Patent Application
20090067615
The present invention relates to reducing echo in a telecommunications system and more specifically relates to reducing echo by controlling microphone gain in a telecommunications system.
An echo results from the delay in a reflected audio signal. Most are familiar with the echo heard when an individual shouts across a valley. The echo is the sound wave reflecting back from the opposing valley wall (the reflection point), delayed by the distance the sound waves must travel back across the valley. The louder the original sound wave and further across the valley, i.e. the extra distance the reflected sound wave must travel, the more noticeable the echo will be. Humans generally will notice an echo with a delay exceeding twenty-five milliseconds (ms).
While an echo does not present a problem in open spaces, it is often unpleasant when heard in a communications system. Assume two people are having a conversation over a network. The network can be Internet Protocol, satellite, or another network type that may result in a delay. On the telephone there is an 80 ms or more (one-way) delay from the reflection point. This is equivalent to yelling across a valley. The individual would hear two different echoes of his own voice. One echo is the electrical echo that occurs at the transition from 2- to 4-wire cable, called a hybrid echo. The hybrid itself is typically located in the Central Office (CO) or another location, e.g. Private Branch Exchange (PBX). The hybrid is the reflection point of the electrical echo. Another echo involved in communication systems is the acoustic echo. The voice coming out of the loudspeaker bounces back from the wall to the microphone. The wall is the reflection point of the acoustic echo.
In the case of both electrical and acoustic echoes, the individual hears his own voice repeated with a delay. If an echo is encountered in the network, echo cancellation may be required. The echo canceller simulates the end echo path with a special algorithm. The signal that is reflected from the hybrid is subtracted from the calculated or simulated signal of the echo canceller. Ideally, the signal at the output of the echo canceller does not contain any echo. Another type of echo filter uses Non Linear Processing (NLP) to remove the echo portion. An NLP removes the audio segment when a user is not talking, similar to that heard on a walkie-talkie with noticeable breaks at the beginning and end of a conversation.
However, the above echo filters may not remove the echo. The echo tail-end delay is the time the voice needs to travel from the echo canceller to the hybrid and back. The tail-end delay can differ depending on the distance between the echo canceller and the hybrid, the quality of the hybrid (dispersion), and the acoustic echo. The capacity of an echo canceller may be limited by the echo tail-end delay (e.g., 64 ms). In addition, NLP filters present an unpleasing interruption between conversation and silence. NLP filters may lack the ability to handle interruptions. In a dialog it may be natural for a listener to interrupt the talker with a response prior to the talker completing the dialogue. The filter may not respond fast enough or may not respond adequately, thus cutting off dialogue of either the talker or listener. Accordingly, there is a need for an efficient system that reduces or limits echo in a communication system. The system may also reduce the echo tail-end delay without cutting off dialogue of a party involved in the communication. The system allows for far end audio and eliminates silence or noise fill providing more natural conversation. The system allows the echo detection and cancellation devices to communication and cooperates with audio gain controls.
Accordingly, the present invention is a novel system and device for reducing echo by controlling gain in a telecommunications system. An exemplary device may have an echo detector for detecting an echo in a transmitted audio communication signal. The exemplary device may also have an echo level detector for determining the volume level of the detected echo. The exemplary device also has a gain control for adjusting the gain of a microphone transmitting the audio communication signal and/or the gain of a speaker broadcasting the communication signal based on the echo level detected. The gain control may communicate and cooperate with echo cancellation devices.
Embodiments of the invention may have one or more of the following features. According to one exemplary embodiment, the gain may be reduced based on the echo level detected. In another embodiment, the gain may be reduced by increments of eight decibels based on the echo level detected. The exemplary device may also have a dynamic echo cancellation filter for reducing the echo introduced into the audio communication signal. In another embodiment, the device may have a dynamic echo cancellation filter for reducing the echo introduced into the audio communication signal and working in cooperation with the gain control. In yet another embodiment, the echo level detector and the gain control are housed within the telephone receiving the transmitted audio communication signal.
These and other features and advantages of the present invention will be better understood by reading the following detailed description, taken together with the drawings wherein:
The echo reduction system of the present invention helps to reduce the disturbance caused by echo in a communication system. The invention reduces the gain of audio signal thereby reducing the volume of the transmitted echo. Often the volume of received audio is above a threshold needed for pleasant and effective communication. By reducing the volume, the parties may still effectively communicate without contributing to the disturbing effect of echo in the communication system. The echo reduction system may work in concert with other echo filter systems to minimize the echo heard and minimize the volume of any echo that cannot be filtered.
Referring to
A second source of echo may result from the audio broadcast by speaker of the second station 112 reflecting off a wall 114 or surface of the second station 112 and being picked up by a microphone of the second station 112. The reflected sound produces an acoustic echo that is picked up by the microphone. Again the acoustic echo may be treated and amplified as a legitimate communication from the second station 112.
Both acoustic echo and electrical echo may produce a disturbing effect to the listener at the first station 102. To reduce the echo effect, the invention reduces the incoming audio gain and/or outgoing audio gain on the side opposite the side receiving the echo. Therefore, the microphone gain and/or speaker gain may be reduced in station 102 to reduce the effects of the echo introduced in station 112.
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If the echo is determined to be above the desired threshold level, the gain of the communication signal is reduced. The reduction in the gain of the communication signal may be accomplished in increments. For example, the gain may be reduced by 4 decibels. If the echo is still above the desired level, the gain may be reduced again by 4 decibels. The total change would be 8 decibels in gain, which would not impair conversation of the users.
