Change order of sub-band matching in the Downchannelizer. Fixes possi…

…ble aliasing issues. Fixes #1846
f4exb · Oct 15, 2023 · 8ca7dbb · 8ca7dbb
1 parent 8c98a48
commit 8ca7dbb
Showing 1 changed file with 12 additions and 12 deletions.
diff --git a/sdrbase/dsp/downchannelizer.cpp b/sdrbase/dsp/downchannelizer.cpp
@@ -233,34 +233,34 @@ Real DownChannelizer::createFilterChain(Real sigStart, Real sigEnd, Real chanSta
 	Real sigBw = sigEnd - sigStart;
 	Real rot = sigBw / 4;
 
-	//qDebug("DownChannelizer::createFilterChain: Signal [%.1f, %.1f] (BW %.1f), Channel [%.1f, %.1f], Rot %.1f", sigStart, sigEnd, sigBw, chanStart, chanEnd, rot);
+	qDebug("DownChannelizer::createFilterChain: Signal [%.1f, %.1f] (BW %.1f), Channel [%.1f, %.1f], Rot %.1f", sigStart, sigEnd, sigBw, chanStart, chanEnd, rot);
+
+	// check if it fits into the center
+	if(signalContainsChannel(sigStart + rot, sigEnd - rot, chanStart, chanEnd))
+    {
+		qDebug("DownChannelizer::createFilterChain: -> take center half (decimate by 2)");
+		m_filterStages.push_back(new FilterStage(FilterStage::ModeCenter));
+		return createFilterChain(sigStart + rot, sigEnd - rot, chanStart, chanEnd);
+	}
 
 	// check if it fits into the left half
 	if(signalContainsChannel(sigStart, sigStart + sigBw / 2.0, chanStart, chanEnd))
     {
-		//qDebug("DownChannelizer::createFilterChain: -> take left half (rotate by +1/4 and decimate by 2)");
+		qDebug("DownChannelizer::createFilterChain: -> take left half (rotate by +1/4 and decimate by 2)");
 		m_filterStages.push_back(new FilterStage(FilterStage::ModeLowerHalf));
 		return createFilterChain(sigStart, sigStart + sigBw / 2.0, chanStart, chanEnd);
 	}
 
 	// check if it fits into the right half
 	if(signalContainsChannel(sigEnd - sigBw / 2.0f, sigEnd, chanStart, chanEnd))
     {
-		//qDebug("DownChannelizer::createFilterChain: -> take right half (rotate by -1/4 and decimate by 2)");
+		qDebug("DownChannelizer::createFilterChain: -> take right half (rotate by -1/4 and decimate by 2)");
 		m_filterStages.push_back(new FilterStage(FilterStage::ModeUpperHalf));
 		return createFilterChain(sigEnd - sigBw / 2.0f, sigEnd, chanStart, chanEnd);
 	}
 
-	// check if it fits into the center
-	if(signalContainsChannel(sigStart + rot, sigEnd - rot, chanStart, chanEnd))
-    {
-		//qDebug("DownChannelizer::createFilterChain: -> take center half (decimate by 2)");
-		m_filterStages.push_back(new FilterStage(FilterStage::ModeCenter));
-		return createFilterChain(sigStart + rot, sigEnd - rot, chanStart, chanEnd);
-	}
-
 	Real ofs = ((chanEnd - chanStart) / 2.0 + chanStart) - ((sigEnd - sigStart) / 2.0 + sigStart);
-	//qDebug("DownChannelizer::createFilterChain: -> complete (final BW %.1f, frequency offset %.1f)", sigBw, ofs);
+	qDebug("DownChannelizer::createFilterChain: -> complete (final BW %.1f, frequency offset %.1f)", sigBw, ofs);
 	return ofs;
 }