cleanup

plugin/alphaosc.cpp

@@ -29,23 +29,10 @@ AlphaOsc::AlphaOsc() : Plugin(parameterCount, 0, 0), sampleRate(getSampleRate())
 void AlphaOsc::initAudioPort(bool input, uint32_t index, AudioPort &port) {
     // port.groupId = kPortGroupStereo;
     Plugin::initAudioPort(input, index, port);
-
     if (!input && index == 0) port.name = "Osc Out";
 }
 
-// Processing functions
+// Processing function
-
-void AlphaOsc::activate() {
-    // calculate filter coefficients and stuff
-    printf("called activate()\n");
-    lfoOmega = (1 << 31) / sampleRate * 3.51;
-    omega = (130 / sampleRate) * (1 << 23);
-}
-
-void AlphaOsc::deactivate() {
-    printf("called deactivate()\n");
-}
-
 void AlphaOsc::run(const float **, float **outputs, uint32_t frames, const MidiEvent *midiEvents, uint32_t midiEventCount) {
     bzero(outputs[0], sizeof(float) * frames);
 
@@ -53,9 +40,9 @@ void AlphaOsc::run(const float **, float **outputs, uint32_t frames, const MidiE
     (void)midiEventCount;
     (void)midiEvents;
 
-    uint16_t i;
+    uint32_t i;
     uint32_t osc;
-    uint8_t lfo;
+    uint8_t lfo, pw;
 
     // oscillator outputs
     float saw, sqr, sub, pwg;
@@ -65,11 +52,15 @@ void AlphaOsc::run(const float **, float **outputs, uint32_t frames, const MidiE
 
     float out, in;
 
+    // handle any MIDI events
+
     // steeply "logarithmic" curve similar to the Juno 106 LFO rate curve
     // goes from about 0.1Hz to about 60Hz because this "feels about right"
     // totally unscientific
     lfoOmega = (0.1 + (pwmrate / (1 + (1 - pwmrate) * 4.75) * 60)) / sampleRate * (1 << 23);
-    omega = (130 / sampleRate) * (1 << 23);
+
+    // set the frequency for the phase counter
+    omega = (freq / sampleRate) * (1 << 23);
 
     // calculate an entire block of samples
 
@@ -77,19 +68,26 @@ void AlphaOsc::run(const float **, float **outputs, uint32_t frames, const MidiE
         // increment phase of saw counter
         // phase is a 24-bit counter because we're on a PC and we can afford to be profligate with silicon
         // the actual Alpha Juno oscillators might well have been 8-bit for reasons loosely explained in the README
-
         phase += omega;
         lfoPhase += lfoOmega;
 
-        // now osc is a ten-bit counter, to give room for the sub osc outputs
+        // osc is the top ten bits of the phase counter, to give room for the sub osc outputs
-        // square output will be bit 7 of osc, 25% will be bit 7 & bit 6
+        // bits 8 and 9 will be used for the sub squares
-        // PWM square will be bit 7 & comparator, with the PWM being compared against bits 0-6
+        // bit 7 for the squarewave
+        // bits 0-7 of this will be used for the saw wave
+        // and bits 6, 5, and 4 for the "modulators"
         osc = phase >> 14;
 
         // LFO is 7-bit triangle
-        lfo = (lfoPhase >> 16) & 0x7f;
+        // the counter is 24-bit, but we take the top byte for 0-255 with fine control of speed
-        lfo = (lfoPhase & 0x00800000) ? lfo : 127 - lfo;
+        // by taking bits 0-6 we have a value that counts from 0-127 twice as fast as the
+        // desired LFO speed, which is fine
+        // by then taking bit 7 and using that to set whether we're counting up or down (subtract
+        // the counter from 127) we get a lovely triangle wave
+        lfo = (lfoPhase >> 16) & 0x7f;                     // top eight bits of the counter, keep only 0-6
+        lfo = (lfoPhase & 0x00800000) ? lfo : 0x7f - lfo;  // bit 7 is the polarity
 
+        // scale the LFO output to get our adjustable PWM
         pw = lfo * pwmdepth;
 
