Can the background music be turned off?

Silencing Background Music

Yes. You can turn off the background music.

When you are listening to a passage, click the "music" button in the bottom of your screen. 

From there, you'll be select the music, sound or "No Music".  Click the "x" and your selection will be saved.

You are able to do this in real time, as the passage is playing, so you can understand how the changes you made impact the auditory experience on the fly.