Patent ID: 6993126

Claim:
Detection apparatus for detecting far end speech in a telephone apparatus having a first transducer for reproducing far end sound from a far end signal, when received by the telephone apparatus, and a second transducer for generating a near end signal from near end sound, for transmission from the telephone apparatus, and in which the near end signal is muted for transmission from the telephone apparatus in the case where it is intended that a user of the telephone apparatus should listen to the reproduced far end sound, and an hybrid for passing the near and far end signals from an external two wire link to and from the first and second transducers on respective first and second paths of a four wire link, the detection apparatus being in use responsive to effect said muting of the near end signal when signal derived from said first path of said four wire link is detected as being representative of a condition of existence of a far end signal, and subtracting, from the signal derived from said first path of said four wire link, signal determined as representing sidetone signal deriving from the near end signal from the second transducer and appearing in the signal on said first path of said four wire link pursuant to traverse of at least part of the near end signal through the hybrid, existence of said condition being determined on the basis of the result of the subtraction of the signal determined as representing sidetone signal from the signal on said first path of said four wire link; wherein the signal determined as representing sidetone signal is, in use, derived from said second path of said four wire link; wherein said subtracting is effected by generating, from the signal on said second path of said four wire link, a first relatively fast tracing envelope of the signal on said second path of said four wire link, and subtracting a proportion of the first envelope from the signal derived from the first path of the four wire link; and wherein the first envelope is, in the case where a condition of existence of far end speech was previously detected, the envelope of the muted near end signal, and otherwise is the envelope of the non-muted near end signal.