Audio fade
Also known as: fade in, fade out
A gradual rise or fall in level at the start or end of a sound, which is what stops a cut from producing an audible click.
Updated
What it means
An audio fade is a short ramp in volume rather than an instant change. Cutting a waveform at an arbitrary point leaves a step in the signal, and a step is heard as a click or a thump.
A few milliseconds of ramp removes it completely. That is why almost every audio edit in a finished video has a fade on it, usually too short for anybody to notice as a fade.
The longer kind is an editorial choice rather than a repair. A two second fall under a closing shot is pacing, and it works with the Pacing of the picture rather than against it.
How it works in practice
Short fades at every cut are the default for a reason. Ten to twenty milliseconds is inaudible as a fade and reliably removes the click, so there is no reason to leave them off.
Music wants longer shapes. A fade in under an opening shot and a fall at the end frame the video, and matching the fall to the last cut rather than to the final frame avoids a dead tail.
Fading is also the gentle alternative to muting. Dropping camera audio to nothing under a Voiceover sounds abrupt, while easing it down reads as deliberate.
What to watch out for
Fades applied to the wrong material sound like a fault. A ramp in the middle of continuous Ambient sound draws attention to itself, because the room tone audibly dips and recovers.
Equal length fades on both sides of a cut can also leave a hole. Overlapping them slightly keeps the level continuous, which matters most when both sides carry the same background.
Automatic fades on every clip boundary are easy to overdo. A sequence of rapid cuts each with its own ramp produces a pumping effect nobody chose, which Audio levels work cannot fix afterwards.
How RawClip handles it
Every cut in the finished audio carries a short fade, so a highlight assembled from dozens of clips has no clicks in it. The music is shaped around the first and last cuts rather than the first and last frames, which keeps the ending from trailing off into silence.