crossfade buffer for removing clicks on note changes

Source/Maker/main.c

@@ -1,5 +1,6 @@
 
 #include <stdio.h>
+#include <string.h>
 
 #define SOKOL_IMPL
 #define SOKOL_GLCORE
@@ -9,6 +10,7 @@
 
 #include "../config.h"
 #include "../envelope.c"
+// #include "../interp.c"
 #include "../oscillators.c"
 #include "../phaser.c"
 
@@ -20,17 +22,45 @@ static struct stfu_envelope envelope;
 
 static float key_frequency = STFU_C4_FREQUENCY;
 
+#define CROSSFADE_RING_RANGE                                                   \
+  (STFU_CROSSFADE_BUFFER_FRAMES * STFU_AUDIO_CHANNEL_COUNT)
+static float crossfade_ring[CROSSFADE_RING_RANGE] = {0};
+static size_t crossfade_ring_needle = 0;
+static unsigned int crossfade_frames_left = 0;
+
+static void sample(float buffer[static 2]) {
+  phaser0 = stfu_pump_phaser(phaser0);
+  phaser1 = stfu_pump_phaser(phaser1);
+  phaser2 = stfu_pump_phaser(phaser2);
+  envelope = stfu_pump_envelope(envelope);
+
+  float left = envelope.v * sinf(phaser2.v + sinf(phaser0.v + sinf(phaser1.v)));
+  float right =
+      envelope.v * sinf(phaser2.v + sinf(phaser0.v + sinf(phaser1.v)));
+
+  buffer[0] = left;
+  buffer[1] = right;
+}
+
 static void stream(float *buffer, int num_frames, int num_channels) {
-  for (int i = 0; i < num_frames; ++i) {
-    // sine0 = stfu_pump_sinewave(sine0); // Carrier
-    phaser0 = stfu_pump_phaser(phaser0);
-    phaser1 = stfu_pump_phaser(phaser1);
-    phaser2 = stfu_pump_phaser(phaser2);
-    envelope = stfu_pump_envelope(envelope);
-    buffer[2 * i + 0] =
-        envelope.v * sinf(phaser2.v + sinf(phaser0.v + sinf(phaser1.v)));
-    buffer[2 * i + 1] =
-        envelope.v * sinf(phaser2.v + sinf(phaser0.v + sinf(phaser1.v)));
+  /* Fade away */
+  for (size_t i = 0; crossfade_frames_left > 0;
+       crossfade_frames_left--, i += 2) {
+    crossfade_ring[(crossfade_ring_needle + i) % CROSSFADE_RING_RANGE] *=
+        (float)crossfade_frames_left / STFU_CROSSFADE_BUFFER_FRAMES;
+    crossfade_ring[(crossfade_ring_needle + i + 1) % CROSSFADE_RING_RANGE] *=
+        (float)crossfade_frames_left / STFU_CROSSFADE_BUFFER_FRAMES;
+  }
+
+  /* Drive the ring buffer */
+  // todo: Use memcpy for left and right side of the ring.
+  while (num_frames--) {
+    buffer[0] = crossfade_ring[crossfade_ring_needle % CROSSFADE_RING_RANGE];
+    buffer[1] =
+        crossfade_ring[(crossfade_ring_needle + 1) % CROSSFADE_RING_RANGE];
+    sample(&crossfade_ring[crossfade_ring_needle % CROSSFADE_RING_RANGE]);
+    buffer = &buffer[2];
+    crossfade_ring_needle += 2;
   }
 }
 
@@ -46,9 +76,10 @@ static void init(void) {
   phaser1 = stfu_init_phaser(key_frequency * 0.25);
   phaser2 = stfu_init_phaser(key_frequency * 2.0);
   envelope = stfu_init_envelope(
-      (struct stfu_envelope_point[]){
-          [0] = {.dur = 0.5, .vol = 0.33}, [1] = {.dur = 1.0, .vol = 0}},
-      2);
+      (struct stfu_envelope_point[]){[0] = {.dur = 0.02, .vol = 1.0},
+                                     [1] = {.dur = 0.5, .vol = 0.33},
+                                     [2] = {.dur = 1.0, .vol = 0}},
+      3);
 }
 
 static void cleanup(void) { saudio_shutdown(); }
@@ -102,10 +133,11 @@ static void event(const sapp_event *e) {
       break;
     }
 
-    phaser0 = stfu_set_phaser_frequency(phaser0, key_frequency * 0.25);
-    phaser1 = stfu_set_phaser_frequency(phaser1, key_frequency * 0.125);
-    phaser2 = stfu_set_phaser_frequency(phaser2, key_frequency);
+    phaser0 = stfu_set_phaser_frequency(phaser0, key_frequency);
+    phaser1 = stfu_set_phaser_frequency(phaser1, key_frequency * 0.25);
+    phaser2 = stfu_set_phaser_frequency(phaser2, key_frequency * 2.0);
     envelope = stfu_trigger_envelope(envelope);
+    crossfade_frames_left = STFU_CROSSFADE_BUFFER_FRAMES;
 
     break;
   }

Source/config.h

@@ -8,4 +8,8 @@
 #define STFU_NOTE_UPSCALE_FACTOR 1.059463094f
 #define STFU_NOTE_DOWNSCALE_FACTOR 0.943874313f
 
+/* Introduces delayed buffering for purposes of crossfading channels when notes
+ * are retriggered, needed for filtering clicks */
+#define STFU_CROSSFADE_BUFFER_FRAMES 64
+
 // todo: Array of precomputed note frequencies?

Source/envelope.c

@@ -9,7 +9,7 @@ float stfu_get_envelope_duration(struct stfu_envelope envelope);
 struct stfu_envelope stfu_trigger_envelope(struct stfu_envelope envelope);
 
 /* Basic linear envelope generator with up to 16 points max.
- * First virtual point is always max volume (1.0f).
+ * First virtual point is always silent (0.0f).
  *
  * todo: Sustain?
  */
@@ -39,7 +39,7 @@ struct stfu_envelope stfu_pump_envelope(struct stfu_envelope envelope) {
   for (uint8_t i = 0;; ++i) {
     float ends = p + envelope.pnts[i].dur;
     if (envelope.p < ends) {
-      float pv = i == 0 ? 1.0f : envelope.pnts[i - 1].vol;
+      float pv = i == 0 ? 0.0f : envelope.pnts[i - 1].vol;
       envelope.v = stfu_linear_interpolate(p, pv, ends, envelope.pnts[i].vol,
                                            envelope.p);
       break;
@@ -60,6 +60,6 @@ float stfu_get_envelope_duration(struct stfu_envelope envelope) {
 
 struct stfu_envelope stfu_trigger_envelope(struct stfu_envelope envelope) {
   envelope.p = 0.0f;
-  envelope.v = 1.0f;
+  envelope.v = 0.0f;
   return envelope;
 }