| 摘要 |
PURPOSE:To surely distinguish presence/absence of sound by converting an analog signal into a digital signal and using an m-bit up-down counter and a sound presence period decision circuit so as to detect the gradient of a change of absence of sound into presence of sound. CONSTITUTION:In inputting a delta modulation code for leading/trailing of a waveform of an analog sound presence signal, a 4-bit up-down counter 2 outputs a value deviated from a value near '0'. A sound presence period decision circuit 3 decides it as presence of sound when the output of the counter 2 is equal to or more than a set value whose bipolar absolute values are equal to detect the sound presence period. Further, the sound presence/absence decision circuit 4 counts up an n-bit counter 5 at the absence of sound and clears the counter 5 at the presence of sound. When a sound absence signal is continued for (2<n>-1) times, a sound absence period decision circuit 6 detects the sound absence period.
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