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Fixing the annoying stereo-mono external monitoring bug in OS X with Final Cut Pro X

fcpx audio monitoring bug

After some heavy FCPX sessions, we thought it was a good idea to document one of the most annoying bugs with Final Cut Pro X, OS X and external audio. With some amazing timing and help we also found a fix!

FCPX is a slick piece of software no doubt, but it still does have its quirks and bugs. Apple can't test every feature in every editing situation, so hopefully any information fed back to them should help to get rid of bugs. 

One particular problem has been annoying us a lot. Audio monitoring, or lack of it in the browser when deselecting tracks. 

If a clip in the browser has stereo channels, by deselecting the audio in the Inspector to just one channel, lets say the left, the audio is routed out of third party devices as a mono channel (down 3 or 4 we think) and thus you can't hear it.

This is annoying as camera originals fed back over satellite feeds (with a stick mic on one leg and a loud camera mic on the other) can be difficult to monitor in stereo and also it means having to disable the other channels on the timeline every time to hear it.

 stereo mono fcpx


If you have a lot of one-legged interviews then you don't have the choice of being able to set the clip in the browser to the track you want, then continue to edit  laying down each interview with the correct audio.

If you are using the internal speakers with your Mac, you shouldn't experience this issue. It is only with external devices used for monitoring such as an AJA IO 4K or Blackmagic Ultrastudio Express.

Just as we were writing up this article (It actually started off as a bigger bug rant, but we will save that for later) we came across @Vordio's tweet describing exactly the same problem.



Then after a few Twitter exchanges where we both came up with incorrect theories as to why this was happening, Vordio posted a link to this Apple Knowledgebase Article. It was last modified on April 17 2015.

If you can’t monitor mono or dual mono audio from Final Cut Pro X 10.2 in OS X 10.10.3

The good news is that following the instructions, it fixed the issue. We can now listen to a mono track through a stereo output device. Cheers all round and a huge thank you to Vordio for doing the homework.

 Here's what you have to do:

  • Open Audio MIDI Setup.
  • Select your audio output device in the audio device list.
  • Click Configure Speakers in the bottom right of the window.
  • Click Multichannel.
  • Choose Stereo from the pop-up menu and click Done.
  • Where is the Audio MIDI Setup? You'll find it in the Utilities folder within the Applications folder. Once found, this is the page you will need.

    midi stup fcpx


    Ours was already set to stereo, but putting it into 5.1 then back and then selecting 'done' fixed the problem.

    A fix and we are very, very pleased, but this really shouldn't be an issue in the first place. 



    Written by
    Top Blogger Thought Leader

    I am the Editor-in-Chief of FCP.co and have run the website since its inception ten years ago.

    I have also worked as a broadcast and corporate editor for over 30 years, starting on one inch tape, working through many formats, right up to today's NLEs.

    Under the name Idustrial Revolution, I have written and sold plugins for Final Cut Pro for 13 years.

    I was made a Freeman of Lichfield through The Worshipful Company of Smiths (established 1601). Though I haven't yet tried to herd a flock of sheep through the city centre!

    Current Editing

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    Covid cancelled some of the regular corporate events that I edit such as trade shows & events. I was lucky however to edit, from home, on projects for Amazon Kindle, Amazon Black Friday, Mastercard and very proud to have helped local charitable trust Kendall & Wall secure lottery funding.

    As for software, my weapon of choice is Final Cut Pro and Motion, but I also have a good knowledge and broadcast credits with Adobe Premiere Pro, MOGRT design and Photoshop.

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    I'm the creative force behind Idustrial Revolution, one of the oldest Final Cut Pro plugin developers. It hosts a range of commercial and free plugins on the site. One free plugin was downloaded over a thousand times within 24 hours of release.

    I also take on custom work, whether it is adapting an existing plugin for a special use or designing new plugins for clients from scratch. Having a good knowledge of editing allows me to build-in flexibility and more importantly, usability.


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