I have a Mackie Onyx Blackjack audio interface, and my microphone is plugged into the first of two inputs ("left"). The other input doesn't have anything plugged into it. What this means is that whenever I record audio in QuickTime, it produces a stereo file with my voice on the left track and silence on the right track. However, Mac OS X sees the device as a 2-channel stereo device, and I can't seem to convince it otherwise.

Here is a screenshot from Audio MIDI Setup to show what I mean:

Audio MIDI Setup screen

The only thing I can change is the "Format" from "44100.0 Hz" to "48000.0 Hz". Everything else is greyed out.

I investigated creating an aggregate device, but I see no way to eliminate audio channels from that either. How can I get Mac OS X to see this device as a mono input?

  • You could always do in hardware what the software can't: split the signal from the mic with a small mixer and feed both inputs, or get a stereo mic.
    – IconDaemon
    Commented Dec 11, 2012 at 1:09

1 Answer 1


whenever I record audio in QuickTime

This is the problem. QuickTime doesn't offer the ability to change the recording type or to pan inputs to a particular track in the recording when you're making it. It records stereo. And it captures one input left, the other input right. I just tried it out with my Duet and, no matter where I set the pan on the mic input in the Maestro mix console, QuickTime captured that signal input on the left channel only.

The solution, I'm afraid, is to stop using QuickTime.

Garageband, which is likely already on your Mac, will let you capture a mono source and then pan and bounce a master mix with the mono source placed in any location you like in the stereo field. It definitely is a more suitable interface for capturing and manipulating audio than QuickTime.

  • Yeah, for the podcast I've been recording in stereo and splitting with Audition. However, I went to create a screencast with QT and it suffered from the same problem, and I'm trying to avoid having to edit the resulting video file. I suppose I could try using other screencasting software besides QuickTime though. However, it's frustrating that this can't be solved at the system level. Commented Jan 19, 2012 at 19:31

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