diff --git a/libs/ardour/ardour/audioregion.h b/libs/ardour/ardour/audioregion.h
index 97a4db9c1b..e907971319 100644
--- a/libs/ardour/ardour/audioregion.h
+++ b/libs/ardour/ardour/audioregion.h
@@ -247,7 +247,7 @@ class LIBARDOUR_API AudioRegion : public Region, public AudioReadable
   protected:
 	/* default constructor for derived (compound) types */
 
-	AudioRegion (Session& s, timecnt_t const &, timecnt_t const &, std::string name);
+	AudioRegion (Session& s, timepos_t const &, timecnt_t const &, std::string name);
 
 	int _set_state (const XMLNode&, int version, PBD::PropertyChange& what_changed, bool send_signal);
 };
diff --git a/libs/ardour/ardour/midi_source.h b/libs/ardour/ardour/midi_source.h
index 717c28565b..64d090a2cb 100644
--- a/libs/ardour/ardour/midi_source.h
+++ b/libs/ardour/ardour/midi_source.h
@@ -102,7 +102,7 @@ class LIBARDOUR_API MidiSource : virtual public Source
 	virtual timecnt_t midi_read (const Lock&                       lock,
 	                             Evoral::EventSink<samplepos_t>&    dst,
 	                             timepos_t const &                  source_start,
-	                             timecnt_t const &                  start,
+	                             timepos_t const &                  start,
 	                             timecnt_t const &                  cnt,
 	                             Temporal::Range*                   loop_range,
 	                             MidiCursor&                        cursor,
@@ -209,7 +209,7 @@ class LIBARDOUR_API MidiSource : virtual public Source
 	virtual timecnt_t read_unlocked (const Lock&                     lock,
 	                                 Evoral::EventSink<samplepos_t>& dst,
 	                                 timepos_t const &               position,
-	                                 timecnt_t const &               start,
+	                                 timepos_t const &               start,
 	                                 timecnt_t const &               cnt,
 	                                 Temporal::Range*                loop_range,
 	                                 MidiStateTracker*               tracker,
diff --git a/libs/ardour/ardour/region.h b/libs/ardour/ardour/region.h
index 364b4b03e2..6f94ad6277 100644
--- a/libs/ardour/ardour/region.h
+++ b/libs/ardour/ardour/region.h
@@ -62,12 +62,12 @@ namespace Properties {
 	LIBARDOUR_API extern PBD::PropertyDescriptor<bool>              hidden;
 	LIBARDOUR_API extern PBD::PropertyDescriptor<bool>              position_locked;
 	LIBARDOUR_API extern PBD::PropertyDescriptor<bool>              valid_transients;
-	LIBARDOUR_API extern PBD::PropertyDescriptor<timecnt_t>         start;
+	LIBARDOUR_API extern PBD::PropertyDescriptor<timepos_t>         start;
 	LIBARDOUR_API extern PBD::PropertyDescriptor<timecnt_t>         length;
 	LIBARDOUR_API extern PBD::PropertyDescriptor<timepos_t>         position;
-	LIBARDOUR_API extern PBD::PropertyDescriptor<timecnt_t>         sync_position;
+	LIBARDOUR_API extern PBD::PropertyDescriptor<timepos_t>         sync_position;
 	LIBARDOUR_API extern PBD::PropertyDescriptor<layer_t>           layer;
-	LIBARDOUR_API extern PBD::PropertyDescriptor<timecnt_t>         ancestral_start;
+	LIBARDOUR_API extern PBD::PropertyDescriptor<timepos_t>         ancestral_start;
 	LIBARDOUR_API extern PBD::PropertyDescriptor<timecnt_t>         ancestral_length;
 	LIBARDOUR_API extern PBD::PropertyDescriptor<float>             stretch;
 	LIBARDOUR_API extern PBD::PropertyDescriptor<float>             shift;
@@ -119,7 +119,7 @@ public:
 	 */
 
 	timepos_t position ()  const { return _length.val().position(); }
-	timecnt_t start ()     const { return _start.val(); }
+	timepos_t start ()     const { return _start.val(); }
 	timecnt_t length ()    const { return _length.val(); }
 	timepos_t end()        const;
 	timepos_t nt_last()       const { return end().decrement(); }
@@ -146,13 +146,13 @@ public:
 
 	samplecnt_t ancestral_start_sample ()  const { return _ancestral_start.val().samples(); }
 	samplecnt_t ancestral_length_samples () const { return _ancestral_length.val().samples(); }
-	timecnt_t ancestral_start ()  const { return _ancestral_start.val(); }
+	timepos_t ancestral_start ()  const { return _ancestral_start.val(); }
 	timecnt_t ancestral_length () const { return _ancestral_length.val(); }
 
 	float stretch () const { return _stretch; }
 	float shift ()   const { return _shift; }
 
