Voice control circuit

Claim 1

In a voice control circuit of the type comprising a variolosser circuit connected in series with a signal line, and a voice level detecting circuit responsive to the presence of a voice signal having a level above a predetermined threshold value for operating said variolosser circuit, the improvement which comprises a noise control circuit connected on the input side of said voice level detecting circuit, said noise control circuit including a timer which determines as noise the input signal having a constant amplitude and persisting for greater than a predetermined interval thereby detecting the presence of the noise applied to said signal line concurrently with the voice signal, a noise level detector connected to the output of said timer, and a variable attenuator connected on the input side of said voice level detecting circuit and constituted by a plurality of transistor switches controlled by the output from said noise level detector thereby attenuating a signal to said voice level detecting circuit at a value proportional to the level of the input signal, said noise control circuit further comprising a plurality of sets of a timer and a noise level detector, said sets having different operating points and being respectively connected to said plurality of transistor switches, thus producing stepwisely varying attenuation.