AnalogTapeModel

commit 704824feb90e36400d65d5bd100769958d773c72
parent a8d5bfc406714f6fed22d42e43bafaf689c9b408
Author: jatinchowdhury18 <[email protected]>
Date:   Sun, 27 Sep 2020 17:03:22 -0700

Improve internal clipping characteristics for hysteresis processing

Diffstat:
M
CHANGELOG.md
 | 
1
+
M
Plugin/Source/Processors/Hysteresis/HysteresisProcessing.h
 | 
15
++++++++++-----
M
Plugin/Source/Processors/Hysteresis/HysteresisProcessor.cpp
 | 
21
+++++++++++++++++++--
M
Plugin/Source/Processors/Hysteresis/HysteresisProcessor.h
 | 
1
+

4 files changed, 31 insertions(+), 7 deletions(-)
diff --git a/CHANGELOG.md b/CHANGELOG.md
@@ -7,6 +7,7 @@ this file.
 - Added "mix groups" to allow instances of the plugin to be synced across a mix.
 - Added Chew variance parameter to control the randomness of the chew dropouts.
 - Improved behavior for thickness slider.
+- Improved internal clipping characteristic (to preserve stability).
 - Improved DC blocker for hysteresis processor.
 
 ## [2.5.0] - 2020-08-23
diff --git a/Plugin/Source/Processors/Hysteresis/HysteresisProcessing.h b/Plugin/Source/Processors/Hysteresis/HysteresisProcessing.h
@@ -33,10 +33,15 @@ public:
         double H_d = deriv (H, H_n1, H_d_n1);
         double M = (this->*solver) (H, H_d);
 
-        if (std::isnan (M) || M > upperLim)
-        {
-            M = 0.0;
-        }
+        // check for instability
+        bool illCondition = std::isnan (M) || M > upperLim;
+        M = illCondition ? 0.0 : M;
+        H_d = illCondition ? 0.0 : H_d;
+
+        // if (std::isnan (M) || M > upperLim)
+        // {
+        //     M = 0.0;
+        // }
 
         M_n1 = M;
         H_n1 = H;
@@ -51,7 +56,7 @@ private:
     inline double langevinD2 (double x) const noexcept;  // 2nd derivative of Langevin function
     inline double deriv (double x_n, double x_n1, double x_d_n1) const noexcept // Derivative by alpha transform
     {
-        constexpr double dAlpha = 0.9;
+        constexpr double dAlpha = 0.75;
         return (((1.0 + dAlpha) / T) * (x_n - x_n1)) - dAlpha * x_d_n1;
     }
 
diff --git a/Plugin/Source/Processors/Hysteresis/HysteresisProcessor.cpp b/Plugin/Source/Processors/Hysteresis/HysteresisProcessor.cpp
@@ -50,6 +50,23 @@ void HysteresisProcessor::setSolver (int newSolver)
 
     for (int ch = 0; ch < 2; ++ch)
         hProcs[ch].setSolver (static_cast<SolverType> (newSolver));
+
+    // set clip level for solver
+    switch (newSolver)
+    {
+    case 0: // RK2
+    case 1: // RK4
+        clipLevel = 10.0f;
+        return;
+
+    case 2: // NR4
+    case 3: // NR8
+        clipLevel = 12.5f;
+        return;
+
+    default:
+        clipLevel = 20.0f;
+    };
 }
 
 float HysteresisProcessor::calcMakeup()
@@ -166,10 +183,10 @@ void HysteresisProcessor::processBlock (AudioBuffer<float>& buffer, MidiBuffer& 
 
     wasV1 = useV1;
 
-    // clip input to +9 dB
+    // clip input to avoid unstable hysteresis
     for (int ch = 0; ch < buffer.getNumChannels(); ++ch)
         FloatVectorOperations::clip (buffer.getWritePointer (ch),
-            buffer.getWritePointer (ch), -8.0f, 8.0f, buffer.getNumSamples());
+            buffer.getWritePointer (ch), -clipLevel, clipLevel, buffer.getNumSamples());
 
     dsp::AudioBlock<float> block (buffer);
     dsp::AudioBlock<float> osBlock = overSample[curOS]->processSamplesUp (block);
diff --git a/Plugin/Source/Processors/Hysteresis/HysteresisProcessor.h b/Plugin/Source/Processors/Hysteresis/HysteresisProcessor.h
@@ -62,6 +62,7 @@ private:
     float biasFreq = 48000.0f;
     float biasAngle[2];
     bool wasV1 = false, useV1 = false;
+    float clipLevel = 20.0f;
 
     JUCE_DECLARE_NON_COPYABLE_WITH_LEAK_DETECTOR (HysteresisProcessor)
 };