diff --git a/gtk2_ardour/audio_region_view.cc b/gtk2_ardour/audio_region_view.cc
index b1ca071e8a..4d45d6d837 100644
--- a/gtk2_ardour/audio_region_view.cc
+++ b/gtk2_ardour/audio_region_view.cc
@@ -21,7 +21,6 @@
 #include <algorithm>
 
 #include <boost/scoped_array.hpp>
-#include <boost/scoped_ptr.hpp>
 
 #include <gtkmm.h>
 
@@ -1538,7 +1537,7 @@ AudioRegionView::redraw_end_xfade_to (boost::shared_ptr<AudioRegion> ar, framecn
 	}
 
 	Points* points = get_canvas_points ("xfade edit redraw", npoints);
-	boost::scoped_ptr<float> vec (new float[npoints]);
+	boost::scoped_array<float> vec (new float[npoints]);
 
 	ar->fade_out()->curve().get_vector (0, ar->fade_out()->back()->when, vec.get(), npoints);
 
diff --git a/libs/ardour/ardour/audiosource.h b/libs/ardour/ardour/audiosource.h
index cbdcd296af..344541d945 100644
--- a/libs/ardour/ardour/audiosource.h
+++ b/libs/ardour/ardour/audiosource.h
@@ -21,6 +21,7 @@
 #define __ardour_audio_source_h__
 
 #include <boost/shared_ptr.hpp>
+#include <boost/shared_array.hpp>
 #include <boost/enable_shared_from_this.hpp>
 
 #include <time.h>
@@ -116,8 +117,8 @@ class AudioSource : virtual public Source,
 	   thread, or a lock around calls that use them.
 	*/
 
-	static std::vector<boost::shared_ptr<Sample> > _mixdown_buffers;
-	static std::vector<boost::shared_ptr<gain_t> > _gain_buffers;
+        static std::vector<boost::shared_array<Sample> > _mixdown_buffers;
+	static std::vector<boost::shared_array<gain_t> > _gain_buffers;
         static Glib::Threads::Mutex    _level_buffer_lock;
 
 	static void ensure_buffers_for_level (uint32_t, framecnt_t);
diff --git a/libs/ardour/audio_playlist.cc b/libs/ardour/audio_playlist.cc
index b008e4ff98..6ef4ec6454 100644
--- a/libs/ardour/audio_playlist.cc
+++ b/libs/ardour/audio_playlist.cc
@@ -164,8 +164,8 @@ ARDOUR::framecnt_t
 AudioPlaylist::read (Sample *buf, Sample *mixdown_buffer, float *gain_buffer, framepos_t start,
 		     framecnt_t cnt, unsigned chan_n)
 {
-	DEBUG_TRACE (DEBUG::AudioPlayback, string_compose ("Playlist %1 read @ %2 for %3, channel %4, regions %5\n",
-							   name(), start, cnt, chan_n, regions.size()));
+	DEBUG_TRACE (DEBUG::AudioPlayback, string_compose ("Playlist %1 read @ %2 for %3, channel %4, regions %5 mixdown @ %6 gain @ %7\n",
+							   name(), start, cnt, chan_n, regions.size(), mixdown_buffer, gain_buffer));
 
 	/* optimizing this memset() away involves a lot of conditionals
 	   that may well cause more of a hit due to cache misses
diff --git a/libs/ardour/audio_playlist_source.cc b/libs/ardour/audio_playlist_source.cc
index 915aee9595..f82cb7de00 100644
--- a/libs/ardour/audio_playlist_source.cc
+++ b/libs/ardour/audio_playlist_source.cc
@@ -127,8 +127,8 @@ AudioPlaylistSource::set_state (const XMLNode& node, int version, bool with_desc
 framecnt_t
 AudioPlaylistSource::read_unlocked (Sample* dst, framepos_t start, framecnt_t cnt) const
 {
-	boost::shared_ptr<Sample> sbuf;
-	boost::shared_ptr<gain_t> gbuf;
+	boost::shared_array<Sample> sbuf;
+	boost::shared_array<gain_t> gbuf;
 	framecnt_t to_read;
 	framecnt_t to_zero;
 
diff --git a/libs/ardour/audiosource.cc b/libs/ardour/audiosource.cc
index 4deb053cd8..5b60c577ee 100644
--- a/libs/ardour/audiosource.cc
+++ b/libs/ardour/audiosource.cc
@@ -47,8 +47,8 @@ using namespace ARDOUR;
 using namespace PBD;
 
 Glib::Threads::Mutex AudioSource::_level_buffer_lock;
-vector<boost::shared_ptr<Sample> > AudioSource::_mixdown_buffers;
-vector<boost::shared_ptr<gain_t> > AudioSource::_gain_buffers;
+vector<boost::shared_array<Sample> > AudioSource::_mixdown_buffers;
+vector<boost::shared_array<gain_t> > AudioSource::_gain_buffers;
 size_t AudioSource::_working_buffers_size = 0;
 bool AudioSource::_build_missing_peakfiles = false;
 
@@ -984,11 +984,19 @@ AudioSource::ensure_buffers_for_level_locked (uint32_t level, framecnt_t frame_r
 {
 	framecnt_t nframes = (framecnt_t) floor (Config->get_audio_playback_buffer_seconds() * frame_rate);
 
+	/* this may be called because either "level" or "frame_rate" have
+	 * changed. and it may be called with "level" smaller than the current
+	 * number of buffers, because a new compound region has been created at
+	 * a more shallow level than the deepest one we currently have.
+	 */
+
+	uint32_t limit = max ((size_t) level, _mixdown_buffers.size());
+
 	_mixdown_buffers.clear ();
 	_gain_buffers.clear ();
 
-	while (_mixdown_buffers.size() < level) {
-		_mixdown_buffers.push_back (boost::shared_ptr<Sample> (new Sample[nframes]));
-		_gain_buffers.push_back (boost::shared_ptr<gain_t> (new gain_t[nframes]));
+	for (uint32_t n = 0; n < limit; ++n) {
+		_mixdown_buffers.push_back (boost::shared_array<Sample> (new Sample[nframes]));
+		_gain_buffers.push_back (boost::shared_array<gain_t> (new gain_t[nframes]));
 	}
 }