    gComp = 1.0;
    sampleRate = samplerate;
    
    SetDrive(0.0f);
    SetCutoff(1000.0f);
    SetResonance(0.1f);
	}
  
  inline void SetResonance(float r) 
	{
		resonance = r*1.3f;
		gRes = (float)( resonance * (1.0029f + 0.0526f * wc - 0.926f * wc*wc + 0.0218f * wc*wc*wc));
	}
	
	virtual void SetCutoff(float c) 
	{
		cutoff = c;
		wc = (float)(TWOPI * cutoff * DIV_SAMPLE_RATE);
		g = (float)(0.9892f * wc - 0.4342f * wc*wc + 0.1381f * wc*wc*wc - 0.0202f * wc*wc*wc*wc);
	}

  inline void SetDrive(float dr) {
    drive = dr * 2.0f + 1.0f;  
  }
private:
	// volatile is a workaround because of random NANs during Process()???
  float state[5];
  float delay[5];
	float wc; // The angular frequency of the cutoff.
	float g; // A derived parameter for the cutoff frequency
	float gRes; // A similar derived parameter for resonance.
	float gComp; // Compensation factor.
	float drive; // A parameter that controls intensity of nonlinearities.
	float sampleRate, cutoff, resonance;
 

};
#endif