CN1219391C - Echo eliminator and method for evaluating echo - Google Patents
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Abstract
本发明公开了一种回声消除器,其包含自适应滤波器、远端输入信号缓存、近端输入信号缓存和信号加法器,增加了远端信号降采样处理模块、近端信号降采样处理模块和互相关回声有效部分搜索模块;互相关回声有效部分搜索模块对经过远端信号降采样处理模块和近端信号降采样处理模块降采样后的信号进行互相关运算得到回声有效参数,自适应滤波器根据回声有效参数对接收信号进行回声估计,产生回声估计值;信号加法器将从回声消除器外部接收到的混有回声信号的输入信号减去回声估计值进行回声抵消。同时公开了一种应用该回声消除器进行回声估计的方法。应用本发明方案不仅不影响回声抵消的效果,而且提高了效率,能够大量地节省系统成本。
The invention discloses an echo canceller, which includes an adaptive filter, a far-end input signal buffer, a near-end input signal buffer and a signal adder, and adds a far-end signal down-sampling processing module and a near-end signal down-sampling processing module and the cross-correlation echo effective part search module; the cross-correlation echo effective part search module performs cross-correlation operation on the signal down-sampled by the far-end signal down-sampling processing module and the near-end signal down-sampling processing module to obtain the echo effective parameters, and adaptive filtering The echo estimation device performs echo estimation on the received signal according to the effective parameters of the echo to generate an echo estimation value; the signal adder subtracts the echo estimation value from the input signal mixed with the echo signal received from the outside of the echo canceller to perform echo cancellation. At the same time, a method for echo estimation using the echo canceller is disclosed. The application of the scheme of the invention not only does not affect the effect of echo cancellation, but also improves the efficiency and can greatly save the system cost.
Description
技术领域technical field
本发明涉及通信系统中对回声的处理技术,特别涉及一种回声消除器及回声估计方法。The invention relates to echo processing technology in a communication system, in particular to an echo canceller and an echo estimation method.
背景技术Background technique
在固定电话通讯系统中,交换机内部使用的是四线的系统,而用户的电话线使用的是二线系统,这样,在传输过程中需要通过一个转换器(Hybrid)来实现信号从交换机到用户的传输。由于四线系统和二线系统的阻抗不可能做到准确的匹配,信号在传输的过程中就会出现反射,反射的信号到达用户侧用户就会听到自己的说话声音又返回了过来,形成了回声。回声将大大的降低通话质量,是在通信系统中必须解决的一个问题。如图1中A端的信号经过转换器101又返回到A端,从而A用户听到了自己的回声。In the fixed telephone communication system, the switchboard uses a four-wire system, while the user's telephone line uses a two-wire system. In this way, a converter (Hybrid) is needed to realize the transmission of signals from the switchboard to the user during the transmission process. transmission. Since the impedance of the four-wire system and the two-wire system cannot be accurately matched, the signal will be reflected during transmission, and when the reflected signal reaches the user side, the user will hear his own voice returning, forming a echo. Echo will greatly reduce the call quality, and it is a problem that must be solved in the communication system. As shown in FIG. 1 , the signal at terminal A passes through the converter 101 and returns to terminal A, so that user A hears his own echo.
