How do music apps separate the input audio channels?

Question

Biochili OP

Created Jul ’21

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Hello,

In my iPadOS app I need to be able to apply AUv3 effects to individual input channels. However, AVAudioEngine's inputNode delivers one output bus with all input channels in that bus. How can I separate these input channels?

For example, an audio interface with 6 input channels yields an inputNode with 6 channels on the input bus and output bus. How can I apply an effect to channel 1?

AVAudioEngine only lets me connect busses between audio units. AVAudioConnectionPoint is an auxiliary class that allows me to establish a one-to-many routing.

It seems that with the V3 API I cannot achieve my goal. What other solutions are there? Use the V2 API and install a callback... exactly where? Or is there some kind of audio format conversion foreseen?

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Answer 1

Biochili OP

May ’22

Ok I'll answer my post myself:

I have written my own audio "engine". It runs in my own effect plugin. In the render callback I can do whatever I want with the input channels. This means I have to invoke render callbacks of all generators and effects myself, and I have to mix buffers myself, Accelerate framework to the rescue.

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