I have a 13" MBP (December, 2010). It only has one audio port, but can function as two; I can change it to function as audio-output to an audio-input via my system preferences. However, how can I find technical specs behind the audio-input function? Specifically, is this a Mic-In or a Line-In, or can it function as both? I want to record audio from various sources, such as a PA sound board system and cassette decks. Both, the PA sound board and the cassette deck can plug right into my audio port via a 1/8" audio jack. But, if I remember correctly, there is a significant (and dangerous) difference between a Mic-In and a Line-In. Because Microphones produce a very weak signal output, a Mic-In jack is directly connected to a 60dB pre-amp. In contrast, Line-In sources are usually strong, and thus do not need the pre-amp. This is important because connecting a Line-Out (from my PA system or cassette deck) to my Mic-In will amplify my already-strong electronic signal by 60dB, and can thus cause my system to malfunction permanently by overloading the circuitry. Microphones need this 60dB to obtain a proper recording signal, but Line-Out sources do not. Thus, a Mic-Out should be connected to a Mic-In, and a Line-Out should be connected to a Line-In. I can buy an external USB sound card with proper input capabilities, but these things are around $30-$50 and a hassle to carry around. I'd really rather plug right into my audio jack. So, what's the deal with the MBP audio-input, is this a Line-In or a Mic-In?