SSB demod: use log (dB) to set volume from the GUI

plugins/channelrx/demodssb/readme.md

@@ -106,7 +106,7 @@ Values are expressed in kHz and step is 100 Hz.
 
 <h4>11.1: Volume</h4>
 
-This is the volume of the audio signal from 0.0 (mute) to 10.0 (maximum). It can be varied continuously in 0.1 steps using the dial button.
+This is the volume of the audio signal in dB from 0 (no gain) to 40 (10000). It can be varied continuously in 1 dB steps using the dial button. When AGC is engaged it is recommended to set a low value in dB not exceeding 3 db (gain 2). When AGC is not engaged the volume entirely depends on the RF power and can vary in large proportions. Hence setting the value in dB is more convenient to accomodate large differences.
 
 <h4>11.2: AGC toggle</h4>
 

plugins/channelrx/demodssb/ssbdemodgui.cpp

@@ -147,8 +147,8 @@ void SSBDemodGUI::on_lowCut_valueChanged(int value)
 
 void SSBDemodGUI::on_volume_valueChanged(int value)
 {
-	ui->volumeText->setText(QString("%1").arg(value / 10.0, 0, 'f', 1));
-	m_settings.m_volume = value / 10.0;
+	ui->volumeText->setText(QString("%1").arg(value));
+	m_settings.m_volume = CalcDb::powerFromdB(value);
 	applySettings();
 }
 
@@ -545,8 +545,9 @@ void SSBDemodGUI::displaySettings()
     ui->lowCut->setValue(m_settings.m_lowCutoff / 100.0);
     ui->lowCutText->setText(tr("%1k").arg(m_settings.m_lowCutoff / 1000.0));
 
-    ui->volume->setValue(m_settings.m_volume * 10.0);
-    ui->volumeText->setText(QString("%1").arg(m_settings.m_volume, 0, 'f', 1));
+    int volume = CalcDb::dbPower(m_settings.m_volume);
+    ui->volume->setValue(volume);
+    ui->volumeText->setText(QString("%1").arg(volume));
 
     ui->agcTimeLog2->setValue(m_settings.m_agcTimeLog2);
     s = QString::number((1<<ui->agcTimeLog2->value()), 'f', 0);

plugins/channelrx/demodssb/ssbdemodgui.ui

@@ -682,6 +682,12 @@
           <height>24</height>
          </size>
         </property>
+        <property name="toolTip">
+         <string>Audio volume in dB</string>
+        </property>
+        <property name="maximum">
+         <number>40</number>
+        </property>
         <property name="pageStep">
          <number>1</number>
         </property>
@@ -689,14 +695,11 @@
       </item>
       <item>
        <widget class="QLabel" name="volumeText">
-        <property name="maximumSize">
-         <size>
-          <width>30</width>
-          <height>16777215</height>
-         </size>
+        <property name="toolTip">
+         <string>Audio volume in dB</string>
         </property>
         <property name="text">
-         <string>2.0</string>
+         <string>10</string>
         </property>
         <property name="alignment">
          <set>Qt::AlignRight|Qt::AlignTrailing|Qt::AlignVCenter</set>