JPH08279777A - Echo canceler - Google Patents

Abstract

PURPOSE: To cancel echo with pseudo echo generated based on the delay time of a returned reference signal by sending the reference signal defining the specified frequency component of a transmitted signal as a carrier wave. CONSTITUTION: A ring buffer 12 samples a transmitted signal T in the cycle of 125μs and time sequentially stores amplitude data for 250ms. A reference signal generator 2 extracts the frequency component of 2400±50Hz in the transmitted signal and sends out the reference signal modulated by the rectangular wave of 250ms as the carrier wave. A level comparator 5 finds an amplitude ratio from the amplitudes of the reference signal returned through a BPF 7 and the transmitted reference signal. A phase comparator 10 finds the delay time of the transmitted reference signal and the returned reference signal. An echo quantity estimator 11 specifies correspondent data in the ring buffer 12 and outputs the pseudo echo, for which these data are adjusted by the amplitude ratio, through an amplifier 13. An adder 14 subtracts the pseudo echo from a received audio signal and cancels the received echo.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an eco-canceller for canceling eco-returns from a partner station via a telephone line.

[0002]

2. Description of the Related Art In a long-distance telephone line, one's own voice is delayed and returns through a telephone device of the other party, which may cause an ecological problem and seriously impede a telephone call. A device for preventing this is an eco-canceller, which is installed in the transmission / reception circuit of the main device of the telephone device. Figure 3 shows the conventional eco-
It is a block diagram which shows the structure of a canceller. As shown in the figure, the conventional eco-canceller includes an FIR filter (non-recursive filter) 30, a coefficient updating unit 34, and an adder 35. The FIR filter (non-recursive filter) 30 includes a plurality of delay elements 31-1, 31-2, ...
2-1, 32-2, ... Adder 33, and the coefficient updating unit 34 is configured to set the coefficient (gain) of the FIR filter 30.

Each delay element 31-of the FIR filter 30
, 31-2, ... Are connected in series from the transmission signal line 36 with a delay time set, and the amplifier 32 is connected from each connection point.
, 32-2, ... Are connected, and the output of each amplifier is connected to the input of the adder 33. Furthermore, the adder 33
Is connected to the input of the adder 35 together with the reception signal line 37. The output of the adder 35 is connected to the input of the coefficient updating unit 34, and the output of the coefficient updating unit 34 is connected so as to adjust the gain of each amplifier.

The transmission signal is transmitted from the transmission signal line 36 to the station and is input to each amplifier through each delay element 31-1, 31-2, ..., And the output signals of each amplifier are added by the adder 33. Then, the pseudo eco-signal s is generated. The reception signal received by the reception signal line 37 is subjected to reception processing after the pseudo echo signal s is subtracted by the adder 35, and is input to the coefficient updating unit 34. The coefficient updating unit 34 includes a CPU (central processing unit), adjusts the gain of each amplifier so that the echo signal included in the received signal is minimized, and the adder 33 outputs an optimum pseudo echo signal s. To do. The echo signal included in the received signal varies depending on the telephone line, and the coefficient updating unit 34 repeatedly learns for each telephone line to optimize the pseudo echo signal s.

[0005]

However, when the eco-timer (the time until the echo of the transmitted signal returns) is long, the conventional eco-canceler described above has a FIR.
It is necessary to increase the number of delay elements and amplifiers of the filter (non-recursive filter) 30, and the amount of processing for optimizing the coefficient (gain) of each amplifier becomes enormous and the coefficient updating unit 34
There was a problem that it could not be processed in.

The present invention has been made in view of the above points, and an object of the present invention is to eliminate the above problems and provide an eco-canceller in which the amount of cancellation processing is constant regardless of the length of the eco-time. .

[0007]

SUMMARY OF THE INVENTION In order to solve the above problems, the present invention is an echo canceller, which is provided in a telephone and cancels an echo signal included in a voice signal from a partner station. A voice data storage means (12) for constantly sampling a signal and storing it in a time series in a cyclic manner, and a reference signal periodically generated by extracting a specific frequency component of a voice signal to be transmitted to a partner station and using it as a carrier wave. And a reference signal transmitting means (2) for transmitting the reference signal, an amplitude comparing means (5) for comparing the amplitudes of the reference signal to be transmitted and the reference signal returned from the partner station to obtain an amplitude ratio, and the reference signal to be transmitted and the partner. The phase comparison means (10) for obtaining the delay time of the reference signal returned from the station and the predetermined data position of the voice data storage means (12) for the delay time are combined with the amplitude ratio. Pseudo echo output means (echo amount estimator 11 and amplifier 13) for adjusting and outputting the pseudo echo S, and subtracting the pseudo echo S from the voice signal received from the partner station, and including it in the received voice signal It is characterized in that means (14) for canceling the generated echo is provided.

