Document the output-limiter config option

Expose it in alsoft-config as well.

alsoftrc.sample

@@ -181,6 +181,12 @@
 #  than the default has no effect.
 #sends = 16
 
+## output-limiter:
+#  Applies a gain limiter on the final mixed output. This reduces the volume
+#  when the output samples would otherwise clamp, avoiding excessive clipping
+#  noise.
+#output-limiter = true
+
 ## volume-adjust:
 #  A global volume adjustment for source output, expressed in decibels. The
 #  value is logarithmic, so +6 will be a scale of (approximately) 2x, +12 will

utils/alsoft-config/mainwindow.cpp

@@ -328,6 +328,7 @@ MainWindow::MainWindow(QWidget *parent) :
 
     connect(ui->stereoEncodingComboBox, SIGNAL(currentIndexChanged(QString)), this, SLOT(enableApplyButton()));
     connect(ui->ambiFormatComboBox, SIGNAL(currentIndexChanged(QString)), this, SLOT(enableApplyButton()));
+    connect(ui->outputLimiterCheckBox, SIGNAL(stateChanged(int)), this, SLOT(enableApplyButton()));
 
     connect(ui->decoderHQModeCheckBox, SIGNAL(stateChanged(int)), this, SLOT(enableApplyButton()));
     connect(ui->decoderDistCompCheckBox, SIGNAL(stateChanged(int)), this, SLOT(enableApplyButton()));
@@ -641,6 +642,13 @@ void MainWindow::loadConfig(const QString &fname)
         updatePeriodCountSlider();
     }
 
+    if(settings.value("output-limiter").isNull())
+        ui->outputLimiterCheckBox->setCheckState(Qt::PartiallyChecked);
+    else
+        ui->outputLimiterCheckBox->setCheckState(
+            settings.value("output-limiter").toBool() ? Qt::Checked : Qt::Unchecked
+        );
+
     QString stereopan = settings.value("stereo-encoding").toString();
     ui->stereoEncodingComboBox->setCurrentIndex(0);
     if(stereopan.isEmpty() == false)
@@ -896,6 +904,14 @@ void MainWindow::saveConfig(const QString &fname) const
     settings.setValue("stereo-encoding", getValueFromName(stereoEncList, ui->stereoEncodingComboBox->currentText()));
     settings.setValue("ambi-format", getValueFromName(ambiFormatList, ui->ambiFormatComboBox->currentText()));
 
+    Qt::CheckState limiter = ui->outputLimiterCheckBox->checkState();
+    if(limiter == Qt::PartiallyChecked)
+        settings.setValue("output-limiter", QString());
+    else if(limiter == Qt::Checked)
+        settings.setValue("output-limiter", QString("true"));
+    else if(limiter == Qt::Unchecked)
+        settings.setValue("output-limiter", QString("false"));
+
     settings.setValue("decoder/hq-mode",
         ui->decoderHQModeCheckBox->isChecked() ? QString("true") : QString(/*"false"*/)
     );

utils/alsoft-config/mainwindow.ui

@@ -129,7 +129,7 @@ to stereo output.</string>
         <x>380</x>
         <y>20</y>
         <width>91</width>
-        <height>21</height>
+        <height>29</height>
        </rect>
       </property>
       <property name="toolTip">
@@ -236,9 +236,9 @@ otherwise be suitable for speakers.</string>
       <property name="geometry">
        <rect>
         <x>-11</x>
-        <y>200</y>
+        <y>180</y>
         <width>551</width>
-        <height>181</height>
+        <height>201</height>
        </rect>
       </property>
       <property name="title">
@@ -483,6 +483,27 @@ receiver.</string>
         </rect>
        </property>
       </widget>
+      <widget class="QCheckBox" name="outputLimiterCheckBox">
+       <property name="geometry">
+        <rect>
+         <x>30</x>
+         <y>160</y>
+         <width>231</width>
+         <height>20</height>
+        </rect>
+       </property>
+       <property name="toolTip">
+        <string>Applies a gain limiter on the final mixed output. This reduces the
+volume when the output samples would otherwise be clamped,
+avoiding excessive clipping noise.</string>
+       </property>
+       <property name="text">
+        <string>Enable Gain Limiter</string>
+       </property>
+       <property name="tristate">
+        <bool>true</bool>
+       </property>
+      </widget>
      </widget>
      <widget class="QGroupBox" name="groupBox_4">
       <property name="geometry">
@@ -2107,7 +2128,7 @@ added by the ALC_EXT_DEDICATED extension.</string>
         <x>160</x>
         <y>20</y>
         <width>123</width>
-        <height>21</height>
+        <height>29</height>
        </rect>
       </property>
       <property name="sizeAdjustPolicy">