Abstract:
Processing requirements for echo cancellation in voice communications are significant and are even more so as the bandwidth of the communication increases. Whilst voice communication occupies a relatively narrow band of frequencies the processing requirements and so forth for wideband communication render echo cancellation difficult to achieve in a cost effective manner. The invention provides for provides echo cancellation within wideband communications by dividing the communications into sub-bands and applying echo cancellation to some sub-bands whilst processing other sub-bands according to the status of the communications. Additional sub-bands are transmitted at either full-duplex or half-duplex.

Description:
FIELD OF THE INVENTION 
       [0001]    The invention relates generally to audio communication and more particularly to acoustic echo cancellation within wideband audio communication. 
       BACKGROUND 
       [0002]    In audio communication, there is a known problem of echo. Echo is particularly problematic when speakerphone (“handsfree”) functionality is used because voice data from both ends of a communication path is incident on a microphone at either end. To solve the echo problem, digital signal processing is used to subtract what is perceived by the digital signal processing to be echo related noise. To this end, converging processes have been designed to, over time, converge on an echoless or near echoless communication. As new processes have been designed, a time to converge and a quality of echoless communication has greatly improved. 
         [0003]    Unfortunately, though a lot of research has been done in echo cancellation for voice communications having very limited bandwidth, complexity, processing requirements, and memory requirements increase as a supported bandwidth of the communication increases. Thus for wideband communication the processing requirements and so forth render echo cancellation difficult to achieve in a cost effective manner. 
         [0004]    It would be advantageous to provide a voice communication system that overcomes some of the limitations of the prior art. 
       SUMMARY OF THE INVENTION 
       [0005]    In accordance with an embodiment of the invention there is provided a method comprising: receiving at a first port a first signal representative of a first audio signal; receiving a second signal representative of a second audio signal for transmission; performing echo cancellation of the second signal within at least a first band of audio frequencies; detecting within at least one of the first signal and the second signal speech activity within at least a predetermined band; when speech activity is detected other than providing portions of the first audio signal within a second other band, at least some of the second other band outside the first band, to a loudspeaker while providing portions of the first audio signal within the first band to the loudspeaker; and when acoustic activity is other than detected providing portions of the first audio signal within the second other sub-band to a loudspeaker while providing portions of the first audio signal within the first band to the loudspeaker. 
         [0006]    In accordance with another embodiment of the invention there is provided a method comprising: filtering a first signal representative of a first audio signal from a first location into a plurality of sub-band signals, each sub-band signal representing the portion of the first signal within a predetermined range of acoustic frequencies; filtering a second signal representative of a second audio signal from a second location into a plurality of sub-band signals, each sub-band signal representing the portion of the second signal within a predetermined range of acoustic frequencies; transmitting a predetermined portion of the plurality of sub-band signals of each of the first audio signal and the second audio signal to the other location in a half-duplex arrangement; and transmitting the remainder of the plurality of sub-bands of at least one of the first audio signal and the second audio signal to the other location in a full-duplex arrangement. 
         [0007]    In accordance with another embodiment of the invention there is provided a method comprising: receiving a first signal representative of a first audio signal; receiving a second signal representative of a second audio signal; performing echo cancellation of the second signal within a first band of audio frequencies; detecting within the first signal acoustic activity within the first band of audio frequencies; when acoustic activity is detected other than providing portions of the first audio signal within a second other band, at least some of the second other band outside the first band, to a loudspeaker while providing portions of the first audio signal within the first band to the loudspeaker; and, when acoustic activity is other than detected providing portions of the first audio signal within the second other band to a loudspeaker while providing portions of the first audio signal within the first band to the loudspeaker. 
         [0008]    In accordance with another embodiment of the invention there is provided a method of transmitting acoustic information comprising: transmitting acoustic information within a first band and third band of frequencies in full duplex; and transmitting acoustic information within a second and fourth other band of frequencies and having half-duplex echo cancellation applied thereto. 
