| 摘要 |
A circuit is disclosed in which the effect of ambient noise on the voice control in a hands-free subset is greatly reduced. Frequency components of the ambient noise which lie outside the voice-frequency range are determined on a selective basis and are used, together with the voice levels of the two transmission paths of the subset, to control the send path. The control signal selectively derived from the ambient noise counteracts the control by the voice level of the send path. In the simplest case, it is derived via a filter (12, 18) designed to pass the desired frequency range, an amplifier (13, 19), and a sign-reversing rectifier stage (14, 20) whose output is combined in an adder (11) with the control signal derived from the voice level. |
