SSB demod: reworked AGC to handle the threshold gate properly

plugins/channelrx/demodssb/readme.md

@@ -2,7 +2,7 @@
 
 <h2>Introduction</h2>
 
-This plugin can be used to listen to a single sideband or double sidebands modulated signal. 
+This plugin can be used to listen to a single sideband or double sidebands modulated signal.
 
 <h2>Interface</h2>
 
@@ -24,7 +24,7 @@ Average total power in dB relative to a +/- 1.0 amplitude signal received in the
 
   - Monaural: the scalar signal is routed to both left and right audio channels
   - Binaural: the complex signal is fed with the real part on the left audio channel and the imaginary part to the right audio channel
-  
+
 <h3>4: Invert left and right channels</h3>
 
 Inverts left and right audio channels. Useful in binaural mode only.
@@ -91,7 +91,7 @@ This is how the Span (8) and bandpass (9, 10) filter controls look like in the 3
 Values are expressed in kHz and step is 100 Hz.
 
   - In SSB mode this is the upper (USB: positive frequencies) or lower (LSB: negative frequencies) cutoff of the in channel single side band bandpass filter. The value triggers LSB mode when negative and USB when positive
-  - In DSB mode this is half the bandwidth of the double side band in channel bandpass filter therefore the value is prefixed with the &#177; sign. 
+  - In DSB mode this is half the bandwidth of the double side band in channel bandpass filter therefore the value is prefixed with the &#177; sign.
 
 <h3>10: "Low cut": In channel bandpass filter cutoff frequency closest to zero</h3>
 
@@ -140,7 +140,7 @@ The signal power is calculated as the moving average over the AGC time constant
 
 Active only in AGC mode with squelch enabled.
 
-To avoid unwanted squelch opening on short transient bursts only signals with power above threshold during this period in milliseconds will open the squelch.It can be varied from 0 to 20 ms in 1 ms steps.
+To avoid unwanted squelch opening on short transient bursts only signals with power above threshold during this period in milliseconds will open the squelch.It can be varied from 0 to 20 ms in 1 ms steps then from 30 to 500 ms in 10 ms steps.
 
 When the power threshold is close to the noise floor a few milliseconds help in preventing noise power wiggle to open the squelch.
 

plugins/channelrx/demodssb/ssbdemodgui.cpp

@@ -202,9 +202,10 @@ void SSBDemodGUI::on_agcPowerThreshold_valueChanged(int value)
 
 void SSBDemodGUI::on_agcThresholdGate_valueChanged(int value)
 {
-    QString s = QString::number(value, 'f', 0);
+    int agcThresholdGate = value < 20 ? value : ((value - 20) * 10) + 20;
+    QString s = QString::number(agcThresholdGate, 'f', 0);
     ui->agcThresholdGateText->setText(s);
-    m_settings.m_agcThresholdGate = value;
+    m_settings.m_agcThresholdGate = agcThresholdGate;
     applySettings();
 }
 
@@ -565,10 +566,7 @@ void SSBDemodGUI::displaySettings()
 
     ui->agcPowerThreshold->setValue(m_settings.m_agcPowerThreshold);
     displayAGCPowerThreshold(ui->agcPowerThreshold->value());
-
-    ui->agcThresholdGate->setValue(m_settings.m_agcThresholdGate);
-    s = QString::number(ui->agcThresholdGate->value(), 'f', 0);
-    ui->agcThresholdGateText->setText(s);
+    displayAGCThresholdGate(m_settings.m_agcThresholdGate);
 
     blockApplySettings(false);
 }
@@ -586,6 +584,19 @@ void SSBDemodGUI::displayAGCPowerThreshold(int value)
     }
 }
 
