Pink noise has equal energy per octave, so it sounds flat to a listener and reads flat on an octave analyser; white noise has equal energy per hertz, so it rises 3 dB per octave on the same display.
Pink noise: equal energy per octave, and where that misleads
checked 2026-09-16responsible Room Tone Register (a named register, not a person)
Why octave bands change the answer
An octave band is a fixed ratio, not a fixed width. The band from 500 to 1000 Hz is 500 Hz wide; the band from 8 to 16 kHz is 8000 Hz wide. White noise puts energy in proportion to bandwidth, so the top band carries sixteen times the power of the one at 500 Hz. Pink noise is shaped to compensate, which is exactly why it is used to excite a room and measure the result: a flat reading means a flat room.
Three places it misleads
- It is not music and it is not speech. A room that measures flat on pink noise can still sound wrong on a voice, because the spectrum of speech is nothing like pink.
- It hides time. Pink noise is stationary, so it tells you nothing about decay, flutter echo or a slap between parallel walls. Those need an impulse or a swept sine.
- It excites the room, not the loudspeaker. If you measure a system with pink noise and a microphone, you are measuring the product of both, and you cannot tell which one produced a peak without a second measurement.
What to use instead, and when
| Question | Signal | Why |
|---|---|---|
| Is the room flat? | Pink noise, octave bands | Equal energy per octave matches the display |
| What is the decay time? | Impulse or swept sine | Pink noise is stationary and has no decay |
| Is the loudspeaker flat? | Swept sine, gated | Separates the source from the room |
| Will this hum be audible? | Pink noise at a known level, then the source | Gives a reference to compare the tonal source against |
Near kin: white, brown and swept signals
White noise has equal energy per hertz and therefore rises 3 dB per octave on an octave display. Brown or red noise falls 3 dB per octave. A swept sine moves a single tone through the band, which lets you separate a source from a room in a way a stationary signal cannot. MLS and other coded sequences do the same job with a different noise-immunity trade.
| Term | What it is | How it differs from pink noise |
|---|---|---|
| White noise | Equal energy per hertz | Rises 3 dB per octave on an octave display |
| Brown / red noise | Falls 3 dB per octave | Tilted the other way |
| Swept sine | One tone moving through the band | Non-stationary; separates source from room |
| Impulse | A single broadband click | Carries decay information pink noise cannot |
The common misread is using pink noise to measure decay. Pink noise is stationary: it has no decay to measure. Decay needs an impulse or a swept sine and a decay curve. Using pink noise and watching the level fall when you switch it off measures the meter's averaging, not the room.
Source log
- 01White noise, pink noise and sweep signals (HBK)supports the distinction between white, pink and swept signals and where each is used
- 02Sound: spectrum and waveform, UNSW Music Acousticssupports the relationship between a waveform and its spectrum
- 03Introduction to Digital Filters, CCRMA (Stanford)supports the filtering that turns white noise into pink noise
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