Is there an easy way to mix headphones and mic into one output for recording purposes?

Question

I’d like to have a portable setup that I can use to record conference calls for work, in particular I want to cover the cases where I want or need to use headphones.

I often use more than one kind of setup I work off of, for example some possible combos for the headphones use case:

Headphones w/mic TRRS 3.5mm —-> Apple TRRS-USBC adapter —-> iPad Pro
Headphones w/mic TRRS 3.5mm —-> Apple TRRS-Lightning adapter —-> iPhone
Headphones w/mic TRRS 3.5mm —-> Macbook
Headphones w/mic TRRS 3.5mm —-> TRRS to TRS mic and TRS phones for PC front panel —-> Desktop PC running Windows or Linux

I’d like to have a device that sits at the position of the first arrow which splits the TRRS signal out into one 3.5mm output which I will plug into the recording device.

So the TRRS is dealing with 3 channels: L, R, and Mic with a shared ground (4 wires). My main goal is to achieve the mixing of these 3 channels together into either a single mono signal or to mix the mic channel evenly on top of the L and R, as both would be acceptable, or I suppose if I could somehow find a recording device that takes this kind of 3 channel input then I can get an off-the-shelf TRRS splitter and be done with it.

The question is, assuming I only have a simple run-of-the-mill audio input device to use and I want to record my mic input mixed together with the headphones output into that device, what type of (portable!) product would I need to use to achieve this?

Answer 1

It's easiest to do this digitally. For example, on Mac OS, you can use Audio Hijack to record the audio streams. Similar software is likely to be available for your other platforms too.

Answer 2

This is too impractical to do digitally under all cases because sometimes I want to record a phone call and sometimes a call within software running on a computer. In particular it does not work well when I would need to set up a convoluted software setup on each device that this applies to.

The solution appears to be a 4-channel audio recorder, where the stereo output from the computer can be split into my headphones and the recorder line-in, and being a 4-channel, the recorder's own mics would be able to also record simultaneously. This has several benefits: It does not have to interfere with the TRRS 3.5mm headphone/mic setups, and it captures my voice in high quality as well as the sound directly from the device, and splits it into separate recording channels, which can be useful as I can easily perform the mixing after the fact.

Answer 3

Exploring the software implementation though, a few years later:

• We have Blackhole available which allows for system audio output to be put into something that can be referenced as an audio input, which can be handy
• The above is not even needed for OBS, I don't know if this always worked like this but I am able to get system audio in the audio mixer for the screen capture, and we can choose from OBS the same mic we may be using. So out of the box OBS will work to record both sides of the conversation when it comes to something like a Zoom call
• if we want to e.g. record both sides of a zoom call into one audio channel using a less-featured recorder like quicktime player, then blackhole can be used in conjunction with both a multi output device (to provide monitoring ability for system output in blackhole) and aggregate device (to combine system sound via blackhole and the mic input stream into the one input stream to send to quicktime screen recording), both are set up in Audio MIDI Setup.

I still think a hardware solution is needed if you want to be able to capture any kind of call you might make on your phone though, since jailbreaking iOS isn't a practical solution anymore these days. So there are different setups for different use cases of course.