Patent Publication Number: US-9412378-B2

Title: Device and method for supplying a reference audio signal to an acoustic processing unit

Description:
The present invention relates to equipment comprising a first interface intended to be connected to a sound reproduction device and at least one second interface intended to be connected to at least one microphone, said equipment comprising an acoustic processing unit adapted for delivering an audio signal filtered by attenuation or suppression of a reference audio signal from an audio signal received via said second interface. 
     At the present time one can find numerous applications for voice recognition thus controlling equipment by voice. The difficulty lies in being able to distinguish these voice commands from a noisy environment. 
     The same type of problem is found in the teleconferencing world. It may sometimes be difficult to clearly distinguish the words of a speaker because of a noisy environment. 
     This noisy environment is often related to an audio or audiovisual content that is reproduced during the teleconference or while the user is transmitting his voice command. Let&#39;s take for example the case of a home-theatre system that one would wish to control by voice. When the home-theatre system is operating, an audible signal is reproduced in the room, potentially with a high sound volume. It would then be difficult for the system to distinguish voice commands in this situation. 
     There exist components for suppressing a reference audio signal using an audio signal captured thanks to one or more microphones. Electronic evaluation boards are available on the shelf on the basis of such components. However, these components and electronic evaluation boards do not enable obtaining a satisfactory result in many installation configurations. This is because, if the example is taken of the aforementioned home-theatre system, the propagation time in air of audible signals issuing from loudspeakers are dependent on the actual location of these loudspeakers and the configuration of these components and electronic boards is often unsuitable, which means that the component does not find the reference signal in the audio signal captured by the microphone. 
     It is therefore desirable to overcome these drawbacks of the prior art. 
     The invention concerns equipment comprising a first interface intended to be connected to a sound reproduction device and at least one second interface intended to be connected to at least one microphone, said equipment comprising an acoustic processing unit adapted for delivering an audio signal filtered by attenuation or suppression of a reference audio signal from an audio signal received via said second interface. The equipment is such that it comprises means for implementing an initialisation phase, comprising: means for determining a propagation latency between an instant of transmission of a first audio signal via said first interface and an instant of reception of a second audio signal via said second interface; means for configuring a buffer with a reading-triggering threshold defined according to said determined propagation latency. The equipment is such that it further comprises means for implementing a nominal operating phase, comprising: means for transmitting a third audio signal via said first interface, said third audio signal being the reference signal after passing through said buffer. 
     Thus it is possible to perfectly adapt the configuration of the equipment to various situations in which the voice of a user must be distinguished in a noisy or even very noisy environment because of an audio signal that the equipment sends to the reproduction device. 
     According to a particular embodiment, said first audio signal consists of a predefined pattern. 
     According to a particular embodiment, said means for determining the propagation latency comprise means for detecting the crossing of an amplitude threshold of said second audio signal. 
     According to a particular embodiment, said means for determining the propagation latency comprise a North filter applied between said first audio signal and said second audio signal. 
     According to a particular embodiment, said means for implementing the initialisation phase are implemented in a control unit connected to an output of the acoustic processing unit so as to receive said filtered audio signal, and the control unit deactivates any transmission of a reference audio signal to said acoustic processing unit during said initialisation phase. 
     According to a particular embodiment, said means for implementing the initialisation phase, said first interface and said means for transmitting the third audio signal are implemented in a first device, and the acoustic processing unit and said second interface are implemented in a second device intended to be connected to said first device. 
     According to a particular embodiment, said microphone(s) being unidirectional, the acoustic processing unit and said microphone(s) are implemented in a box comprising, for each microphone, a first slot and a second slot, and each microphone is installed in a cavity of a support in which a first slot and a second slot are also formed, and placed so as to correspond respectively to said slots in the box when said support is mounted in said box, said support being adapted so that the distances between said first slots and a face of said microphone placed in the direction of an audible signal to be favoured and the distances between said second slots and a face opposite said microphone are substantially identical. 
     The invention also relates to a method implemented by equipment comprising a first interface intended to be connected to a sound reproduction device and at least one second interface intended to be connected to at least one microphone, said equipment comprising an acoustic processing unit adapted for delivering an audio signal filtered by attenuation or suppression of a reference audio signal from an audio signal received via said second interface. The method is such that it comprises an initialisation phase comprising the following steps: determining a propagation latency between an instant of transmission of a first audio signal via said first interface and an instant of reception of a second audio signal via said second interface; configuring a buffer with a reading-triggering threshold defined according to said determined propagation latency. The method is such that it further comprises a nominal operating phase comprising the following step: transmitting a third audio signal via said first interface, said third audio signal being said reference signal after passing through said buffer. 
     The invention also concerns a computer program, which may be stored on a medium and/or downloaded from a communications network, so as to be read by a processor. This computer program comprises instructions for implementing any of the methods mentioned above, when said program is executed by the processor. The invention also relates to storage means comprising such a computer program. 
    
