Using Turtle Beach XO Four Stealth Headset with Macbook Pro Retina 15", Mid-2012 I've read a few older posts about headsets and the TRRS headphone/mic input here, here, here, here and the consensus seems to be that the Macbook is expecting "line-level" input (either that or you have the mysterious occasional answer of "mine works!").

My question is more clearly related to this answer: which is, if these Macbook Pros only accept a powered/line-level input, then how do they recognize the iPhone earbuds/microphone? I have not seen this addressed anywhere else.

My Turtle Beach XO Four Stealth is not powered, its only hookup is a TRRS jack. When I plug it in the Input doesn't switch from internal to external as it does for my Apple earbuds/mic.

Any explanations for the difference in behavior? I assume this may just be dependent on the hardware of the headset, but what would this difference be.
Apple use the CTIA standard TRRS while most other companies use the OMTP standard.

These 2 pictures should short it out. Notice the Ground and microphones are switched.


OMTP
CTIA


Hope this answers your question.