How to add longer pause to end of song

[GIacona]

I have a lot of music I want to add into I-Tunes. However some songs don't have a long enough pause at the end of the song, and it goes right into the next song. Is there a way I can add a longer pause at the end of a song? Not sure if this can be done within ITunes, or if I need a 3rd party software. Hopefully this will not affect the quality of the song either