It is when the volume drops gradually to silence at the end of the song, instead of cutting abruptly.

Which curve should I use?

The smooth curve usually sounds more natural for music; linear is more even and predictable.

Can I do only a fade out?

Yes. You can apply only the fade in, only the fade out, or both.

Online audio tool

Make your song enter and leave smoothly, with no abrupt cuts. Choose the curve type so the fade feels natural.

Target search: add fade in fade out to audio

Upload your song or audio.

Set the fade in and fade out length.

Choose the curve (smooth, exponential or linear).

Listen and download the result.