Equipment: Plugable USD Audio Adapter (headphone out/line[mic] in) and iMac macOS High Sierra

My old MacBook Pro (OSX 10.9.5) had a built-in headphone out port (3mm) and a mic/line in port (3mm). I used to use this to record from my Sibelius software (as playback) to GarageBand (to record) by taking a single 3mm audio cable and hooking one end to headphone out and the other end to mic/line in. It worked perfectly. The problem: I just bought a new iMac. There are no headphone or mic/line ports. I bought a single Plugable USB Audio Adapter that has a headphone out and a mic/line in. HOWEVER, if I try to plug my audio cable from the headphone out to the mic/line in GarageBand doesn’t hear it. Is the plugin only capable of using only ONE jack at a time? I.e., do I need to buy another to use ONE for headphone out and the OTHER for line/mic in? Or am I programming my internal mixer (output) and GarageBand’s input incorrectly.

Hello Joel,

Thank you for your message.

Both the microphone and headphone jack on the USB-AUDIO may be used at the same time on a device.

I think this is likely a setting issue somewhere with the audio options if you’ve verified either jack works independently (audio out only and microphone input only).

I’m not familiar with using the two particular software packages that you’re using, and it may be better to contact Apple for Garageband and the makers of the Sibelius software for assistance.

If there are issues identified with the USB-AUDIO adapter, we’ll certainly help to replace it.

Please feel free to contact us at so that we can help if you can’t make further progress.

I hope this helps.

Plugable Support