目前,通过使用回声消除器的方法可以实现消除回声的功能。图2为现有技术回声消除器的结构框图,如图2所示,现有技术回声消除器包含一个自适应滤波器202、一个远端输入信号缓存201、一个近端输入信号缓存203和一个信号加法器204。其中远端指的是四线端,近端是指二线端。它的核心是自适应滤波器202,通过用自适应滤波器202来模拟转换器的传输特性,这个自适应滤波器202参考由远端输入信号缓存201发送的远端输入信号及近端输入信号缓存203发送的近端输入信号以及作为自适应滤波器的反馈信号的近端输出信号来估计回声的值,自适应滤波器202的作用就是模仿出一个类似于真实的反射路径(echopath)的环境,而它能够在多长时间内使自己估计出的回声接近真实回声,这个估计出的回声与真实回声的差小于一个规定值,然后通过信号加法器204将从回声消除器外部接收的混有回声的信号减去估计的回声值,进行回声抵消。估计的回声和真实回声的差越小,回声抵消的效果就越好。At present, the echo cancellation function can be realized by using an echo canceller. Fig. 2 is the structural block diagram of prior art echo canceller, as shown in Fig. 2, prior art echo canceller comprises an
图3-1和图3-2为产生回声的原理示意图。其中,图3-1为发送理想脉冲激励信号的示意图,图3-2为图3-1所发送的理想脉冲激励信号的响应示意图,对于图3-1中的A点而言,在A点发出的一个理想冲击信号将会得到图3-2中的响应,其中,tp是净回声部分,即回声有效部分,tr是纯延时部分,td是总回声延时。如图3-2所示,净回声部分在总回声延时中占比较小的部分。可见,如果能够将净回声部分进行有效的抵消,就可以实现回声消除的工作,然而,目前的回声消除器都是对全程时间td段信号进行抵消。显然,这样做的结果是带来了大量地系统资源浪费。Figure 3-1 and Figure 3-2 are schematic diagrams of the principle of echo generation. Among them, Figure 3-1 is a schematic diagram of sending an ideal pulse excitation signal, and Figure 3-2 is a schematic diagram of the response of the ideal pulse excitation signal sent in Figure 3-1. For point A in Figure 3-1, at point A An ideal impulse signal sent out will get the response in Figure 3-2, where tp is the net echo part, that is, the effective part of the echo, tr is the pure delay part, and td is the total echo delay. As shown in Figure 3-2, the net echo part accounts for a relatively small part of the total echo delay. It can be seen that if the net echo part can be effectively canceled, the echo cancellation can be realized. However, the current echo cancellers all cancel the signal of the whole time td segment. Obviously, the result of doing this is to bring a lot of waste of system resources.
可见,现有技术的主要缺点就是进行回声抵消时,没有考虑到回声的特性,直接对回声全程时间段的信号进行抵消,所以需要的资源太多,而导致无法提高系统资源利用率和降低成本。It can be seen that the main disadvantage of the existing technology is that the characteristics of the echo are not considered when performing echo cancellation, and the signal of the entire time period of the echo is directly canceled, so too many resources are required, which makes it impossible to improve the utilization of system resources and reduce costs. .
发明内容Contents of the invention
由回声产生的基本原理表明,回声的有效部分在整个回声长度中只占很小的一块,如果能够找到这部分,就可以使用较少的资源实现回声抵消的效果,从而可以大量地节省系统成本。The basic principle generated by the echo shows that the effective part of the echo only occupies a small part of the entire echo length. If this part can be found, the effect of echo cancellation can be realized with less resources, which can save a lot of system cost .
有鉴于此,本发明的主要目的在于提供一种回声消除器,能够找到回声的有效部分,并只对该部分回声进行抵消,不仅不影响回声抵消的效果,而且提高了效率,能够大量地节省系统成本。In view of this, the main purpose of the present invention is to provide an echo canceller, which can find the effective part of the echo, and only cancel this part of the echo, which not only does not affect the effect of echo cancellation, but also improves the efficiency and can save a lot system cost.
本发明的另一个主要目的在于提供一种回声估计方法,能够高效、准确地得到回声估计值。Another main purpose of the present invention is to provide an echo estimation method, which can efficiently and accurately obtain an echo estimation value.
