MoogVCF: Scale resonance to 0..1

ideoforms · Aug 16, 2024 · f80ee37 · f80ee37
1 parent 0d98efa
commit f80ee37
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Showing 2 changed files with 9 additions and 2 deletions.
diff --git a/source/include/signalflow/node/processors/filters/moog.h b/source/include/signalflow/node/processors/filters/moog.h
@@ -6,7 +6,8 @@
 namespace signalflow
 {
 /**--------------------------------------------------------------------------------*
- * Moog ladder low-pass filter.
+ * Simulation of the Moog ladder low-pass filter. `cutoff` sets the cutoff
+ * frequency; `resonance` should typically be between 0..1.
  *---------------------------------------------------------------------------------*/
 class MoogVCF : public UnaryOpNode
 {

diff --git a/source/src/node/processors/filters/moog.cpp b/source/src/node/processors/filters/moog.cpp
@@ -35,7 +35,13 @@ void MoogVCF::process(Buffer &out, int num_frames)
         for (int frame = 0; frame < num_frames; frame++)
         {
             float cutoff = signalflow_scale_lin_lin(this->cutoff->out[channel][frame], 0, this->graph->get_sample_rate() / 2, 0.005, 1);
-            float resonance = this->resonance->out[channel][frame];
+
+            /*------------------------------------------------------------------------
+             * The original algorithm typically expects resonance values between
+             * [0, 4]. Rescale in this implementation, for consistency with other
+             * filter nodes that expect [0, 1].
+             *-----------------------------------------------------------------------*/
+            float resonance = this->resonance->out[channel][frame] * 4.0;
             float f = cutoff * 1.16;
             float fb = resonance * (1.0 - 0.15 * f * f);