Patent EP0627840A2 successfully refreshed from Google Patents.
EP0627840A2
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Echo canceller
Assignee: Panasonic Holdings Corp
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Filing: 1994-05-27
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Granted: —
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Expires: 2014-05-27
Abstract
Abstract In an echo canceller, a first adaptive filter (1) estimates an impulse response of an echo path between reception and transmission side by an NLMS algorithm to synthesize a pseudo echo, while a second adaptive filter (3) determines whether there is an echo path change or a double talk. A voice detector (8) detects a short time power of the received input signal (x) to determine whether far-end speech is present or absent, wherein said voice detector controls said second adaptive filter (3) to execute adaptation of said second adaptive filter for renewal of an impulse response of an echo path when far-end speech is present and otherwise to suspend the adaptation of said second adaptive filter when far-end speech is absent, while a double talk detector (9) controls the first adaptive filter to execute or suspend adaptation of the first adaptive filter according to the determination results of the voice detector.
Inventors
- 👤 Hiroki Furukawa
- 👤 Junichi Tagawa
- 👤 Takeo Kanamori
- 👤 Satoru Ibaraki
Bibliographic Details
Application Number
—
Jurisdiction
EP
Data Source
google_patents
Last Synchronized
2026-11-05 23:10
CPC Classifications
H; H04; H04B; H04B3/00; H04B3/02; H04B3/20; H04B3/23; H04B3/234; H04M; H04M9/00; H04M9/08; H04M9/082
Claims Analysis
Total Claims: 13
Claim 1
Independent Claim
355 words
An echo canceller comprising: a first adaptive filter (1) for estimating an impulse response of an echo path between reception and transmission sides, holding the estimated impulse response as a filter coefficient, and convoluting the filter coefficient with a received input signal to thereby synthesize a pseudo echo (Yh); a first subtracter (2) for subtracting the pseudo echo synthesized by said first adaptive filter (1) from a transmitting input signal (y) to thereby cancel an echo contained in the transmitting input signal; a second adaptive filter (3) for estimating an impulse response of the echo path, holding the estimated impulse response as a filter coefficient, and convoluting the received input signal with the filter coefficient to thereby synthesize a pseudo echo (Yhs); a second subtracter (4) for subtracting the pseudo echo (Yhs) synthesized by said second adaptive filter (3) from the transmitting input signal to thereby cancel the echo: a first input-output power ratio estimator (5) which detects short time powers of input and output signals of said first subtracter (2) to calculate a first I/O power ratio (R1) of an input-short-time-power/output-short-time power of said first subtracter (2); a second input-output power ratio estimator (6) which detects short time powers of input and output signals of said second subtracter (4) to calculate a second I/O power ratio (R2) of an input-short-time-power/output-short-time-power of said second subtracter (4); a divider (7) for dividing the second I/O power ratio (R2) by the first I/O power ratio (R1) to calculate a third ratio (R3); a voice detector (8) for detecting a short time power of the received input signal (x) to determine whether far-end speech is present or absent, wherein said voice detector controls said second adaptive filter (3) to execute adaptation of said second adaptive filter for renewal of an impulse response of an echo path when far-end speech is present and otherwise to suspend the adaptation of said second adaptive filter when far-end speech is absent; and a double talk detector (9) for controlling said first adaptive filter to execute or suspend adaptation of said first adaptive filter according to the determination results of said voice detector.
Claim 2
Dependent Claim
112 words
The echo canceller as claimed in claim 1, wherein said double talk detector (9) controls said first adaptive filter to suspend adaptation of said first adaptive filter for renewal of an impulse response of an echo path when said voice detector determines that far-end speech is absent, and otherwise to execute the adaptation of said first adaptive filter when said voice detector determines that far-end speech is present under at least one of the following conditions (a) and (b) is satisfied: (a) either the first or the second I/O power ratio is greater than a first threshold (Th1); or (b) the third ratio (R3) is greater than a fixed second threshold (Th2).