         [0009]    In accordance with another embodiment of the invention there is provided a method of transmitting acoustic information comprising: transmitting acoustic information within a first band of frequencies in full duplex; detecting voice activity within the first band; and controlling switched loss within at least another band of frequencies of the acoustic information in dependence upon the detected voice activity. 
         [0010]    In accordance with another aspect of the invention there is provided a system for transmitting acoustic information within a first band of frequencies in full duplex; detecting voice activity within the first band; and controlling switched loss within at least another band of frequencies of the acoustic information in dependence upon the detected voice activity. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]    Exemplary embodiments of the invention will now be described in conjunction with the following drawings, in which: 
           [0012]      FIG. 1A  depicts a typical environment within which a speakerphone is employed; 
           [0013]      FIG. 1B  depicts an echo cancellation approach according to the prior art; 
           [0014]      FIG. 2  depicts an embodiment of the invention employing two sub-bands, a first band operating in half-duplex and a second other sub-band operating in full duplex with echo cancellation; and, 
           [0015]      FIG. 3  is a simplified flow diagram of an embodiment of the invention with two sub-bands. 
       
    
    
     DETAILED DESCRIPTION OF INVENTION 
       [0016]    The following description is presented to enable a person skilled in the art to make and use the invention, and is provided in the context of a particular application and its requirements. Various modifications to the disclosed embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be applied to other embodiments and applications without departing from the scope of the invention. Thus, the present invention is not intended to be limited to the embodiments disclosed, but is to be accorded the widest scope consistent with the principles and features disclosed herein. 
         [0017]    The term multipath is used in the description below and in the claims to refer to audio information received at a transducer along more than a single path from a same source allowing for different delay between same audio information received via different paths. 
         [0018]    The term videoconferencing as used herein or in the claims that follow refers to a video communication between two or more parties, at least two of the parties remote from one another such that an audio and a video signal is transmitted electronically therebetween. 
         [0019]    The term band is used herein to refer to a grouping of frequencies. Though typically a band will consist of a contiguous range of frequencies, band, as used herein also refers to non-contiguous ranges of frequencies and is intended to be interpreted as a set of frequencies falling within a predetermined range or group of ranges. 
         [0020]    Referring to  FIG. 1A , a simplified diagram of a first end of a communication connection is shown. A second distant end (not shown) is essentially similar in content to the first end shown. In  FIG. 1 , a room  100  is shown having a speaker phone therein. The speaker phone in the form of a conferencing system comprises a microphone  112  on a desk or table  102  and located for proximity to a person speaking (not shown), an optional video monitor  114  for displaying an image is shown for when the conferencing system comprises video conferencing, and one or more audio loudspeakers  116  for playing sounds from the second distant end of the communication connection. Of course, when video conferencing is not supported, the video monitor is optionally omitted. It is known that loudspeaker  116  may or may not be part of a same physical device comprising the microphone  112 . 
         [0021]    Sound emitted by the loudspeaker  116  is not perfectly focused and, as shown at  116   a,    116   b,  and  116   c,  traverses a plurality of paths. The signal  116   a  reflects off of wall  104  and is then incident upon microphone  112 . The signal  116   b,  reflects off of walls  104  and  108  and is then incident upon microphone  112 . The signal  116   c  reflects off walls  106  and  108  and is then incident upon microphone  112 . As is evident, each of these signals traverses a different path length and is incident on the microphone at different angles. It will be evident to those of skill in the art that a number of signals incident on the microphone  112  is not limited to three signals and includes signals that traverse a straight path between the loudspeaker  116  and microphone  112  and signals having reflections, attenuations, and so forth along their path. 
         [0022]    When several acoustic paths lead to the microphone  112  the effects are noticeable and difficult to characterize. This is further aggravated with the introduction of one or more further loudspeakers. Further, when sound originating from the far end of the communication path is resent to the far end of the communication path, an echo results which is uncomfortable for a user of the system. Because of this problem, most modern speakerphones employ echo cancellation to cancel voice signals in the room that are likely reflective of echo. When no multipath exists, data indicative of the signal provided to the speaker  116  is provided to a processor for being subtracted from a signal provided by the microphone  112 . Unfortunately, due to multipath and other acoustic effects observed in a speakerphone such as speaker distortion, echo cancellation is not a simple task. 
