diff --git a/libs/ardour/audioengine.cc b/libs/ardour/audioengine.cc
index fe8ed27bbb..69418c1911 100644
--- a/libs/ardour/audioengine.cc
+++ b/libs/ardour/audioengine.cc
@@ -1299,6 +1299,7 @@ AudioEngine::thread_init_callback (void* arg)
 int
 AudioEngine::sync_callback (TransportState state, samplepos_t position)
 {
+	DEBUG_TRACE (DEBUG::BackendCallbacks, string_compose (X_("sync callback %1, %2\n"), state, position));
 	if (_session) {
 		return _session->backend_sync_callback (state, position);
 	}
@@ -1308,12 +1309,14 @@ AudioEngine::sync_callback (TransportState state, samplepos_t position)
 void
 AudioEngine::freewheel_callback (bool onoff)
 {
+	DEBUG_TRACE (DEBUG::BackendCallbacks, string_compose (X_("freewheel callback onoff %1\n"), onoff));
 	_freewheeling = onoff;
 }
 
 void
 AudioEngine::latency_callback (bool for_playback)
 {
+	DEBUG_TRACE (DEBUG::BackendCallbacks, string_compose (X_("latency callback playback ? %1\n"), for_playback));
 	if (_session) {
 		_session->update_latency (for_playback);
 	}
@@ -1330,6 +1333,7 @@ AudioEngine::update_latencies ()
 void
 AudioEngine::halted_callback (const char* why)
 {
+	DEBUG_TRACE (DEBUG::BackendCallbacks, string_compose (X_("halted callback why: [%1]\n"), why));
 	if (_in_destructor) {
 		/* everything is under control */
 		return;
diff --git a/libs/ardour/port_manager.cc b/libs/ardour/port_manager.cc
index 0eff8cede0..24c693c431 100644
--- a/libs/ardour/port_manager.cc
+++ b/libs/ardour/port_manager.cc
@@ -656,6 +656,8 @@ PortManager::reconnect_ports ()
 void
 PortManager::connect_callback (const string& a, const string& b, bool conn)
 {
+	DEBUG_TRACE (DEBUG::BackendCallbacks, string_compose (X_("connect callback %1 + %2 connected ? %3\n"), a, b, conn));
+
 	boost::shared_ptr<Port> port_a;
 	boost::shared_ptr<Port> port_b;
 	Ports::iterator x;
@@ -695,6 +697,8 @@ PortManager::connect_callback (const string& a, const string& b, bool conn)
 void
 PortManager::registration_callback ()
 {
+	DEBUG_TRACE (DEBUG::BackendCallbacks, "port registration callback\n");
+
 	if (!_port_remove_in_progress) {
 
 		{
@@ -767,6 +771,8 @@ PortManager::my_name() const
 int
 PortManager::graph_order_callback ()
 {
+	DEBUG_TRACE (DEBUG::BackendCallbacks, "graph order callback\n");
+
 	if (!_port_remove_in_progress) {
 		GraphReordered(); /* EMIT SIGNAL */
 	}