To be more exact, in audio the fade-out effect is used to make a sound gradually disappear and the fade-in to increase the sound from a song gradually. If you want to use these effects with your playlist when you listen to your music collection, you can use Crossfading Output.
Crossfading Output is an output plug-in for Winamp that mixes the sound files played on Winamp in an optimized manner, starting a fade at the right moment of the sound file. Furthermore, it allows you to send the mix to a compressor or shoutcast.
This plug-in accepts the following output formats: 11,025 Hz, 22,050 Hz, 44,100 Hz and 48,000 Hz, both in mono and stereo, and it allows us to control the start (fade-in) and end (fade-out) level and control of the mixing curve.