a sound in which tonality is absent or implicitly expressed. Known varieties of noise: **white noise** (Johnson noise) – has a spectrum with approximately constant spectral density over its entire length; **pink noise –** its spectrum has a spectral density decreasing by 3 dB with each subsequent octave (spectral density is inversely proportional to the frequency); **orange noise** is a quasi-constant noise with a finite spectral density, the spectrum of such noise has strips of zero energy scattered throughout its length, such strips are located near the frequencies corresponding to musical notes; **green noise –** similar to pink noise with an amplified frequency range in the region of 500 Hz; **blue noise**– its spectral density increases by 3 dB with each subsequent octave (spectral density is proportional to frequency); **purple noise** – differentiated white noise, its spectral density increases by 6 dB with each subsequent octave (spectral density is proportional to the square of the frequency); **gray noise – the** spectrum of such noise has a graph similar to the graph of the psychoacoustic curve of the threshold of audibility, which means that for a person’s hearing aid this noise has the same volume over the entire audible frequency range; **brown noise** – its spectral density decreases by 6 dB with each subsequent octave (spectral density is inversely proportional to the square of the frequency); **black noise**– there are a lot of definitions of this noise, one of them: black noise is supersonic white noise, such noise has a constant finite spectral density beyond the threshold of audibility (20 KHz). **Broadband noise** is noise whose energy is distributed over a wide frequency range (more than one octave).