fixed envelope sustain level, basic LFO + PWM

plugin/ic29.cpp

@@ -17,17 +17,19 @@
 */
 
 #include "ic29.hpp"
+
 #include "ic29tables.hpp"
 
 Synth ic29;
 
 Synth::Synth() {
     d_debug("initialising synth\n");
-    envAtk = 0x20;
+    envAtk = 0x00;
     envDcy = 0x50;
-    envStn = 0x1f;
+    envStn = 0x7f;
     envRls = 0x3f;
     portaCoeff = 0x0;
+    lfo.speed = 0x1f;
 }
 
 void Synth::buildTables(double sampleRate) {
@@ -35,7 +37,7 @@ void Synth::buildTables(double sampleRate) {
         // slightly flat middle C from ROM divider table
         // actually adjusted a little so that the notes are bang on
         // on the real synth the tuning knob is tweaked a little off to pull it in
-        pitchTable[i] = 260.15f * powf(2, (i - 36) / 12.0f) / sampleRate;  
+        pitchTable[i] = 260.15f * powf(2, (i - 36) / 12.0f) / sampleRate;
     }
 }
 
@@ -43,6 +45,10 @@ void Synth::run() {
     // handle a "loop" worth of envelopes, pitch calculations, etc
     // callled once every 4.3ms block of samples
 
+    ic29.lfo.run();
+
+    masterPitch = 0x1818;
+
     for (uint8_t i = 0; i < NUM_VOICES; i++) {
         ic29.voices[i].update();
     }
@@ -60,14 +66,32 @@ void Synth::voiceOff(uint8_t voice) {
     ic29.voices[voice].off();
 }
 
-void Synth::basePitch() {
+LFO::LFO() {
-    uint16_t pitch = 0x1818;
+    lfoOut = 0;
+    phase = 0;
 
-    pitch += lfoPitch;
+    // phase is where we are in the LFO delay cycle
-    pitch += bendPitch;
+    // the delay envelope sets the depth of pitch and VCF modulation
-    // tuning too but that's zero by default;
+    // running normally the amplitude is maxed out, and when the first
+    // key is struck the holdoff timer and envelope will be reset to zero
+    delayPhase = LFO_RUN;
+}
 
-    masterPitch = pitch;
+void LFO::run() {
+    // slightly different from the real synth code which does not use signed
+    // variables, since the CPU doesn't support them
+
+    lfoOut += phase ? lfoRateTable[speed] : -lfoRateTable[speed];
+    if (lfoOut > 0x1fff) {
+        lfoOut = 0x1fff;
+        phase = 0;
+    }
+    if (lfoOut < -0x1fff) {
+        lfoOut = -0x1fff;
+        phase = 1;
+    }
+
+    //printf("lfoOut=%04x\n", lfoOut);
 }
 
 Envelope::Envelope() {
@@ -76,8 +100,7 @@ Envelope::Envelope() {
 }
 
 void Envelope::run() {
-
+    uint16_t tempStn = ic29.envStn << 7;
-    uint16_t tempStn = ic29.envStn << 6;
     switch (phase) {
         case ENV_ATK:
             level += atkTable[ic29.envAtk];
@@ -88,9 +111,7 @@ void Envelope::run() {
             break;
         case ENV_DCY:
             if (level > tempStn) {
-//                level = ((level * ic29.envDcy) >> 16;
+                level = (((level - tempStn) * dcyTable[ic29.envDcy]) >> 16) + tempStn;
-            level = (((level - tempStn) * dcyTable[ic29.envDcy]) >> 16) + tempStn;
-
             } else {
                 level = tempStn;
             }
@@ -105,19 +126,26 @@ void Envelope::run() {
 }
 
 Voice::Voice() {
-    subosc = 1;
+    subosc = .11;
 }
 
 void Voice::calcPitch() {
     uint16_t target = note << 8;
 
