The USB adapter is a AT USB duplex (two way)adapter that digitizes the audio in USB format. In addition, the 102A has a mute button to block audio transfer when engaged. Use of a USB adapter is essential for Macs because the Voice Tracker I's analog output cannot be used with Macs since the Mac expects line level audio whereas the Voice Tracker has mic level analog audio The USB adapter is especially useful for computers with average quality soundcards. For example, when used with Dragon NaturallySpeaking, the Voice Tracker's score on the Dragon signal to noise test is 25 without the USB adapter, and 31 with the USB adapter. The USB adapter can be used with computers that have no soundcard.