I remember, many, many years ago, finding a plugin for WinAMP that allowed (IIRC) easy looping of a section of an MP3. I wanted to do this again. Only this time, there was no WinAMP and I am a foobar2000 user.
Looping a section of a song in foobar2000 can be done using the foo_seek component (plugin). The download page is here which is also where the author provides some generally vague answers to questions. Besides this, there is no documentation whatsoever. But this is what I did to get things working.
Firstly, after downloading the component, you can install it via Preferences -> Components in foobar2000. Once installed (and after the restart), check out the Playback menu which should now have a Seek Control option with a whole bunch of submenu options. The ones we are interested in are Loop and two items within the Loop length submenu named End point mode and Set end point. What we want to do next is to create keyboard shortcuts for these three menu items via foobar's preferences. Along with a control key combination, I assigned \ for Loop, [ for End point mode and ] for Set end point.
Once you have the keyboard shortcuts ready, play the song. When you want the loop to begin, press the Loop shortcut. Then press [ to switch to End point mode and when you want the loop to end and repeat itself, press ] to set the end point. That should do it :)
There are more options available for this component if you go to Preferences and Advanced.
All that said, the loop is not seamless and it's tough to set the end points exactly. While the plugin is cool, I just installed Audacity and had a perfect loop going in about 2 minutes :)
Hope this helps!