IIR filter optimisation.

modules/juce_audio_basics/effects/juce_IIRFilter.cpp

@@ -31,17 +31,15 @@
 
 //==============================================================================
 IIRFilter::IIRFilter()
-    : active (false)
+    : active (false), v1 (0), v2 (0)
 {
-    reset();
 }
 
 IIRFilter::IIRFilter (const IIRFilter& other)
-    : active (other.active)
+    : active (other.active), v1 (0), v2 (0)
 {
     const ScopedLock sl (other.processLock);
     memcpy (coefficients, other.coefficients, sizeof (coefficients));
-    reset();
 }
 
 IIRFilter::~IIRFilter()
@@ -52,27 +50,17 @@ IIRFilter::~IIRFilter()
 void IIRFilter::reset() noexcept
 {
     const ScopedLock sl (processLock);
-
-    x1 = 0;
-    x2 = 0;
-    y1 = 0;
-    y2 = 0;
+    v1 = v2 = 0;
 }
 
 float IIRFilter::processSingleSampleRaw (const float in) noexcept
 {
-    float out = coefficients[0] * in
-                 + coefficients[1] * x1
-                 + coefficients[2] * x2
-                 - coefficients[4] * y1
-                 - coefficients[5] * y2;
+    float out = coefficients[0] * in + v1;
 
     JUCE_SNAP_TO_ZERO (out);
 
-    x2 = x1;
-    x1 = in;
-    y2 = y1;
-    y1 = out;
+    v1 = coefficients[1] * in - coefficients[4] * out + v2;
+    v2 = coefficients[2] * in - coefficients[5] * out;
 
     return out;
 }
@@ -88,18 +76,12 @@ void IIRFilter::processSamples (float* const samples,
         {
             const float in = samples[i];
 
-            float out = coefficients[0] * in
-                         + coefficients[1] * x1
-                         + coefficients[2] * x2
-                         - coefficients[4] * y1
-                         - coefficients[5] * y2;
+            float out = coefficients[0] * in + v1;
 
             JUCE_SNAP_TO_ZERO (out);
 
-            x2 = x1;
-            x1 = in;
-            y2 = y1;
-            y1 = out;
+            v1 = coefficients[1] * in - coefficients[4] * out + v2;
+            v2 = coefficients[2] * in - coefficients[5] * out;
 
             samples[i] = out;
         }

modules/juce_audio_basics/effects/juce_IIRFilter.h

@@ -138,7 +138,7 @@ protected:
 
     bool active;
     float coefficients[6];
-    float x1, x2, y1, y2;
+    float v1, v2;
 
     // (use the copyCoefficientsFrom() method instead of this operator)
     IIRFilter& operator= (const IIRFilter&);