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What Does Pink Noise Sound Like

by Kristin Beck
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What Does Pink Noise Sound Like

What Does Pink Noise Sound Like

“If you’ve ever been in a car on a freeway at night, you may have noticed that it’s quiet except for one particular sound: a loud hiss-like buzz. The reason? A truck driving by has its air brakes set too low, causing them to pump air continuously through the brake system. This produces what we call “”brake squeal.”” But not all noise can be so easily explained away as an unfortunate engineering choice. Some noises are truly inexplicable. One such noise is pink noise.
Pink noise is also known as flicker noise, brown noise and random telegraph signal (RTS). If you’re unfamiliar with these names, don’t fret; they each refer to the same phenomenon — a type of high frequency background noise that’s usually quite soft and barely audible until you pay close attention. In fact, most people aren’t even aware that there’s anything amiss when listening to standard white noise. For instance, if your computer’s fan is running, you might hear a typical amount of white noise coming from your speakers — just a constant stream of clicking and whirring. However, if you turn up the volume a little bit, you’ll notice that this noise isn’t quite right. Instead of hearing a continuous flow of sound, you may begin to pick out individual clicks and buzzing sounds. You’ll then realize that those seemingly unconnected pieces actually make up part of a larger pattern: a kind of musical tone.
The sound of pink noise is similar to standard white noise. However, unlike white noise, which contains equal amounts of every possible pitch within a given range of notes, pink noise consists mostly of two notes — a lower note followed by a slightly higher note — separated by only a small interval, or distance between pitches. When played back, they form a pleasing melody that lacks any distinct rhythm. Most people describe the effect as being like rainfall or the hum of an electric motor. However, others say pink noise reminds them of waves lapping against a beach [sources: Kukla, Wikipedia].
So why does pink noise sound different to everyone? What makes certain sounds stand out among the rest? And how did scientists come upon this strange new noise? Read the next page to learn about the history behind pink noise.
History of Pink Noise

Where Did Pink Noise Come From?

How Do We Hear Pink Noise?

