I use screen capture utilities like Movavi and Snagit on my MacBook Pro 2019 (Big Sur) to record software demos. When using a headset or any other microphone connected to a USB port, the recorded audio is in stereo.

When I use any external audio interface (PreSonus Studio 24C or Behringer U-Phoria UM2) as the captured audio source, I only get one side (the left side) of the audio. Using either interface with an application that doesn't capture the screen in any way works perfectly, clear audio from both sides.

I'm certain that the audio interfaces are working properly. For instance, I can record my voice just fine using Vector 3 (or any other audio recorder) and the audio interface, and it's clear stereo.

I need to use an audio interface because the mic I need to make a good recording needs an interface in order to work with my MacBook Pro. I haven't had a lot of luck troubleshooting this, even through contacting support from Movavi and Snagit. I'm trying my best to go through all possible system settings and configuration tweaks that I can - is this a common problem with screen capture scenarios? I was about to chalk it up to a third-party bug, but this seems to persist no matter what utility I use, yet the audio interfaces work perfectly fine with any other software that isn't doing a screen recording and I'm a little baffled as to why.

  • I've never fully tracked this down, as it's just not a task I ever need to do personally, but my guess is it simply cannot see both sides of the input - basically I think it thinks in mono & split stereo 'scares' it into recording just one side. Maybe the best tool to track this down once & for all would be Audio Hijack [I think it has a 30-day demo]. You could split incoming stereo to further investigate - maybe using un-similar inputs for L/R so you could see what's going on.
    – Tetsujin
    Commented Apr 6, 2021 at 12:36
  • I'm quite prepared to fumble through this with you - as soon as I can find a cable to get my phone into my USB interface… cable hunt...
    – Tetsujin
    Commented Apr 6, 2021 at 12:36
  • It looks like the input has no way to sum the channels, so a mic from a stereo or multi-channel device doesn't get balanced equally to both side of the image. I've got Audio Hijack, Loopback & Audio/Midi setup running & I cannot find a way to sum the inputs…. I can do it using the software preamp software for my Line6 - set it to just 'Input 1' & that hands off to the OS as dual mono, so QT etc captures panned centre. I can't figure out how to do that from inside the Mac itself.
    – Tetsujin
    Commented Apr 6, 2021 at 13:04
  • This is my interface's software control - Setting to Line 1 [or 2 as appropriate to actual input] will send dual mono to the Mac. Setting to Line Stereo will send each channel input to hard left or right only, the other side being just silence, of course. i.sstatic.net/45tRo.png I'd guess this is "as expected" for a stereo source with audio only on one side - but the Mac won't sum it itself, seems like you have to sum it beforehand.
    – Tetsujin
    Commented Apr 6, 2021 at 13:10
  • I'm going to leave these comments in place as a "how I got there" even though they start with an incorrect assumption ;)
    – Tetsujin
    Commented Apr 6, 2021 at 18:36

1 Answer 1


The task as asked is in effect "how to sum two inputs to one, stereo to dual mono?" one side being the mic/line etc, the other side being just silence.

If you could persuade QuickTime, or any other recorder to record only mono audio this would be one way. If you need additional music etc that must be in stereo, then somehow you need to persuade the Mac itself to sum both yout input channels to mono.

I cannot seem to find any way to achieve that with the Mac itself, nor much of the commonly-available audio routing tools - Audio Hijack, Loopback, Audio-Midi setup etc, testing with Aggregate inputs & everything I could think of.

All I did manage to achieve was to sum before sending to the Mac. In my case, it needed the input software of my Line 6 interface. Setting the input to only one of the 2 potential channels Line 1, Mic 1 etc, then the software itself was doing the sum to mono for me & the Mac would then be happy to place it in the centre of the stereo image.
Setting the input to Stereo Line/Mic etc would send to just one side or the other.

Presumably, this would be considered 'expected behaviour' for a stereo source, though it does look like if you use the Mac's headphone input or a webcam etc, then it already 'knows' there is a single mic, not stereo.

Interface image, just as an example -

enter image description here

I didn't take the time to clean the 'amplifier' setup to be straight clean, so it still looks more like a guitar amp & pedals. That doesn't affect the routing, only the audio quality]

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