根据上述目的的一个方面,本发明提供了一种回声消除器,其包含自适应滤波器、远端输入信号缓存、近端输入信号缓存和信号加法器;该远端输入信号缓存将接收到的远端输入信号作为参考信号发送给自适应滤波器;该近端输入信号缓存将接收到的近端输入信号发送给自适应滤波器;该自适应滤波器产生回声估计值并将其发送给信号加法器;该信号加法器将从回声消除器外部接收到的混有回声信号的输入信号减去回声估计值进行回声抵消,并产生近端输出信号,将该近端输出信号作为反馈信号发送给自适应滤波器;该回声消除器进一步包含:According to an aspect of above-mentioned object, the present invention provides a kind of echo canceller, it comprises adaptive filter, far-end input signal buffer, near-end input signal buffer and signal adder; This far-end input signal buffer will receive The far-end input signal is sent as a reference signal to the adaptive filter; the near-end input signal buffer sends the received near-end input signal to the adaptive filter; the adaptive filter generates an echo estimate and sends it to the signal Adder; the signal adder subtracts the echo estimated value from the input signal mixed with the echo signal received from the outside of the echo canceller to perform echo cancellation, and generates a near-end output signal, and sends the near-end output signal as a feedback signal to an adaptive filter; the echo canceller further comprising:
远端信号降采样处理模块,其将从远端输入信号缓存接收的远端输入信号进行降采样处理,并将处理后的信号发送给互相关回声有效部分搜索模块;The remote signal down-sampling processing module, which performs down-sampling processing on the remote input signal received from the remote input signal buffer, and sends the processed signal to the cross-correlation echo effective part search module;
近端信号降采样处理模块,其将从近端输入信号缓存接收的近端输入信号进行降采样处理,并将处理后的信号发送给互相关回声有效部分搜索模块;A near-end signal down-sampling processing module, which performs down-sampling processing on the near-end input signal received from the near-end input signal buffer, and sends the processed signal to the cross-correlation echo effective part search module;
互相关回声有效部分搜索模块,其将收到的上述两种处理后的信号进行互相关运算,从计算结果中找出回声最大值,在回声最大值左右两侧根据通信协议,取距离最远的部分作为回声有效部分,将其作为有效回声参数发送给自适应滤波器;Cross-correlation echo effective part search module, which performs cross-correlation calculation on the above two processed signals received, finds the echo maximum value from the calculation result, and selects the farthest distance on the left and right sides of the echo maximum value according to the communication protocol The part of the echo is used as an effective part, and it is sent to the adaptive filter as an effective echo parameter;
自适应滤波器接收远端输入信号缓存和近端输入信号缓存发送的信号以及近端输出信号,并接收有效回声参数,根据有效回声参数查找到接收信号中的有效回声部分,对接收的上述信号的有效回声部分进行回声估计,产生回声估计值。The adaptive filter receives the signal sent by the far-end input signal buffer and the near-end input signal buffer as well as the near-end output signal, and receives the effective echo parameters, and finds the effective echo part in the received signal according to the effective echo parameters. Echo estimation is performed on the effective echo part to generate an echo estimation value.
其中,远端信号降采样处理模块或近端信号降采样处理模块可以进一步包含远端信号低通滤波器或近端信号低通滤波器,分别用于将从远端输入信号缓存或近端输入信号缓存接收的远端输入信号或近端输入信号进行低通滤波,再进行降采样处理。Wherein, the far-end signal down-sampling processing module or the near-end signal down-sampling processing module may further include a far-end signal low-pass filter or a near-end signal low-pass filter, which are respectively used to cache the far-end input signal or the near-end input The far-end input signal or the near-end input signal received by the signal buffer is low-pass filtered, and then down-sampled.
远端信号低通滤波器和近端信号低通滤波器分别可以为截止频率为1000赫兹的低通滤波器。The far-end signal low-pass filter and the near-end signal low-pass filter may respectively be low-pass filters with a cutoff frequency of 1000 Hz.