+void SSBDemodGUI::displayAGCThresholdGate(int value)
+{
+    QString s = QString::number(value, 'f', 0);
+    ui->agcThresholdGateText->setText(s);
+    int dialValue = value;
+
+    if (value > 20) {
+        dialValue = ((value - 20) / 10) + 20;
+    }
+
+    ui->agcThresholdGate->setValue(dialValue);
+}
+
 void SSBDemodGUI::leaveEvent(QEvent*)
 {
 	m_channelMarker.setHighlighted(false);

plugins/channelrx/demodssb/ssbdemodgui.h

@@ -73,8 +73,8 @@ private:
 	void applyBandwidths(int spanLog2, bool force = false);
     int spanLog2Limit(int spanLog2);
 	void displaySettings();
-
 	void displayAGCPowerThreshold(int value);
+    void displayAGCThresholdGate(int value);
 
 	void leaveEvent(QEvent*);
 	void enterEvent(QEvent*);

plugins/channelrx/demodssb/ssbdemodgui.ui

@@ -6,7 +6,7 @@
    <rect>
     <x>0</x>
     <y>0</y>
-    <width>412</width>
+    <width>414</width>
     <height>190</height>
    </rect>
   </property>
@@ -18,7 +18,7 @@
   </property>
   <property name="minimumSize">
    <size>
-    <width>412</width>
+    <width>414</width>
     <height>0</height>
    </size>
   </property>
@@ -36,13 +36,13 @@
     <rect>
      <x>0</x>
      <y>0</y>
-     <width>410</width>
+     <width>415</width>
      <height>171</height>
     </rect>
    </property>
    <property name="minimumSize">
     <size>
-     <width>410</width>
+     <width>415</width>
      <height>0</height>
     </size>
    </property>
@@ -836,7 +836,7 @@
          <string>Power threshold gate (ms)</string>
         </property>
         <property name="maximum">
-         <number>20</number>
+         <number>68</number>
         </property>
         <property name="pageStep">
          <number>1</number>
@@ -850,7 +850,7 @@
        <widget class="QLabel" name="agcThresholdGateText">
         <property name="minimumSize">
          <size>
-          <width>16</width>
+          <width>22</width>
           <height>0</height>
          </size>
         </property>
@@ -858,7 +858,7 @@
          <string>Power threshold gate (ms)</string>
         </property>
         <property name="text">
-         <string>00</string>
+         <string>000</string>
         </property>
         <property name="alignment">
          <set>Qt::AlignRight|Qt::AlignTrailing|Qt::AlignVCenter</set>

plugins/channelrx/demodssb/ssbplugin.cpp

@@ -9,7 +9,7 @@
 
 const PluginDescriptor SSBPlugin::m_pluginDescriptor = {
 	QString("SSB Demodulator"),
-	QString("4.8.2"),
+	QString("4.10.0"),
 	QString("(c) Edouard Griffiths, F4EXB"),
 	QString("https://github.com/f4exb/sdrangel"),
 	true,

sdrbase/dsp/agc.cpp

@@ -50,7 +50,7 @@ MagAGC::MagAGC(int historySize, double R, double threshold) :
 	m_stepLength(std::min(2400, historySize/2)), // max 50 ms (at 48 kHz)
     m_stepDelta(1.0/m_stepLength),
 	m_stepUpCounter(0),
-    m_stepDownCounter(m_stepLength),
+    m_stepDownCounter(0),
 	m_gateCounter(0),
 	m_stepDownDelay(historySize),
 	m_clamping(false),
@@ -68,7 +68,7 @@ void MagAGC::resize(int historySize, int stepLength, Real R)
     m_stepLength = stepLength;
     m_stepDelta = 1.0 / m_stepLength;
     m_stepUpCounter = 0;
-    m_stepDownCounter = m_stepLength;
+    m_stepDownCounter = 0;
     AGC::resize(historySize, R);
     m_moving_average.fill(0);
 }
@@ -85,7 +85,7 @@ void MagAGC::setThresholdEnable(bool enable)
     if (m_thresholdEnable != enable)
     {
         m_stepUpCounter = 0;
-        m_stepDownCounter = m_stepLength;
+        m_stepDownCounter = 0;
     }
 