         [0023]    Shown in  FIG. 1B  is simplified block diagram of a prior art echo cancellation speakerphone  155 . A user (not shown) speaks in a room (not shown) comprising walls  153  and objects  154  and speakerphone  155  (not shown to scale) that is in communication via a network  156  and to a second user system  157 . 
         [0024]    The speakerphone  155  is coupled to the network  156  via a network interface  158 . Electrically coupled to the network interface  158  is controller  159  comprising a transceiver for providing an Rx signal to DSP circuit  160  and for transmitting a TX signal via the network interface  158  and the network  156  to a destination system in the form of the remote user system  157 . The Rx signal and the TX signal comprise data relating to an audio signal received from or for provision to the remote user system  157 . The DSP circuit  160  is coupled to loudspeaker  161  and microphone  162 . Typically, DSP circuits comprise digital to analogue (DAC) and analogue to digital (ADC) conversion circuitry. When this is not the case, an external DAC and ADC circuit is employed. Optionally, the external DAC is part of the loudspeaker  161 . Further optionally the ADC is part of the microphone  162 . The DSP circuit  160  processes the Rx signal from the second user system  157  to provide to the loudspeaker  161  a loudspeaker signal and processes the digitized signal from the microphone  162  to generate a TX signal to be provided to the controller for transmission to the second user system  157 . The DSP circuit  160  reduces an echo portion of the TX signal based on the Rx signal and an echo cancellation process. Additional processing is often employed to remove residual echo not removed by the echo cancellation process. When an adaptive echo cancellation process is used, the echo cancellation process converges over time to adjust for different room dynamics. 
         [0025]    Referring to  FIG. 2 , a simplified block diagram of an echo cancellation system according to the invention is shown. The echo cancellation system provides a speaker signal representative of an audio signal that is provided to a loudspeaker (not shown) from port  200 A and receives an audio signal indicative of a sound impinging on a microphone (not shown) at port  200 B. The speaker signal and audio signal comprise the signals received/provided at interfaces at a local end of a communications link. A distant end of the communications link is provided a signal via the communications link to the echo cancellation system for use in echo cancellation. This signal comprises an Rx signal  205  received at port  200 C. Further a Tx signal is provided from the echo cancellation system to the network via port  200   d.  When more than one speaker is used, a same signal is optionally provided to each speaker. Alternatively, each speaker receives a different signal. Further alternatively, each speaker receives a different signal generated by a different circuit. Similarly, when more than one microphone is used, each microphone provides a different signal to a separate circuit for digitization thereof and for processing thereof to perform echo cancellation. Alternatively, the microphone signals are multiplexed to a same circuit for digitization and processing thereof. Preferably, for a plurality of microphones, a plurality of identical processing paths is provided, one for each microphone. 
         [0026]    Considering initially the path for the Rx signal from port  200 C to port  200 A, the Rx signal is coupled to first filter bank  201  wherein it is separated into at least two bands, a first band and a second other band, with the first band selected a priori such that it contains more speech energy than the second other band. In a system dividing the signal into only two bands, this is generally the lower-frequency band. Optionally, the filter bank separates the signal into more than two bands. A second band is coupled to first variable gain stage  219  for attenuating the signal in accordance with a control signal received from HDX Echo Control  221 . From the variable gain stage  219  the signal propagates to first summation circuit  202  before being coupled to port  200 A as part of the signal provided to the loudspeaker. The first band from the filter bank  201  is converted by first down-converter  204 , resulting in a lower sample-rate, then adjusted via second variable gain stage  210  before being re-converted to the original sample rate, using first up-converter  203  and coupled to the first summation circuit  202  as the remainder of the signal provided to the loudspeaker. Additionally the down-converted first band from the first filter bank  201  is coupled to first HDX control block and the AEC control block. The first band from the first filter bank  201  once amplified by the variable gain stage  210  is provided to adaptive echo canceller  209  for use in canceling of echo within a transmit path. 