根据上述目的的另一个方面,本发明提供了一种回声估计方法,采用上述的回声消除器进行回声估计,该方法包括以下步骤:According to another aspect of the above-mentioned purpose, the present invention provides a method for echo estimation, which uses the above-mentioned echo canceller to perform echo estimation, and the method includes the following steps:
1)远端信号降采样处理模块和近端信号降采样处理模块分别对远端输入信号和近端输入信号进行降采样;1) The far-end signal down-sampling processing module and the near-end signal down-sampling processing module respectively down-sample the far-end input signal and the near-end input signal;
2)将经过降采样的两种信号发送给互相关回声有效部分搜索模块,进行互相关运算;2) Send the two down-sampled signals to the cross-correlation echo effective part search module to perform cross-correlation operations;
3)互相关回声有效部分搜索模块从互相关结果中找出回声最大值,在回声最大值左右两侧根据通信协议,取距离最远的部分作为回声有效部分,将其作为回声有效参数,发送给自适应滤波器;3) The cross-correlation echo effective part search module finds the maximum value of the echo from the cross-correlation results, and according to the communication protocol on the left and right sides of the maximum echo value, takes the part with the farthest distance as the effective part of the echo, and uses it as the effective parameter of the echo, and sends to the adaptive filter;
4)自适应滤波器根据有效回声参数查找到接收信号中的有效回声部分,对接收的远端输入信号、近端输入信号和近端输出信号的有效回声部分进行回声估计,产生回声估计值。其中,该方法步骤1)可以进一步包括:对远端输入信号和近端输入信号进行降采样之前先分别进行低通滤波。步骤3)所述找出回声最大值的方法可以为:通过对互相关结果的每个点幅值进行比较搜索出回声最大值。4) The adaptive filter finds the effective echo part in the received signal according to the effective echo parameters, performs echo estimation on the effective echo part of the received far-end input signal, near-end input signal and near-end output signal, and generates an echo estimate value. Wherein, step 1) of the method may further include: performing low-pass filtering respectively before down-sampling the far-end input signal and the near-end input signal. Step 3) The method for finding the maximum value of the echo may be: searching for the maximum value of the echo by comparing the amplitude values of each point of the cross-correlation result.
由上述方案可以看出,本发明的关键在于:先对远端输入信号和近端输入信号分别进行降采样;再对上述信号进行互相关运算;从互相关结果中搜索出回声有效部分,求出回声有效参数;自适应滤波器据此参数估计出回声值。因此,本发明的这种回声消除器及回声估计方法,能够准确地定位有效回声部分,只对该回声的有效部分进行回声抵消,不仅不影响回声抵消的效果,而且能提高效率,并大量节省系统成本。由于本发明采用了降采样的方法,所以在进行延时搜索的时候可以减少计算量和数据的存储量。As can be seen from the above-mentioned scheme, the key of the present invention is: firstly down-sampling the far-end input signal and the near-end input signal respectively; then performing cross-correlation calculation on the above-mentioned signals; searching out the effective part of the echo from the cross-correlation result, and finding Echo effective parameter; the adaptive filter estimates the echo value based on this parameter. Therefore, this echo canceller and echo estimation method of the present invention can accurately locate the effective echo part, and only perform echo cancellation on the effective part of the echo, which not only does not affect the effect of echo cancellation, but also improves efficiency and saves a lot system cost. Since the present invention adopts the down-sampling method, the amount of computation and data storage can be reduced when performing delay search.
附图说明Description of drawings
图1为现有技术通信系统中产生回声的系统示意图;Fig. 1 is a schematic diagram of a system that generates an echo in a prior art communication system;
图2为现有技术回声消除器的结构框图;Fig. 2 is the structural block diagram of prior art echo canceller;
图3-1为发送理想脉冲激励信号的示意图;Figure 3-1 is a schematic diagram of sending an ideal pulse excitation signal;
图3-2为图3-1所发送的理想脉冲激励信号的响应示意图;Figure 3-2 is a schematic diagram of the response of the ideal pulse excitation signal sent in Figure 3-1;
图4为本发明回声消除器一个较佳实施例的结构框图;Fig. 4 is a structural block diagram of a preferred embodiment of the echo canceller of the present invention;
图5为本发明回声消除器的外部应用示意图;5 is a schematic diagram of the external application of the echo canceller of the present invention;
图6为本发明进行互相关运算的原理示意图;Fig. 6 is a schematic diagram of the principle of cross-correlation calculation in the present invention;
图7为本发明进行回声估计的过程示意图。Fig. 7 is a schematic diagram of the echo estimation process in the present invention.
具体实施方式Detailed ways
为使本发明的目的、技术方案和优点更加清楚明白,以下举实施例,并参照附图,对本发明进一步详细说明。In order to make the object, technical solution and advantages of the present invention clearer, the following examples are given and the present invention is further described in detail with reference to the accompanying drawings.
