sample rate stuff for chorus

plugin/chorus.cpp

@@ -21,24 +21,21 @@
 #include <math.h>
 #include <string.h>
 
-#include <cstdio>
-
 Chorus::Chorus() {
     lpfOut1 = new float[bufferSize];
     lpfOut2 = new float[bufferSize];
-    ram = new float[DELAYSIZE];  // probably needs to be calculated based on sample rate
+    ram = new float[DELAYSIZE];
 
-    fastPhase = 0;
+    lfoPhase = 1;
+    lfoSpeed = 6.283 * 10.7 / sampleRate;  // plainly silly value to show if it hasn't been set
 
     // not quite Butterworth but you'd never hear the difference
+    // these are calculated from the real-world component values
     postFilter1l = new SVF(9688, .549);
     postFilter2l = new SVF(10377, 1.291);
     postFilter1r = new SVF(9688, .549);
     postFilter2r = new SVF(10377, 1.291);
 
-    // lfo values taken from a rough simulation
-    fastOmega = 6.283 * 0.7 / sampleRate;  // approximate, can be adjusted
-
     // zero out the delay buffer
     memset(ram, 0, sizeof(float) * DELAYSIZE);
     memset(lpfOut1, 0, sizeof(float) * bufferSize);
@@ -56,32 +53,33 @@ Chorus::~Chorus() {
 }
 
 void Chorus::run(float* input, float** outputs, uint32_t frames) {
-    // actual effects here
+    // run highpass / bass boost and stereo chorus effect for one full block
 
-    // FIXME add highpass filter
-
-    // now run the DSP
     float s0 = 0, s1 = 0;
     float lfoMod, dly1, frac, flt;
     uint16_t tap, delay;
 
     for (uint32_t i = 0; i < frames; i++) {
         // run a step of LFO
-        fastPhase += fastOmega;
-        if (fastPhase > 6.283) fastPhase -= 6.283;
+        lfoPhase += (lfoState & 0x01) ? lfoSpeed : -lfoSpeed;
 
-        flt = ((hpdelay - input[i]) * hpcut) + input[i];
-        hpdelay = flt;
-        input[i] += (flt * hpgain);
+        if (abs(lfoPhase) > 1) {
+            // lfoPhase -= 2;
+            lfoState++;
+        }
+
+        // highpass/bass boost
+        flt = ((input[i] - hpDelay) * hpCut) + hpDelay;
+        hpDelay = flt;
+        input[i] += (flt * hpGain);
 
         ram[delayptr] = input[i];
 
+// delays in milliseconds
 #define BASE 0.005
 #define AMT 0.00175
 
-        // FIXME make this triangle not sine, and move arithmetic out of mainloop
-        lfoMod = sin(fastPhase);
-        dly1 = (BASE + (AMT * lfoMod)) * sampleRate;
+        dly1 = (BASE + (AMT * lfoPhase)) * sampleRate;
         delay = (int)dly1;
         frac = dly1 - delay;
 
@@ -90,7 +88,7 @@ void Chorus::run(float* input, float** outputs, uint32_t frames) {
         s0 = ram[tap & 0x3ff];
         lpfOut1[i] = ((s1 - s0) * frac) + s0;
 
-        dly1 = (BASE - (AMT * lfoMod)) * sampleRate;
+        dly1 = (BASE - (AMT * lfoPhase)) * sampleRate;
         delay = (int)dly1;
         frac = dly1 - delay;
 
@@ -99,9 +97,6 @@ void Chorus::run(float* input, float** outputs, uint32_t frames) {
         s0 = ram[tap & 0x3ff];
         lpfOut2[i] = ((s1 - s0) * frac) + s0;
 
-        // lpfOut1[i] = input[i] + 1.2 * out0; //(out0 + (out120 * 0.66) + (out240 * 0.33));
-        //  lpfOut2[i] = input[i] + 1.2 * out120; //(out0 + (out120 * 0.33) + (out240 * 0.66));
-
         delayptr++;
         delayptr &= 0x3ff;
     }
@@ -119,22 +114,27 @@ void Chorus::run(float* input, float** outputs, uint32_t frames) {
 }
 
 void Chorus::setHpf(uint8_t mode) {
+    // the simple 1-pole lowpass has its output
+    // subtracted from input for the highpass
+    // or added for bass boost
+    // cutoff is calculated as
+    // k = 1-exp(-2pi * Fc * sampleRate)
     switch (mode) {
         case 0x00:
-            hpcut = 0.91245;
-            hpgain = -1;
+            hpCut = 1 - exp(-6.283 * 720 / sampleRate);
+            hpGain = -1;
             break;
         case 0x08:
-            hpcut = 0.97097;
-            hpgain = -1;
+            hpCut = 1 - exp(-6.283 * 225 / sampleRate);
+            hpGain = -1;
             break;
         case 0x10:
-            hpcut = 1;
-            hpgain = 0;
+            hpCut = 1;
+            hpGain = 0;
             break;
         case 0x18:
-            hpcut = 0.99088;
-            hpgain = 1;
+            hpCut = 1 - exp(-6.283 * 85 / sampleRate);
+            hpGain = 1.707;
             break;
     }
 }
@@ -147,11 +147,11 @@ void Chorus::setChorus(uint8_t mode) {
             break;
         case 0x40:
             gain = 1.2;
-            fastOmega = 6.283 * 0.5 / sampleRate;
-            break;  // approximate, can be adjusted
+            lfoSpeed = 6.283 * 0.5 / sampleRate;
+            break;
         case 0x00:
             gain = 1.2;
-            fastOmega = 6.283 * 0.9 / sampleRate;
-            break;  // approximate, can be adjusted
+            lfoSpeed = 6.283 * 0.9 / sampleRate;
+            break;
     }
 }

plugin/chorus.hpp

@@ -38,16 +38,18 @@ class Chorus {
     void setChorus(uint8_t mode);
 
    private:
-    double fastPhase = 0, fastOmega = 0;
+    double lfoPhase = 0, lfoSpeed = 0;
+    uint8_t lfoState=0;
     float gain = 1.2;
 
+
     uint16_t delayptr = 0;
 
     float* ram;
     float* lpfIn;
     float *lpfOut1, *lpfOut2;
 
-    float hpdelay=0, hpcut=0, hpgain=1;
+    float hpDelay=0, hpCut=0, hpGain=0;
 
     SVF *postFilter1l, *postFilter2l, *postFilter1r, *postFilter2r;
 };