diff --git a/include/boo/audiodev/IAudioVoiceEngine.hpp b/include/boo/audiodev/IAudioVoiceEngine.hpp
index 736b43d..e38b922 100644
--- a/include/boo/audiodev/IAudioVoiceEngine.hpp
+++ b/include/boo/audiodev/IAudioVoiceEngine.hpp
@@ -64,6 +64,9 @@ struct IAudioVoiceEngine
 
     /** Open named MIDI in/out port, name format depends on OS */
     virtual std::unique_ptr<IMIDIInOut> newRealMIDIInOut(const char* name, ReceiveFunctor&& receiver)=0;
+    
+    /** If this returns true, MIDI callbacks are assumed to be *not* thread-safe; need protection via mutex */
+    virtual bool useMIDILock() const=0;
 };
 
 /** Construct host platform's voice engine */
diff --git a/include/boo/audiodev/IMIDIPort.hpp b/include/boo/audiodev/IMIDIPort.hpp
index 3c78c54..aae09ea 100644
--- a/include/boo/audiodev/IMIDIPort.hpp
+++ b/include/boo/audiodev/IMIDIPort.hpp
@@ -9,7 +9,7 @@
 namespace boo
 {
 
-using ReceiveFunctor = std::function<void(std::vector<uint8_t>&&)>;
+using ReceiveFunctor = std::function<void(std::vector<uint8_t>&&, double time)>;
 
 class IMIDIPort
 {
diff --git a/lib/audiodev/AQS.cpp b/lib/audiodev/AQS.cpp
index 38c1676..7ee881b 100644
--- a/lib/audiodev/AQS.cpp
+++ b/lib/audiodev/AQS.cpp
@@ -231,7 +231,8 @@ struct AQSAudioVoiceEngine : BaseAudioVoiceEngine
         for (int i=0 ; i<pktlist->numPackets ; ++i)
         {
             std::vector<uint8_t> bytes(std::cbegin(packet->data), std::cbegin(packet->data) + packet->length);
-            readProcRefCon->m_receiver(std::move(bytes));
+            ;
+            readProcRefCon->m_receiver(std::move(bytes), AudioConvertHostTimeToNanos(packet->timeStamp) / 1.0e9);
             packet = MIDIPacketNext(packet);
         }
     }
@@ -533,6 +534,8 @@ struct AQSAudioVoiceEngine : BaseAudioVoiceEngine
 
         return ret;
     }
+    
+    bool useMIDILock() const {return true;}
 
     AQSAudioVoiceEngine()
     {
diff --git a/lib/audiodev/AudioSubmix.hpp b/lib/audiodev/AudioSubmix.hpp
index a9215d7..7bec528 100644
--- a/lib/audiodev/AudioSubmix.hpp
+++ b/lib/audiodev/AudioSubmix.hpp
@@ -6,6 +6,8 @@
 #include <list>
 #include <vector>
 
+struct AudioUnitVoiceEngine;
+
 namespace boo
 {
 class BaseAudioVoiceEngine;
@@ -15,6 +17,7 @@ class AudioSubmix : public IAudioSubmix, public IAudioMix
 {
     friend class BaseAudioVoiceEngine;
     friend struct WASAPIAudioVoiceEngine;
+    friend struct ::AudioUnitVoiceEngine;
 
     /* Mixer-engine relationships */
     BaseAudioVoiceEngine& m_root;
diff --git a/lib/audiodev/AudioVoice.hpp b/lib/audiodev/AudioVoice.hpp
index 2b75dcd..d4e0ef7 100644
--- a/lib/audiodev/AudioVoice.hpp
+++ b/lib/audiodev/AudioVoice.hpp
@@ -6,6 +6,8 @@
 #include "boo/audiodev/IAudioVoice.hpp"
 #include "AudioMatrix.hpp"
 
+struct AudioUnitVoiceEngine;
+
 namespace boo
 {
 class BaseAudioVoiceEngine;
@@ -17,6 +19,7 @@ class AudioVoice : public IAudioVoice
     friend class BaseAudioVoiceEngine;
     friend class AudioSubmix;
     friend struct WASAPIAudioVoiceEngine;
+    friend struct ::AudioUnitVoiceEngine;
 
 protected:
     /* Mixer-engine relationships */
@@ -68,6 +71,8 @@ public:
     void start();
     void stop();
     void unbindVoice();
+    double getSampleRateIn() const {return m_sampleRateIn;}
+    double getSampleRateOut() const {return m_sampleRateOut;}
 };
 
 class AudioVoiceMono : public AudioVoice