图4为本发明回声消除器一个较佳实施例的结构框图,如图4所示,本发明的回声消除器包含:一个自适应滤波器402、一个远端输入信号缓存401、一个近端输入信号缓存406、一个远端信号降采样处理模块403、一个近端信号降采样处理模块405、一个互相关回声有效部分搜索模块404和一个信号加法器407。Fig. 4 is the structural block diagram of a preferred embodiment of the echo canceller of the present invention, as shown in Fig. 4, the echo canceller of the present invention comprises: an adaptive filter 402, a far-end input signal buffer 401, a near-end input A signal buffer 406 , a far-end signal down-sampling processing module 403 , a near-end signal down-sampling processing module 405 , a cross-correlation echo effective part search module 404 and a signal adder 407 .
其中,远端输入信号缓存401将接收到的远端输入信号作为参考信号发送给自适应滤波器402。近端输入信号缓存401将接收到的近端输入信号发送给自适应滤波器402。远端信号降采样处理模块403将从远端输入信号缓存401接收的远端输入信号进行降采样处理,远端信号降采样处理模块403还可以含一个远端信号低通滤波器,本实施例采用了一个截止频率为1000赫兹的低通滤波器,该模块先将从远端输入信号缓存401接收的远端输入信号进行低通滤波,再进行降采样处理,并将处理后的信号发送给互相关回声有效部分搜索模块404。近端信号降采样处理模块405将从近端输入信号缓存406接收的近端输入信号进行降采样处理,近端信号降采样处理模块405还可以包含一个近端信号低通滤波器,本实施例采用了一个截止频率为1000赫兹的低通滤波器,该模块先将从近端输入信号缓存401接收的近端输入信号进行低通滤波,再进行降采样处理,并将处理后的信号发送给互相关回声有效部分搜索模块404。互相关回声有效部分搜索模块404将收到的上述两种处理后的进行互相关运算,即对上述两种信号进行相关运算,然后从互相关的结果中搜索到回声中的最大值及有效部分,再根据回声的最大值及有效部分产生有效回声参数,并将该参数发送给自适应滤波器402。自适应滤波器402接收远端输入信号缓存401和近端输入信号缓存406发送的信号,以及作为自适应滤波器的反馈信号402的近端输出信号,同时接收有效回声参数,并根据上述信号和有效回声参数产生回声估计值并将其发送给信号加法器407。信号加法器407将从回声消除器外部接收到的混有回声信号的输入信号减去回声估计值进行回声抵消。Wherein, the far-end input signal buffer 401 sends the received far-end input signal to the adaptive filter 402 as a reference signal. The near-end input signal buffer 401 sends the received near-end input signal to the adaptive filter 402 . The remote signal down-sampling processing module 403 performs down-sampling processing on the remote input signal received from the remote input signal buffer 401, and the remote signal down-sampling processing module 403 may also include a remote signal low-pass filter. A low-pass filter with a cutoff frequency of 1000 Hz is adopted. This module first performs low-pass filtering on the remote input signal received from the remote input signal buffer 401, then performs down-sampling processing, and sends the processed signal to Cross-correlation echo effective part search module 404 . The near-end signal down-sampling processing module 405 performs down-sampling processing on the near-end input signal received from the near-end input signal buffer 406, and the near-end signal down-sampling processing module 405 may also include a near-end signal low-pass filter. A low-pass filter with a cutoff frequency of 1000 Hz is adopted. This module first performs low-pass filtering on the near-end input signal received from the near-end input signal buffer 401, then performs down-sampling processing, and sends the processed signal to Cross-correlation echo effective part search module 404 . The cross-correlation echo effective part search module 404 performs a cross-correlation operation on the above-mentioned two processed signals received, that is, performs a correlation operation on the above-mentioned two signals, and then searches for the maximum value and the effective part of the echo from the cross-correlation results. , and then generate effective echo parameters according to the maximum value and effective part of the echo, and send the parameters to the adaptive filter 402 . The adaptive filter 402 receives the signals sent by the far-end input signal buffer 401 and the near-end input signal buffer 406, and the near-end output signal as the feedback signal 402 of the adaptive filter, and simultaneously receives effective echo parameters, and according to the above signals and The effective echo parameters generate an echo estimate and send it to the signal adder 407 . The signal adder 407 subtracts the estimated echo value from the input signal mixed with the echo signal received from outside the echo canceller to perform echo cancellation.
