I'm looking for basically the opposite of a splitter. I recently bought a Roland OctaCapture interface, and it'd be great if my bandmates and I could plug our headphones into each of the 5 pairs of output channels (10 in total). These channels are all mono, so I'd need to combine two channels to get stereo through the headphones.

Am I doing this completely wrong, or is there a product that takes two individual stereo channels and combines them into one?

I'm looking for two male connectors to plug into the interface, combining into one female connector into which I'll plug my headphones.


These devices do indeed exist, in fact I bet if you did a search for the title of this question on any retailers website then you would find exactly what you need!

The actual name of the device is more likely to be something like “stereo/mono summing box”.

P.S.: Be aware that these devices invite problems with proper gain-staging (specifically you can easily overdrive the input to the next device in the signal chain). The higher-quality versions will usually have input volume trim controls to mitigate this problem.

A more robust solution to this problem is to use a proper mixing console, or a device specifically designed for headphone splitting (with a stereo input).

Your interface’s control software might have the option to mix 2 mono inputs into 1 mono bus and then route that out to the mono outputs.

  • Thanks, is there a specific term for combining 2 mono inputs into 1? – Danny Kopping Mar 20 '18 at 5:54
  • 1
    Yep, that is “summing”. It also applies to combining any number of inputs. – user9881 Mar 20 '18 at 12:31

You need a headphone amp for that since the line levels (and particularly impedances) are not sufficient for driving a headphone. I use just some soundcard with power supply for that (no need to hook it up to a computer if it has no software mixer or a suitable standalone mode), but for 5 headphones, you are likely better off with a dedicated headphone amp, at least for 4 of those (which would be a typical size).

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