diff --git a/libs/ardour/ardour/port.h b/libs/ardour/ardour/port.h
index 020a9bf66e..ff35b1a550 100644
--- a/libs/ardour/ardour/port.h
+++ b/libs/ardour/ardour/port.h
@@ -140,7 +140,8 @@ public:
 	static PBD::Signal0<void> PortDrop;
 	static PBD::Signal0<void> PortSignalDrop;
 
-	static void set_speed_ratio (double s);
+	static void set_varispeed_ratio (double s); //< varispeed playback
+	static bool set_engine_ratio (double session, double engine); //< SR mismatch
 	static void set_cycle_samplecnt (pframes_t n);
 
 	static samplecnt_t port_offset() { return _global_port_buffer_offset; }
@@ -158,11 +159,13 @@ public:
 
 	static pframes_t cycle_nframes () { return _cycle_nframes; }
 	static double speed_ratio () { return _speed_ratio; }
+	static double engine_ratio () { return _engine_ratio; }
+	static double resample_ratio () { return _resample_ratio; } // == _speed_ratio * _engine_ratio
 
 	static uint32_t resampler_quality () { return _resampler_quality; }
 	static uint32_t resampler_latency () { return _resampler_latency; }
 	static bool     can_varispeed ()     { return _resampler_latency > 0; }
-	static void     setup_resampler (uint32_t q = 17);
+	static bool     setup_resampler (uint32_t q = 17);
 
 protected:
 
@@ -179,6 +182,8 @@ protected:
 	LatencyRange _private_capture_latency;
 
 	static double _speed_ratio;
+	static double _engine_ratio;
+	static double _resample_ratio; // = _speed_ratio * _engine_ratio (cached)
 
 private:
 	std::string _name;  ///< port short name
diff --git a/libs/ardour/ardour/port_manager.h b/libs/ardour/ardour/port_manager.h
index 4ef36563fc..4ebcd62a2d 100644
--- a/libs/ardour/ardour/port_manager.h
+++ b/libs/ardour/ardour/port_manager.h
@@ -128,6 +128,9 @@ public:
 	uint32_t    port_name_size () const;
 	std::string my_name () const;
 
+	size_t total_port_count () const { return _ports.reader ()->size (); }
+	size_t session_port_count () const;
+
 #ifndef NDEBUG
 	void list_cycle_ports () const;
 	void list_all_ports () const;
diff --git a/libs/ardour/audioengine.cc b/libs/ardour/audioengine.cc
index eac9932b6c..2bfe036a42 100644
--- a/libs/ardour/audioengine.cc
+++ b/libs/ardour/audioengine.cc
@@ -234,7 +234,7 @@ AudioEngine::process_callback (pframes_t nframes)
 {
 	TimerRAII tr (dsp_stats[ProcessCallback]);
 	Glib::Threads::Mutex::Lock tm (_process_lock, Glib::Threads::TRY_LOCK);
-	Port::set_speed_ratio (1.0);
+	Port::set_varispeed_ratio (1.0);
 
 	PT_TIMING_REF;
 	PT_TIMING_CHECK (1);
@@ -490,7 +490,7 @@ AudioEngine::process_callback (pframes_t nframes)
 		*/
 		double catch_speed = tmm.pre_process_transport_masters (nframes, sample_time_at_cycle_start());
 		catch_speed = _session->plan_master_strategy (nframes, tmm.get_current_speed_in_process_context(), tmm.get_current_position_in_process_context(), catch_speed);
-		Port::set_speed_ratio (catch_speed);
+		Port::set_varispeed_ratio (catch_speed);
 		DEBUG_TRACE (DEBUG::Slave, string_compose ("transport master (current=%1) gives speed %2 (ports using %3)\n", tmm.current() ? tmm.current()->name() : string("[]"), catch_speed, Port::speed_ratio()));
 
 #if 0 // USE FOR DEBUG ONLY
diff --git a/libs/ardour/midi_port.cc b/libs/ardour/midi_port.cc
index 831289bc16..f5ff712a3a 100644
--- a/libs/ardour/midi_port.cc
+++ b/libs/ardour/midi_port.cc
@@ -123,7 +123,7 @@ MidiPort::get_midi_buffer (pframes_t nframes)
 				continue;
 			}
 
