Hi Aluminum213,
The nature of spoken language redundancy and the remarkable ability of the human ear/brain to accurately interpret badly mangled speech because of that redundancy means that the internal microphones on a MBP work fine for most speech applications, just as on an iPhone.
If you are after fidelity in recording, however, say the recording of music, then you will find much better reproduction of music when using an external microphone with preamps and USB adapter, such as the Audio-Technica AT8035 or similar microphones and the Focusrite Scarlett 2i4 USB adapter.
Regards,
Switon
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Oh, sorry, so you were referring to the reproduction of audio by headphones plugged into the MBP. I find that the D/A converters in the MBP to be relatively good, especially when listening to speech through a pair of headphones which don't require large power resources. Of course, the fidelity depends upon the quality of the headphones, but most any of today's headphones will provide a bandwidth surpassing what the human ear can detect. If you wish to play music, especially with large dynamics, on a set of external speakers, then you will probably find that an external D/A converter designed to provide greater power and faster speeds (for the dynamics) will give better fidelity on your external speakers.
Switon
P.S. I don't know what the slew rate/power output/D-to-A conversion specifications are for the MBP, but of course you can get faster/more power/higher bit counts from an external unit than from the internal unit built into the MBP.