         [0027]    Similarly the audio signal received at port  200 B is processed by the echo cancellation system to provide the TX signal at port  200 D. In this path the audio signal is coupled to a second filter bank  205  wherein the audio signal is separated into a third band and a fourth band. Also the claims seem to refer only to bands  1  and  2 —please double-check. Typically, the third band spans an approximately same range of frequencies as the first band. Therefore, it is ideal when filter bank  205  and filter bank  201  are similar filter circuits. Optionally, the audio signal is separated into more than two bands. The fourth band is coupled to third variable gain stage  220  for attenuating the signal in accordance with a control signal received from HDX Echo Control  221  and then to second summation circuit  206  to form part of the TX signal. The third band from the second filter bank  205  is initially down-converted by down-converter  207  before being coupled to mixer  211 . The signal within the third band is also provided to the AEC control block  213 . Mixer  211  also receives a signal from the adaptive echo canceller  209 . The mixed signal from the mixer  211  is then input to a residual echo control stage (prior art)  222  before being up-converted via up-converter  208  and provided to the second summation circuit  206  to form the remainder of the TX signal  214 . Additionally, the output signal from the mixer  211  is coupled to second VAD  217 . The AEC  209 , AEC control block  213  and the HDX echo control block  221  are optionally implemented using various methods many of which are well known. 
         [0028]    The output signal from the first VAD  218  and second VAD  217  are input to a half-duplex (HDX) echo controller  221  and to adaptive echo canceller (AEC) controller  213 . The HDX echo controller  221  based upon these inputs determines control signals to be applied to the first variable gain stage  219  and the third variable gain stage  220 . Optionally, the HDX echo controller  221  also determines control signals for the amplifiers  210  and  222 . The AEC controller  213  provides a control signal to adaptive echo canceller (AEC)  209  which processes a tapped portion of the first band from the first filter bank  201  after the second variable gain stage  210  and couples a result of the processing to the mixer  211 . 
         [0029]    The HDX echo controller  221  determines gain settings for the first variable attenuation stage (i.e, max gain for these components is 0 dB) and for the third variable gain stage  220 . This allows for an adjustment to an amplitude (volume) of those signals before being summed at first summation circuit  202  and at second summation circuits  206 , respectively, to provide the received Rx signal to the speaker signal output port  200 A and TX signal output port  200 D. By controlling the amplifier in a digital fashion, the signals provided to variable gain stage  219  and to variable gain stage  220  are optionally one of “on” and “off” supporting half duplex communication for the second band and for the fourth band. When operated in half duplex, voice detected at second VAD  217  when there is no voice activity at first VAD  218 , results in turning off variable gain amplifier  219 , and optionally also adding some attenuation at gain amplifier  210 . Voice detected at VAD  218  results in turning off variable gain amplifier  220  and optionally also adding some attenuation at variable gain amplifier  222 . Optionally, when voice is detected at both of VAD  217  and VAD  218  only variable gain amplifier  220  is turned off. Preferably, the first and third bands consist of approximately a same range of frequencies. Of course it will be apparent to those of skill in the art that the block diagram shown is simplified and that other circuit elements such as gain blocks, power sources, out of band filters and so fourth may be added to the overall circuit. Further, other processing of the signals by the DSP is optionally performed but is outside the scope of the present invention. 
