Echo canceller having two echo path models

Claim 2

An echo canceller for cancelling the echo signal appearing from an actual echo path, comprising self-adaptive means retaining a first set of parameters approximating the characteristics of said echo path, wherein the improvement comprises first means retaining a second set of parameters approximating said characteristics, second means for comparing said first and said second sets of parameters, and third means responsive to the results of comparison for substituting the parameters retained by one of said self-adaptive means and said first means for those retained by the other.

Claim 3

An echo canceller according to claim 1, wherein said second means produces a command signal when said first set of parameters gives significantly better approximation of said characteristics than said second set of parameters and said third means substitutes the parameters retained by said self-adaptive means for those retained by said first means in response to said command signal.

Claim 4

An echo canceller according to claim 1, wherein said second means produces a first command signal when said first set of parameters gives significantly better approximation of said characteristics than said second set of parameters and a second command signal when said second set of parameters gives significantly better approximation of said characteristics than said first set of parameters and said third means responsive to said first command signal substitutes the parameters retained by said self-adaptive means for those retained by said first means and responsive to said second command signal substitutes the parameters retained by said first means for those retained by said self-adaptive means.

Claim 5

An echo canceller to be interposed between an echo path and a communication line and having self-adaptive means retaining a first set of parameters approximating the characteristics of said echo path for modifying a receive-in signal incoming to said echo path from said communication line to produce a first synthesized signal, means for combining said first synthesized signal with a send-in signal outgoing from said echo path to said echo canceller to produce a combined signal, means for adjusting said first set of parameters in compliance with said receive-in signal and said combined signal so as to reduce the echo signal comprised in said combined signal, first means retaining a second set of parameters approximating the characteristics of said echo path for modifying said receive-in signal to produce a second synthesized signal, second means for combining said second synthesized signal with said send-in signal to produce a send-out signal transmitted to said communication line, third means for comparing said combined signal with said send-out signal, and fourth means responsive to the results of comparison for substituting the parameters retained by said self-adaptive means for those retained by said first means.

Claim 6

An echo canceller to be interposed between an echo path and a communication line and having self-adaptive means retaining a first set of parameters approximating the characteristics of said echo path for modifying a receive-in signal incoming to said echo path from said communication line to produce a first synthesized signal, means for combining said first synthesized signal with a send-in signal outgoing from said echo path to said echo canceller to produce a combined signal, means for adjusting said first set of parameters in compliance with said receive-in signal and said combined signal so as to reduce the echo signal comprised in said combined signal, first means retaining a second set of parameters approximating the characteristics of said echo path for modifying said receive-in signal to produce a second synthesized signal, second means for combining said second synthesized signal with said send-in signal to produce a send-out signal transmitted to said communication line, third means for comparing said combined signal with said send-out signal, and fourth means responsive to the results of comparison for substituting the parameters retained by said self-adaptive means for those retained by said first means.

Claim 7

An echo canceller according to claim 4, wherein said third means compares said combined signal with said send-out signal for a predetermined time to derive the results of the comparison to produce a command signal when said combined signal is significantly smaller than said send-out signal and said fourth means comprises switching means responsive to said command signal for supplying the parameters retained by said self-adaptive means to said first means as the parameters retained by the latter.

Claim 8

An echo canceller according to claim 5, further comprising fifth means for comparing the approximation given by said first echo path model parameters with that given by said second echo path model parameters to derive the results of the comparison as a further command signal while the latter is significantly smaller than the former and sixth means responsive to the presence of said further command signal for replacing said second set of echo path model parameters to said self-adaptive means as said first set of echo path model parameters.