White Noise Definition Vs. Pink Noise

I receive a lot of questions regarding the difference between white noise and pink noise definitions. When we examine the definition of both terms, it will become evident on how to use both pink and white noise correctly. They are similar in sound producing activities but do it differently and both have different applications.

In this video I take you through a discussion of what the key differences are between white noise and pink noise and why it’s important to test with them.

White Noise Vs Pink Noise

White noise has to do with energy and it is an equal energy for each frequency. All frequencies across the human audible spectrum are represented by equal amounts of energy. Pink noise is all about octaves and pink noise has equal energy per octave. Octave bands are how we hear music and sounds. When we hear, we hear in octaves. If we have real good hearing, we will hear pitches within octaves, but for normal listening practices, we just hear in octaves.

Octave Bands

When a note, either a high note or low note increases by an octave, we hear this change. It works the same in both directions. When we look at the process to produce the original note and the octave jump that occurs from this original note, there is not much that we hear other than the octave band jump. We use the same number of frets on a guitar or the same number of keys on a piano to accomplish this octave increase. When we look at the number of frequencies within that octave jump, we discover that there are many frequencies involved to create that octave increase.

One Octave Magic

Here’s an example. The difference between 400 Hz and 800 Hz is one octave. The difference between 5 kHz and 10 kHz is also one octave. However, in terms of frequencies the difference between 400 Hz and 800 Hz is only 100 Hz, whereas the difference between 6,000 Hz. and 11,000 Hz. is 5,000 Hz. The relative relationship is the same, but the actual difference mathematically is quite substantial. With white noise, there is a ton more energy in-between 5 kHz. and 10 kHz compared to between 400 Hz. and 800 Hz., because it spans a wider range of frequencies and they all contribute to the overall level per octave. The whole point of pink noise is to distribute the energy according to how we hear. The pink noise energy between 400 Hz. and 800 Hz. is the same as between 6,000 Hz. and 11,000 Hz. You can see that there is equal energy per octave.

Five Frequency Bands

Five Frequency Bands

No EQ In Pink Noise

People mistakenly think that pink noise is somehow equalized or calibrated to the human ear’s response, but that is simply not the case. It is calibrated or adjusted to how we hear and how the human ear is designed to hear, namely, in octave bands. There are 5 main octave bands and you can see them represented in the graphic. When we increase by one octave, we expect to hear the right amount of energy increase. We use this “octave band familiarity” to calibrate or adjust our stereo systems. We also use this pink noise in calibrating the desired sound pressure level at the listening position.

Pink Is Hearing

So, it’s not that pink noise is calibrated to the human ear’s frequency response. It’s just calibrated to how we hear, which is very well grounded in math. Each time the frequency doubles, we hear that as an octave. From one octave to the next, we expect to hear an appropriate amount of sound energy (depending upon the program material), which is why we calibrate our audio systems to pink noise. Octave bands are easier for our hearing mechanism to understand.

Room Response With Pink

On a practical level, this means you can run pink noise through your system and set your overall EQ, so you get a flat line on a typical RTA display. A flat line would signify equal energy at every octave. Some audio engineers feel that this can produce an unnaturally “bright” sounding system and do an additional roll off of 3 dB per octave above 4 kHz or so. They may just do one 3dB roll off at some frequency and leave it at that. The specific techniques vary, but the perceived need for it has more to do with the dispersion characteristics of the equipment involved, the measurement accuracy, and personal tastes than anything.

Pink Or White?

You now know that white noise and pink noise are all about energy distribution. White noise is equal energy per frequency and pink noise is equal energy per octave. Pink noise is not calibrated to human hearing, it simply represents the energy divisions in which human hearing operates within. There is a correlation between the structure of our ear mechanism and the octave band hearing range, we humans operate within. White noise, with its equal energy per frequency is best used to test electronic instrument performance parameters, since it is structural more accurate.

In Summary

So I hope that helps you. If you have any further questions about the difference between the definitions of white and pink noise, feel free to contact me as I am always on hand to help answer them. Leave them in the comments section or email me at info@acousticfields.com. If you would like to learn more about room acoustics please sign up for my free videos and ebook by joining the mailing list here. I send room tuning tips and things for you to test in your room every Wednesday. They are easy to follow and really help you enjoy more of your music.

Thanks and speak soon
Dennis

About Dennis Foley

I am an acoustic engineer with over 30 years’ experience in the business. My technology has been used in Electric Lady Land Studios, Sony Music of New York, Cello Music and Films founded by Mark Levinson, and Saltmines Studios in Mesa, Arizona, along with hundreds of others.

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