Abstract: A noise signal supplied from a microphone by way of an analog to digital converter is Fourier converted to calculate a power spectrum of the noise signal by a Fourier converting section. A system controller compares an average value of the power spectrum of the signal being outputted from the microphone at present and an average value of the power spectrum of a noise signal stored in a noise memory at present with each other. When the system controller determines that the difference between the average value of the power spectrum of the signal being outputted from the microphone at present and the average value of the power spectrum of the noise signal stored in the noise memory at present is higher than a predetermined reference value, it outputs a controlling signal to a sound storing and reading out section to store the signal being outputted from the microphone at present into the noise memory.

Abstract: A radio telephone comprising a main body enclosing a transmitting circuit and a receiving circuit; a handset removably mounted to the main body, the handset including a microphone electrically connected to the transmitting circuit and a speaker electrically connected to the receiving circuit; a voice recognition circuit for recognizing a voice input to the microphone and for performing a dialing operation based on the voice. An extension module is removably mounted on the main body. A mute switch, which also enables the voice recognition circuit, is removably connected to the main body, or to an extension module removably mounted on the main body, thus adding to the portability of the radio telephone.