    
     
       The features of the invention mentioned above, as well as others, will emerge more clearly from a reading of the following description of an example embodiment, said description being given in relation to the accompanying drawings, among which: 
         FIG. 1  schematically illustrates a system in which the invention may be implemented; 
         FIG. 2A  schematically illustrates an example of hardware architecture of a source device of the system of  FIG. 1 ; 
         FIG. 2B  schematically illustrates an example of hardware architecture of an acoustic processing device of the system of  FIG. 1 ; 
         FIG. 3  schematically illustrates another example of hardware architecture of a source device; 
         FIG. 4  schematically illustrates an algorithm for initialising the source device; 
         FIG. 5  schematically illustrates an algorithm of nominal operating of the source device; 
         FIG. 6  schematically illustrates a simplified perspective view of a shell of a box in which the acoustic processing device may be installed; 
         FIG. 7A  schematically illustrates a perspective view of a microphone support intended to be placed in the box; 
         FIG. 7B  illustrates schematically another view of the microphone support. 
     
    
    
     In a system in which a reproduction device is intended to reproduce, in the form of an audible signal, an audio signal supplied by source equipment, it is proposed to implement an initialisation phase in which a propagation latency is determined between the emission of the audio signal by the source equipment and the reception of a corresponding audible signal by at least one microphone intended to capture at least the voice of a user in a nominal operating phase. A buffer is then configured with a reading-triggering threshold defined according to the determined propagation latency. Then, in the nominal operating phase, when the equipment transmits an audio signal to the reproduction device, the equipment also transmits it to the buffer, which thus causes a delay. An acoustic processing unit adapted for delivering an audio signal filtered by attenuation or suppression of a reference audio signal from a received audio signal is used, with, as input, what is captured by the microphone or microphones and with, as reference signal, the signal delayed by the buffer. 
       FIG. 1  schematically illustrates a system in which the invention may be implemented. 
     The system in  FIG. 1  comprises an audio or audiovisual signal source device  103 . According to a first example, the source device  103  is a digital decoder adapted for receiving and decoding audiovisual signals coming from a satellite link or an Ethernet link to a home gateway via which audiovisual contents are received from the Internet. According to a second example, the source device  103  is a Blu-Ray (registered trade mark) reader or a computer on which a media player is executed. Any device adapted for supplying an audio signal intended to be reproduced by a sound reproduction device can be used. 
     The system of  FIG. 1  further comprises a sound reproduction device  101 , which may be an audiovisual reproduction device. According to a first example, the sound reproduction device  101  is a screen comprising integrated loudspeakers. According to a second example, the sound reproduction device  101  is a hi-fi amplifier. 
     The source device  103  comprises an interface  151  for being connected to the sound reproduction device  101  by means of a link  141 . The sound reproduction device  101  comprises an interface  110  for being connected to the source device  103  via the link  141 . For example, the link  141  is in accordance with the HDMI (High-Definition Multimedia Interface), WHDI (Wireless Home Digital Interface), SPDIF (Sony/Philips Digital Interconnect Format) or Peritel (registered trade mark) specifications. Thus the sound reproduction device  101  is capable of reproducing any audio signal received from the source device  103  via the link  141 . 
     The system of  FIG. 1  further comprises an acoustic processing device  102  and at least one microphone  111 ,  112 . The acoustic processing device  102  comprises at least one interface  121 ,  122  adapted for connecting the microphone or microphones  111 ,  112 . The acoustic processing device  102  is thus able to receive audio signals corresponding to sound signals captured by the microphone or microphones  111 ,  112 . The acoustic processing device  102  also comprises an interface  123  for being connected to the source device  103  by means of a link  142 . The source device  103  comprises an interface  153  for being connected to the acoustic processing device  102  via the link  142 . For example, the link  142  is in accordance with the HDMI, USB (Universal Serial Bus) or IEEE 1394 specifications. 
