JPS6471370A - Speaker phone telephone set - Google Patents

Abstract

PURPOSE:To prevent the hawling of the title set without breaking the word beginning or word end of a sound signal by shifting a transmitting sound signal outputted from a microphone only by set frequencies. CONSTITUTION:Since a frequency shifting circuit 2, which is inserted into either of a speaker circuit or a microphone circuit and shifts the signal frequencies of the circuit only by the prescribed frequencies, is provided, the howling can be restrained. When the sound signal at frequencies (fa) is inputted to the circuit 2, a modulator 21 modulates a sine wave at frequencies f1 of the oscillator 22, inserts it into an LPF 23, and the sound signal, whose frequency element is f1-fa, is obtained. Next, a modulator 24 modulates the sine wave at frequen cies f2 of an oscillator 25 with the sound signal, whose frequency element is f1-fa, is inserted into an LPF 26, and the sound signal, whose frequency element is fa+f2-f1, is outputted. The loss to be inserted into a calling circuit by a transmission variable attenuating circuit 14 and a receiving variable attenuator 15 can be reduced by the portion of the howling restriction effect. For this reason, the word beginning and word end of the sound signal can be prevented from breaking.