| 摘要 |
PURPOSE:To avoid a malfunction of a sound switch with a detection circuit which prevents both echoes and singings, by preventing both echoes and singings through the same comparison regardless of the circuit loss. CONSTITUTION:The speech sending signal of each circuit is supplied to a variable loss circuit 12 to receive a loss in response to the level of an input signal and delivered as a long-time sound means level signal after conversion into DC. This level signal is compared with referance voltage 15 by a differential amplifier circuit 16, and this differential output controls the circuit 12. While the sound level signal of each circuit is averaged by a smoothing circuit 17, and an envelope curve signal is delivered. A comparator 18 performs comparison or levels of envelope curve signals of each circuit. Thus sound switches 4 and 5 are controlled. |
