| 摘要 |
A first speech-responsive microphone (1) and a second noise-responsive microphone (11) are each connected to an input (7, 8) of a comparator (9) through an amplifier (3, 13), a rectifier (5, 15) and a low pass filter (6, 16). The amplification grades for given microphone sensibilities are determined so that the input voltages of the comparator (9) are equal when the ratio between the speech voltage and the noise voltage is sufficient for the speech intelligibility. The comparator (9) sets a monostable flip/flop (21) when its input voltage originated from the speech voltage exceeds the input voltage originated from the noise. At this time, the speech channel is set on and remains on until the monostable flip/flop (21) returns to its rest condition. When the speech channel is set on, a sound signal is supplied to the receiver (36) thereby informing the user that the speech channel is on. A little before the reset of the flip/flop (21) to a rest condition, the sound signal is periodically interrupted to indicate that, if the speech channel is to remain on, one has to immediately continue speaking, respectively speaking louder. |
