AUGraph Mixing & Rendering to file, as a background task? (Objective-C)

I'm currently working on a pretty straight forward app which records the users singing voice using开发者_StackOverflow社区 AVAudioRecorder and processes it using AUGraph (from the iPhoneMixerEQGraphTest example) which applies an effect to the voice and then merges the song + voice eventually.

The only problem I have now is that I record beforehand, and try to process it afterwards. However I don't want the user to have to listen out the whole song + his singing to be able to render it to a file.

My questions are:

• Is there a way to let AUGraph render (using CAAudioUnitOutputCapturer.h) in the background? Which would be faster (not realtime speed) and no output through the speakers.
• Or is there a way to mix in the microphone audio immediately as an AudioUnit without the mic being outputted through the speakers but just the music.

Cheers,

M0rph3v5

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Eventually I just got an external company to do the audio processing which supplied an library which would output the microphone through the speakers, throw some eq's over it and merges it eventually.

CoreAudio's a bitch :(