A lot of people are confused about the difference between pink and white noise. Pink noise is the right type of noise to use to calibrate audio equipment (at least if you are using it for equalization calibration). Here’s where everyone gets confused: White noise is equal energy per frequency and pink noise is equal energy per octave. Now, think about how we perceive sound. Think about what an octave is to us. Other than the pitches involved we don’t hear anything more substantial happening when a high note jumps up an octave than we do a low note. It’s the same number of frets on a guitar, or keys on a keyboard either way. But in terms of the actual frequencies being produced the difference is great. Here’s an example. The difference between 100 Hz and 200 Hz is one octave. The difference between 5 kHz and 10 kHz is also one octave. However, in terms of frequencies the difference between 100 Hz and 200 Hz is only 100 Hz, whereas the difference between 5,000 Hz and 10,000 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 100 Hz and 200 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. So the pink noise energy between 100 Hz and 200 Hz is the same as between 5,000 Hz and 10,000 Hz. Equal energy per octave. So it’s not that pink noise is calibrated to the human ear’s frequency response per se. 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.
Posted on: Sat, 25 Jan 2014 13:20:50 +0000
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