How to route dual audio input to single output in macOS

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In this post I’m going to show you how you can use a CalDigit TS3 Plus (other possible input/output dongle or device can be used for this) and Audio Hijack by Rogue Amoeba to route two audio input sources (with 3.5mm jacks) to a single audio output (3.5mm jack, desktop speakers).

Prerequisites #

  • (optional) CalDigit TS3 Plus if you don’t already have one. You don’t actually need this exact dock and may use any dock/dongle that supplies an audio in and an audio out port separately. I purchased mine from Apple.ca as Amazon didn’t have any in stock at my time of purchase.
  • Audio Hijack by Rogue Amoeba for macOS. This is the key piece of software that allows us to route audio input from the CalDigit TS3Plus through to the audio ouput (speakers), within macOS.

The motivation to do this in the first place is because I have a gaming PC and my work MacBook Pro connected to the same dual-monitor setup through different cables. Both monitors also have audio output 3.5mm ports on them, and I use one for audio output from my gaming PC which is connected to that monitor via an HDMI cable. The issue I faced was, although my MacBook Pro gets used primarily as the main input to my monitors connected through my CalDigit TS3 Plus which also has my desktop speakers plugged in, I have to unplug my speakers from the dock to plug them into a short audio extension cable plugged into my gaming PC monitor. This is a hassle and sometimes I forget when the speakers are not plugged back into the dock.

My desktop setup looks like this:

My desktop setup diagram, make note of the asterisks in pink highlighting the desktop speaker connection and the audio cable from the gaming PC monitor

My main audio output source is the desktop speakers which comes from my MacBook Pro and is set as “CalDigit Thunderbolt 3 Audio: Speaker” in the macOS Sound > Output settings. The second audio input source comes from a 3.5mm male-to-male connector from one of the monitors to the audio input port on the front of the TS3Plus. On it’s own, this audio input port is used as a Input device in Sound > Input macOS settings, however this is where Audio Hijack comes in.

Once Audio Hijack is installed, you can create a Blank Session, then drag an Input Device and an Output Device to the work area of the window. The Input Device should be set as “CalDigit Thunderbolt 3 Audio” and the Output Device should be set as “CalDigit Thunderbolt 3 Audio: Speaker”. Once these have been set, hit the Start Session button in the bottom left and you should be able to hear your secondary audio source through your speakers!

Audio Hijack has a great article on how to enable this.

Notable points #

I had to set the output volume of the gaming PC to 30% in Windows 10 in order to reduce a high level of gain received in Audio Hijack. I then set the Input volume level in macOS to about 75% with the Output volume set to 100%. The final audible volume level is controlled by the physical volume knob on the speakers.

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