Adjust recording levels for standard sound cards
Adjust levels if recordings are too quiet (causing background noise) or too loud (causing distortion). To get the best sounding results, record audio as loud as possible without clipping. When setting recording levels, watch the meters in the Record dialog box, and try to keep the loudest peaks in the yellow range below ‑3 dB.
Soundbooth doesn’t directly control a sound card’s recording levels. For a professional sound card, you adjust these levels with the mixer application provided with the card (see the card’s documentation for instructions). For a standard sound card, you use the mixer provided by Windows or Mac OS.
Adjust sound card levels in Windows Vista and Windows 7
Adjust sound card levels in Windows XP
Adjust sound card levels in Mac OS