diff --git a/libs/ardour/ardour/diskstream.h b/libs/ardour/ardour/diskstream.h
index 2c1e8b01c1..4baf2668a6 100644
--- a/libs/ardour/ardour/diskstream.h
+++ b/libs/ardour/ardour/diskstream.h
@@ -110,6 +110,7 @@ class Diskstream : public SessionObject, public PublicDiskstream
 	virtual int use_new_playlist () = 0;
 	virtual int use_copy_playlist () = 0;
 
+	/** @return Capture start position in session frames */
 	framepos_t current_capture_start() const { return capture_start_frame; }
 	framepos_t current_capture_end()   const { return capture_start_frame + capture_captured; }
 	framepos_t get_capture_start_frame (uint32_t n=0);
@@ -260,7 +261,7 @@ class Diskstream : public SessionObject, public PublicDiskstream
 	bool         _seek_required;
 
 	bool          force_refill;
-	framepos_t    capture_start_frame;
+	framepos_t    capture_start_frame; ///< session frames
 	framecnt_t    capture_captured;
 	bool          was_recording;
 	nframes_t     adjust_capture_position;
diff --git a/libs/ardour/sndfilesource.cc b/libs/ardour/sndfilesource.cc
index b2b486813c..a8811cc9ff 100644
--- a/libs/ardour/sndfilesource.cc
+++ b/libs/ardour/sndfilesource.cc
@@ -631,6 +631,7 @@ SndFileSource::clear_capture_marks ()
 	_capture_end = false;
 }
 
+/** @param pos Capture start position in session frames */
 void
 SndFileSource::mark_capture_start (framepos_t pos)
 {