White, pink and brown noise
Noise signals are random, but their spectrum is not: the colour describes how energy is spread over frequency.
| Colour | Power per hertz | Level per octave band | Sounds like |
|---|---|---|---|
| White | flat | rises 3 dB per octave | bright hiss |
| Pink | falls 3 dB per octave | flat | balanced rain or waterfall |
| Brown | falls 6 dB per octave | falls 3 dB per octave | deep rumble |
White noise
Every hertz carries the same power. Because each octave spans twice as many hertz as the one below, the energy doubles every octave, so white noise sounds bright and looks like a rising line on an octave-band display.
Pink noise
Power per hertz falls with frequency (1/f), which makes the energy in each octave equal. On a real-time analyzer with octave or third-octave bands, pink noise appears flat. That is why it is the standard signal for tuning loudspeaker systems and checking room response.
Brown noise
Power falls with 1/f², which is −6 dB per octave. It is dominated by bass and is used mostly for masking and for testing subwoofers.
Practical tips
- Keep the level low: noise has a high crest factor, so peaks can be well above its average level.
- Analyze pink noise in the spectrum analyzer with the 1/3-octave display: summed band power makes pink noise appear flat. The FFT line display shows the level per frequency bin, where pink noise falls by 3 dB per octave; that slope is expected and is not a room fault.
- Generate it with the noise generator.
Draft: written by an AI assistant, awaiting technical review.
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