Half echo-suppressor for a four-wire telephone line

Claim 1

A half echo-suppressor for a terminal of a fourwire telephone circuit, said suppressor comprising: a send channel including a controlled transmission blocking element; a receive channel including a controlled transmission attenuator; and first and second speech detectors, respectively connected to said send and receive channels, for directing said transmission blocking element to block said send channel when said second speech detector detects speech on said receive channel and for directing said attenuator to attenuate said receive channel when said first speech detector detects speech on said send channel, wherein said first speech detector comprises: means, connected to said send channel, for periodically assigning an index to said send signal, the resulting indices being representative of the amplitude characteristics of the speech signal present on said send channel, said assigning means assigning a negative index to noise; a digital accumulator, connected to said assigning means, for accumulating said indices, said send channel being considered active when the contents of said accumulator reaches an upper limit, and inactive when the contents of said accumulator reaches a lower limit; and at least one digital comparator connected to said accumulator, for generating a send channel unblocking command for said blocking element when the contents of said accumulator, when increasing, exceeds a first threshold intermediate said upper and lower limits, said unblocking command being discontinued when the content of said accumulator, while decreasing, falls below a second threshold lower than the first.