iTunes: auto ramping up/down to avoid dead air As a simple solution to avoid dead air, I'd like to overlap each pair of consecutive songs in a playlist by ramping them down/up.

In effect this would be a poor man's DJ solution.

I wouldn't mind if it's entirely non-interactive, just so long as it is suitable for dinner parties, dance events, and the like. Indeed, the DJ software applications on the app store all seem to require an operator. Does an automatic solution exist, one that takes no more input than: 1. playlist, and 2. duration of overlap ?
There is also a trimming function within iTunes that works separately from the crossfade solution proposed by @timothymh. This would work better for your dance scenario. If you right-click a song and select Get Info, you get an info window about the song. Under the Options tab, you can set a start and stop point for each song.

As an example, here I've set this song to start 20 seconds from the beginning.