I understand Soundflower to be a tool to capture computer system audio, and thus setting up as an input makes sense (or as an Aggregate Device) in Audio Midi Setup.

But then...

Q1) Why is Soundflower (2ch) an Output choice in System Preferences > Sound menu?

Q2) Why do many Soundflower tutorials recommend creating a Multi-Output Device and adding Soundflower (2ch) along side Built-in Output?

Q3) When using Soundflower, why is it even a choice to choose in a Multi-Output Device?

This make no sense to me, as I understand Soundflower to be an input only, like a microphone.

Thank you for your help!

  • 1
    As mentioned in ReadMe : To send the output of one application to another, simply select Soundflower as the output device within the first application and Soundflower as the input device within the second application.
    – audionuma
    Commented May 16, 2018 at 5:41

1 Answer 1


Soundflower is used to Route audio from one application to another. Soundflower itself can't capture audio, only route signals.

For routing you need at least 1 input and 1 output. So say you want to route the sound from DAW1 to DAW2. You select Soundflower input in DAW1 as output and Soundflower output as input in DAW2.

Most people use Soundflower for recording audio during a screencast. Then you want to make a combination of the Built-in Output and the Soundflower input. This way you can send the audio to your recording software via Soundflower while still listening to the sound from the Built-in Output

  • Ah yes, it wasn't immediately clear that Soundflower acts like a pipe for any audio sources. It's job is not to necessarily capture computer audio like I had originally thought.
    – Michael R
    Commented May 29, 2018 at 6:26

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