Have you ever noticed how, on a rainy night, all other sounds seem to disappear? The sound of the rain drowns them out. And even though the sound of the rain goes on all night, it doesn't keep you awake. Rain is a kind of white noise—a steady, unchanging, unobtrusive sound. White noise is made up of sounds from all the frequencies a human ear can hear, with the sound at each frequency having equal power. It's called "white" because the definition is like that of white light, which is a combination of all the light wavelengths we can see. You might think that a combination of all possible sound frequencies would be terrible, but it's not—quite the opposite. The reason for this is that white noise masks other sounds. Think of it like the rain: the sound of one drop falling, like from a leaky tap, would be very distinct and annoying. Two drops would be the same. You could even tell three steady drips apart. But if there were five or 10 or 1,000, you couldn't pick out each individual drip. They'd all blend into a sort of hum or a quiet roar and probably lull you to sleep. The calming properties of white noise are starting to be used to treat different problems. White noise can help restless people sleep and help migraine sufferers sleep through their pain. It can be very useful for people with attention deficit disorders, who have trouble tuning out background noise. White noise can help them concentrate. It's even used to mask the sound of individual conversations by therapists and others who want to maintain privacy. Who would have thought that mashing lots of sounds together would actually turn out to promote peace and quiet?
你是否曾注意到，在下著雨的夜裡，四周彷彿鴉雀無聲？雨聲淹沒了一切。而且，即使雨下 了一整夜不停歇，也不會讓你徹夜難眠。雨聲就是一種「白噪音」，意即穩定、不變、低調的聲音。 「白噪音」是以人耳可聽見的各種音頻所構成，只是每一種頻率的強度皆相同。之所以稱為 「白噪音」，其實是和白光的原理一樣，白光也是由肉眼可見的所有波長光線組成。你可能會以為所有的音頻加起來應該很吵才對，其實恰恰相反。原因在於白噪音能掩蓋其他聲音。想像一下雨聲，如果是一滴水，例如水龍頭漏水的聲音，會非常明顯而惱人，兩滴水也是一樣，甚至連續滴落的三滴水，我們都能聽得很清楚。但若是五滴、十滴或一千滴，你已經聽不出每一滴水聲。所有的水聲融合成一種低鳴或輕悄的隆隆聲，說不定還能助眠。 白噪音的鎮靜特性，已開始被用於治療各種問題。白噪音對容易焦躁者有助眠作用，也能讓 偏頭痛患者一覺好眠。對於注意力不集中的人亦十分有用，這些人很容易被周遭的聲音影響，因此白噪音有助於他們專心。診療師或其他希望保護隱私的人，會運用白噪音來掩蓋個別的談話內容。誰能想到，聲音的大雜燴反而帶來平和與寧靜呢？ | 
