Hello,

It may have to do something with the property listener. Have you tried using 
AVAudioSession.routeChangeNotification instead?
Did you connect more than 8 AUMIDISynth to your mixer? (IIRC 8 is the maximum 
possible, at least with AVAudioMixerNode)

In any case it is hard to tell without seeing code. I recommend to set up a 
minimal test project with only 1 AUMIDISynth.

Have you considered using AVFoundation classes instead of the old V2 API? (at 
least to reproduce the problem)

Best regards,
Sven

> Am 09.07.2018 um 21:32 schrieb Bartosz Nowotny <[email protected]>:
> 
> Hello,
> 
> I am trying to programmatically reconfigure AUGraph at runtime, in response 
> to a route change.
> 
> My set up consists of a couple of AUMIDISynth nodes connected to a multi 
> channel mixer node which in turn is connected to RemoteIO node. This set up 
> works fine and I am able to produce audio by sending MIDI note on/off events.
> 
> I want to avoid audio data resampling at any point in the graph. I can start 
> with a properly set up AUGraph that has all audio units use the same sample 
> rate (starting from midi synths, through mixer to remote IO). Route changes 
> (e.g. plugging in headphones) can change the output sample rate and thus 
> introduce resampling and other side effects.
> 
> To respond to a route change I set up a property listener for StreamFormat on 
> my IO unit. When the stream format changes, I call a method that reconfigures 
> the AUGraph in the following manner:
> 1. Stop the AUGraph
> 2. Uninitialize the AUGraph
> 3. Clear all graph connections
> 4. Set mixer output sample rate (propagates to IO input sample rate)
> 5. Set synth output sample rates (propagates to mixer input sample rates)
> 6. Connect synth nodes to mixer node
> 7. Connect mixer node to IO node
> 8. Update, Initialize and Start the AUGraph
> 
> None of the above operations returns an error result.
> 
> The issue occurs when I send some note on/off events - the app crashes. What 
> am I missing?
> 
> Regards,
> Bartosz Nowotny
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