[0008]

According to the present invention, as described above, the echo is estimated based on the amplitude ratio at the time of transmitting and receiving the reference signal and the delay time from the transmission to the reception of the reference signal, and the stored voice signal is stored. Since the pseudo echo-S is calculated from this data and subtracted from the received audio signal, the processing amount of the pseudo echo output means becomes constant regardless of the length of the echo time. Therefore, there is no need to increase the number of hardware elements as in the past,
You can expect a stable call regardless of the length of time. Further, since the carrier wave for transmitting the reference signal is extracted from the transmission signal, interference such as noise is reduced.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below in detail with reference to the drawings. FIG. 1 is a block diagram showing the configuration of the eco-canceller of the present invention. As shown in the figure, the eco-canceller of the present invention comprises a bandpass filter 1, a reference signal generator 2, a modulator 3, an adder 4, a level comparing section 5, a differentiator 6,
A bandpass filter 7, a detector 8, a differentiator 9, a phase comparator 10, an eco-quantity estimator 11, a ring buffer 12, an amplifier 13, and an adder 14 are provided.

The transmission signal line 15 is connected to the input of the bandpass filter 1 and one input of the adder 4, and the output of the bandpass filter 1 is a reference signal generator (square wave generator).
The output of 2 is connected to the input of modulator 3, the output of modulator 3 is connected to one input of adder 4, and the output of adder 4 is connected to output line 16.

The reception signal line 17 is connected to the input of the adder 14 and is also connected to the detector 8 through the bandpass filter 7. The output of the detector 8 and the output of the reference signal generator 2 are connected to the input of the level comparator 5, and are also connected to the input of the phase comparator 10 through the differentiator 9 and the differentiator 6, respectively.

Output of level comparator 5 and phase comparator 1
The output of 0 is connected to the input of the eco quantity estimator 11, and its output is connected to the ring buffer 12 and the gain adjustment terminal of the amplifier 13. The transmission signal line 15 is the ring buffer 1
2, the output of the ring buffer 12 is connected to the input of the amplifier 13, the output of the amplifier 13 is connected to the input of the adder 14 together with the reception signal line 17, and the adder 1
The output of 4 is connected to the input line 18.

The ring buffer 12 is a storage device that constantly samples the transmission signal T (voice signal) at a sampling period of 125 μs and cyclically and sequentially stores 250 ms of data (amplitude).

Next, the operation will be described. The transmission signal T (voice signal) is 2.4 KHz ± 50 Hz with the bandpass filter 1.
Signal is extracted, and its output signal is modulated (amplitude modulated) by the output signal of the reference signal generator 2 (square wave of 250 ms period) in the modulator 3, and the output signal of the modulator 3 is added to the transmission signal T and the adder. 4 is added and output from the output line 16.

The reception signal R is received by the reception signal line 17,
2.4 KHz ± 50 Hz through band pass filter 7
Signal is extracted and the reference signal is demodulated by the detector 8, and the signal amplitude is compared with the output signal of the reference signal generator 2 (square wave having a period of 250 ms) by the level comparator 5 to transmit and receive the reference signal. The amplitude ratio at time is output. Further, the signal demodulated by the wave detector 8 is differentiated by the differentiator 9, the output signal of the reference signal generator 2 is differentiated by the differentiator 6, both rising parts are extracted, and the phases are compared by the phase comparator 10. The delay time from the transmission to the reception of the reference signal is output to the eco quantity estimator 11.

The eco quantity estimator 11 estimates the eco quantity from the output signal (amplitude ratio) of the level comparator 5 and the output signal (delay time) of the phase comparator 10 to generate a pseudo echo signal ( Details later). That is, a position for taking out predetermined data from the data stored in the ring buffer 12 (data stored in time series) is designated, and the gain of the amplifier 13 for amplifying the data is designated. . The amplifier 13 sets the gain according to the instruction of the eco quantity estimator 11 and outputs a signal (pseudo eco signal S) corresponding to the data to the adder 14. The adder 14 subtracts the pseudo echo signal S from the received signal R and outputs it to the input line 18.