-	void set_ancestral_data (timecnt_t const & start, timecnt_t const & length, float stretch, float shift);
+	void set_ancestral_data (timepos_t const & start, timecnt_t const & length, float stretch, float shift);
 
 	timecnt_t sync_offset (int& dir) const;
 	timepos_t sync_position () const;
@@ -241,7 +241,7 @@ public:
 	/* EDITING OPERATIONS */
 
 	void set_length (timecnt_t const &);
-	void set_start (timecnt_t const &);
+	void set_start (timepos_t const &);
 	void set_position (timepos_t const &);
 	void set_initial_position (timepos_t const &);
 	void special_set_position (timepos_t const &);
@@ -439,7 +439,7 @@ protected:
 	Region (boost::shared_ptr<const Region>, const SourceList&);
 
 	/** Constructor for derived types only */
-	Region (Session& s, timecnt_t const & start, timecnt_t const & length, const std::string& name, DataType);
+	Region (Session& s, timepos_t const & start, timecnt_t const & length, const std::string& name, DataType);
 
 	virtual bool can_trim_start_before_source_start () const {
 		return false;
@@ -451,8 +451,8 @@ protected:
 	virtual int _set_state (const XMLNode&, int version, PBD::PropertyChange& what_changed, bool send_signal);
 	virtual void set_position_internal (timepos_t const & pos);
 	virtual void set_length_internal (timecnt_t const &);
-	virtual void set_start_internal (timecnt_t const &);
-	bool verify_start_and_length (timecnt_t const &, timecnt_t&);
+	virtual void set_start_internal (timepos_t const &);
+	bool verify_start_and_length (timepos_t const &, timecnt_t&);
 	void first_edit ();
 
 	DataType _type;
@@ -461,10 +461,10 @@ protected:
 	PBD::Property<bool>      _left_of_split;
 	PBD::Property<bool>      _right_of_split;
 	PBD::Property<bool>      _valid_transients;
-	PBD::Property<timecnt_t> _start;
+	PBD::Property<timepos_t> _start;
 	PBD::Property<timecnt_t> _length;
 	/** Sync position relative to the start of our file */
-	PBD::Property<timecnt_t> _sync_position;
+	PBD::Property<timepos_t> _sync_position;
 
 	SourceList              _sources;
 	/** Used when timefx are applied, so we can always use the original source */
@@ -496,7 +496,7 @@ private:
 
 	void maybe_uncopy ();
 
-	bool verify_start (timecnt_t const &);
+	bool verify_start (timepos_t const &);
 	bool verify_start_mutable (timecnt_t&);
 	bool verify_length (timecnt_t&);
 
@@ -513,7 +513,7 @@ private:
 	PBD::Property<bool>        _external;
 	PBD::Property<bool>        _hidden;
 	PBD::Property<bool>        _position_locked;
-	PBD::Property<timecnt_t>   _ancestral_start;
+	PBD::Property<timepos_t>   _ancestral_start;
 	PBD::Property<timecnt_t>   _ancestral_length;
 	PBD::Property<float>       _stretch;
 	PBD::Property<float>       _shift;
diff --git a/libs/ardour/ardour/smf_source.h b/libs/ardour/ardour/smf_source.h
index d8407ddcd3..3f4ff7e0cf 100644
--- a/libs/ardour/ardour/smf_source.h
+++ b/libs/ardour/ardour/smf_source.h
@@ -83,7 +83,7 @@ public:
 	Temporal::Beats   _last_ev_time_beats;
 	samplepos_t       _last_ev_time_samples;
 	/** end time (start + duration) of last call to read_unlocked */
-	mutable timecnt_t _smf_last_read_end;
+	mutable timepos_t _smf_last_read_end;
 	/** time (in SMF ticks, 1 tick per _ppqn) of the last event read by read_unlocked */
 	mutable timepos_t _smf_last_read_time;
 
