Trainer commentary is optional in every class.
We'd recommend keeping commentary on during your workouts as your Trainer will be giving out helpful instruction on form, as well as encouragement as you're working out. However, we understand that the might now be for everyone, and so you're able to disable it in any class from the Pause Menu.
By default, you can access this during any class by pressing the Pause button on your left hand controller. Then, all you need to do is select "Off" for Voice Commentary.
This will remove Trainer commentary, but keep the music playing for you π