The iMic Control utility provides additional features and control for the iMic USB audio adapter. The software is free for iMic users. Currently the iMic control supports output treble, bass, volume, balance, and mute as well as input gain. Some functions such as audio input gain require that you hot plug the iMic before the new settings take effect.
What's new in Griffin iMic Control
Version 1.5 includes an adjustable input gain control. This allows
users to adjust their sound input level when recording music or voice into
the Mac. This is especially useful for people recording sound into iMovie.
Although iMovie can record voiceovers and music directly, it has no way of
adjusting the level of sound being recorded.