Is there a way to digitize audio using the headphone input on the 15-inch (late 2013) Macbook Pro with Retina display?

I'd like to digitize audio from a minidisc player into my 15-inch (late 2013) Macbook Pro with retina display, but can't see a way to change the internal mic input. I understand that previous MacBooks allowed the headphone jack to double as a mic input, but mine doesn't seem capable of switching. I've tried using a mini to mini cable, with no luck, and also tried using a headset splitter adapter (3.5 mm 4-pin to 2x3-pin 3.5 mm headset splitter adapter from Amazon) because I read that that would allow me to plug in headphones and input audio. But in both cases, the only "input" available in my sound preferences is the built-in internal microphone. Am I missing something? Is there a way to digitize audio through the headphone jack?