commit 246fa6062f2ae4384eef52d1c8d00d58d7f00a75
parent 4a3f7d9a13b6de460c49f9eb5de0bde42e5a4767
Author: Friedolino <mkirchn@freenet.de>
Date: Wed, 9 Jun 2021 23:32:05 +0200
fix instability at maximum fcutoff in moog filter
Diffstat:
2 files changed, 14 insertions(+), 11 deletions(-)
diff --git a/src/DSP/MoogFilter.cpp b/src/DSP/MoogFilter.cpp
@@ -28,13 +28,6 @@ MoogFilter::~MoogFilter(void)
}
-inline float MoogFilter::tan_2(const float x) const
-{
- //Pade approximation tan(x) hand tuned to map fCutoff
- float x2 = x*x;
- return ((9.54f*x*((11.08f - x2)))/(105.0f - x2*(45.0f + x2)));
-}
-
inline float MoogFilter::tanhX(const float x) const
{
// Pade approximation of tanh(x) bound to [-1 .. +1]
@@ -48,7 +41,8 @@ inline float MoogFilter::tanhXdivX(float x) const
{
// Pade approximation for tanh(x)/x used in filter stages
float x2 = x*x;
- return ((15.0+x2)/(15.0+6.0*x2));
+ //~ return ((15.0+x2)/(15.0+6.0*x2)); // more accurate but instable at high frequencies
+ return (1.0f-(0.35f*x2)+(0.1f*x2*x2));
}
inline float MoogFilter::step(float input)
@@ -123,12 +117,20 @@ void MoogFilter::setfreq_and_q(float frequency, float q_)
setq(q_);
}
+inline float MoogFilter::tan_2(const float x) const
+{
+ //Pade approximation tan(x) hand tuned to map fCutoff
+ float x2 = x*x;
+ //~ return ((9.54f*x*((11.08f - x2)))/(105.0f - x2*(45.0f + x2)));
+ return (x+0.15f*x2+0.3f*x2*x2);
+}
+
void MoogFilter::setfreq(float ff)
{
- // limit cutoff to prevent overflow
- ff = limit(ff,0.0002f,0.48f);
// pre warp cutoff to map to reality
- c = tan_2(PI * ff);
+ c = tan_2(PI * ff);
+ // limit cutoff to prevent overflow
+ c = limit(c,0.0006f,1.5f);
// pre calculate some stuff outside the hot zone
ct2 = c * 2.0f;
cp2 = c * c;
diff --git a/src/globals.h b/src/globals.h
@@ -179,6 +179,7 @@ typedef std::complex<fftw_real> fft_t;
#define LOG_2 0.693147181f
#define PI 3.1415926536f
+#define PIDIV2 1.5707963268f
#define LOG_10 2.302585093f
/*
