There are a couple ways to add music to iMovie on mobile devices, depending on whether you're trying to add a soundtrack or sound effects. How to add a soundtrack. 1. Tap the plus sign "+" icon.

So, play with the EQ, filter noise, or add an unhealthy amount of reverb, just don’t cut or add anything to the file. ... the file won’t be in sync when you add it to your iMovie project.) ...