Microphone expander

Abstract

A microphone expander attenuates background noise in a digitized microphone signal from a wireless telephone by using a loss function that exhibits hysteresis when the signal is passing through a transition range. This allows the microphone expander to apply loss more effectively because it allows for decreases in speech levels without attenuation. An attenuation level is determined using a first loss function when an averaged signal, derived from the digitized microphone signal using an algorithm that causes the averaged signal to clearly exhibit speech components in the digitized microphone signal, increases from below a lower noise threshold. However, if the averaged signal increases to above an upper speech threshold and then decreases to below that threshold, the attenuation level is determined using a different loss function, which delays introducing loss into the microphone signal as compared to the first loss function. The thresholds are increased, the amount of hysteresis is decreased, and the minimum amount of loss is increased as the noise level increases. The noise level is derived from the averaged signal using an algorithm that isolates noise components. Thus, the exact loss applied to any given sample of the microphone signal can be tailored to account for phenomena such as the tendency of people to speak louder when there is more background noise.