-			timestamp = floor (timestamp * _speed_ratio);
+			timestamp = floor (timestamp * resample_ratio ());
 
 			/* check that the event is in the acceptable time range */
 			if ((timestamp <  (_global_port_buffer_offset)) ||
@@ -241,7 +241,7 @@ MidiPort::resolve_notes (void* port_buffer, MidiBuffer::TimeType when)
 	for (uint8_t channel = 0; channel <= 0xF; channel++) {
 
 		uint8_t ev[3] = { ((uint8_t) (MIDI_CMD_CONTROL | channel)), MIDI_CTL_SUSTAIN, 0 };
-		pframes_t tme = floor (when / _speed_ratio);
+		pframes_t tme = floor (when / resample_ratio ());
 
 		/* we need to send all notes off AND turn the
 		 * sustain/damper pedal off to handle synths
@@ -282,7 +282,7 @@ MidiPort::flush_buffers (pframes_t nframes)
 			port_buffer = port_engine.get_buffer (_port_handle, nframes);
 		}
 
-		double speed_ratio = (flags () & TransportGenerator) ? 1.0 : _speed_ratio;
+		double speed_ratio = (flags () & TransportGenerator) ? 1.0 : resample_ratio ();
 
 		for (MidiBuffer::iterator i = _buffer->begin(); i != _buffer->end(); ++i) {
 
diff --git a/libs/ardour/port.cc b/libs/ardour/port.cc
index 410886d4a3..8033e449f2 100644
--- a/libs/ardour/port.cc
+++ b/libs/ardour/port.cc
@@ -46,6 +46,8 @@ bool         Port::_connecting_blocked = false;
 pframes_t    Port::_global_port_buffer_offset = 0;
 pframes_t    Port::_cycle_nframes = 0;
 double       Port::_speed_ratio = 1.0;
+double       Port::_engine_ratio = 1.0;
+double       Port::_resample_ratio = 1.0;
 std::string  Port::state_node_name = X_("Port");
 uint32_t     Port::_resampler_quality = 17;
 uint32_t     Port::_resampler_latency = 16; // = _resampler_quality - 1;
@@ -706,20 +708,19 @@ Port::set_state (const XMLNode& node, int)
 	return 0;
 }
 
-/* static */ void
+/* static */ bool
 Port::setup_resampler (uint32_t q)
 {
 	/* configure at application start (Ardour::init) */
-	static bool setup_done = false;
-	if (setup_done) {
-		return;
+	if (port_manager && port_manager->session_port_count() > 0) {
+		return false;
 	}
-	setup_done = true;
+
 	if (q == 0) {
 		/* no vari-speed */
 		_resampler_quality = 0;
 		_resampler_latency = 0;
-		return;
+		return true;
 	}
 	// range constrained in VMResampler::setup
 	if (q < 8) {
@@ -730,22 +731,49 @@ Port::setup_resampler (uint32_t q)
 	}
 	_resampler_quality = q;
 	_resampler_latency = q - 1;
+	return true;
 }
 
+/*static*/ bool
+Port::set_engine_ratio (double session_rate, double engine_rate)
+{
+	bool rv = true;
+	if (session_rate > 0 && engine_rate > 0 && can_varispeed ()) {
+		_engine_ratio = session_rate / engine_rate;
+	} else {
+		_engine_ratio = 1.0;
+		rv = false;
+	}
+
+	/* constrain range to provide for additional vari-speed.
+	 * but do allow 384000 / 44100 = 8.7
+	 */
+	if (_engine_ratio < 0.11 || _engine_ratio > 9) {
+		_engine_ratio = 1.0;
+		rv = false;
+	}
+
+	/* apply constraints, and calc _resample_ratio */
+	set_varispeed_ratio (_speed_ratio);
+	return rv;
+}
 