     m_thresholdEnable = enable;
@@ -136,50 +136,55 @@ double MagAGC::feedAndGetValue(const Complex& ci)
 
     if (m_thresholdEnable)
     {
+        bool open = false;
+
         if (m_magsq > m_threshold)
         {
-            if (m_gateCounter < m_gate)
-            {
+            if (m_gateCounter < m_gate) {
                 m_gateCounter++;
-            }
-            else
-            {
-                m_count = 0;
+            } else {
+                open = true;
             }
         }
         else
         {
-            if (m_count < m_stepDownDelay) {
-                m_count++;
-            }
-
             m_gateCounter = 0;
         }
 
-        if (m_count <  m_stepDownDelay)
+        if (open)
         {
-            m_stepDownCounter = m_stepUpCounter;
+            m_count = m_stepDownDelay; // delay before step down (grace delay)
+        }
+        else
+        {
+            m_count--;
+            m_gateCounter = m_gate; // keep gate open during grace
+        }
 
-            if (m_stepUpCounter < m_stepLength)
+        if (m_count > 0) // up phase
+        {
+            m_stepDownCounter = m_stepUpCounter; // prepare for step down
+
+            if (m_stepUpCounter < m_stepLength) // step up
             {
                 m_stepUpCounter++;
                 return hardLimiter(m_u0 * StepFunctions::smootherstep(m_stepUpCounter * m_stepDelta), m_magsq);
             }
-            else
+            else // steady open
             {
                 return hardLimiter(m_u0, m_magsq);
             }
         }
-        else
+        else // down phase
         {
-            m_stepUpCounter = m_stepDownCounter;
+            m_stepUpCounter = m_stepDownCounter; // prepare for step up
 
-            if (m_stepDownCounter > 0)
+            if (m_stepDownCounter > 0) // step down
             {
                 m_stepDownCounter--;
                 return hardLimiter(m_u0 * StepFunctions::smootherstep(m_stepDownCounter * m_stepDelta), m_magsq);
             }
-            else
+            else // steady closed
             {
                 return 0.0;
             }
@@ -191,25 +196,13 @@ double MagAGC::feedAndGetValue(const Complex& ci)
     }
 }
 
-float MagAGC::getStepDownValue() const
-{
-    if (m_count <  m_stepDownDelay)
-    {
-        return 1.0f;
-    }
-    else
-    {
-        return StepFunctions::smootherstep(m_stepDownCounter * m_stepDelta);
-    }
-}
-
 float MagAGC::getStepValue() const
 {
-    if (m_count <  m_stepDownDelay)
+    if (m_count > 0) // up phase
     {
         return StepFunctions::smootherstep(m_stepUpCounter * m_stepDelta); // step up
     }
-    else
+    else // down phase
     {
         return StepFunctions::smootherstep(m_stepDownCounter * m_stepDelta); // step down
     }

sdrbase/dsp/agc.h

@@ -46,12 +46,11 @@ public:
     double getMagSq() const { return m_magsq; }
     void setThreshold(double threshold) { m_threshold = threshold; }
     void setThresholdEnable(bool enable);
-    void setGate(int gate) { m_gate = gate; }
-    void setStepDownDelay(int stepDownDelay) { m_stepDownDelay = stepDownDelay; }
+    void setGate(int gate) { m_gate = gate; m_gateCounter = 0; m_count = 0; }
+    void setStepDownDelay(int stepDownDelay) { m_stepDownDelay = stepDownDelay; m_gateCounter = 0; m_count = 0; }
     void setClamping(bool clamping) { m_clamping = clamping; }
     void setClampMax(double clampMax) { m_clampMax = clampMax; }
     int getStepDownDelay() const { return m_stepDownDelay; }
-    float getStepDownValue() const;
     float getStepValue() const;
     void setHardLimiting(bool hardLimiting) { m_hardLimiting = hardLimiting; }