src/oscillators.c: Two-zeros at Nyquist to make white noise pinker.

shorepine · Aug 18, 2024 · 503f020 · 503f020
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commit 503f020
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Showing 3 changed files with 16 additions and 1 deletion.
diff --git a/src/amy.c b/src/amy.c
@@ -818,6 +818,7 @@ void osc_note_on(uint16_t osc, float initial_freq) {
     if(synth[osc].wave==PULSE) pulse_note_on(osc, initial_freq);
     if(synth[osc].wave==PCM) pcm_note_on(osc);
     if(synth[osc].wave==ALGO) algo_note_on(osc);
+    if(synth[osc].wave==NOISE) noise_note_on(osc);
     if(AMY_HAS_PARTIALS == 1) {
         if(synth[osc].wave==PARTIAL)  partial_note_on(osc);
         if(synth[osc].wave==PARTIALS) partials_note_on(osc);

diff --git a/src/amy.h b/src/amy.h
@@ -504,6 +504,7 @@ extern void saw_down_note_on(uint16_t osc, float initial_freq);
 extern void saw_up_note_on(uint16_t osc, float initial_freq); 
 extern void triangle_note_on(uint16_t osc, float initial_freq); 
 extern void pulse_note_on(uint16_t osc, float initial_freq); 
+extern void noise_note_on(uint16_t osc);
 extern void pcm_note_on(uint16_t osc);
 extern void pcm_note_off(uint16_t osc);
 extern void custom_note_on(uint16_t osc, float freq);

diff --git a/src/oscillators.c b/src/oscillators.c
@@ -486,15 +486,28 @@ SAMPLE amy_get_random() {
 
 /* noise */
 
+void noise_note_on(uint16_t osc) {
+    synth[osc].last_two[0] = 0;
+    synth[osc].last_two[1] = 0;
+}
+
 SAMPLE render_noise(SAMPLE *buf, uint16_t osc) {
     SAMPLE amp = F2S(msynth[osc].amp);
     SAMPLE max_value = 0;
+    SAMPLE last_white = synth[osc].last_two[0];
+    SAMPLE last_last_white = synth[osc].last_two[1];
     for(uint16_t i=0;i<AMY_BLOCK_SIZE;i++) {
-        SAMPLE value = MUL4_SS(amy_get_random(), amp);
+        SAMPLE white = MUL4_SS(amy_get_random(), amp);
+        // Two-zero LPF to make the noise a little more pink, closer to Juno noise.
+        SAMPLE value = white + last_white + last_white + last_last_white;
+        last_last_white = last_white;
+        last_white = white;
         buf[i] += value;
         if (value < 0) value = -value;
         if (value > max_value) max_value = value;
     }
+    synth[osc].last_two[0] = last_white;
+    synth[osc].last_two[1] = last_last_white;
     return max_value;
 }