Signal processing

#a. Field of the Invention

#The present invention relates to detection of echo in telecommunications networks. In this context the term echo refers to the problem encountered when someone speaking into a telephone system hears their own speech come back through their handset or speaker after a short delay. Even small amounts of audible echo can be disturbing to a talker and in extreme cases can render natural conversation virtually impossible.

#The two most common sources of echo in a telephony system are electrical reflections and acoustical coupling (see FIG. 1 and FIG. 2). The main source of electrical reflections indicted by arrows 8 are two-wire/four wire conversion hybrid circuits 1, 2 used to interconnect two-wire transmission system 3 used between a local exchange 4 and phone 5 at the customer premises with four-wire transmission systems 6,7 used in the core network and telephone handsets. Acoustical coupling indicated by arrow 9 occurs in the remote party's telephone equipment when sound leaks from the earpiece or speaker into the microphone.

#Embodiments of the present invention will now be described, with reference to the accompanying drawings, in which:

#FIG. 1: is an illustration of electrical echo generation by 2/4 wire conversion hybrid circuits;

#FIG. 2: is an illustration of acoustic echo generation;

#The method of the invention analyses send and receive signals at an arbitrary point in a telephony network to determine if audible echo is present and if so, determines the delay of the echo path. The following description describes the analysis of a single echo path, i.e. echo from one direction; however it will be apparent that the analysis can be used to detect echo in either direction.

#The method uses two buffers, an outbound buffer 100 containing a sequence of feature vectors of an outbound speech signal and an inbound buffer 200 containing sequence of feature vectors of an inbound speech signal. The following description relates to a single analysis phase which produces a single result set comprising the likelihood that echo is present and an estimate of an average (mean) echo path delay. It will be apparent that the analysis phase can be repeated over successive sections of a signal to produce a series of results sets.

#The echo detection method will now be described with reference to FIGS. 4 and 6.