Different noise types can be characterised by their spectral composition.
White noise has a uniform spectrum, which means that it has equally intense components at every audible frequency. Noise has no effect on intelligibility when the speech intensity is more than 100 times greater (20 dB) than the noise intensity. This is called a 20 dB signal-to-noise ratio.
- White noise
- the energy is equally distributed over the spectrum.
- Pink noise
- there is a downward slope of -6 dB/octave in the spectrum. This slope imitates the spectral slope found for human speech.