basics of oscillator

plugin/Makefile

@@ -12,6 +12,7 @@ NAME = peacock
 FILES_DSP = \
 	peacock.cpp \
 	ic1.cpp \
+	oscillator.cpp \
 	ic29.cpp
 
 include ../dpf/Makefile.plugins.mk

plugin/ic29.cpp

@@ -101,6 +101,7 @@ void Envelope::run() {
 }
 
 Voice::Voice() {
+    subosc = 1;
 }
 
 void Voice::calcPitch() {
@@ -156,13 +157,3 @@ void Voice::off() {
         env.off();
     }
 }
-
-void Voice::run(float *buffer, uint32_t samples) {
-    float gain = env.level / 16384.0;
-    gain *= 0.125;
-    for (uint32_t i = 0; i < samples; i++) {
-        phase += omega;
-        if (phase > 1.0f) phase -= 1.0f;
-        buffer[i] += phase * gain;
-    }
-}

plugin/ic29.hpp

@@ -59,6 +59,10 @@ class Voice {
    private:
     Envelope env;             // calculated envelope value
     uint16_t pitch = 0x1818;  // calculated pitch value with porta and master pitch etc
+    float delay;              // delay slot for polyblep
+    bool pulseStage;
+    float lastpw;
+    float subosc = -1;
     float phase = 0, omega = 0;
     enum { V_DONE,
            V_OFF,

plugin/oscillator.cpp

@@ -0,0 +1,73 @@
+/*
+   Peacock-8 VA polysynth
+
+   Copyright 2024 Gordon JC Pearce <gordonjcp@gjcp.net>
+
+   Permission to use, copy, modify, and/or distribute this software for any
+   purpose with or without fee is hereby granted, provided that the above
+   copyright notice and this permission notice appear in all copies.
+
+   THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+   WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+   MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY
+   SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+   WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION
+   OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN
+   CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+*/
+
+#include "ic29.hpp"
+
+static inline float poly3blep0(float t) {
+    float t2 = t * t;
+    return 2 * (t * t2 - 0.5f * t2 * t2);
+}
+
+static inline float poly3blep1(float t) {
+    return -poly3blep0(1 - t);
+}
+
+void Voice::run(float *buffer, uint32_t samples) {
+    // generate a full block of samples for the oscillator
+
+    float y, out, pw = 0.0, t;
+
+    float gain = env.level / 16384.0;
+
+    // this uses an adaptation of Mystran's Polyblep oscillator
+    for (uint32_t i = 0; i < samples; i++) {
+        y = delay;
+        delay = 0;
+        phase += omega;
+
+        // this is the clever bit
+        while (true) {
+            if (!pulseStage) {
+                if (phase < pw) break;                     // it's not time for the PWM output to step
+                t = (phase - pw) / (lastpw - pw + omega);  // calculate fractional sample allowing for PW amount
+                y -= 0.63 * poly3blep0(t);                 // magic numbers observed on oscilloscope from real synth
+                delay -= 0.63 * poly3blep1(t);
+                pulseStage = true;
+            }
+            if (pulseStage) {
+                if (phase < 1) break;  // it's not time to reset the saw
+                t = (phase - 1) / omega;
+                y += poly3blep0(t) * (0.8 + 0.63 - subosc);
+                delay += poly3blep1(t) * (0.8 + 0.63 - subosc);
+                pulseStage = 0;
+                phase -= 1;
+                subosc = -subosc;
+            }
+        }
+
+        delay += (0.8 - (1.6 * phase));                                 // magic numbers observed on oscilloscope from real synth
+        delay += (0.63 - (pw * 1.26)) + (pulseStage ? -0.63f : 0.63f);  // add in the scaled pulsewidth to restore DC level
+        // the DC correction is important because the hardware synth is AC-coupled effectively high-passing
+        // the signal at about 10Hz or so, preventing any PWM rumble from leaking through!
+        delay += subosc;
+
+        out = y * 0.15;
+        lastpw = pw;
+        buffer[i] += out * gain;
+    }
+}