Claim 3
Dependent Claim
230 words
The echo canceller as claimed in claim 1 or 2, wherein said double talk detector (9) comprises: a threshold controller (41) for controlling the first threshold (Th1) to be produced therefrom, which receives the first I/O power ratio (R1) generated by said first I/O power ratio estimator (5) to thereby control the first threshold (Th1) to be produced according to an output result (VD) of said voice detector (8) in such a manner that, the first threshold (Th1) is gradually increased so as not to exceed the first ratio (R1) when far-end speech is present and besides the first ratio (R1) is greater than the first threshold (Th1), while the first threshold (Th1) is gradually decreased when the first ratio (R1) is smaller than the current threshold (Th1) irrespective of the presence of far-end speech, and otherwise the previous value of the first threshold (Th1) is held when no speech is present; and an adaptation controller (42) for controlling an adaptation of said first adaptive filter (1) in such a manner that said adaptation controller determines to execute the adaptation of said first adaptive filter (1) in either case when far-end speech is present and besides at least one of the first and second ratios (R1, R2) is greater than the first threshold (Th1) or in a case when the third ratio (R3) is greater than the second threshold (Th2).
Claim 4
Dependent Claim
217 words
The echo canceller according to claim 3, wherein said threshold controller (41) comprises: a memory (51) for storing the first threshold (Th1); a comparator (52) for comparing the first I/O power ratio (R1) with the first threshold (Th1); a switch (53) which selects a constant (Kup) when the comparator (52) has determined that the first I/O power ratio (R1) is greater than the first threshold (Th1) and otherwise which selects a constant (Kdn); a subtracter (54) which subtracts the first threshold (Th1) from the first I/O power ratio (R1); a multiplier (55) which calculates a product of a time constant (Kup or Kdn) selected by the switch (53) and an output (R1-Th1) of the subtracter (54); an adder (56) for adding together an output of the multiplier (55) and the first threshold (Th1); a limiter (57) for limiting the maximum and minimum of an output of the adder (56); a switch (58) which selects an output of the limiter (57) when far-end speech is present, and which selects an output of the memory (51) when no speech is present, in accordance with the output signal (VD) of said voice detector; a delay unit (59) for delaying an output of the switch (58) by one sample and the resultant output thereof is transferred to the memory ( 51).
Claim 5
Dependent Claim
197 words
The echo canceller according to claim 3 or 4, wherein said adaptation controller (42) comprises: a first comparator (61) for comparing the first threshold (Th1) created by the threshold controller (41) with the first I/O power ratio (R1) calculated by the first input-output power ratio estimator ( 5) to yield a positive output when the first ratio is greater that the other and otherwise to yield a negative output; a second comparator (62) for comparing the second ratio (R2) calculated by the second input-output power ratio estimator (6) with the first threshold (Th1) to yield a positive output when the second ratio is greater than the other and otherwise to yield a negative output; a third comparator (63) for comparing the third ratio (R3) calculated by the divider (7) with the second fixed threshold (Th2) to yield a positive output when the third ratio is greater than the other and otherwise to yield a negative output; an OR circuit (64) for determining a logical OR of the three comparators; and an AND circuit (65) for determining a logical AND between a determination result (VD) of the voice detector (8) and a logic output of the OR circuit.
Claim 6
Dependent Claim
46 words
The echo canceller as claimed in any preceding claim, further comprising a step gain controller (10) for controlling a step gain (α1) to be applied to said first adaptive filter according to both the determination result (VD) of said voice detector and the third ratio (R3).
Claim 7
Dependent Claim
97 words
The echo canceller as claimed in claim 6, wherein said step gain controller further comprises: a divider (71) for calculating a reciprocal of the third ratio; a subtracter (72) for subtracting an output of said divider (71) from 1; a limiter (73) for limiting an output of said subtracter (72) within a specified range; and an averaging circuit (74) for averaging an output of said limiter by a specified time constant when said voice detector has detected speech, and otherwise for yielding a value of a previous step gain when said voice detector has detected no speech.
