Echo canceller device and voice telecommunications device
Disclosed is an echo canceller ( 10 ) including: a false echo calculator ( 32 ) that acquires current and previous filter-coefficient groups used by an adaptive filtering unit ( 20 ), and that calculates plural false echo signals by performing a filtering operation using each of the current and previous filter-coefficient groups on a sequence of reception signals (x(n)); a voice-transmission signal buffer that outputs a previous voice-transmission signal (y(n−1)); an evaluation value calculator ( 34 ) that calculates plural evaluated values of an echo cancellation quantity by using the previous voice-transmission signal; a filter selector ( 36 ) that selects a new filter-coefficient group on the basis of the plural evaluated values of the echo cancellation quantity; a foreground filter ( 39 ) that performs a filtering operation using the new filter-coefficient group on the sequence of reception signals (x(n)) to generate an estimated echo component; and a subtractor ( 25 ) that subtracts the estimated echo component from a voice-transmission signal to generate a residual signal (e(n)).
1. An echo canceller device comprising:
an adaptive filtering unit to perform a filtering operation using a filter-coefficient group on a reception signal sequence input thereto, and to update the filter-coefficient group on a basis of a voice-transmission signal input thereto from a sound collector;
a false echo calculator to acquire current and previous filter-coefficient groups which have been used by the adaptive filtering unit, and to perform filtering operations using the current and previous filter-coefficient groups, respectively, on the input reception signal sequence to thereby calculate false echo signals;
a voice-transmission signal buffer to output, as a previous voice-transmission signal, a voice-transmission signal input thereto from the sound collector, after temporarily storing the voice-transmission signal;
an evaluation value calculator to calculate evaluated values of an echo cancellation quantity corresponding to the respective false echo signals on a basis of the previous voice-transmission signal and the false echo signals;
a filter selector to select a new filter-coefficient group from among the current and previous filter-coefficient groups on a basis of the evaluated values of the echo cancellation quantity;
a foreground filter to perform a filtering operation using the new filter-coefficient group on the of input reception signal sequence to thereby generate an estimated echo component; and
a subtractor to subtract the estimated echo component from a voice-transmission signal input thereto from the sound collector, to thereby generate a residual signal.
2. The echo canceller device according to claim 1 , further comprising a reception signal buffer to output, as a previous reception signal sequence, a reception signal sequence input thereto, after temporarily storing the reception signal sequence, wherein
the false echo calculator performs filtering operations using the current and previous filter-coefficient groups, respectively, on the previous reception signal sequence to thereby calculate the false echo signals.
3. The echo canceller device according to claim 1 , wherein the filter selector selects, as the new filter-coefficient group, a filter-coefficient group corresponding to a largest one of the evaluated values of the echo cancellation quantity from among the current and previous filter-coefficient groups.
4. The echo canceller device according to claim 1 , wherein the evaluation value calculator calculates, as each of the evaluated values of the echo cancellation quantity, a square of a ratio of the previous voice-transmission signal to a difference between the previous voice-transmission signal and each of the false echo signals.
5. The echo canceller device according to claim 1 , wherein the foreground filter performs a filtering operation using only the new filter-coefficient group to thereby generate the estimated echo component.
6. The echo canceller device according to claim 1 , wherein the foreground filter generates a combination filter-coefficient group by performing a linear combination of the new filter-coefficient group and a previous filter-coefficient group which has been used by the foreground filter, and also performs a filtering operation using the combination filter-coefficient group to thereby generate the estimated echo component.
7. A voice telecommunications device comprising:
a communication function unit to communicate with another voice telecommunications device via an electrical communication network; and
the echo canceller device according to claim 1 connected to both a speaker for converting into an acoustic wave a reception signal sequence input thereto from the communication function unit to emit the acoustic wave, and a sound collector, wherein
the echo canceller device reduces an acoustic echo component in a voice-transmission signal input thereto from the sound collector, using the reception signal sequence.
