Guide: How to add Fade In and Fade out effect to MP3 Here is the guide with the steps to follow. Kanto Audio Mix is one of the best software to add fade in and fade out effect to MP3 songs. Thanks to Fade in and Fade out effect you will be able to merge several audio tracks without audio gaps and without abrupt transitions between them. Instead, Fade in is the gradual increase or decrease in the level of an audio signal. Fade Out is that audio effect that changes audio level over time falling gradually to silence. We already describe how to cut mp3 with fade in/out effect to create a perfect ringtone for your smartphone or a background music for your video or website.