From 5cc2a5c9caaeb810c95596d3b01f7650059e12d3 Mon Sep 17 00:00:00 2001
From: Gordon JC Pearce <gordonjcp@gmail.com>
Date: Tue, 7 Jan 2025 14:19:50 +0000
Subject: [PATCH] renamed osc components for clarity

---
 plugin/alphaosc.cpp | 65 +++++++++++++++++++++++++--------------------
 1 file changed, 36 insertions(+), 29 deletions(-)

diff --git a/plugin/alphaosc.cpp b/plugin/alphaosc.cpp
index 7bb0562..af9afed 100644
--- a/plugin/alphaosc.cpp
+++ b/plugin/alphaosc.cpp
@@ -56,10 +56,13 @@ void AlphaOsc::run(const float **, float **outputs, uint32_t frames, const MidiE
     uint16_t i;
     uint32_t osc;
     uint8_t lfo;
-    float saw, sqr, sub;
-    float oct1, oct3, pwg;
-    float sub1, sub2;
 
+    // oscillator outputs
+    float saw, sqr, sub, pwg;
+
+    // counter bits derived from osc
+    float bit4, bit5, bit6, bit7, bit8, bit9;
+    
     float out, in;
 
     // steeply "logarithmic" curve similar to the Juno 106 LFO rate curve
@@ -97,76 +100,80 @@ void AlphaOsc::run(const float **, float **outputs, uint32_t frames, const MidiE
         // 8-bit saw scaled
         saw = (osc & 0xff) / 256.0f;
 
-        // square scaled to 0-1, along with one and three octaves up
-        sqr = (float)(osc & 0x80) != 0;
-        oct1 = (float)(osc & 0x40) != 0;
-        oct3 = (float)(osc & 0x10) != 0;
-        sub1 = (float)(osc & 0x40) != 0;
-        sub2 = (float)(osc & 0x10) != 0;
-
-
+        // various counter bits scaled from 0-1
+        bit4 = (float)(osc & 0x010) != 0;    // 3 octaves up
+        bit5 = (float)(osc & 0x020) != 0;    // 2 octaves up
+        bit6 = (float)(osc & 0x040) != 0;    // 1 octave up
+        bit7 = (float)(osc & 0x080) != 0;    // square wave, top bit of saw counter
+        bit8 = (float)(osc & 0x100) != 0;    // 1 octave down
+        bit9 = (float)(osc & 0x200) != 0;    // 2 octaves down
 
         // pulse width gate
         // lower seven bits of the saw osc, compared with PW setting
         pwg = (float)((osc & 0x7f) >= pw) != 0;
 
-
-
         // calculate the oscillator output
-        
+        // because all the "bits" are scaled to floats from 0 to 1
+        // we can just multiply them
+        // in the real chip it probably uses AND gates to control outputs
+        // including an AND gate driving the DAC latch pin
         switch (submode) {
             case 0:
-                sub = sub1;
+            default:
+                sub = bit8;
                 break;      // one octave down
             case 1:
-                sub = sub1 * sqr;
-                break;      // saw is fine, do nothing
+                sub = bit8 * bit7;  // one octave down, 25% PW
+                break;
             case 2:
-                saw *= oct1;    // pulsed
+                sub = bit8 * bit6;  // one octave down modulated by one octave up 
                 break;
             case 3:
-                saw *= pwg;    // pwm
+                sub = bit8 * bit5;  // one octave down modulated by two octaves up
                 break;
             case 4:
-                saw *= oct3;   // oct3 pulse
+                sub = bit9;         // two octaves down
                 break;
             case 5:
-                saw *= oct1 * oct3;    // both pulse
+                sub = bit9 * bit8;  // two octaves down, 25% PW
                 break;
         }
 
         switch (sqrmode) {
             case 0:
             case 4:
+            default:
                 sqr = 0;    // oscillator is off
                 break;
-            case 1:         // do nothing, sqr is fine
+            case 1:         // fundamental
+                sqr = bit7;
                 break;      
             case 2:
-                sqr *= oct1;    // 25% pulse
+                sqr = bit7 * bit6;    // 25% pulse
                 break;
             case 3:
-                sqr *= pwg;     // pwm
+                sqr = bit7 * pwg;     // pwm
                 break;
         }
 
         switch (sawmode) {
             case 0:
+            default:
                 saw = 0;
                 break;      // oscillator is off
             case 1:
                 break;      // saw is fine, do nothing
             case 2:
-                saw *= oct1;    // pulsed
+                saw *= bit6;    // pulsed
                 break;
             case 3:
                 saw *= pwg;    // pwm
                 break;
             case 4:
-                saw *= oct3;   // oct3 pulse
+                saw *= bit4;   // oct3 pulse
                 break;
             case 5:
-                saw *= oct1 * oct3;    // both pulse
+                saw *= bit6 * bit4;    // both pulse
                 break;
         }
 
@@ -174,7 +181,7 @@ void AlphaOsc::run(const float **, float **outputs, uint32_t frames, const MidiE
 
 
         // mix the signals, probably done with some resistors in the chip
-        in = (saw * 0.8) + (sqr * 0.63); // scaled similarly to Juno 106
+        in = (sub * sublevel) + (saw * 0.8) + (sqr * 0.63); // scaled similarly to Juno 106
 
         // DC removal highpass filter
         // this is very approximately 6Hz at 44.1kHz and 48kHz
@@ -183,7 +190,7 @@ void AlphaOsc::run(const float **, float **outputs, uint32_t frames, const MidiE
         hpfx = in;
         hpfy = out;
 
-        outputs[0][i] = out;
+        outputs[0][i] = out*0.5;
     }
    // printf("%f %f\n", sqr, saw);
 }