To fade in a clip’s audio, drag an audio transition from the Effects panel to the Timeline panel so that it snaps to the In point of the audio clip. You can also double‑click the applied transition in the Effects Controls and choose Start At Cut from the Alignment pop‑up menu.
To fade out a clip’s audio, drag an audio transition from the Effects panel to the Timeline panel so that it snaps to the Out point of the audio clip. You can also double‑click the applied transition in the Effect Controls panel and choose End At Cut from the Alignment pop‑up menu.