Initial release — InstaShadow mastering compressor v1.0

Dual-stage compressor (optical + VCA) with output transformer saturation.
- Port-Hamiltonian T4B opto-cell model with implicit trapezoidal integration
- Feed-forward VCA with 7 ratios, 6 attack/release presets, Dual release mode
- 3 transformer types (Nickel/Iron/Steel) with 4x oversampled waveshaping
- Analog-style needle VU meters, horizontal GR meters
- Sidechain HPF, stereo link, independent section bypass
- Full state save/restore, CI/CD for Windows/macOS/Linux

Source/TransformerSaturation.cpp

@@ -0,0 +1,108 @@
+#include "TransformerSaturation.h"
+
+TransformerSaturation::TransformerSaturation() {}
+
+void TransformerSaturation::prepare (double sampleRate, int samplesPerBlock)
+{
+    sr = sampleRate;
+    oversampler.initProcessing ((size_t) samplesPerBlock);
+
+    // Iron tonestack: very subtle low shelf +0.2dB at 110Hz
+    auto ironCoeffs = juce::dsp::IIR::Coefficients<float>::makeLowShelf (
+        sampleRate, 110.0f, 0.707f, juce::Decibels::decibelsToGain (0.2f));
+    ironBoostL.coefficients = ironCoeffs;
+    ironBoostR.coefficients = ironCoeffs;
+
+    // Steel tonestack: subtle low shelf +0.4dB at 40Hz
+    auto steelCoeffs = juce::dsp::IIR::Coefficients<float>::makeLowShelf (
+        sampleRate, 40.0f, 0.707f, juce::Decibels::decibelsToGain (0.4f));
+    steelBoostL.coefficients = steelCoeffs;
+    steelBoostR.coefficients = steelCoeffs;
+}
+
+void TransformerSaturation::reset()
+{
+    oversampler.reset();
+    ironBoostL.reset(); ironBoostR.reset();
+    steelBoostL.reset(); steelBoostR.reset();
+}
+
+void TransformerSaturation::processBlock (juce::AudioBuffer<float>& buffer, Type type)
+{
+    if (type == Off) return;
+
+    const int numChannels = std::min (buffer.getNumChannels(), 2);
+    const int numSamples = buffer.getNumSamples();
+
+    // Select parameters per type:
+    //   drive:  how hard the tanh clips (1.0 = no effect)
+    //   even:   2nd harmonic amount (asymmetric warmth)
+    //   odd:    3rd harmonic amount (edge/presence)
+    //   mix:    wet/dry blend (keeps effect very subtle)
+    float drive, even, odd, mix;
+
+    switch (type)
+    {
+        case Nickel:
+            drive = 1.05f;  even = 0.002f;  odd = 0.0005f; mix = 0.3f;
+            break;
+        case Iron:
+            drive = 1.15f;  even = 0.008f;  odd = 0.002f;  mix = 0.5f;
+            break;
+        case Steel:
+            drive = 1.3f;   even = 0.012f;  odd = 0.008f;  mix = 0.6f;
+            break;
+        default:
+            return;
+    }
+
+    // 4x upsample
+    juce::dsp::AudioBlock<float> block (buffer);
+    auto oversampledBlock = oversampler.processSamplesUp (block);
+
+    const int osNumSamples = (int) oversampledBlock.getNumSamples();
+    const int osNumChannels = std::min ((int) oversampledBlock.getNumChannels(), 2);
+
+    // Apply waveshaping at oversampled rate
+    for (int ch = 0; ch < osNumChannels; ++ch)
+    {
+        float* data = oversampledBlock.getChannelPointer ((size_t) ch);
+
+        for (int i = 0; i < osNumSamples; ++i)
+        {
+            float x = data[i];
+            float dry = x;
+
+            // Soft-clip: tanh(drive*x)/drive — unity gain at DC
+            float shaped = std::tanh (drive * x) / drive;
+
+            // Add subtle harmonic content
+            shaped += even * x * std::abs (x);    // 2nd harmonic (even-order)
+            shaped -= odd * x * x * x;            // 3rd harmonic (odd-order)
+
+            // Blend dry/wet to keep the effect subtle
+            data[i] = dry + (shaped - dry) * mix;
+        }
+    }
+
+    // 4x downsample
+    oversampler.processSamplesDown (block);
+
+    // Post-saturation tonestack (very subtle EQ coloration)
+    if (type == Iron)
+    {
+        for (int i = 0; i < numSamples; ++i)
+        {
+            if (numChannels > 0) buffer.setSample (0, i, ironBoostL.processSample (buffer.getSample (0, i)));
+            if (numChannels > 1) buffer.setSample (1, i, ironBoostR.processSample (buffer.getSample (1, i)));
+        }
+    }
+    else if (type == Steel)
+    {
+        for (int i = 0; i < numSamples; ++i)
+        {
+            if (numChannels > 0) buffer.setSample (0, i, steelBoostL.processSample (buffer.getSample (0, i)));
+            if (numChannels > 1) buffer.setSample (1, i, steelBoostR.processSample (buffer.getSample (1, i)));
+        }
+    }
+}