v3 Audio Units and Sidechain on iOS & OSX

Question

Created Jul ’16

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I've looked around the documentation and searched a bit on google and I'm curious if it possible to have a sidechain input using the v3 Audio Units API in both iOS and OSX. I would like to be able to instantiate a plug-in on one track and select another track to manipulate the Audio Units effect on the first track. If so I was wondering where I might find documentation on this.

Answered by theanalogkid in 151769022

Yes - Audio Units feature the concept of separate audio busses. As an example of how a host uses separate busses, Logic usually uses Input bus 0 as the AU input and the next input bus as a side chain input.

More specifically:

If you have an Instrument (kAudioUnitType_MusicDevice) which has no audio input - the first Input bus (bus 0) is used as side chain.
For Effects (for example kAudioUnitType_Effect), Logic uses the second input bus (bus 1) as a side chain if the AU reports it has at least two input busses.

For the v3 API see AUAudioUnitBus, AUAudioUnitBusArray & inputBusses property for details.

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Answer 1

theanalogkid OP

Jul ’16

Accepted Answer

Yes - Audio Units feature the concept of separate audio busses. As an example of how a host uses separate busses, Logic usually uses Input bus 0 as the AU input and the next input bus as a side chain input.

More specifically:

If you have an Instrument (kAudioUnitType_MusicDevice) which has no audio input - the first Input bus (bus 0) is used as side chain.
For Effects (for example kAudioUnitType_Effect), Logic uses the second input bus (bus 1) as a side chain if the AU reports it has at least two input busses.

For the v3 API see AUAudioUnitBus, AUAudioUnitBusArray & inputBusses property for details.

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Answer 2

bbrysiuk OP

Jul ’16

Cool Thank you! I'll look into that

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Answer 3

jfjs OP

May ’17

Did you manage to get it to work?

I am trying to add an input bus to the InstrumentDemo provided in the Apple Sample Code (for detailed description see my thread: https://forums.developer.apple.com/thread/76746) but I can't seem to get it to work in hosts (yet works as a standaole app, tested with the AUv3Host from the Sample Code on iOS and macOS and with Logic Pro X 10.3.1).

Any help or experiences woudl be appreciated.

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Answer 4

stef.b OP

Mar ’22

in Xcode 13.1 I create an Effect Audio Unit Extension and simply add the second bus to the boiler plate code that xcode offers, following the same pattern as for the main input bus, but still the sidechain menu does not appear in logic pro. Any hints?

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