Fade in / out and crossfade

A fade is a gradual volume change into or out of a clip. A crossfade is two fades overlapped, one clip going down while the next comes up, so the handoff has no seam. Both are level automation drawn over time, and both come in shapes: linear, logarithmic, S-curve, and equal power.

Two very different jobs use the same tool. Tiny fades of 5ms to 20ms sit on every hard edit to kill clicks, because cutting mid-waveform leaves a vertical jump that a speaker reproduces as a pop. Long fades of one to several seconds are musical: bringing a bed up under an intro, taking it out under the last line. Dialogue edits usually want a short crossfade plus room tone underneath, otherwise the background hiss pumps at every cut.

The gotcha worth memorizing: a linear crossfade between two unrelated sounds dips in the middle. Halfway through, each clip is at half amplitude, which is a quarter of its original power. Unrelated signals do not line up, so their powers simply add: a quarter plus a quarter is half the power you started with, an audible 3 dB hole. An equal power (constant power) crossfade fixes it by holding each side near 71 percent amplitude at the midpoint instead, so the two halves total back to one. Use equal gain only when the clips are near-identical, like a repaired take, because correlated signals add coherently and equal power would hand you a bump instead of a dip.