shows us how to sync double-system sound in FCP-X:
Double-system sound is where you record the video on one device (a DSLR camera, for example), while the audio is recorded on a separate device (such as a digital audio recorder). Many video cameras don’t have high-quality audio recording built into them. This process resolves that issue.
In this short video, Larry explains what double-system sound is, illustrates the differences in audio quality between a mic on the DSLR camera and one recorded to a separate device, then shows how to sync the two files. In fact, there are two ways to sync double-system sound: one is very fast, and the other is very easy. Larry illustrates both.