+    // Portamento is a linear change of pitch - it'll take twice as long
+    // to jump two octaves as it takes to jump one
+    // By comparison "glide" is like an RC filter, for example in the TB303
+    // This is implemented here by adding on a step value until you pass
+    // the desired final pitch. Once that happens the value is clamped to the
+    // desired pitch.
+
     if (ic29.portaCoeff != 0) {
-        // porta up
+        // portamento up
         if (pitch < target) {
             pitch += ic29.portaCoeff;
             if (pitch > target) pitch = target;
         }
-        // porta down
+        // portamento down
         if (pitch > target) {
             pitch -= ic29.portaCoeff;
             if (pitch < target) pitch = target;
@@ -126,17 +154,17 @@ void Voice::calcPitch() {
         pitch = target;
     }
 
-    pitch += 0x1818; //ic29.masterPitch;
+    pitch += ic29.masterPitch;
 
     if (pitch < 0x3000) pitch = 0x3000;  // lowest note
     if (pitch > 0x9700) pitch = 0x6700;  // highest note
 
     pitch -= 0x3000;
-    //pitch &= 0xff00;
 
+    // interpolate between the two table values
     double o1 = ic29.pitchTable[pitch >> 8];
     double o2 = ic29.pitchTable[(pitch >> 8) + 1];
-    double frac = (pitch & 0xff) / 255.0;
+    double frac = (pitch & 0xff) / 256.0f;
 
     omega = ((o2 - o1) * frac) + o1;
 }
@@ -155,7 +183,7 @@ void Voice::on(uint8_t key) {
 }
 
 void Voice::off() {
-    // I need to rethink this bit FIXME
+    // sustain - I need to rethink this bit FIXME
     voiceState = V_OFF;
     if (!ic29.sustained) {
         env.off();

plugin/ic29.hpp

@@ -20,6 +20,24 @@
 
 #include "peacock.hpp"
 
+class LFO {
+   public:
+    LFO();
+    void run();
+    int16_t lfoOut;
+    uint8_t speed;
+
+   private:
+    uint8_t
+     phase;
+    uint16_t holdoff;
+    uint16_t envelope;
+    enum { LFO_RUN,
+           LFO_HOLDOFF,
+           LFO_RAMP } delayPhase;
+    static const uint16_t lfoRateTable[128];
+};
+
 class Envelope {
    public:
     Envelope();
@@ -99,9 +117,8 @@ class Synth {
     int16_t lfoPitch;
     int16_t bendPitch;
     Voice voices[NUM_VOICES];
+    LFO lfo;
 
-    void runLfo();
-    void basePitch();
 };
 
 // global

plugin/ic29tables.hpp

@@ -67,7 +67,7 @@ extern const uint8_t lfoDepthTable[128] = {
     0xb0, 0xb4, 0xb8, 0xbc, 0xc0, 0xc4, 0xc8, 0xcc, 0xd0, 0xd4, 0xd8, 0xdc,
     0xe0, 0xe4, 0xe8, 0xec, 0xf0, 0xf8, 0xff, 0xff};
 
-extern const uint16_t lfoRateTable[128] = {
+const uint16_t LFO::lfoRateTable[128] = {
     0x0005, 0x000f, 0x0019, 0x0028, 0x0037, 0x0046, 0x0050, 0x005a, 0x0064,
     0x006e, 0x0078, 0x0082, 0x008c, 0x0096, 0x00a0, 0x00aa, 0x00b4, 0x00be,
     0x00c8, 0x00d2, 0x00dc, 0x00e6, 0x00f0, 0x00fa, 0x0104, 0x010e, 0x0118,

plugin/oscillator.cpp

@@ -30,7 +30,10 @@ static inline float poly3blep1(float 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 y, out, pw = .50, t;
+
+    float saw = 0;
+    pw = 0.5-(ic29.lfo.lfoOut + 0x2000) / 61600.0f;
 
     float gain = env.level / 16384.0;
 
@@ -52,15 +55,15 @@ void Voice::run(float *buffer, uint32_t samples) {
             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);
+                y += poly3blep0(t) * (0.8 * saw + 0.63 - subosc);
-                delay += poly3blep1(t) * (0.8 + 0.63 - subosc);
+                delay += poly3blep1(t) * (0.8 * saw + 0.63 - subosc);
                 pulseStage = 0;
                 phase -= 1;
                 subosc = -subosc;
             }
         }
 
-        delay += (0.8 - (1.6 * phase));                                 // magic numbers observed on oscilloscope from real synth
+        delay += saw * (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!