I use an air filter for that. I have a Levoit Vital 200S and it allows to set up an automatic filter power schedule so I don't have to think about that when going to bed. Mine switches to the white noise mode at 9:30pm and then back to the silent mode at 8:00am (I usually wake up much earlier than that, but hearing the air filter sound change also tells that it's 8:00am without looking at a clock).