We at Marpac have a confession to make. The Dohm is actually not a white noise machine.
What?! Yes, it's true. The Marpac Dohm produces, not white noise, butpink noise. Well, you might be wondering, what's the difference? We're glad you asked.
White noise refers to a type of sound that's an equal intensity across all frequencies audible by the human ear; similar to white light, which contains all visible light at equal intensity. White noise is produced by randomly generating noise across the entire sound spectrum, and it ends up sounding similar to radio static, which some people enjoy as background noise, while others find it irritating.
Mathematically, white noise has equal power perfrequency, whilepink noise has equal power peroctave. Here's an example: the difference between 5 Hz and 10 Hz is one octave, as is the difference between 50 and 100 Hz. But, in terms of absolute frequency, the difference between the first two is 5 Hz, whereas the difference between the second two is 50 Hz. In white noise, the difference is obvious, but in pink noise, they’re both one octave apart, so they’re functionally the same.
This is the major difference between pink and white noise. In white noise, the power is constant, but in pink noise, as the numbers get bigger, the difference in power becomes smaller, so the higher-pitched sounds are softer.
Because the lower frequencies are louder than the higher frequencies in pink noise, it sounds less abrasive and leads to a better night's sleep. Less like radio static and more like leaves rustling.
There are other colors of noise, including brown noise (even more low-frequency than pink noise, like thunder rumbling), and blue noise (emphasizes the higher frequencies instead of the lower ones, like water hissing out of a spout). But pink noise has been found by many studies to be the most soothing background sound. Not only that, studies have shown that going to sleep listening to pink noise from a sound machine helps improve memory the next day, and could have long-lasting positive effects on memory and concentration.
Often, other noise colors are lumped under the "white noise" umbrella, because it's a common term people understand, but the distinctions are important. Understanding noise colors helps you understand what color of noise is best for you.