Circulate: A fan with an electrical undertone, like an air conditioner.
Altitude: Airplane cabin ambient noise.
Swell: Rolling and crashing waves.
Campfire: Crackling fire and softly chirping crickets.
Warm static: Broadband noise with high frequency content removed (also known as “brown” noise).
Downstream: A gentle stream.
Tranquility: A drone-like melody that some might also refer to as a spa-like sound.