#36 NBFM squelch control. Updates NBFM decoder to incorporate squelch control. Squelch is a configuration item and also available to adjust at runtime with new 'Channel' tab in Now Playing window. All decoders were updated to produce continuous channel power (dB) measurements that are displayed in the Channel tab's new Power Meter. (#1100)

Co-authored-by: Dennis Sheirer <dsheirer@github.com>

src/main/java/io/github/dsheirer/source/SourceEvent.java

@@ -34,6 +34,7 @@ public class SourceEvent
     {
         NOTIFICATION_CHANNEL_COUNT_CHANGE,
         NOTIFICATION_CHANNEL_FREQUENCY_CORRECTION_CHANGE,
+        NOTIFICATION_CHANNEL_POWER,
         NOTIFICATION_CHANNEL_SAMPLE_RATE_CHANGE,
         NOTIFICATION_FREQUENCY_AND_SAMPLE_RATE_LOCKED,
         NOTIFICATION_FREQUENCY_AND_SAMPLE_RATE_UNLOCKED,
@@ -45,6 +46,7 @@ public class SourceEvent
         NOTIFICATION_MEASURED_FREQUENCY_ERROR_SYNC_LOCKED,
         NOTIFICATION_RECORDING_FILE_LOADED,
         NOTIFICATION_SAMPLE_RATE_CHANGE,
+        NOTIFICATION_SQUELCH_THRESHOLD,
         NOTIFICATION_STOP_SAMPLE_STREAM,
         NOTIFICATION_ERROR_STATE,
 
@@ -53,6 +55,8 @@ public class SourceEvent
         REQUEST_FREQUENCY_ROTATION,
         REQUEST_FREQUENCY_SELECTION,
         REQUEST_SOURCE_DISPOSE,
+        REQUEST_CHANGE_SQUELCH_THRESHOLD,
+        REQUEST_CURRENT_SQUELCH_THRESHOLD,
         REQUEST_START_SAMPLE_STREAM,
         REQUEST_STOP_SAMPLE_STREAM;
 
@@ -421,6 +425,50 @@ public class SourceEvent
         return new SourceEvent(Event.NOTIFICATION_FREQUENCY_ROTATION_FAILURE, source, frequency);
     }
 
+
+    /**
+     * Creates a notification of current channel power level
+     * @param source producing the notification
+     * @param powerDb of the channel (avg)
+     * @return new source event
+     */
+    public static SourceEvent channelPowerLevel(Source source, double powerDb)
+    {
+        return new SourceEvent(Event.NOTIFICATION_CHANNEL_POWER, source, powerDb);
+    }
+
+    /**
+     * Creates a squelch threshold change notification
+     * @param source for the event
+     * @param thresholdDb setting for the power squelch
+     * @return new source event
+     */
+    public static SourceEvent squelchThreshold(Source source, double thresholdDb)
+    {
+        return new SourceEvent(Event.NOTIFICATION_SQUELCH_THRESHOLD, source, thresholdDb);
+    }
+
+    /**
+     * Requests the current squelch threshold value
+     * @param source optional
+     * @return source event
+     */
+    public static SourceEvent requestCurrentSquelchThreshold(Source source)
+    {
+        return new SourceEvent(Event.REQUEST_CURRENT_SQUELCH_THRESHOLD, source, 0);
+    }
+
+    /**
+     * Creates a new squelch threshold level be applied to the channel's power squelch control
+     * @param source of the request
+     * @param thresholdDb setting to apply
+     * @return new source event
+     */
+    public static SourceEvent requestSquelchThreshold(Source source, double thresholdDb)
+    {
+        return new SourceEvent(Event.REQUEST_CHANGE_SQUELCH_THRESHOLD, source, thresholdDb);
+    }
+
     @Override
     public String toString()
     {