History of Pink Noise
Scientists first encountered pink noise in 1877 during experiments involving radio signals. By adjusting the sensitivity of receivers, they were able to isolate specific frequencies of radio waves in order to better understand their properties. They discovered that a narrow band of electromagnetic radiation emitted by distant stars was comprised almost entirely of two tones: one very deep and one much higher.
In 1924, researchers began experimenting with recording and reproducing these tones using mechanical devices instead of electrical currents. Their results showed the two tones could be combined into one single waveform without affecting the sound quality. Over time, they developed methods to produce purer versions of the original tones. These became known as sine waves because they resemble alternating current flowing through an idealized coil of wire.
When scientists applied these findings to other types of waves, including audio, they found that pink noise worked well as a means of masking unwanted sounds. One researcher used pink noise to eliminate the annoying humming produced by fans in a laboratory setting. Another group successfully utilized it to block out the screeching of trains passing by outside a building. Since then, pink noise has become increasingly popular as a method of eliminating distracting environmental sounds.
Now let’s take a closer look at where pink noise comes from.
One of the most common sources of pink noise is traffic. As mentioned earlier, when drivers’ air brakes malfunction, they pump air continuously through the brake pedal, resulting in a continuous buzz. On top of that, cars’ internal combustion engines typically revolve around the same basic engine speed, creating a steady hum. Although both of these sounds are technically white noise, they lack the characteristic frequency patterns of normal speech. Therefore, they can sometimes seem disconcertingly loud when compared to the relative silence of pink noise.
Where Did Pink Noise Come From?
As we learned earlier, scientists stumbled onto pink noise while studying electromagnetic radiation. Because it turned out that certain wavelengths of light contained the two main components needed to create it, scientists soon realized that the mechanism responsible for producing it wasn’t limited to radio transmissions. Rather, it existed across many different fields of physics, including electricity, mechanics and acoustics.
Although the term “”pink noise”” appears to suggest something vaguely feminine, the color itself has nothing to do with it. Many people mistakenly believe that pink represents the highest frequency possible for audio colors, yet that’s simply not true. Instead, pink refers to the lowest frequency possible for visual colors. So, although pink noise looks like white noise, it differs in terms of color. It’s also worth noting that since pink noise originated in electromagnetism studies, physicists use it to represent alternating current. As a result, electrical engineers commonly refer to it as RTS, short for Random Telegraph Signal.
Let’s move on to finding out how we hear pink noise.
Most people know that sound travels through vibrations caused by particles moving toward or away from us. However, few appreciate just how complex the process really is. There are three major categories of sound waves: compressional, shear and surface waves. Compressional waves cause particles closest to our ears to vibrate faster. Shear waves cause particles furthest from our ears to vibrate faster. Surfaces waves, meanwhile, affect particles along a plane perpendicular to our ear canal.
How Do We Hear Pink Noise?
Since pink noise doesn’t contain any discernible rhythm or melody, it shouldn’t register as sound inside our ears. However, when we listen closely, we can sometimes detect subtle differences in volume. Even though these changes occur over a microscopic scale, they still prove useful for understanding how pink noise works. To see how this works, imagine watching someone walk toward you wearing headphones. As they get closer, you’ll notice their footsteps becoming louder and clearer. Eventually, you’ll be able to make out individual steps.
This is essentially what happens when we listen to pink noise. Our brain analyzes the incoming sound waves looking for slight variations in volume, then groups together adjacent sections containing the same variation. Once our brains identify the pattern, our auditory cortex begins processing information accordingly. According to science writer David Priess, this phenomenon explains why we perceive pink noise as sounding quieter than white noise despite having the same overall decibel level.
To test this theory, Priess conducted an experiment in which he listened to a pair of identical oscillators playing white noise. He varied the amplitudes of one of the oscillators by 5 percent increments. At no point did he change the overall volume of either generator, thus ensuring that any perceived differences in volume came solely from the varying levels of input. He found that when the amplitude increased, the volume of the white noise gradually decreased. Conversely, when the amplitude decreased, the volume rose. Priess concluded that our brains analyze the input according to the strength of the fluctuations rather than absolute volume.
For additional resources on pink noise, check out the links below.
­Another interesting aspect of pink noise is that it doesn’t rely on the cochlea, the inner ear organ responsible for converting sound waves into nerve impulses. While most animals possess the ability to locate sound sources using eardrums, humans can pinpoint locations using external sensors. This allows us to distinguish different sounds based on location. Scientists theorize that our earliest ancestors possessed this skill, enabling them to orient themselves in relation to potential threats. Afterward, evolutionarily speaking, this trait helped ensure survival in dangerous environments. Today, however, this skill proves less important than it once did, largely thanks to the widespread availability of technology. Nevertheless, recent research suggests that pink noise enables human beings to focus on tasks requiring improved spatial awareness.
Noise Cancellation Technology

Many companies now offer products designed specifically to filter out unwanted ambient sounds. The best noise cancellation technologies, such as QuietComfort 35 II Headphones, utilize special microphones to measure surrounding noise levels before filtering out corresponding frequencies. Other gadgets, such as Bose NoiceCanceling Headphones, employ digital signal processors to alter the incoming waveforms, effectively cancelling any accompanying noise.
However, while such devices certainly provide effective solutions for blocking out unwanted noises, they tend to suffer from several drawbacks. First, they require batteries to function properly. Second, they often introduce their own unique noise profile. Finally, some users complain that the filters degrade music quality significantly. Fortunately, manufacturers continue developing alternative approaches to noise reduction. For example, Sony recently unveiled the XBA-1 wireless headset, which promises greater sound quality and virtually zero distortion from noise cancellation. Meanwhile, Google continues to develop its experimental Project Aura concept, which aims to enhance situational awareness via advanced audio technologies.
For more information on pink noise and related topics, explore the links on the following page.”

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