diff --git a/src/dataformatpanel.cpp b/src/dataformatpanel.cpp
--- a/src/dataformatpanel.cpp
+++ b/src/dataformatpanel.cpp
@@ -93,6 +93,7 @@ void DataFormatPanel::enableDemo(bool en
     if (enabled)
     {
         readerBeforeDemo = currentReader;
+        demoReader.setNumChannels(readerBeforeDemo->numChannels());
         selectReader(&demoReader);
     }
     else