         [0030]    The present embodiment allows the portions of the band wherein adaptive echo cancellation is performed to propagate through paths designed according to well known echo cancellation arrangements and architectures. Further, the present embodiment allows the portions of the band wherein half duplex operation is supported to propagate through paths designed according to well known half duplex arrangements and architectures. Of note in the above described embodiment the signals are separated into at least two bands and at least one of said bands is provided to a circuit for echo cancellation and another of said bands is provided to a circuit for operation in a half duplex mode of communication. The first band is provided for acoustic echo cancellation using a known technique within the prior art or another technique suitable for acoustic echo cancellation. The second band does not have adaptive echo cancellation applied thereto and, instead, a half-duplex echo cancellation mechanism is applied. Such a half-duplex echo cancellation being for example switched loss and/or non-linear processing (NLP). Since half-duplex echo cancellation relies upon decisions about voice activity, such as is there activity and if so in which communication direction—Tx or Rx, the HDX echo controller  221  receives indication of voice activity in each of the Tx and Rx signals, the voice activity detected outside the bands to which HDX echo control is applied. 
         [0031]    Optionally, the approach outlined supra in respect of echo cancellation system is extended to three or more bands. In such a case, acoustic echo cancellation is performed on one band and the HDX echo controller  221  optionally controls each of the other bands. The control decisions are based upon measurements from one or more of the bands including at least one band outside the bands for which half-duplex echo cancellation is performed. Alternatively, a plurality of the sub-bands has adaptive echo cancellation performed thereon and one or more of the other sub-bands is operated in half duplex mode. 
         [0032]    Alternatively, in the embodiment of  FIG. 2 , the downsampling operation on the Rx path (at  201 ), is omitted as is the upconverting at  203  in the same path. 
         [0033]    Beneficially the invention allows a wideband audio bandwidth wider than a mere telephony band supporting full-duplex communication within some bands to be achieved, without the processing requirements or artifacts of wideband audio echo cancellation. 
         [0034]    Illustrated in  FIG. 3  is a simplified flow diagram of an embodiment of the invention for a speakerphone at one end of an audio conference call. At  300  the conference call is initiated between a local user and a remote user. At  301   a  the audio signal from the remote user is received, and then at  303   a  is filtered into bands. At  305   a  a first band associated with a predetermined bandwidth associated with speech is down-converted and at  307  a determination of whether vocal activity from the remote user is present is made. This determination is then employed at  309   a,    309   b,  and  309   c  to determine a course of action. 
         [0035]    At  301   b  the audio signal from the local user is received, and then at  303   b  is filtered into bands. At  305   b  a first band associated with a predetermined bandwidth associated with speech is down-converted and at  307  a determination is made of whether vocal activity from the local user is present. This determination is then employed at  309  to determine a course of action. At  309   a,  half duplex echo control is applied to the second and fourth bands. Adaptive echo cancellation is applied to the first band from the local user at  309   b  and  309   c,  wherein a converging process is used. At  311 , residual echo within the first band from the local user is controlled. 
         [0036]    The respective echo controlled signals are summed to their respective output ports  313 . The flow then returns at  315  for a next sample in time of each of the respective signals. 
         [0037]    Accordingly the first band associated with speech is transmitted continuously and when the speech is remote, echo cancellation is applied using the remote first band signal. The second band is transmitted in half-duplex (HDX). Half Duplex echo control is well known in the art of echo cancellation. 
         [0038]    Alternatively, the second band is operated in half duplex mode based solely on a content of the second band in the local and remote signals. 
         [0039]    Though the above noted embodiments are described with a speaker, more than one speaker is useable with the present invention. Further, the speaker(s) is optionally integrated within a communication device or peripheral thereto. Optionally, the peripheral speaker is wirelessly coupled to the communication device. In an embodiment, some speakers are integrated within the communication device and some are peripheral thereto. 
         [0040]    The network is one of various available communication networks. Examples of communication networks include but are not limited to an Ethernet network, an IP network, a broadband network, a public telephone network, a satellite communication network. 
         [0041]    Though the invention is described with reference to conferencing systems, it is also applicable to video conferencing systems, speakerphones, to hands free telephones or telephones operated in a hands free mode of operation, and to other communication devices providing bidirectional voice communication wherein echo cancellation is advantageous. 
         [0042]    Numerous other embodiments may be envisaged without departing from the spirit or scope of the invention.