@@ -94,7 +94,7 @@ public:
 	timecnt_t read_unlocked (const Lock&                     lock,
 	                         Evoral::EventSink<samplepos_t>& dst,
 	                         timepos_t const &               position,
-	                         timecnt_t const &               start,
+	                         timepos_t const &               start,
 	                         timecnt_t const &               cnt,
 	                         Temporal::Range*                loop_range,
 	                         MidiStateTracker*               tracker,
diff --git a/libs/ardour/audioregion.cc b/libs/ardour/audioregion.cc
index 3f63d14218..b26212f2fd 100644
--- a/libs/ardour/audioregion.cc
+++ b/libs/ardour/audioregion.cc
@@ -242,7 +242,7 @@ AudioRegion::init ()
 }
 
 /** Constructor for use by derived types only */
-AudioRegion::AudioRegion (Session& s, timecnt_t const &  start, timecnt_t const & len, std::string name)
+AudioRegion::AudioRegion (Session& s, timepos_t const &  start, timecnt_t const & len, std::string name)
 	: Region (s, start, len, name, DataType::AUDIO)
 	, AUDIOREGION_STATE_DEFAULT
 	, _envelope (Properties::envelope, boost::shared_ptr<AutomationList> (new AutomationList (Evoral::Parameter(EnvelopeAutomation), Temporal::AudioTime)))
diff --git a/libs/ardour/lua_api.cc b/libs/ardour/lua_api.cc
index f9a39c54d7..a86ed57132 100644
--- a/libs/ardour/lua_api.cc
+++ b/libs/ardour/lua_api.cc
@@ -1243,7 +1243,7 @@ LuaAPI::Rubberband::finalize ()
 	ar->set_fade_out (_region->fade_out ());
 	*(ar->envelope ()) = *(_region->envelope ());
 
-	ar->set_ancestral_data (timecnt_t (_read_start), timecnt_t (_read_len), _stretch_ratio, _pitch_ratio);
+	ar->set_ancestral_data (timepos_t (_read_start), timecnt_t (_read_len), _stretch_ratio, _pitch_ratio);
 	ar->set_master_sources (_region->master_sources ());
 	ar->set_length (ar->length () * _stretch_ratio); // XXX
 	if (_stretch_ratio != 1.0) {
diff --git a/libs/ardour/midi_region.cc b/libs/ardour/midi_region.cc
index e595612211..88a0b92d63 100644
--- a/libs/ardour/midi_region.cc
+++ b/libs/ardour/midi_region.cc
@@ -490,7 +490,7 @@ MidiRegion::model_shifted (timecnt_t distance)
 
 	if (!_ignore_shift) {
 		PropertyChange what_changed;
-		_start += distance;
+		_start.call().operator+= (distance);
 		what_changed.add (Properties::start);
 		what_changed.add (Properties::contents);
 		send_change (what_changed);
@@ -532,9 +532,9 @@ MidiRegion::fix_negative_start ()
 {
 	_ignore_shift = true;
 
-	model()->insert_silence_at_start (-_start.val().beats());
+	model()->insert_silence_at_start (-start().beats());
 
-	_start = timecnt_t::zero (_start.val().time_domain());
+	_start = timepos_t::zero (start().time_domain());
 }
 
 bool
diff --git a/libs/ardour/midi_source.cc b/libs/ardour/midi_source.cc
index 7e76a32dd9..b59e524bf2 100644
--- a/libs/ardour/midi_source.cc
+++ b/libs/ardour/midi_source.cc
@@ -176,7 +176,7 @@ timecnt_t
 MidiSource::midi_read (const Lock&                        lm,
                        Evoral::EventSink<samplepos_t>&    dst,
                        timepos_t const &                  source_start,
-                       timecnt_t const &                  start,
+                       timepos_t const &                  start,
                        timecnt_t const &                  cnt,
                        Temporal::Range*                   loop_range,
                        MidiCursor&                        cursor,
@@ -189,7 +189,7 @@ MidiSource::midi_read (const Lock&                        lm,
 	                             source_start, start, cnt, tracker, name()));
 
 	if (!_model) {
-		return timecnt_t (read_unlocked (lm, dst, source_start, start, cnt, loop_range, tracker, filter), start.position());
+		return timecnt_t (read_unlocked (lm, dst, source_start, start, cnt, loop_range, tracker, filter), start);
 	}
 
