In the above movie clip, the scene shifts from inside the radar dome to the control center. The machine noise in the first location is both different and louder from that in the second. If we just "cut" the audio, the results can be distracting, especially if the ambience level is quite high relative to that of the narration.
Illustrate with a movie clip having "cut" audio
It's important to balance the ambience at the transition point between the two shots. This can be accomplished by cross fading the audio from one shot into the other.
Illustrate with the audio cross faded between the shots
What this means is that whenyou're on location, it's important to record on tape the background sound corresponding to each location, indoors and outside. Back at your desktop editing station, you can digitize this sound and edit it with the video and other audio elements to create a balanced soundtrack for your production.