Click here to purchase the entire book in PDF format. Noise Spectra The theory explained in Section 3.1.17 that the combination of all frequencies results in a single click relies on an important point that we didn't talk about - relative phase. The click can only happen if all of the phases of the harmonics are aligned properly - if not, then things tend to go awry... If we have all frequencies with random relative amplitude and phase, the result is noise in its various incarnations. There is an official document defining different types of noise. The specifications for white, pink, blue and black noise are all found in The Federal Standard 1037C Telecommunications: Glossary of Telecommunication Terms. (I got the definitions from Rane's online dictionary of audio terms at http://www.rane.com.)