 	// Find appropriate model iterator
diff --git a/libs/ardour/rb_effect.cc b/libs/ardour/rb_effect.cc
index 538097c473..1c75496d34 100644
--- a/libs/ardour/rb_effect.cc
+++ b/libs/ardour/rb_effect.cc
@@ -352,7 +352,7 @@ RBEffect::run (boost::shared_ptr<Region> r, Progress* progress)
 	/* now reset ancestral data for each new region */
 
 	for (vector<boost::shared_ptr<Region> >::iterator x = results.begin (); x != results.end (); ++x) {
-		(*x)->set_ancestral_data (timecnt_t (read_start),
+		(*x)->set_ancestral_data (timepos_t (read_start),
 		                          timecnt_t (read_duration, timepos_t (read_start)),
 		                          stretch,
 		                          shift);
diff --git a/libs/ardour/region.cc b/libs/ardour/region.cc
index 8496cb898e..ce2156ead6 100644
--- a/libs/ardour/region.cc
+++ b/libs/ardour/region.cc
@@ -69,13 +69,13 @@ namespace ARDOUR {
 		PBD::PropertyDescriptor<bool> hidden;
 		PBD::PropertyDescriptor<bool> position_locked;
 		PBD::PropertyDescriptor<bool> valid_transients;
-		PBD::PropertyDescriptor<timecnt_t> start;
+		PBD::PropertyDescriptor<timepos_t> start;
 		PBD::PropertyDescriptor<timecnt_t> length;
 		PBD::PropertyDescriptor<double> beat;
-		PBD::PropertyDescriptor<timecnt_t> sync_position;
+		PBD::PropertyDescriptor<timepos_t> sync_position;
 		PBD::PropertyDescriptor<timepos_t> position;
 		PBD::PropertyDescriptor<layer_t> layer;
-		PBD::PropertyDescriptor<timecnt_t> ancestral_start;
+		PBD::PropertyDescriptor<timepos_t> ancestral_start;
 		PBD::PropertyDescriptor<timecnt_t> ancestral_length;
 		PBD::PropertyDescriptor<float> stretch;
 		PBD::PropertyDescriptor<float> shift;
@@ -183,9 +183,9 @@ Region::register_properties ()
 	, _left_of_split (Properties::left_of_split, false) \
 	, _right_of_split (Properties::right_of_split, false) \
 	, _valid_transients (Properties::valid_transients, false) \
-	, _start (Properties::start, timecnt_t (s, _type == DataType::MIDI ? timepos_t (Temporal::Beats()) : timepos_t::from_superclock (0))) \
-	, _length (Properties::length, timecnt_t (l, timepos_t (s))) \
-	, _sync_position (Properties::sync_position, timecnt_t (s, _type == DataType::MIDI ? timepos_t (Temporal::Beats()) : timepos_t::from_superclock (0))) \
+	, _start (Properties::start, (s)) \
+	, _length (Properties::length, (l)) \
+	, _sync_position (Properties::sync_position, (s)) \
 	, _transient_user_start (0) \
 	, _transient_analysis_start (0) \
 	, _transient_analysis_end (0) \
@@ -200,7 +200,7 @@ Region::register_properties ()
 	, _external (Properties::external, false) \
 	, _hidden (Properties::hidden, false) \
 	, _position_locked (Properties::position_locked, false) \
-	, _ancestral_start (Properties::ancestral_start, timecnt_t (s, _type == DataType::MIDI ? timepos_t (Temporal::Beats()) : timepos_t::from_superclock (0))) \
+	, _ancestral_start (Properties::ancestral_start, (s)) \
 	, _ancestral_length (Properties::ancestral_length, (l)) \
 	, _stretch (Properties::stretch, 1.0) \
 	, _shift (Properties::shift, 1.0) \
@@ -241,10 +241,10 @@ Region::register_properties ()
 	, _contents (Properties::contents, other->_contents)
 
