| 摘要 |
PURPOSE:To prevent the interruption of training and to eliminate a need for the readjustment of level pertinent to said interruption by providing an attenuation control circuit and a constant gain circuit, and automatically setting the attenuation amount of the indoor echo route at the time of the training of an echo canceler. CONSTITUTION:The followings are provided: a level detector 5 to detect the output signal level of the echor canceler 2 and to output a first signal represent a level value, an attenuation amount control circuit 6 to calculate an insertion attenuation amount necessary to make the level value below a prescribed threshold corresponding to a first signal generated during the training time of the echo canceler 2 and to output a second signal representing the insertion attenuation amount value, and a constant gain circuit 4 having an attenuator 42 capable of setting attenuation amount in response to the second signal and an amplifier 41 capable of setting a gain to maintain the gain given to a reception signal in a prescribed constant value which is connected in a reception circuit so that an output signal from the amplifier 42 is conducted to the echor canceler 2 and the attenuator 42. As a result, the attenuation amount of the indoor echo route can be automatically set as well as the level readjustment pertinent to said setting is made unnecessary. |
