Fading out/Stopping Looped Music in Passage(s)

Hello, I'm brand spanking new to Twine, but I'm a huge fan of computers and an even bigger fan of telling stories.

I'm using the Harlowe story format. I managed to get a sound to loop in the background over all my passages, but it has come to my attention that I need the sound to fade out and then stop for a few passages, and then fade in and loop once more. Help would be appreciated! Thank you!