revised svf.

src/filters/svf.c

@@ -14,48 +14,34 @@
 #include <math.h>
 #include <stdlib.h>
 #include <stdio.h>
+#ifndef M_PI
 #define M_PI   3.14159265358979323846
+#endif
 #define MAX(a,b) (a>b?a:b)
 #define MIN(a,b) (a<b?a:b)
 
-typedef enum DBO { _6dbo, _12dbo, _18dbo, _24dbo, _36dbo = 6, _48dbo } DBO;
 
 typedef struct SVF {
     float notch;
     float low;
     float high;
     float band;
-    float drive;
     float freq;
     float q;
-    DBO dbo;
     float out;
-    float(*damp)(struct SVF*);
     float(*process)(struct SVF*,float in);
     void(*reset)(struct SVF*);
 } SVF;
 
-
-float svf_damp(SVF *self) {
-    float freq = 2.0*sin(M_PI * MIN(0.25, self->freq/(44100*2)));
-    return MIN(2.0 * (1.0 - powf(self->q,0.25)), MIN(2.0, 2.0/freq - freq * 0.5));
-    // return MIN(2.0 * (1.0 - pow(self->q,0.25)), MIN(2.0, (2.0/freq - freq * 0.5)));
-
-}
 float svf_process(SVF *self,float in) {
     float a = in;
-    float freq = 2.0*sin(M_PI * MIN(0.25, self->freq/(44100*2)));
-    float damp = self->damp(self);
-    //printf("prefilt status: freq: %f, drive: %f, damp: %f, in: %f, low: %f, notch: %f, high: %f, band: %f\n",self->freq,self->drive, damp,in, self->low, self->notch, self->high, self->band);
-    for (unsigned int i = 0; i <= self->dbo; i++) {
-	self->notch = a - damp * self->band;
-	self->low   = self->low + freq * self->band;
-	self->high  = self->notch - self->low;
-	self->band  = freq * self->high + self->band - self->drive * self->band * self->band * self->band;
-	a = self->low;
-    }
+    float q = 1-self->q;
+    float freq = 2.0*sin(M_PI * MIN(0.25, self->freq/(44100)));
+    self->low = self->low + freq * self->band;
+    self->high = q * a - self->low - q * self->band;
+    self->band = freq * self->high + self->band;
+    self->notch = self->high + self->low;
     self->out = a;
-    //printf("postfilt status: freq: %f, drive: %f, damp: %f, in: %f, low: %f, notch: %f, high: %f, band: %f\n",self->freq,self->drive, damp,in, self->low, self->notch, self->high, self->band);
     return self->out;
 }
 
@@ -67,15 +53,11 @@ void svf_reset(SVF* self){
     self->out = 0;
 }
 
-SVF* svf_new(float freq,float q,float drive) {
+SVF* svf_new(float freq,float q) {
     SVF *self = malloc(sizeof(SVF));
-    
     self->freq = freq;
     self->q = q;
-    self->drive = drive;
-    self->dbo = _12dbo;
     // functions.
-    self->damp = svf_damp;
     self->process = svf_process;
     self->reset = svf_reset;
     self->reset(self);

src/filters/svf.h

@@ -17,26 +17,21 @@
 
 #define MIN(X, Y) (((X) < (Y)) ? (X) : (Y))
 
-typedef enum DBO { _6dbo, _12dbo, _18dbo, _24dbo, _36dbo = 6, _48dbo } DBO;
 
 typedef struct SVF {
     float notch;
     float low;
     float high;
     float band;
-    float drive;
     float freq;
     float q;
-    DBO dbo;
     float out;
-    float(*damp)(struct SVF*);
     float(*process)(struct SVF*,float in);
     void(*reset)(struct SVF*);
 } SVF;
 
 
-float svf_damp(SVF *self);
 float svf_process(SVF *self,float in);
 void svf_reset(SVF* self);
-SVF* svf_new(float freq,float q,float drive);
+SVF* svf_new(float freq,float q);
 #endif

src/synththing.c

@@ -86,7 +86,7 @@ int main(int argc, char**argv) {
     Envelope b = *envelope_new();
     saw = *basic_new(_waveform_saw, b);
     saw.freq = 440;
-    filt = *svf_new(7000.0f, 0.99f, 0.000001f);
+    filt = *svf_new(7000.0f, 0.5f);
     //data.sample_rate=SAMPLE_RATE;
     PaStream *stream;
     /* Open an audio I/O stream. */
@@ -104,7 +104,7 @@ int main(int argc, char**argv) {
     if( err != paNoError ) goto error;
     /* start anything intersting */
     saw.gate = true;
-    for (int freq = 7000; freq >= 60; freq--) {
+    for (int freq = 7000; freq >= 60; freq = freq - 0.0001) {
 	filt.freq = freq;
 	usleep(500);
     }