Coway 2-in-1 Air Purifier and White Noise Machine, AP-0512NH Sound Therapy6 Sounds developed by Doctors: 3 nature sounds, white noise, 2 lullabies Quiet Operation High-efficiency air in-take fan and filters designed to operate more quietly than other brands Filter Change Indicator light transmits filter status and will inform when a change is needed Separate Timers2 timers allow separate control; Air Purification: 1/4/8 hour &amp; Sound Therapy 15/30/60 minutes Volume Control The volume of the sound therapy feature is easily set for any preferences.