HEARING AID HAVING CIRCUMFERENTIAL NOISE SUPPRESSING FUNCTION

PURPOSE:To amplify excellently only voice, and to suppress an amplification degree of fussy noise or noise to low by providing an stretching circuit, making a ratio of an input and output characteristics of the stretching circuit comparatively abrupt, and setting the ratio near to 1:2. CONSTITUTION:A part of an input signal including a speech signal inputted together with circumferential noise is applied to an stretching circuit 13 through a preamplifier 12. In the circuit 13, the input signal is amplified till it goes to a predetermined amplitude, rectified by a rectifier 15 and supplied to a ratio adjusting section 16. In the ratio adjusting section 16, as shown in the figure (b), the ratio of the stretching circuit 13 is adjusted so as to make a grade steeper than the conventional amplification characteristic, The ratio of about 1:2 is suitable and comfortable for hearing. In such a manner, the output of the ratio adjusting section 16 is supplied to one input B of a voltage control amplifier VCA 17. To the other A of a voltage control amplifier 17, a voice signal including circumferential noise from the microphone 11 is fed directly through the preamplifier 12, so that the other direct input A of the voltage control amplifier 17 controlled by the output fed to the B input of the amplifier 17 through the ratio adjusting section 16.