Theoretically, true white noise would contain all frequencies with equal power across the entire spectrum from zero hertz to infinity. However, such a signal would contain an infinite amount of energy and therefore, cannot exist. In the real world, white noise contains all frequencies within a certain frequency range. For instance, a white noise signal in the radio frequency band may contain all frequencies from one hundred thousand Hz to several billion Hz. White noise in the audio frequency band contains all frequencies which span the range of human hearing (from 20 Hz to 20,000 Hz). White noise sounds similar to radio static but has a much cleaner and smoother sound. The sound of rainfall or leaves rustling in the wind are good examples of audio white noise produced in nature. Some people find the sound of white noise pleasing, while others don't.

Since our ears perceive frequency ranges in a logarithmic manner, it is much easier for us to distinguish the pitch distance between 100 Hz and 200 Hz than it is for us to distinguish the same pitch distance between 10,000 Hz and 10,200 Hz. In other words, 100 Hz sounds very different than 200 Hz, but 10,000 Hz sounds only very slightly different than 10,200 Hz despite the fact that both sets of frequencies contain the same frequency difference of 200 Hz. Since higher frequencies are less distinguishable from each other than the lower ones, the upper frequencies would seem to "bunch up" together and overpower the lower frequencies. Because of this, most people cannot hear the lower bass frequencies that are also present in white noise.

White noise can be highly effective at creating a sound curtain to help prevent eavesdropping on private conversations, masking noise in busy offices, providing a true random noise source for computer applications such as cryptography, and even for paranormal research.

Just like white noise, pink noise contains all frequencies within the audio band. Pink noise sounds similar to white noise, the only difference is that much of the higher frequencies in pink noise are not as prominent, allowing the lower frequencies to be much more perceptible. In other words, the bass has been increased while the treble has been reduced. The sound of a waterfall, ocean surf, or a raging river are some examples of pink noise produced in nature.

The true random pink noise produced by the PNG-400 is created by passing the white noise signal through an electronic circuit called a pink noise filter. The noise filter reduces the noise output by 3 decibels per octave, thereby producing a signal where the power is inversely proportional to its frequency. In other words, the intensity of the higher frequencies are significantly reduced. Thus, the lower frequencies sound just as loud as the higher ones, producing a much more uniform sound. 

Although white noise is important for some applications, most people agree that pink noise is more soothing to listen to. The soothing sound of pink noise can help promote a state of relaxation & sleep for both babies and those suffering from insomnia. Pink noise can also provide relief for those suffering from tinnitus. I have found that it is highly effective at masking distracting noises (like your neighbor's barking dog), which can help improve focus and concentration. Some people even use pink noise as an aid for meditation practices. Other uses include testing and calibrating sound systems.

Click here to see why analog noise generators are far superior to white noise CDs and ordinary sound conditioners.

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