Numerous attempts have been made to establish a noise reduction scheme, which provides good listening comfort and good speech intelligibility at the same time.
In prior art document EP 1326479 a method of reducing noise in a signal is described whereby an input signal is supplied to an amplification unit where the input signal is subject to an auxiliary noise reduction algorithm, to generate an auxiliary signal. The auxiliary signal is used to determine a control input for the amplification unit; and the amplification unit is then controlled with the control signal, to generate an output signal with reduced noise. According to this prior art the method comprises the further steps of: detecting the presence and absence of speech utterances; and in the absence of speech, determining a noise magnitude spectral estimate; and in the presence of speech comparing the magnitude spectrum of the audio signal to the noise magnitude spectral estimate; calculating an attenuation function from the magnitude spectrum of the audio signal and the noise magnitude spectral estimate; and modifying the input signal by the attenuation function, to generate an output signal with reduced noise. This prior art technique has the problem, that it requires a speech pause in which to determine the noise magnitude spectrum. In a typical party noise situation such a pause may not be detectable and the system then has little or no clue as to how to calculate the right attenuation function.