Acoustic echo canceller

• US 5,477,534 A
• Filed: 07/20/1994
• Issued: 12/19/1995
• Est. Priority Date: 07/30/1993
• Status: Expired due to Term

• Current Assignee: Kyocera Corporation
• Original Assignee: Kyocera Corporation
• Inventors: Kusano, Yoshimasa
• Primary Examiner(s): Olms, Douglas W.
• Assistant Examiner(s): Patel, Ajit
• Application Number:
  US08/278,375
• Time in Patent Office: 517 Days
• Field of Search: 370/32.1, 370/32, 379/410, 379/406, 379/411, 379/407, 379/345, 364/724.19, 364/724.16
• US Class Current: 370/286
• CPC Class Codes: H04M 9/082 using echo cancellers echo cancellers per se H04B3/23

Abstract

An acoustic echo canceller for cancelling an acoustic echo component produced when a signal on a receiving communication line appears on a transmitting communication line via an acoustic echo path. In the acoustic echo canceller, a variable coefficient series is divided into blocks, among which selected is a block requiring a coefficient correction amount update operation conforming to the attenuation characteristic of an impulse response in a sound field. A coefficient fitted to the attenuation characteristic of the impulse response in the sound field is set for the selected block. Therefore, convergence speed degradation of the acoustic echo cancellation characteristic involved in divided update can be compensated, and even if an echo path characteristic fluctuates, an excellent follow-up characteristic is provided, so that stable and high-speed acoustic echo cancellation can always be executed.

Claims

1. An acoustic echo canceller comprising:

a receive signal input terminal,

a receive signal output terminal,

a transmit signal input terminal,

a transmit signal output terminal,

a variable coefficient digital filter comprising an artificial impulse response register processed in N divided coefficient blocks, where N is a positive integer, in response to a receive signal from the receive signal input terminal and for generating an artificial acoustic echo signal,

a subtractor located between the transmit signal input terminal and the transmit signal output terminal for subtracting the artificial acoustic echo signal generated by the variable coefficient digital filter from an acoustic echo component of the receive signal input from the receive signal output terminal via an acoustic echo path to the transmit signal input terminal to find a difference signal,

a coefficient correction amount calculation circuit, to which the receive signal from the receive signal input terminal and the difference from the subtractor are supplied, for sequentially updating division coefficients so as to minimize the difference signal,

a first switch located between the receive signal input terminal and the receive signal output terminal,

a second switch located between the transmit signal input terminal and the transmit signal output terminal, the first and second switches being connectable to an associated party terminal,

a code generator for generating a code for observing an external acoustic echo characteristic in a state in which the first and second switches are disconnected from the associated party terminal,

operation means for calculating the external acoustic echo characteristic when the code is input from the receive signal output terminal via the acoustic echo path to the transmit signal input terminal and for generating an operation result,

storage means for storing data, the data stored in the storage means including the operation result generated by the operation means,

means, when the first and second switch means are connected to the associated party terminal after a predetermined time has elapsed, for calculating a sum power for each block in response to the data stored in the storage means,

means for comparing sum power values between blocks of the artificial impulse response register which are contiguous and for generating a comparison result, and

update means for arbitrarily setting an update frequency of each division coefficient in response to the comparison result.

2. The acoustic echo canceller of claim 1, wherein the operation means comprises:

a synchronous adder for calculating an impulse response of the code input from the receive signal output terminal via the acoustic echo path to the transmit signal input terminal, and

a convolution integral operation circuit for performing a convolution integral operation on an output of the synchronous adder and the code to calculate an impulse response of the acoustic echo path.

3. An acoustic echo canceller comprising:

a receive signal input terminal,

a receive signal output terminal connected to the receive signal input terminal,

a transmit signal input terminal,

a transmit signal output terminal,

a variable coefficient digital filter having an artificial impulse response register divided into N blocks to which a receive signal through the receive signal input terminal is input and for generating an artificial acoustic echo signal, where N represents a positive integer, the impulse response register storing a plurality of coefficients,

a coefficient series block selector for selecting n blocks to be updated at a time among a total of N divided blocks of the artificial impulse response register,

a subtractor located between the transmit signal input terminal and the transmit signal output terminal for subtracting the artificial acoustic echo signal generated by means of the variable coefficient digital filter from an acoustic echo component of the receive signal input from the receive signal output terminal via an acoustic echo path to the transmit signal input terminal to find a difference signal,

a coefficient correction amount calculation circuit, to which the receive signal from the receive signal input terminal and the difference from the subtractor are supplied, for sequentially updating coefficient series so as to minimize the difference signal,

a first power calculation circuit for finding a power of each of the plurality of coefficients stored in the impulse response register, and

a power comparator for totaling power values for each block output by the first power calculation circuit and comparing the totaled power values, wherein an update frequency of each divided block adapted to a sound field characteristic is determined in response to the comparison result of the power comparator and coefficient correction is executed with P fixed position blocks and Q (n-P) variable position blocks in response to the determined update frequency.

