ENVELOPE DETECTOR

PURPOSE:To protect against a drop-out and to accurately detect it in an envelope detector to be used for a tape recorder, etc. CONSTITUTION:A first counter 21 counts when an input signal exceeds a threshold value. A second counter 22 counts when it does not exceeds the value. When the value of the one of both the counters is a specific range, the other counter is reset, and when the value of the first counter is a specific range or more, it outputs an envelope output. Thus, an instantaneous noise of the input signal is protected by the counter 22, and a drop-out can be protected by the counter 21. Further, resetting of the opposite counter can automatically follow up a change in the input signal to stably detect an envelope.