There are questions regarding audio input on the Mac Pro, which has neither a built-in microphone nor a microphone jack. There are also questions regarding the use of a microphone other than the built-in microphone in other models.
The use of a USB microphone is generally advised in such cases. There is a problem here, as the current version of SGC is not (yet) able to use input from a USB microphone.
There is a solution. The current line of Macintosh computers will accept a headset on one of the audio jacks (for the line or headphones). That port will thus accept audio input from the headset microphone. SGC treats this audio input as the microphone input.
Information for the Mac Pro:
https://support.apple.com/en-us/HT202859For ways to add alternative recording and playing commands, see the Platforms: Linux thread. These work for Mac too.