Muting circuit

Abstract

Disclosed is a muting circuit, in which the generation of click noise is prevented in that the muting operation is caused to occur at an instant when the instantaneous level (i.e., waveform level) of the input audio signal becomes zero for the first time since the appearance of a muting signal. .Iadd.A muting-off circuit is also disclosed for turning off the muting circuit. .Iaddend.

What is claimed is: 
     
       1. A digital muting circuit comprising, an input terminal .[.for.]. receiving a PCM signal having words of plural bits, an output terminal .[.for.]. deriving said PCM signal, a controlling circuit .[.for.]. generating a muting signal, a detecting circuit for examining the bit pattern of said PCM signal to produce a detected signal when the signal level of the waveform corresponding to said PCM signal is less than a predetermined value, and switching means connected between said input terminal and said output terminal and .[.for.]. replacing said PCM .Iadd.output .Iaddend.signal with a PCM signal having a bit pattern representing the zero level by receiving said detected signal while said muting signal is generated. 
     
     
       2. A digital muting circuit according to claim 1, further comprising time counting means .[.for.]. counting a predetermined time elapsed from the instant of change of said muting signal and .[.for.]. producing a switching signal so as to cause the switching operation of said switching means on the basis of the relationship between the time elapsed from the instant of change of said muting signal and the waveform level of said input signal. .Iadd. 
     
     
       3.  A digital muting circuit comprising, an input terminal receiving a PCM signal having words of plural bits, an output terminal deriving said PCM signal, a controlling circuit generating a muting-off signal, a detecting circuit examining the bit pattern of said PCM signal to produce a detected signal when the signal level of the waveform corresponding to said PCM signal is less than a predetermined value, and switching means connected between said input terminal and said output terminal and replacing a PCM output signal having a bit pattern representing the zero level with said PCM signal by receiving said detected signal when said muting-off signal is generated..Iaddend. .Iadd.4. A digital muting circuit according to claim 3, further comprising time counting means counting a predetermined time elapsed from the instant of change of said muting-off signal and producing a switching signal so as to cause the switching operation of said switching means on the basis of the relationship between the time elapsed from the instant of change of said muting-off signal and the waveform level of said input signal..Iaddend.