How can I double a song's length? I have a song in my iTunes (11) library that loops amazingly well, but is rather short in duration.  I'd like to double the length of the song by having it loop once before continuing, so that I can use the extended version in randomly-shuffled playlists.

I know I can extend a song's length by including the same song in a playlist twice in a row, burning the list to a CD, and then merging the songs when I import back (with a gap of 0).  However, this requires throwing away a lot of CDs if I encounter many such songs.

Is there an all-digital way to merge two songs together?
Well you can use any digital audio editor to combine songs. Like Audacity. 


  Audacity is a free open source digital audio editor and recording
  computer software application, available for Windows, Mac OS X, Linux
  and other operating systems.


Here is link that tells step by step how can you do that using Audacity.

http://www.wikihow.com/Combine-Songs-on-Your-Computer-Using-Audacity