由于在通讯系统中信号的采样率都相对较高,例如在公众电路交换电话网络(PSTN)中的采样率为8k等等。如果系统需要搜索的范围为64ms,那么,在进行互相关的时候需要进行互相关计算和搜索的样点数就为512点,其中,每1ms有8样点。这样计算量太大了,不利于提高系统资源利用率。因此,本发明在进行相关运算前进行一些处理。处理的方式是降采样。Since the sampling rate of the signal in the communication system is relatively high, for example, the sampling rate in the public circuit-switched telephone network (PSTN) is 8k and so on. If the range that the system needs to search is 64ms, then the number of samples that need to be calculated and searched for cross-correlation when performing cross-correlation is 512 points, among which there are 8 samples per 1 ms. In this way, the amount of calculation is too large, which is not conducive to improving the utilization rate of system resources. Therefore, the present invention performs some processing before performing the correlation operation. The way to deal with it is downsampling.
降采样的原理是将原先采样的数据,再进行一次均匀抽取,例如对公众电路交换电话网络(PSTN)中采样率为8k的数据,每四个数据抽取一个,即降4采样。这时,对于进行互相关运算的数据而言,相当于采样率降低到了2kHz,计算量得到了很大的降低,虽然语音信号的频谱能量比较宽,但是其能量比较集中的部分在1000Hz以下,由于它能够保持原来信号频率能量集中的部分,所以在进行有效回声搜索的时候不会影响搜索的结果。如果采用更低的采样率,很可能会影响语音信号能量较为集中的频段,这会影响有效回声的搜索。The principle of downsampling is to extract the original sampled data uniformly again. For example, for the data with a sampling rate of 8k in the public circuit switched telephone network (PSTN), extract one out of every four data, that is, downsample by 4. At this time, for the data for cross-correlation calculation, it is equivalent to reducing the sampling rate to 2kHz, and the amount of calculation is greatly reduced. Although the spectrum energy of the speech signal is relatively wide, the part where the energy is relatively concentrated is below 1000Hz. Because it can keep the concentrated part of the original signal frequency energy, it will not affect the search result when performing an effective echo search. If a lower sampling rate is used, it is likely to affect the frequency band where the energy of the speech signal is relatively concentrated, which will affect the search for effective echoes.
在实际应用中,为了避免降采样后导致采样率过低而造成的频谱泄漏和频谱混叠,以至于影响计算的结果,在进行降采样的时候对输入信号进行低通滤波,由于对于互相关的样点而言采样率实际只有2kHz,所以采用的是通频带不高于1000Hz的低通滤波器来进行低通滤波。同时,由于要保证语音信号集中的频带尽可能的保留下来,所以采用通频带高于800Hz而不高于1000Hz的滤波器,例如,本实施例中采用的1000Hz的低通滤波器。In practical applications, in order to avoid the spectrum leakage and spectrum aliasing caused by the low sampling rate after downsampling, so as to affect the calculation results, the input signal is low-pass filtered when downsampling, due to the cross-correlation In terms of sample points, the sampling rate is actually only 2kHz, so a low-pass filter with a passband not higher than 1000Hz is used for low-pass filtering. At the same time, to ensure that the concentrated frequency band of the speech signal is preserved as much as possible, a filter with a passband higher than 800 Hz but not higher than 1000 Hz is used, for example, a 1000 Hz low-pass filter used in this embodiment.
图5为本发明回声消除器的外部应用示意图,如图5所示,图中虚线为A端向B端发送信号时产生的回声信号,该信号经过回声消除器被抵消。Figure 5 is a schematic diagram of the external application of the echo canceller of the present invention, as shown in Figure 5, the dotted line in the figure is the echo signal generated when the A terminal sends a signal to the B terminal, and the signal is canceled by the echo canceller.