4. The acoustic echo canceller of claim 3, comprising:

a second power calculation circuit for finding a power value of each coefficient correction amount generated by the coefficient correction amount calculation circuit for a fixed position block assigned the highest one of update frequencies adapted to a sound field characteristic according to the power comparator,

a coefficient divider for dividing each power value output by the second power calculation circuit by each output of the first power calculation circuit for the fixed position block, and

a coefficient change detector for comparing the calculation result given by the coefficient divider with a predetermined threshold,

wherein when the output value of the coefficient divider is greater than the threshold in the coefficient change detector, coefficient correction operation processing in the same divided blocks as the fixed position blocks is performed for the variable position blocks.

5. An acoustic echo canceller comprising:

a receive signal input terminal,

a receive signal output terminal connected to the receive signal input terminal,

a transmit signal input terminal,

a transmit signal output terminal,

a variable coefficient digital filter for generating an artificial echo signal in response to a receive signal input through the receive signal input terminal,

a subtractor located between the transmit signal input terminal and the transmit signal output terminal for finding a difference between an echo signal from the transmit signal input terminal and the artificial echo signal generated by the variable coefficient digital filter,

a coefficient correction amount calculation circuit, to which a receive signal from the receive signal input terminal and the difference from the subtractor are supplied, for performing division processing in which a coefficient series of the variable coefficient digital filter is divided into N blocks and the entire coefficient series is automatically updated in M steps, where N and M represent positive integers, and

a coefficient series block selector for selecting at least one block to be updated among the N blocks of the coefficient series,

wherein a coefficient correction amount fitted to an attenuation characteristic of an impulse response in a sound field is set for the block selected by the coefficient block selector.

6. The acoustic echo canceller of claim 5, wherein the variable coefficient digital filter comprises an artificial impulse response register which stores the coefficient series of the variable coefficient digital filter, and a sum-of-products operation circuit which performs a convolution integral operation on contents of the artificial impulse response register and the receive signal from the receive signal input terminal.

7. The acoustic echo canceller of claim 6, wherein the variable coefficient digital filter further comprises a receive signal input register which stores the receive signal from the receive signal input terminal.

8. An acoustic echo canceller comprising:

a receive signal input terminal,

a receive signal output terminal connected to the receive signal input terminal,

a transmit signal input terminal,

a transmit signal output terminal,

a variable coefficient digital filter for generating an artificial echo signal in response to a receive signal input through the receive signal input terminal,

a subtractor located between the transmit signal input terminal and the transmit signal output terminal for finding a difference between an echo signal from the transmit signal input terminal and the artificial echo signal generated by the variable coefficient digital filter,

a coefficient correction amount calculation circuit, to which the receive signal from the receive signal input terminal and the difference from the subtractor are supplied, for applying a correction amount to a coefficient series of the variable coefficient digital filter, and

a coefficient block selector for sending an instruction for selecting one of the blocks in sequence for performing a coefficient update operation to the coefficient correction amount calculation circuit so that the coefficient series of the variable coefficient digital filter is divided into N blocks for automatically updating the entire coefficient series in a total of M steps, where N and M are positive integers, wherein an update frequency is set in each block and wherein a correction loop gain interpolated into the coefficient correction amount calculation circuit is set in response to the update frequency set in each block.

9. The acoustic echo canceller of claim 8, wherein the variable coefficient digital filter comprises an artificial impulse response register which stores the coefficient series of the variable coefficient digital filter, and a sum-of-products operation circuit which performs a convolution integral operation on contents of the artificial impulse response register and the receive signal from the receive signal input terminal.

10. The acoustic echo canceller of claim 9, wherein the variable coefficient digital filter further comprises a receive signal input register which stores the receive signal from the receive signal input terminal.