feat(dsp): add core synthesizer oscillators, wavetable and voice engine

Source/SubOscillator.h

@@ -0,0 +1,29 @@
+#pragma once
+
+#include <JuceHeader.h>
+#include "Params.h"
+
+namespace serum
+{
+
+// ===========================================================================
+// Simple sub oscillator: sine or triangle, one/two octaves down or unison.
+// ===========================================================================
+class SubOscillator
+{
+public:
+    void prepare (double sampleRate)  { sr = sampleRate; phase = 0.0; }
+    void reset()                       { phase = 0.0; }
+
+    void noteOn (double freqHz, int octaveShift);
+
+    // Accumulate into out (mono; the caller pans/levels it).
+    void processAdd (double freqHz, int shape, float level, float& out) noexcept;
+
+private:
+    double sr    = 44100.0;
+    double phase = 0.0;
+    static constexpr double kTwoPi = 6.28318530717958647692;
+};
+
+} // namespace serum