 /* derived-from-derived constructor (no sources in constructor) */
-Region::Region (Session& s, timecnt_t const & start, timecnt_t const & length, const string& name, DataType type)
+Region::Region (Session& s, timepos_t const & start, timecnt_t const & length, const string& name, DataType type)
 	: SessionObject(s, name)
-	, _type(type)
-        , REGION_DEFAULT_STATE(start,length)
+	, _type (type)
+        , REGION_DEFAULT_STATE (start,length)
 	, _last_length (length)
 	, _first_edit (EditChangesNothing)
 	, _layer (0)
@@ -259,7 +259,7 @@ Region::Region (Session& s, timecnt_t const & start, timecnt_t const & length, c
 Region::Region (const SourceList& srcs)
 	: SessionObject(srcs.front()->session(), "toBeRenamed")
 	, _type (srcs.front()->type())
-	, REGION_DEFAULT_STATE(_type == DataType::MIDI ? timecnt_t (Temporal::Beats()) : timecnt_t::from_superclock (0),
+	, REGION_DEFAULT_STATE(_type == DataType::MIDI ? timepos_t (Temporal::Beats()) : timepos_t::from_superclock (0),
 	                       _type == DataType::MIDI ? timecnt_t (Temporal::Beats()) : timecnt_t::from_superclock (0))
 	, _last_length (_type == DataType::MIDI ? timecnt_t (Temporal::Beats()) : timecnt_t::from_superclock (0))
 	, _first_edit (EditChangesNothing)
@@ -316,7 +316,7 @@ Region::Region (boost::shared_ptr<const Region> other)
 	if (other->sync_marked()) {
 		if (other->_start < other->_sync_position) {
 			/* sync pos was after the start point of the other region */
-			_sync_position = other->_sync_position - other->_start;
+			_sync_position = timepos_t (other->start().distance (other->_sync_position));
 		} else {
 			/* sync pos was before the start point of the other region. not possible here. */
 			_sync_marked = false;
@@ -670,8 +670,6 @@ Region::set_position_internal (timepos_t const & pos)
 	_last_length.set_position (position());
 
 	if (position() != pos) {
-#warning NUTEMPO is this correct? why would set position set the position of the start (duration)?
-		_start.call().set_position (pos);
 		_length.call().set_position (pos);
 
 		/* check that the new _position wouldn't make the current
@@ -759,7 +757,7 @@ Region::nudge_position (timecnt_t const & n)
 }
 
 void
-Region::set_ancestral_data (timecnt_t const & s, timecnt_t const & l, float st, float sh)
+Region::set_ancestral_data (timepos_t const & s, timecnt_t const & l, float st, float sh)
 {
 	_ancestral_length = l;
 	_ancestral_start = s;
@@ -768,7 +766,7 @@ Region::set_ancestral_data (timecnt_t const & s, timecnt_t const & l, float st,
 }
 
 void
-Region::set_start (timecnt_t const & pos)
+Region::set_start (timepos_t const & pos)
 {
 	if (locked() || position_locked() || video_locked()) {
 		return;
@@ -780,7 +778,7 @@ Region::set_start (timecnt_t const & pos)
 
 	if (_start != pos) {
 
-		timecnt_t p = pos;
+		timepos_t p = pos;
 
 		if (!verify_start (p)) {
 			return;
@@ -802,14 +800,15 @@ Region::move_start (timecnt_t const & distance)
 		return;
 	}
 
-	timecnt_t new_start (_start);
-
+	timepos_t new_start (_start);
+	timepos_t current_start (_start);
+	
 	if (distance.positive()) {
 
-		if (_start > timecnt_t::max() - distance) {
-			new_start = timecnt_t::max(); // makes no sense
+		if (current_start > timepos_t::max (current_start.time_domain()).earlier (distance)) {
+			new_start = timecnt_t::max(current_start.time_domain()); // makes no sense
 		} else {
-			new_start = start() + distance;
+			new_start = current_start + distance;
 		}
 
 		if (!verify_start (new_start)) {
@@ -818,10 +817,10 @@ Region::move_start (timecnt_t const & distance)
 
 	} else {
 
-		if (_start < -distance) {
-			new_start = timecnt_t (_start.val().time_domain());
+		if (current_start < -distance) {
+			new_start = timecnt_t (current_start.time_domain());
 		} else {
-			new_start = start() + distance;
+			new_start = current_start + distance;
 		}
 	}
 