The current gain level may also be taken into consideration when deciding to reduce the gain if the echo is above the desired threshold. For example, the echo may be above the desired threshold, however, since the current gain barely meets a desired level for adequate communication, the gain may not be reduced even though the echo is above the threshold level. The gain adjusted by the system is not limited to the gain of the received audio from the microphone and/or speaker at the first station 102. The system may communicate adjustments to other devices that control gain of the signal within the communication path. For example, the system may control the gain of the received audio from the microphone at the second station 110 thereby reducing the effect of acoustic echo.
The system may adjust both microphone gain on the transmitting end and speaker gain on the receiving end. For example, if a large echo is detected, indicating the microphone gain is higher than needed, the microphone gain may be reduced. At the same time the speaker gain, on the end of the speaking user, may be reduced, as during the time the user is talking, it is not important to be able to clearly hear everything. However unlike non-linear processing audio transmission, the speaker may not be muted, just gain reduced, so that if the user at the other end needs to interrupt, their interruption will be heard (although attenuated). Once interrupted and the first user stops talking the system restores the gain of the transmitting users speaker and the other users audio again returns to as clear as possible transmission.
The system may use information about which user is speaking along with the detected echo levels at different points in transmission to determine which gain should be adjusted for microphones and speakers on both ends of the communication path. This allows for noise from echoes to be minimized while allowing for natural conversions with interruptions between users. The system may reduce gain on the microphone of the speaking user and reduce gain on the speaker of the speaking user to minimize gain. Once the speaking user ends talking and the other user begins speaking, the gains of the now silent user, formally speaking user, are return to prior levels and the now speaking user's microphone gain and speaker gains may be reduces to minimize echo effects.
The system is not limited to two-way conversions and may also be used in three or more way conversation. For example, the system may detect which of the three or more users is producing an echo and currently speaking and adjust the gain of the respective microphones and speakers for each of the three or more parties. The adjustment of gains levels may be predetermined or involve incremental adjustments based on successive detection of echo/noise levels.
The gain control and echo detector 200a and 200b may cooperate and communicate with each other to detect echo and adjust audio gain at various points along the signal path. The gain control and echo detector 200a and 200b may be implemented using hardware or software that is used to perform other functions on the communication signal. For example, the gain control and echo detector 200a and 200b may occur within the first DLC 104 or second DLC 108. Additional hardware or software may be implemented within the first DLC 104 or the second DLC 108 so that the first DLC 104 or the second DLC 108 not only processes the audio signal into digital packets but implements features of the invention described herein.
Processing and determination of gain adjustments may be accomplished on either or both ends of the communication path and communicated to equipment along the communication path. In one example, echo and noise detection may be performed by equipment on a specific end of the communication path without regard to which user is speaking. Gains adjustments may be determined by equipment on the specific end and communicated to equipment controlling the gain on the other end. The gain may be communicated by, for example, adjusting the gain within the transmitted signal protocol or communicating directly with an amplifying device on the other end of the communication path.
In another example, echo and noise detection may be performed by equipment on the listening user's end and communicated to the speaking user's end. Equipment on the speaking end may process the levels to determine adjustments to the microphone gain level equipment and adjustments to the speaker gain on the speaking end. When the listening user begins speaking the detection and processing may flip-flop. The system is not limited to the above example.
The gain control and echo detector 200a and 200b may also occur in a separate dedicated device. The device may have input and output ports, memory, a processor, amplifiers, and other components necessary to perform the function of the invention. The memory may store the threshold values and rules for adjusting the gain. The processor may implement the rules and causes components of the device to alter the communication signal based on the rules stored in memory.
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If the echo is not above the desired level (“No” branch of block 408), the process continues to monitor the communication signal for echo levels above the desired value. If the echo is above the desired level (“Yes” branch of block 4080), the process may reduce the gain based on the detected echo levels (block 410). In another example, the process may take into account the gain imparted at multiple points along the communication path and adjust the gain at the points to better amplify the communication signal and not the echo. This may involve reducing the gain at one point in the communications path and communicating to another point in the communications path to increase the gain.
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If the aspects of the echo are not above the desired level or do not interfere (“No” branch of block 512), the process continues to monitor the communication signal for echo levels above the desired value. If the echo tail-end delay is beyond the capacity of the filter (“Yes” branch of block 512), the process may determine if the gain is above the desired echo levels (block 514). If the echo is not above the desired level (“No” branch of block 514), the process continues to monitor the communication signal for unfiltered echo and echo levels above the desired value. If the echo is above the desired level (“Yes” branch of block 514), the gain of the communication signal is reduced (block 516). The method reduces the echo by using cancellation techniques and reduces the interference of any portion of the echo that may not be filtered by the echo cancellation techniques.
The exemplary embodiments described herein can be implemented in digital electronic circuitry, or in computer hardware, firmware, software, or in combinations of them. The exemplary embodiments described herein can be implemented as a computer program product, i.e., a computer program tangibly embodied in an information carrier, e.g., in a machine-readable storage device or in a propagated signal, for execution by, or to control the operation of, communications processing apparatus, e.g., a processing device, a computer, or multiple computers. A computer program can be written in any form of programming language, including compiled, assembled, or interpreted languages, and it can be deployed in any form, including as a stand-alone program or as a module, component, subroutine, or other unit suitable for use in a computing environment. A computer program can be deployed to be executed on one computer or on multiple computers at one site or distributed across multiple sites and interconnected by a communication network.
Modifications and substitutions by one of ordinary skill in the art are considered to be within the scope of the present invention, which is not to be limited except by the following claims.
