Echo canceller

• US 4,757,527 A
• Filed: 09/04/1985
• Issued: 07/12/1988
• Est. Priority Date: 09/12/1984
• Status: Expired due to Fees

• Current Assignee: Plessey Overseas Limited (Marconi Holdings Company Limited)
• Original Assignee: Plessey Overseas Limited (Marconi Holdings Company Limited)
• Inventors: Beniston, Graham, Wheen, Andrew J. T., Dyer, Nigel P.
• Primary Examiner(s): Ng, Jin F.
• Assistant Examiner(s): Vaas, Randall S.
• Application Number:
  US06/772,571
• Time in Patent Office: 1,042 Days
• Field of Search: 179/170.2, 179/170.6, 179/170.8, 364/724, 333/18, 379/406, 379/399, 379/410, 379/411, 370/32, 370/32.1
• US Class Current: 379/406.09
• CPC Class Codes: H04B 3/234 using double talk detection
• CPC Class Codes: H04B 3/237 using two adaptive filters, e.g. for near end and for end echo cancelling

Abstract

A digital adaptive echo canceller for use in cancelling echo signals caused by trans-hybrid losses in two-wire to four-wire converters comprises first and second adaptive filters (20,22) each arranged to generate synthetic echo signals. Transfer control logic (23) compares difference signals relative to the difference between the synthetic echo signal generated by the first filter (22), and a real echo signal and the synthetic echo signal generated by the second filter (20) and the real echo signal, and if the synthetic echo signal from the first filter (22) is closer to the real echo signal causes transfer of the coefficients of the first filter (22) to the second filter (20) such that the synthetic signal mixed with transmitted speech signals in a mixer (24) is updated when necessary.

Claims

1. A digital adaptive echo canceller for providing echo cancellation signals in a two-wire to four-wire converter, said echo canceller comprising a first adaptive filter for generating a synthetic echo signal and having a plurality of filter coefficients, means to adjust the coefficients of said first filter in dependence upon differences between the synthetic echo signal and a real echo signal to be cancelled, a second programmable filter for generating a synthetic echo signal for mixing with an output signal of the converter, and transfer control logic arranged to determine whether the synthetic echo signal from the first filter matches the real echo signal more closely than the synthetic echo signal from the second filter, and, if so, to cause the coefficients of the second filter to be updated to match the coefficients of the first filter, said transfer control logic comprising first error signal generating means for generating a first error signal in dependance upon the difference between the synthetic echo signal from said first filter and the real echo signal, and second error signal generating means for generating a second error signal in dependance upon the difference between the synthetic echo signal from said second filter and the real echo signal, said transfer control logic comprises delay means arranged to inhibit updating of the coefficients of the second filter until the synthetic echo signal from the first filter is consistently closer to the real echo signal than the synthetic echo signal from the second filter, said delay means includes an up-down counter arranged to count in one direction when the first error signal is smaller than the second error signal and in an opposed direction when the second error signal is smaller then the first error signal, said transfer control logic being arranged to effect updating of the coefficients of the second filter when a pre-determined value of the count is reached, said transfer control logic further comprising means for scaling the second error signal, means for determining the difference between the scaled second error signal and the first error signal and means responsive to said difference when a preselected condition is reached to cause the transfer of coefficients from the first filter to the second filter.