Audibility of modulation noise in stationary signals

Recordings of an acoustic signal on magnetic tape often show noise, which may be divided into two main classes: additive noise and multiplicative noise. A characteristic of the latter is that it is weak with weak signals and strong with strong signals. This modulation noise has been subjected to a number of technical studies (cf. Eldridge, 1964). According to its physical causes one may distinguish asperity noise, friction noise, and to some extent structure noise. In this paper we are not concerned with the causes of modulation noise but with the problem whether a particular modulation noise will be audible or not. The answer to this question depends on three categories of parameters.