First pass at implementing a sidechain compressor, for mostly for lowering music volume when mic is active.

1 files changed, 76 insertions, 0 deletions

diff --git a/src/engine/enginesidechaincompressor.h b/src/engine/enginesidechaincompressor.h
new file mode 100644
index 0000000000..c18326b0ac
--- /dev/null
+++ b/src/engine/enginesidechaincompressor.h
@@ -0,0 +1,76 @@
+#ifndef ENGINECOMPRESSOR_H
+#define ENGINECOMPRESSOR_H
+
+#include "defs.h"
+#include "configobject.h"
+#include "engine/engineobject.h"
+
+class ControlObject;
+
+class EngineSideChainCompressor : public EngineObject {
+    Q_OBJECT
+  public:
+    EngineSideChainCompressor(ConfigObject<ConfigValue>* pConfig, const char* group);
+    virtual ~EngineSideChainCompressor() { };
+
+    void setThreshold(CSAMPLE threshold) {
+        m_threshold = threshold;
+        calculateRates();
+    }
+
+    void setStrength(CSAMPLE strength) {
+        m_strength = strength;
+        calculateRates();
+    }
+
+    void setAttackTime(unsigned int attack_time) {
+        m_attackTime = attack_time;
+        calculateRates();
+    }
+
+    void setDecayTime(unsigned int decay_time) {
+        m_decayTime = decay_time;
+        calculateRates();
+    }
+
+    // Every loop, before calling process, first call processKey to feed
+    // the compressor the input key signal.
+    void processKey(const CSAMPLE* pIn, const int iBufferSize);
+
+    void process(const CSAMPLE* pIn, CSAMPLE* pOut, const int iBufferSize);
+
+  private:
+    // Update the attack and decay rates.
+    void calculateRates();
+
+    // Calculates a new compression value for the next frame
+    // based on the current compression ratio and whether the current input is above threshold.
+    inline double calculateCompression(CSAMPLE currentRatio, bool aboveThreshold) const;
+
+    ConfigObject<ConfigValue>* m_pConfig;
+
+    // The current ratio the signal is being compressed.  This is the same as m_strength
+    // when the compressor is at maximum engagement (not attacking or decaying).
+    CSAMPLE m_compressRatio;
+
+    // True if the input signal is above the threshold.
+    bool m_bAboveThreshold;
+
+    // The sample value above which the compressor is triggered.
+    CSAMPLE m_threshold;
+
+    // The largest ratio the signal can be compressed.
+    CSAMPLE m_strength;
+
+    // The length of time, in frames (samples/2), until maximum compression is reached.
+    unsigned int m_attackTime;
+
+    // The length of time, in frames, until compression is completely off.
+    unsigned int m_decayTime;
+
+    // These are the delta compression values per sample based on the strengths and timings.
+    CSAMPLE m_attackPerFrame;
+    CSAMPLE m_decayPerFrame;
+};
+
+#endif