 /*static*/ void
-Port::set_speed_ratio (double s) {
+Port::set_varispeed_ratio (double s) {
 	if (s == 0.0 || !can_varispeed ()) {
 		/* no resampling when stopped */
 		_speed_ratio = 1.0;
 	} else {
 		/* see VMResampler::set_rratio() for min/max range */
-		_speed_ratio = std::min ((double) Config->get_max_transport_speed(), std::max (0.02, fabs (s)));
+		_speed_ratio = std::min (16.0, std::max (0.02, fabs (s * _engine_ratio))) / _engine_ratio;
+		_speed_ratio = std::min ((double) Config->get_max_transport_speed(), _speed_ratio);
 	}
+	/* cache overall speed */
+	_resample_ratio = _speed_ratio * _engine_ratio;
 }
 
 /*static*/ void
 Port::set_cycle_samplecnt (pframes_t n)
 {
-	_cycle_nframes = floor (n * _speed_ratio);
+	_cycle_nframes = floor (n * resample_ratio ());
 }
diff --git a/libs/ardour/port_manager.cc b/libs/ardour/port_manager.cc
index 943e6bc04b..2f70c696e1 100644
--- a/libs/ardour/port_manager.cc
+++ b/libs/ardour/port_manager.cc
@@ -552,6 +552,19 @@ PortManager::get_ports (const string& port_name_pattern, DataType type, PortFlag
 	return _backend->get_ports (port_name_pattern, type, flags, s);
 }
 
+size_t
+PortManager::session_port_count () const
+{
+	size_t cnt = 0;
+	for (auto const& p : *_ports.reader ()) {
+		if (p.second->flags () & TransportSyncPort) {
+			continue;
+		}
+		++cnt;
+	}
+	return cnt;
+}
+
 void
 PortManager::port_registration_failure (const std::string& portname)
 {
@@ -1230,7 +1243,7 @@ PortManager::cycle_start (pframes_t nframes, Session* s)
 	if (s) {
 		tl = s->rt_tasklist ();
 	}
-	if (tl && fabs (Port::speed_ratio ()) != 1.0) {
+	if (tl && fabs (Port::resample_ratio ()) != 1.0) {
 		for (Ports::iterator p = _cycle_ports->begin (); p != _cycle_ports->end (); ++p) {
 			if (!(p->second->flags () & TransportSyncPort)) {
 				tl->push_back (boost::bind (&Port::cycle_start, p->second, nframes));
@@ -1256,7 +1269,7 @@ PortManager::cycle_end (pframes_t nframes, Session* s)
 	if (s) {
 		tl = s->rt_tasklist ();
 	}
-	if (tl && fabs (Port::speed_ratio ()) != 1.0) {
+	if (tl && fabs (Port::resample_ratio ()) != 1.0) {
 		for (Ports::iterator p = _cycle_ports->begin (); p != _cycle_ports->end (); ++p) {
 			if (!(p->second->flags () & TransportSyncPort)) {
 				tl->push_back (boost::bind (&Port::cycle_end, p->second, nframes));
@@ -1274,7 +1287,7 @@ PortManager::cycle_end (pframes_t nframes, Session* s)
 	for (Ports::iterator p = _cycle_ports->begin (); p != _cycle_ports->end (); ++p) {
 		/* AudioEngine::split_cycle flushes buffers until Port::port_offset.
 		 * Now only flush remaining events (after Port::port_offset) */
-		p->second->flush_buffers (nframes * Port::speed_ratio () - Port::port_offset ());
+		p->second->flush_buffers (nframes * Port::resample_ratio () - Port::port_offset ());
 	}
 
 	_cycle_ports.reset ();
@@ -1374,7 +1387,7 @@ PortManager::cycle_end_fade_out (gain_t base_gain, gain_t gain_step, pframes_t n
 	if (s) {
 		tl = s->rt_tasklist ();
 	}
-	if (tl && fabs (Port::speed_ratio ()) != 1.0) {
+	if (tl && fabs (Port::resample_ratio ()) != 1.0) {
 		for (Ports::iterator p = _cycle_ports->begin (); p != _cycle_ports->end (); ++p) {
 			if (!(p->second->flags () & TransportSyncPort)) {
 				tl->push_back (boost::bind (&Port::cycle_end, p->second, nframes));