how do you change the headphone input to a microphone input on a mac pro 2015
How do you switch the headphone input into a microphone input?
Do you mean Macbook Pro - the laptop? The Mac Pro is a standalone desktop computer with no screen and the comments below wouldn't apply to it.
The early 2015 13 inch Macbook Pro has the dual output/input audio socket; I don't know whether this applies to all the 2015 models. Input or output can be selected in the Sound Preference Pane. The illustration below is from an earlier model but it's likely to be the same or similar on later ones. However when used as an input socket this may be line level, not microphone level, so if you want to use an ordinary mic (i.e. not USB) you would need a preamplifier of some sort or a mixer. Some models will work with the Apple headset (earpiece and microphone, like a telephone operator).
