Noise reducing method, noise reducing apparatus and telephone set

An apparatus for reducing noise in an input speech signal having a microphone for receiving the input speech signal and noise reducing means for reducing noise contained in the input speech signal received by the microphone, the apparatus comprising:

• noise level detection means for detecting a level of a noise component in the input speech signal and outputting a control signal based on the detected noise level;
• modifying means for modifying steps performed in a noise reducing operation for the input speech signal based on the control signal;
• speech level detection means for detecting a level of the input speech signal, whereby the noise reducing means carries out level expansion to give different effects with a predetermined threshold value of the input speech signal level as a boundary and modifies the threshold value responsive to the control signal;
• and
• means for diminishing the level expansion effect for the input speech signal when the level detected by the speech level detection means is less than or equal to the threshold value such that the level expansion effect for an input speech signal level above the threshold value is greater than the level expansion effect for an input speech signal level below the threshold value and a slope of a curve of an output speech signal level plotted as a function of the input speech signal level is greater above the threshold value and is relatively less below the threshold value.

A telephone apparatus having a microphone to which a speech signal is input, a noise reducing circuit for reducing noise contained in the speech signal input to the microphone and a transmitter for transmitting signals produced by the noise reducing circuit, the telephone apparatus comprising:

• noise level detecting means for detecting a level of the noise component in the input speech signal;
• means for generating and outputting a control signal based on the detected noise level;
• speech level detection means for detecting a level of the input speech signal, whereby the noise reducing means carries out level expansion to give different effects with a predetermined threshold value of the input speech signal level as a boundary and modifies the threshold value based on the control signal;
• and
• means for diminishing the level expansion effect of the input speech signal when the level detected by the speech level detection means is less than or equal to the threshold value such that the level expansion effect for an input speech signal level above the threshold value is greater than the level expansion effect for an input speech signal level below the threshold value and a slope of a curve of an output speech signal level plotted as a function of the input speech signal level is greater above the threshold value and is less below the threshold value.