图6为本发明进行互相关运算的原理示意图。其中,a为初始的激励信号,b为响应信号,c为结果,如图6所示,通过从结果c中查找最大值的方法找到ts,随后通过修正,修正的方法为:在回声最大值左右两侧根据通信协议,取距离最远的部分,作为回声有效部分tr,这样就可以找到系统的有效回声部分,找到以后就可以用很小的资源对有效回声部分进行回声消除的工作。FIG. 6 is a schematic diagram of the principle of cross-correlation calculation in the present invention. Among them, a is the initial excitation signal, b is the response signal, and c is the result. As shown in Figure 6, ts is found by finding the maximum value from the result c, and then through correction, the correction method is: in the echo maximum value According to the communication protocol, the left and right sides take the farthest part as the effective echo part tr, so that the effective echo part of the system can be found, and after finding it, the echo cancellation can be performed on the effective echo part with very small resources.
因此,本发明进行回声估计的方法,图7为图4所示实施例进行回声估计的过程示意图。其包括以下步骤:Therefore, for the echo estimation method of the present invention, FIG. 7 is a schematic diagram of the echo estimation process in the embodiment shown in FIG. 4 . It includes the following steps:
首先步骤701和702,对远端输入信号和近端输入信号分别进行降采样,本实施例是先将远端输入信号和近端输入信号分别进行步骤7011、7021,截止频率为1000赫兹的低通滤波,再进行步骤7012、7022,对信号进行降4采样。First step 701 and 702, the remote input signal and the near-end input signal are respectively down-sampled. In this embodiment, the far-end input signal and the near-end input signal are respectively subjected to steps 7011 and 7021, and the cutoff frequency is 1000 Hz. Pass filtering, and then perform steps 7012 and 7022 to down-sample the signal by 4.
然后步骤703,将经过降采样的两种信号进行互相关运算,本实施例中是计算128个样点的互相关。Then in step 703, the two down-sampled signals are subjected to a cross-correlation operation, and in this embodiment, the cross-correlation of 128 sample points is calculated.
接着,步骤704从互相关结果中搜索出回声最大值及有效部分,求出回声有效参数,本实施例中是通过对互相关结果各点幅值进行比较找出回声最大值,在回声最大值左右两侧根据通信协议,取距离最远的部分,作为回声有效部分,将其作为回声有效参数发送给自适应滤波器。Next, step 704 searches out the echo maximum value and the effective part from the cross-correlation result, and obtains the effective parameters of the echo. In this embodiment, the echo maximum value is found by comparing the amplitudes of each point of the cross-correlation result. According to the communication protocol, the left and right sides take the part with the farthest distance as the effective part of the echo, and send it to the adaptive filter as the effective parameter of the echo.
最后步骤705,自适应滤波器根据回声有效参数,查找到其接收的信号的有效回声部分,同时根据该有效回声部分、远端输入信号、近端输入信号以及作为自适应滤波器的反馈信号的近端输出信号估计出回声值。In the last step 705, the adaptive filter finds the effective echo part of the received signal according to the effective parameters of the echo, and at the same time according to the effective echo part, the far-end input signal, the near-end input signal and the feedback signal as the adaptive filter The echo value is estimated from the near-end output signal.
由此可见,本发明的这种回声消除器及回声估计方法,只对回声的有效部分进行回声抵消,不影响回声抵消的效果,提高了效率,大量节省了系统成本。由于本发明采用了降采样的方法,所以在进行延时搜索的时候可以减少计算量和数据的存储量。同时,在降采样之前进行低通滤波保证了信号不会因为降采样的原因而产生频谱混叠以至于影响延时估计的准确性。It can be seen that the echo canceller and the echo estimation method of the present invention only perform echo cancellation on the effective part of the echo without affecting the effect of echo cancellation, which improves efficiency and saves a lot of system cost. Since the present invention adopts the down-sampling method, the amount of computation and data storage can be reduced when performing delay search. At the same time, performing low-pass filtering before down-sampling ensures that the signal will not generate spectrum aliasing due to down-sampling so as to affect the accuracy of delay estimation.
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