1. A noise signal prediction system comprising: a signal detection means for receiving a mixed signal consisting of a wanted signal and a background noise signal and for detecting the presence and absence of said wanted signal contained in said mixed signal; a noise level detecting means for detecting an actual noise level at each sampling cycle during the absence of said wanted signal; a storing means for storing the noise levels for a predetermined number of past sampling cycles, said storing means receiving and storing said actual noise levels during the absence of said wanted signal; a predicting means for predicting a noise level of a next sampling cycle based on said stored noise levels in said storing means; wherein said storing means stores said predicted noise levels during the presence of said wanted signal; further comprising: an attenuation means for attenuating said predicted noise level during the presence of said wanted signal, said attenuation means comprising: an attenuation coefficient setting means for setting an attenuation coefficient in response to the detection of the presence of said wanted signal; and an attenuator connected to said prediction means for attenuating the predicted noise level in accordance with said attenuation coefficient for producing an attenuated predicted noise level during the presence of said wanted signal and for producing a non-attenuated signal in the absence of said wanted signal.