diff --git a/libs/ardour/ardour/types.h b/libs/ardour/ardour/types.h
index d518962288..ef2e51e70f 100644
--- a/libs/ardour/ardour/types.h
+++ b/libs/ardour/ardour/types.h
@@ -353,9 +353,9 @@ namespace ARDOUR {
 	};
 
 	enum MonitorModel {
-		HardwareMonitoring,
-		SoftwareMonitoring,
-		ExternalMonitoring
+		HardwareMonitoring, ///< JACK does monitoring
+		SoftwareMonitoring, ///< Ardour does monitoring
+		ExternalMonitoring  ///< we leave monitoring to the audio hardware
 	};
 
 	enum MonitorChoice {
diff --git a/libs/ardour/io.cc b/libs/ardour/io.cc
index 24bc587c0d..aac2adf784 100644
--- a/libs/ardour/io.cc
+++ b/libs/ardour/io.cc
@@ -1548,7 +1548,9 @@ IO::connected_to (const string& str) const
 	return false;
 }
 
-/** Caller must hold process lock */
+/** Call a processor's ::run() method, giving it our buffers
+ *  Caller must hold process lock.
+ */
 void
 IO::process_input (boost::shared_ptr<Processor> proc, framepos_t start_frame, framepos_t end_frame, pframes_t nframes)
 {