I found a post that has the same error in the same situation here: https://groups.google.com/forum/#!topic/audiokit/SmyuzPJQ6wU
Same as this poster - I'm using the source. However, at the end of the post the user does not say what he did to fix the issue.
I'm currently using an unaltered "ExtendingAudioKitUsingSource" example as I need to add some functionality to audiokit. (unaltered outside of using my provisioning profile and adding "let m = AKMicrophone()" in ViewController.swift.
I receive these errors:
2018-08-31 15:16:50.684 ExtendingAudioKit[6800:8850964] 15:16:50.683
ERROR: [0x39058000] AVAudioIONodeImpl.mm:452:
___ZN13AVAudioIOUnit9EnableBusEm_block_invoke: error -10849
2018-08-31 15:16:50.688 ExtendingAudioKit[6800:8850964] ***
Terminating app due to uncaught exception
'com.apple.coreaudio.avfaudio', reason: 'error -10849'
which traces back to line 46 in AKMicrophone.swift to init(): AudioKit.engine.connect(AudioKit.engine.inputNode, to: self.avAudioNode, format: nil)
I've had no issues using AKMicrphone() outside of this project.
I have fixed an AKMicrophone bug in AudioKit v4.5.1 that may have fixed this for you. If not, I'll withdraw this answer, but please check it out and let me know.