8. An echo canceller device comprising:
an adaptive filtering unit to perform a filtering operation using a filter-coefficient group on a reception signal sequence input thereto, and to adaptively update the filter-coefficient group on a basis of a voice-transmission signal input thereto from a sound collector;
a reception signal buffer to output, as a previous reception signal sequence, the input reception signal sequence, after temporarily storing the reception signal sequence;
a false echo calculator to acquire current and previous filter-coefficient groups which have been used by the adaptive filtering unit, and to perform a filtering operation using the current filter-coefficient group on the previous reception signal sequence to thereby calculate a first false echo signal, and further to perform a filtering operation using the previous filter-coefficient group on the previous reception signal sequence to thereby calculate a second false echo signal;
a voice-transmission signal buffer to output, as a previous voice-transmission signal, a voice-transmission signal input thereto from the sound collector, after temporarily storing the voice-transmission signal;
an evaluation value calculator to calculate a first evaluated value of an echo cancellation quantity on a basis of both the first false echo signal and the previous voice-transmission signal input thereto from the voice-transmission signal buffer, and to calculate a second evaluated value of the echo cancellation quantity on a basis of both the second false echo signal and the previous voice-transmission signal;
a double-talk detector to compare with each other the first and second evaluated values of the echo cancellation quantity to decide whether a double talk occurs;
a foreground filter to generating an estimated echo component by performing, on the input reception signal sequence, a filtering operation using a filter-coefficient group in which the current filter-coefficient group is incorporated with a degree of incorporation depending on the decision result acquired by the double-talk detector; and
a subtractor to subtract the estimated echo component from a voice-transmission signal input thereto from the sound collector, to thereby generate a residual signal.
9. The echo canceller device according to claim 8 , wherein, in a case where it is decided that the double talk has occurred, the foreground filter lower the degree of incorporation in comparison with that in a case where it is decided that no double talk has occurred.
10. The echo canceller device according to claim 8 , wherein:
the false echo calculator calculates a third false echo signal by performing a filtering operation using the current filter-coefficient group on the input reception signal sequence, and calculates a fourth false echo signal by performing a filtering operation using the previous filter-coefficient group on the input reception signal sequence;
the evaluation value calculator calculates a third evaluated value of the echo cancellation quantity on a basis of both the third false echo signal and the voice-transmission signal input thereto from the sound collector, and calculates a fourth evaluated value of the echo cancellation quantity on a basis of both the fourth false echo signal and the voice-transmission signal input thereto from the sound collector; and
the double-talk detector compares with each other the third and fourth evaluated values of the echo cancellation quantity to decide whether the double talk occurs.
11. The echo canceller device according to claim 10 , wherein, the double-talk detector decides that the double talk has occurred, when the first evaluated value of the echo cancellation quantity is equal to or smaller than the second evaluated value of the echo cancellation quantity and the third evaluated value of the echo cancellation quantity is equal to or smaller than the fourth evaluated value of the echo cancellation quantity.
12. The echo canceller device according to claim 11 , wherein the double-talk detector decides that an echo-path variation has occurred, when the first evaluated value of the echo cancellation quantity is equal to or smaller than the second evaluated value of the echo cancellation quantity and the third evaluated value of the echo cancellation quantity is larger than the fourth evaluated value of the echo cancellation quantity.
13. The echo canceller device according to claim 12 , wherein the double-talk detector decides that an echo path is in a normal state, when the first evaluated value of the echo cancellation quantity is larger than the second evaluated value of the echo cancellation quantity.
14. The echo canceller device according to claim 8 , further comprising a filter selector to select a new filter-coefficient group corresponding to the decision result acquired by the double-talk detector, from among the current and previous filter-coefficient groups, wherein
the filter selector replaces the filter-coefficient group in the adaptive filtering unit with the new filter-coefficient group.
15. The echo canceller device according to claim 14 , further comprising a filter coefficient buffer to temporarily store the current and previous filter-coefficient groups, wherein
the filter coefficient buffer supplies the new filter-coefficient group to the adaptive filtering unit under control of the filter selector.
16. The echo canceller device according to claim 8 , wherein the foreground filter generates a combination filter-coefficient group by performing a linear combination of a previous filter-coefficient group which has been used by the foreground filter, and the current filter-coefficient group which has been used by the adaptive filtering unit, and performs a filtering operation using the combination filter-coefficient group to thereby generate the estimated echo component.
17. The echo canceller device according to claim 8 , further comprising a residual echo suppressor to suppress a residual echo component in the residual signal, wherein
the residual echo suppressor adjusts a degree of suppression of the residual echo component in accordance with the decision result acquired by the double-talk detector.
18. A voice telecommunications device comprising:
a communication function unit to communicate with another voice telecommunications device via an electrical communication network; and
the echo canceller device according to claim 8 connected to both a speaker for converting into an acoustic wave a reception signal sequence input thereto from the communication function unit to emit the acoustic wave, and a sound collector, wherein
the echo canceller device reduces an acoustic echo component in a voice-transmission signal input thereto from the sound collector, using the reception signal sequence.