@@ -946,7 +945,7 @@ Region::trim_to (timepos_t const & position, timecnt_t const & length)
 void
 Region::trim_to_internal (timepos_t const & pos, timecnt_t const & len)
 {
-	timecnt_t new_start (len.time_domain());
+	timepos_t new_start (len.time_domain());
 
 	if (locked()) {
 		return;
@@ -957,7 +956,7 @@ Region::trim_to_internal (timepos_t const & pos, timecnt_t const & len)
 	if (start_shift.positive()) {
 
 		if (start() > timecnt_t::max() - start_shift) {
-			new_start = timecnt_t::max();
+			new_start = timepos_t::max (start().time_domain());
 		} else {
 			new_start = start() + start_shift;
 		}
@@ -974,7 +973,7 @@ Region::trim_to_internal (timepos_t const & pos, timecnt_t const & len)
 		new_start = start();
 	}
 
-	timecnt_t ns = new_start;
+	timepos_t ns = new_start;
 	timecnt_t nl = len;
 
 	if (!verify_start_and_length (ns, nl)) {
@@ -1103,7 +1102,7 @@ void
 Region::set_sync_position (timepos_t const & absolute_pos)
 {
 	/* position within our file */
-	const timecnt_t file_pos = start() + position().distance (absolute_pos);
+	const timepos_t file_pos = start() + position().distance (absolute_pos);
 
 	if (file_pos != _sync_position) {
 		_sync_marked = true;
@@ -1129,21 +1128,21 @@ Region::clear_sync_position ()
 	}
 }
 
-/* @return the sync point relative the first sample of the region */
+/* @return the sync point relative the position of the region */
 timecnt_t
 Region::sync_offset (int& dir) const
 {
 	if (sync_marked()) {
 		if (_sync_position > _start) {
 			dir = 1;
-			return _sync_position - _start;
+			return start().distance (_sync_position);
 		} else {
 			dir = -1;
-			return _start - _sync_position;
+			return sync_position().distance (start());
 		}
 	} else {
 		dir = 0;
-		return timecnt_t ();
+		return timecnt_t::zero (start().time_domain());
 	}
 }
 
@@ -1681,7 +1680,7 @@ Region::verify_length (timecnt_t& len)
 }
 
 bool
-Region::verify_start_and_length (timecnt_t const & new_start, timecnt_t& new_length)
+Region::verify_start_and_length (timepos_t const & new_start, timecnt_t& new_length)
 {
 	if (source() && source()->length_mutable()) {
 		return true;
@@ -1699,7 +1698,7 @@ Region::verify_start_and_length (timecnt_t const & new_start, timecnt_t& new_len
 }
 
 bool
-Region::verify_start (timecnt_t const & pos)
+Region::verify_start (timepos_t const & pos)
 {
 	if (source() && source()->length_mutable()) {
 		return true;
@@ -1949,7 +1948,7 @@ Region::is_compound () const
 }
 
 void
-Region::set_start_internal (timecnt_t const & s)
+Region::set_start_internal (timepos_t const & s)
 {
 	_start = s;
 }
diff --git a/libs/ardour/smf_source.cc b/libs/ardour/smf_source.cc
index c39f7d1782..acf807f563 100644
--- a/libs/ardour/smf_source.cc
+++ b/libs/ardour/smf_source.cc
@@ -216,7 +216,7 @@ timecnt_t
 SMFSource::read_unlocked (const Lock&                     lock,
                           Evoral::EventSink<samplepos_t>& destination,
                           timepos_t const &               source_start,
-                          timecnt_t const &               start,
+                          timepos_t const &               start,
                           timecnt_t const &               duration,
                           Temporal::Range*                loop_range,
                           MidiStateTracker*               tracker,
@@ -244,7 +244,7 @@ SMFSource::read_unlocked (const Lock&                     lock,
 
 	DEBUG_TRACE (DEBUG::MidiSourceIO, string_compose ("SMF read_unlocked: start in ticks %1\n", start_ticks));
 
-	if (_smf_last_read_end == 0 || start != _smf_last_read_end) {
+	if (_smf_last_read_end.zero() || start != _smf_last_read_end) {
 		DEBUG_TRACE (DEBUG::MidiSourceIO, string_compose ("SMF read_unlocked: seek to %1\n", start));
 		Evoral::SMF::seek_to_start();
 		while (time < start_ticks) {