When you add clips to the Timeline in Final Cut Pro X, the audio and video portions are automatically added. You may separate the audio and video before adding audio or video to your Timeline by setting the edit mode. There are three edit modes: audio only, video only and both audio and video. If using Final Cut Pro 7, you can separate audio and video by unlinking them in the Timeline. Writer Bio

How to Separate Audio From Video in Final Cut Pro  10 Steps  - 22