Make sure to set the project to TURBO MODE (RIGHT CLICK THE GREEN FLAG)! This will prevent the delays in the transitions between loops and intros.
I did one for Cave Story, so I figured why not do one for Undertale too. Once again this is not the entire game soundtrack, just a handful of the songs. If the project is in Turbo Mode, they SHOULD loop properly. These files were ripped from the game rather than the purchasable soundtrack to ensure that they loop properly. http://store.steampowered.com/app/391540/