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/************************************************************************************
*
* Wavechild670 v0.1
*
* tubemodel.h
*
* By Peter Raffensperger 10 July 2012
*
* Reference:
* Toward a Wave Digital Filter Model of the Fairchild 670 Limiter, Raffensperger, P. A., (2012).
* Proc. of the 15th International Conference on Digital Audio Effects (DAFx-12),
* York, UK, September 17-21, 2012.
*
* Note:
* Fairchild (R) a registered trademark of Avid Technology, Inc., which is in no way associated or
* affiliated with the author.
*
* License:
* Wavechild670 is licensed under the GNU GPL v2 license. If you use this
* software in an academic context, we would appreciate it if you referenced the original
* paper.
*
************************************************************************************/
#ifndef TUBEMODEL_H
#define TUBEMODEL_H
#include "glue.h"
class TriodeModel {
public:
TriodeModel() {}
virtual ~TriodeModel() {}
virtual Real getIa(Real, Real) {
return 0.0;
}
virtual Real getIg(Real, Real) {
return 0.0;
}
virtual TriodeModel* clone() const { return new TriodeModel(*this); }
private:
TriodeModel(const TriodeModel&) { }
};
class TriodeRemoteCutoff6386 : public TriodeModel {
public:
TriodeRemoteCutoff6386() : VgkLast(1.0), numeratorLast(0.0) { }
virtual ~TriodeRemoteCutoff6386() { }
virtual Real getIa(Real Vgk, Real Vak){
if (Vak < 0.0) {
Vak = 0.0;
}
if (Vgk > 0.0) {
Vgk = 0.0;
}
Real p1 = 3.981e-8;
Real p2 = 2.383;
Real p3 = 0.5;
Real p4 = 0.1;
Real p5 = 1.8;
Real p6 = 0.5;
Real p7 = -0.03922;
Real p8 = 0.2;
Real iakAlt = p1*pow(Vak, p2) / (pow((p3-p4*Vgk), p5)*(p6+exp(p7*Vak-p8*Vgk)));
return iakAlt;
}
virtual TriodeModel* clone() const { return new TriodeRemoteCutoff6386(*this); }
private:
TriodeRemoteCutoff6386(const TriodeRemoteCutoff6386& other) {
VgkLast = other.VgkLast;
numeratorLast = other.numeratorLast;
}
protected:
static inline Real getA(Real Vak){
return aa*pow(Vak, ab);
}
static inline Real getF(Real Vak){
return fa*Vak;
}
protected:
Real VgkLast;
Real numeratorLast;
static const Real fa;
static const Real aa;
static const Real ab;
static const Real e;
static const Real d;
static const Real c;
static const Real g;
static const Real h;
};
class WDFTubeInterface {
public:
WDFTubeInterface() { model = NULL; }
WDFTubeInterface(TriodeModel *model_, Real numParallelInstances_=3.0) : model(model_),
numParallelInstances(numParallelInstances_) {
a = 0.0;
Vgk = 0.0;
Iak = 0.0;
VakGuess = 100.0;
}
~WDFTubeInterface() { delete model; }
WDFTubeInterface(WDFTubeInterface& other) {
model = other.model->clone();
numParallelInstances = other.numParallelInstances;
a = other.a;
Vgk = other.Vgk;
Iak = other.Iak;
VakGuess = other.VakGuess;
}
Real getB(Real a_, Real r0_, Real Vgate, Real Vk){
Assert(model);
/*
Reference:
"Wave Digital Simulation of a Vacuum-Tube Amplifier"
By M. Karjalainen and J. Pakarinen, ICASSP 2006
Vak + R0*f(Vgk, Vak) - a = 0 #[Karjalainen and Pakarinen, eq 7]
b = Vak - Ro*f(Vgk, Vak) #[Karjalainen and Pakarinen, eq 8]
*/
r0 = r0_;
a = a_;
Vgk = Vgate - Vk;
Real Vak = VakGuess;
uint iteration = 0;
Real err = 1e6;
Iak = 0.0;
while (fabs(err)/fabs(Vak) > 1e-9){
VakGuess = iterateNewtonRaphson(Vak);
err = Vak - VakGuess;
Vak = VakGuess;
if (iteration > 100){
break;
}
++iteration;
}
Real b = Vak - r0*Iak;
/*
a = v + Ri
b = v - Ri
v = a + b
*/
return b;
}
protected:
Real evaluateImplicitEquation(Real Vak){
Assert(!isnan(Vak));
Assert(!isnan(Vgk));
Iak = model->getIa(Vgk, Vak) * numParallelInstances;
Assert(!isnan(Iak));
return Vak + r0*Iak - a;
}
Real iterateNewtonRaphson(Real x, Real dxFactor=1e-6);
Real numParallelInstances;
Real r0;
Real a;
Real Vgk;
Real Iak;
Real VakGuess;
TriodeModel *model;
};
#endif
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