Claim 8
Dependent Claim
66 words
The echo canceller as claimed in any preceding claim, further comprising a loss controller (11) for calculating a loss to be added to the transmitting output signal according to a determination result of the voice detector, the first ratio, and a third ratio; and an insertion loss circuit (12) for attenuating an output signal of said first subtracter by the loss calculated by said loss controller.
Claim 9
Dependent Claim
210 words
The echo canceller as claimed in claim 8, wherein said loss controller further comprises: a first averaging circuit (81) for averaging the third ratio by a specified time constant to be yielded therefrom when the voice detector has detected speech, and otherwise holding a previous operation result to be yielded when no speech has been detected; a comparator (82) for comparing an output of the first averaging circuit with a predetermined third threshold (Th3), thereby to yield a positive output when the output of the first averaging circuit is greater than the third threshold and otherwise to yield a negative output; an AND circuit (86) for determining a logical AND between an output of said comparator (82) and an output of the voice detector (8); a divider (83) for dividing a predetermined maximum loss (ERLEO) by the first ratio (R1); a second averaging circuit (85) for averaging an output of said divider by a specified time constant when the voice detector has detected speech, and otherwise holding a previous operation result thereof when no speech has been detected; and a switch (87) for selecting an output of said second averaging circuit as a loss when the AND circuit has yielded a positive output and otherwise selecting a numerical value 1.
Claim 10
Dependent Claim
67 words
The echo canceller as claimed in any preceding claim, wherein the renewal of the filter coefficients of said first and second adaptive filters is performed according to an Normalized Least Mean Square algorithm, where the step gain of the second adaptive filter is 1, and optionally the step gain (α1) of the first adaptive filter is smaller than a step gain (α2) of the second adaptive filter.
Claim 11
Dependent Claim
75 words
The echo canceller as claimed in any preceding claim, wherein a reference input signal (x) of said second adaptive filter (3, 17) and an input signal (y) of said second subtracter (4) are band-limited to 1/M, where M is an integer not less than 2, of a pass band of said first adaptive filter by band-limiting filter means (13, 15) and the resultant band-limited signals are further decimated to 1/M by decimator means (14, 16).
Claim 12
Dependent Claim
25 words
The echo canceller as claimed in claim 11, wherein said band-limiting filter means is a low-pass filter whose cut-off frequency is lower than 1 kHz.
Claim 13
Dependent Claim
298 words
The echo canceller as claimed in claim 11 or 12, wherein said second adaptive filter (17) comprises: a first X-memory (101) for storing a received input signal corresponding to N samples where N is an integer; an H-memory (102) for storing filter coefficients corresponding to N samples; a first convoluter (103) for convoluting the latest data corresponding to N samples stored in the first X-memory (101) with data stored in the H-memory (102) to thereby synthesize a pseudo echo; a first coefficient renewer (104) for renewing the filter coefficients stored in the H-memory (102) by using an output signal of the first subtracter (2) and the data stored in the first X-memory when the voice detector has determined that far-end speech is present; a first delay (105) for delaying the received input signal by M samples; a second delay (106) for delaying the transmitting input signal by M samples; a third delay (107) for delaying a detection result of said voice detector by M samples; a second X-memory (108) for storing an output of the first delay corresponding to N samples; a second convoluter (109) for convoluting the data corresponding to N samples stored in the second X-memory (108) with the data stored in the H-memory (102) to synthesize a pseudo echo; a third subtracter (110) for subtracting an output of the second convoluter (109) from an output of the second delay (106); and a second coefficient renewer (111) for renewing the filter coefficients stored in the H-memory (102) by using an output signal and step gain of the third subtracter (110) and the data stored in the second X-memory (108) when a detection result of the voice detector corresponding to the last M samples delayed by the third delay (107) is determined that far-end speech is present.
References Cited (Backward Citations)
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