By creating an aggregate device, you can use more than one audio interface at the same time with audio applications like Logic, Soundtrack Pro, or most other Core Audio-compliant applications. Logic 9 and Soundtrack Pro allow you to use a separate device for input and output, such as using a USB microphone and the built-in output of your computer. Use an aggregate device to combine multiple inputs and outputs, or applications not manufactured by Apple which do not support separate input and output devices.

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How to combine multiple audio interfaces by creating an aggregate device on Mac OS X v10.6 Snow Leopard

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