         // the oscillator outputs in the chip are probably digital signals
@@ -97,10 +95,11 @@ void AlphaOsc::run(const float **, float **outputs, uint32_t frames, const MidiE
         // the square and sub signals picked off the counter bits
         // and a couple of flipflops to generate the sub osc signals
 
-        // 8-bit saw scaled
+        // 8-bit saw scaled to 0-1
         saw = (osc & 0xff) / 256.0f;
 
         // various counter bits scaled from 0-1
+        // these generate various squarewaves to gate the signals
         bit4 = (float)(osc & 0x010) != 0;  // 3 octaves up
         bit5 = (float)(osc & 0x020) != 0;  // 2 octaves up
         bit6 = (float)(osc & 0x040) != 0;  // 1 octave up
@@ -110,18 +109,21 @@ void AlphaOsc::run(const float **, float **outputs, uint32_t frames, const MidiE
 
         // pulse width gate
         // lower seven bits of the saw osc, compared with PW setting
+        // this is on or off for a variable (by PW) proportion of a half-cycle
+        // of the square or sawtooth wave, kind of like you see on the diagram
+        // on the top panel of the Alpha Juno
         pwg = (float)((osc & 0x7f) >= pw) != 0;
 
         // calculate the oscillator output
-        // because all the "bits" are scaled to floats from 0 to 1
+        // because all the "bits" are scaled to floats from 0 to 1,
-        // we can just multiply them
+        // we can just multiply them together to get our gating
         // 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:
             default:
-                sub = bit8;
+                sub = bit8;  // one octave down
-                break;      // one octave down
+                break;
             case 1:
                 sub = bit8 * bit7;  // one octave down, 25% PW
                 break;
@@ -145,8 +147,8 @@ void AlphaOsc::run(const float **, float **outputs, uint32_t frames, const MidiE
             default:
                 sqr = 0;  // oscillator is off
                 break;
-            case 1:         // fundamental
+            case 1:
-                sqr = bit7;
+                sqr = bit7;  // fundamental
                 break;
             case 2:
                 sqr = bit7 * bit6;  // 25% pulse
@@ -177,22 +179,23 @@ void AlphaOsc::run(const float **, float **outputs, uint32_t frames, const MidiE
                 break;
         }
 
-
-
-
         // mix the signals, probably done with some resistors in the chip
-        in = (sub * sublevel) + (saw * 0.8) + (sqr * 0.63); // scaled similarly to Juno 106
+        // these are scaled similarly to my Juno 106 (HS60 really) because it's all
+        // very much just guesswork, and it "feels about right"
+        in = (sub * sublevel) + (saw * 0.8) + (sqr * 0.63);
 
         // DC removal highpass filter
         // this is very approximately 6Hz at 44.1kHz and 48kHz
+        // which corresponds with the 2.2uF capacitor and 12k + 100 ohm resistor between
+        // the voice chip output and filter input in a real Alpha Juno
         // honestly it doesn't matter all that much if it's wrong at higher sample rates
         out = in - hpfx + .99915 * hpfy;
         hpfx = in;
         hpfy = out;
 
+        // scale the output and write it to the buffer
         outputs[0][i] = out * 0.5;
     }
-   // printf("%f %f\n", sqr, saw);
 }
 
 // create the plugin

plugin/alphaosc.hpp

@@ -56,8 +56,6 @@ class AlphaOsc : public Plugin {
     float getParameterValue(uint32_t index) const override;
 
     // Processing
-    void activate() override;
-    void deactivate() override;
     void run(const float **, float **outputs, uint32_t frames, const MidiEvent *midiEvents, uint32_t midiEventCount) override;
 
    private:
@@ -65,7 +63,9 @@ class AlphaOsc : public Plugin {
     uint32_t omega, lfoOmega;
     uint32_t phase, lfoPhase;
 
-    uint8_t pw;
+    uint8_t note = 48;   // last heard MIDI note
+    float freq = 130.8;  // C3, an octave below Middle C
+    float gate = 0;      // output attenuation
 
     float pwmrate, pwmdepth, sublevel;
     uint8_t sqrmode, sawmode, submode;