More Accuracy in SimpleMeter and Node RMS Calculations

include/element/processor.hpp

@@ -263,10 +263,10 @@ class Processor : public juce::ReferenceCountedObject {
      */
     GraphNode* getParentGraph() const;
 
-    void setInputRMS (int chan, float val);
-    float getInputRMS (int chan) const { return (chan < inRMS.size()) ? inRMS.getUnchecked (chan)->get() : 0.0f; }
-    void setOutputRMS (int chan, float val);
-    float getOutputRMS (int chan) const { return (chan < outRMS.size()) ? outRMS.getUnchecked (chan)->get() : 0.0f; }
+    void setInputRMS (int chan, float rms, int numSamples);
+    float getInputRMS (int chan) const { return (chan < inRMS.size()) ? inRMS.getUnchecked (chan)->value.get() : 0.0f; }
+    void setOutputRMS (int chan, float rms, int numSamples);
+    float getOutputRMS (int chan) const { return (chan < outRMS.size()) ? outRMS.getUnchecked (chan)->value.get() : 0.0f; }
 
     //=========================================================================
     /** Connect this node's output audio to another node's input audio */
@@ -553,7 +553,18 @@ class Processor : public juce::ReferenceCountedObject {
     PatchParameterArray _patches;
 
     juce::Atomic<float> gain, lastGain, inputGain, lastInputGain;
-    juce::OwnedArray<AtomicValue<float>> inRMS, outRMS;
+
+    /** Per-channel RMS meter integrator. Accumulates the block mean-square with a
+        fixed time constant so the metered level is independent of the host's
+        buffer size (see updateRMSMeter). */
+    struct RMSMeter {
+        float meanSquare = 0.0f;  // running mean-square, audio thread only
+        AtomicValue<float> value; // smoothed linear RMS handed to the UI thread
+    };
+    juce::OwnedArray<RMSMeter> inRMS, outRMS;
+
+    /** Integrates a block's RMS into the given meter with a fixed time window. */
+    void updateRMSMeter (RMSMeter& meter, float blockRMS, int numSamples);
 
     juce::Atomic<int> keyRangeLow { 0 };
     juce::Atomic<int> keyRangeHigh { 127 };

src/engine/graphbuilder.cpp

@@ -279,7 +279,7 @@ class ProcessBufferOp : public GraphOp
         }
 
         for (int i = numAudioIns; --i >= 0;)
-            node->setInputRMS (i, buffer.getRMSLevel (i, 0, numSamples));
+            node->setInputRMS (i, buffer.getRMSLevel (i, 0, numSamples), numSamples);
 
         // Begin MIDI filters
         {
@@ -448,7 +448,7 @@ class ProcessBufferOp : public GraphOp
         lastMute = muted;
 
         for (int i = 0; i < numAudioOuts; ++i)
-            node->setOutputRMS (i, buffer.getRMSLevel (i, 0, numSamples));
+            node->setOutputRMS (i, buffer.getRMSLevel (i, 0, numSamples), numSamples);
     }
 
     const ProcessorPtr node;

src/engine/processor.cpp

@@ -205,16 +205,34 @@ bool Processor::isMidiDeviceNode() const
 int Processor::getNumAudioInputs() const { return ports.size (PortType::Audio, true); }
 int Processor::getNumAudioOutputs() const { return ports.size (PortType::Audio, false); }
 
-void Processor::setInputRMS (int chan, float val)
+void Processor::updateRMSMeter (RMSMeter& meter, float blockRMS, int numSamples)
+{
+    // Integrate the block mean-square with a one-pole filter whose coefficient
+    // scales with the block length. This yields a fixed integration window
+    // regardless of the host buffer size, so the metered level (and its
+    // ballistics) no longer change when the audio device block size changes.
+    static constexpr double integrationSeconds = 0.3;
+
+    if (numSamples <= 0)
+        return;
+
+    const double fs = sampleRate > 0.0 ? sampleRate : 44100.0;
+    const float ms = blockRMS * blockRMS;
+    const float alpha = (float) (1.0 - std::exp (-(double) numSamples / (integrationSeconds * fs)));
+    meter.meanSquare += (ms - meter.meanSquare) * alpha;
+    meter.value.set (std::sqrt (meter.meanSquare));
+}
+
+void Processor::setInputRMS (int chan, float rms, int numSamples)
 {
     if (chan < inRMS.size())
-        inRMS.getUnchecked (chan)->set (val);
+        updateRMSMeter (*inRMS.getUnchecked (chan), rms, numSamples);
 }
 
-void Processor::setOutputRMS (int chan, float val)
+void Processor::setOutputRMS (int chan, float rms, int numSamples)
 {
     if (chan < outRMS.size())
-        outRMS.getUnchecked (chan)->set (val);
+        updateRMSMeter (*outRMS.getUnchecked (chan), rms, numSamples);
 }
 
 bool Processor::isSuspended() const
@@ -339,19 +357,11 @@ void Processor::prepare (const double newSampleRate,
 
         inRMS.clearQuick (true);
         for (int i = 0; i < getNumAudioInputs(); ++i)
-        {
-            AtomicValue<float>* avf = new AtomicValue<float>();
-            avf->set (0);
-            inRMS.add (avf);
-        }
+            inRMS.add (new RMSMeter());
 
         outRMS.clearQuick (true);
         for (int i = 0; i < getNumAudioOutputs(); ++i)
-        {
-            AtomicValue<float>* avf = new AtomicValue<float>();
-            avf->set (0);
-            outRMS.add (avf);
-        }
+            outRMS.add (new RMSMeter());
     }
 }
 
@@ -778,18 +788,10 @@ void Processor::setPorts (const PortList& newPorts)
     if (isPrepared)
     {
         for (int i = inRMS.size(); i < getNumAudioInputs(); ++i)
-        {
-            auto* avf = new AtomicValue<float>();
-            avf->set (0);
-            inRMS.add (avf);
-        }
+            inRMS.add (new RMSMeter());
 
         for (int i = outRMS.size(); i < getNumAudioOutputs(); ++i)
-        {
-            auto* avf = new AtomicValue<float>();
-            avf->set (0);
-            outRMS.add (avf);
-        }
+            outRMS.add (new RMSMeter());
     }
 }
 

src/ui/simplemeter.cpp

@@ -6,6 +6,10 @@
 // Meter level limits (in dB).
 #define DIGITAL_METER_MAX_DB (+4.0f)
 #define DIGITAL_METER_MIN_DB (-70.0f)
+// AES-17 dBFS calibration: the incoming value is a linear RMS amplitude, whose
+// level for a sine sits 3.01 dB below its peak. Adding this offset defines 0 dBFS
+// as a full-scale sine, so a -20 dBFS sine reads -20 dB rather than -23 dB.
+#define DIGITAL_METER_RMS_CAL_DB (+3.0103f)
 // The decay rates (magic goes here :).
 // - value decay rate (faster)
 #define DIGITAL_METER_DECAY_RATE1 (1.0f - 3E-2f)
@@ -78,7 +82,7 @@ void SimpleMeterValue::paint (Graphics& g)
 
     float dB = DIGITAL_METER_MIN_DB;
     if (value > 0.0f)
-        dB = 20.0f * log10f (value);
+        dB = 20.0f * log10f (value) + DIGITAL_METER_RMS_CAL_DB;
 
     if (dB < DIGITAL_METER_MIN_DB)
         dB = DIGITAL_METER_MIN_DB;