Yesterday I bought a 1/4 inch stereo phone jack adaptor to plug my guitar and cable into my macbook. The problem with garageband is it's giving me piercing loud feedback and not recording my guitar. I can't figure out what i'm doing wrong.
hit up your system preferences and change the default input to line in. it's on mic right now. i had the same problem before.
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Garageband > prefences > audio/midi > audio input > built in audio input