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People who have trouble blocking out noise at bedtime may resort to using a standing fan or a white noise machine, but white is not the only "color" of noise out there. Pink or brown noise may be even more helpful at blocking out unwanted sounds and getting you better sleep. It's the sound inconsistency (noises going from loud to soft or vice versa) rather than the sound level that tends to wake you up. White noise creates a blanket of sounds that masks this inconsistency. White noise is made up of sounds from all over the spectrum, from low-frequency bass notes to high-frequency chimes. These sounds are all blended together to create a constant stream of soft noise. White noises occurring in nature include sprinkling rain, gently running water and a breeze sifting through trees, all sounds that humans tend to find relaxing at any time of day. Pink noise is similar to white noise, but it leans less heavily on high frequencies and more on bass and mid-range tones, so it sounds like moderate rainfall or ocean waves. Those who dislike higher-pitched sounds may find pink noise more pleasing to the ear. Brown noise emphasizes bass notes even further, almost completely eliminating high frequencies from its profile. Natural brown noises can be things like roaring river rapids, heavy rainfall and distant rumbling thunder. This type of noise is named not only for a color, but also for Scottish scientist Robert Brown. In the 1800s, Brown observed pollen particles moving randomly in water and devised a mathematical formula to predict these movements. When this randomizing formula is used to generate electronic sound, a bass-heavy noise profile results. Brown noise is sometimes known as red noise.