FIG. 2 is a flow chart showing the operation of the eco quantity estimator.
It is a chart. The ecological amount estimator 11 includes a CPU and a memory (not shown), and a program for executing this flow is stored in the memory of the ecological amount estimator 11 and executed by the CPU. A description will be given according to the flowchart of FIG. The eco quantity estimator 11 reads the output signals of the level comparator 5 and the phase comparator 10 (step ST1).

The extraction position of the ring buffer 12 is determined based on the output signal of the phase comparator 10 (step ST
2). The gain of the amplifier 13 is determined based on the output signal of the level comparator 5 (step ST3). Ring buffer 1
2 to output the data (output to the amplifier 13) (step ST4), and to the amplifier 13 to set the gain,
The data is output as a pseudo echo signal S (step ST5). The above steps ST1 to ST5 are repeatedly executed.

The above description is for the eco-canceller on the calling side, and the bandpass filter 1 uses the transmission signal T (voice signal).
Among them, a narrow-band signal of 2.4 KHz ± 50 Hz that does not affect perception significantly was extracted and used by modulating with a reference signal (square wave of 250 ms period). Further, the frequency band of the eco-canceller on the called side may be 2.6 KHz ± 50 Hz to prevent interference with the calling side. The frequency and frequency band on which the reference signal is placed, the period of the reference signal (2
50 ms) and associated ring buffer size (2
50 ms storage) is the value used as an example,
Other values may be used.

As described above, according to the present embodiment, the echo amount is estimated based on the amplitude ratio at the time of transmitting and receiving the reference signal and the delay time from the transmission to the reception of the reference signal, and the stored voice is stored. Since the pseudo eco signal S is calculated from the signal data and subtracted from the received signal R, the processing amount of the eco amount estimator 11 becomes constant regardless of the eco time, and the eco time by the telephone line is shortened. You can expect a stable call regardless of the situation. Further, since the carrier wave for transmitting the reference signal is extracted from the transmission signal, interference such as noise is reduced.

[0021]

As described above, according to the present invention, the following excellent effects are expected. The echo is estimated from the amplitude ratio between the reference signal transmission and reception and the delay time from the reference signal transmission to reception, and the pseudo echo-S is calculated from the stored audio signal data and received. Since it is subtracted from the generated audio signal, the processing amount of the pseudo echo output means is eco-friendly.
It is constant regardless of the length of time. Therefore, a stable call can be expected regardless of the length of the eco-time without increasing the number of hardware elements as in the conventional case. Further, since the carrier wave for transmitting the reference signal is extracted from the transmission signal, interference such as noise is reduced.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration example of an eco-canceller of the present invention.

FIG. 2 is a flowchart showing the operation of the eco quantity estimator.

FIG. 3 is a block diagram showing a configuration example of a conventional eco-canceller.

[Explanation of symbols]

 1 band pass filter 2 reference signal generator 3 modulator 4 adder 5 level comparator 6 differentiator 7 band pass filter 8 detector 9 differentiator 10 phase comparator 11 eco-quantity estimator 12 ring buffer 13 amplifier 14 adder

Claims (1)

[Claims] 1. An echo canceller provided in a telephone set for canceling an echo signal included in a voice signal from a partner station, wherein the voice signal transmitted from the own station is constantly sampled and cyclically stored in time series. Audio data storage means, reference signal transmitting means for extracting a specific frequency component of an audio signal to be transmitted to the other station and using it as a carrier wave, and transmitting a reference signal that is periodically generated, the reference signal to be transmitted, and the reference signal Amplitude comparison means for comparing the amplitudes of the reference signals returned from the partner station to obtain an amplitude ratio, phase comparison means for finding the delay time between the reference signal to be sent out and the reference signal returned from the partner station, and the delay time Pseudo echo output means for obtaining a predetermined data position of the audio data storage means from the above and adjusting the data according to the amplitude ratio to output a pseudo echo,
An echo canceller comprising means for subtracting the pseudo echo from the voice signal received from the partner station and canceling the echo contained in the received voice signal.