     The microphone(s)  111 ,  112  enable(s) capturing a sound environment, and in particular the sound signals broadcast by the reproduction device  101  and the voice of a user of the system. 
     The source device  103  and the acoustic processing device  102  may be incorporated in the same box and may further be implemented on a same Printed Circuit Board (PCB), the link  142  then being a track of the Printed Circuit Board. 
       FIG. 2A  schematically illustrates an example of hardware architecture of the source device  103 . 
     The source device  103  comprises an audio signal supplying unit  211  for supplying an audio signal, for example resulting from a demultiplexing and decoding of an audiovisual signal received via a satellite link. The audio signal is supplied to the interface  151  and to the input of a buffer  202  of the FIFO (First-In First-Out) type of the source device  103 . During an initialisation phase, the audio signal is also supplied to a control unit  203  of the source device  103 . During the initialisation phase, another audio signal, coming from the interface  153 , is also supplied to the control unit  203 . 
     The audio signal supplying unit  211  may further comprise a generator generating an audio signal according to a predefined pattern, usable during the initialisation phase. 
     The aforementioned initialisation phase is detailed hereafter in relation to  FIG. 4 , and a subsequent phase of nominal operating of the source device  103  is detailed hereafter in relation to  FIG. 5 . 
     The source device  103  comprises a processing unit  212  intended to apply a processing to a filtered audio signal, coming from the interface  153 . According to a first example, the processing unit  212  implements a voice recognition mechanism. According to a second example the processing unit  212  implements a shaping mechanism for transmitting the filtered audio signal in the context of a teleconference. 
       FIG. 2B  illustrates schematically an example of hardware architecture of the acoustic processing device  102 . 
     The acoustic processing device  102  comprises an acoustic processing unit  201 , the function of which is to suppress a first audio signal, referred to as reference signal, from a second audio signal. The reference audio signal is supplied by the source device via the link  142 . The second audio signal is the audio signal resulting from the sound signal captured by the microphone(s)  111 ,  112 . The acoustic processing unit  201  then supplies, to the source device  103  via the link  142 , a filtered audio signal, i.e. devoid as far as possible of the reference audio signal, when this reference audio signal has been detected in the signal captured by the microphone(s). For example, the acoustic processing unit  201  is a component with reference CX20708-21X from the company Connexant. 
     It should be noted that the acoustic processing unit  201  may comprise an internal buffer performing the processing operations expected by the acoustic processing unit  201 . However, this internal buffer serves only to store the audio signals during a predefined time window, for example around 200 ms, so as to carry out these processing operations. No reading-triggering threshold is associated therewith and cannot be configured. 
       FIGS. 2A and 2B  are respectively complementary examples of hardware architecture of the source device  103  and of the acoustic processing device  102 . A different distribution of the functions implemented can be envisaged. For example, the control unit  203  and/or the FIFO  202  can be implemented in the acoustic processing device  102 . The arrangement according to  FIGS. 2A and 2B  does however have the advantage of allowing easy update of devices supplying audio or audiovisual contents already deployed, for example in private households. This is because, taking the example of satellite decoders or of television over IP (Internet Protocol), these implement numerous functions by software. It is then easy to upgrade this software in order to implement the functions described herein in relation to the source device  103 . It would then be sufficient to add thereto the acoustic processing device  102  in order to implement the invention, without having to replace the hardware platform of these decoders. 
     The term “equipment” will be used to designate either a device or a set of devices implementing these functions. 
       FIG. 3  schematically illustrates another example of hardware architecture of the source device  103 , which then comprises, connected by a communication bus  310 : a processor or CPU (Central Processing Unit)  300 ; a random access memory RAM  301 ; a read-only memory  302 , a storage unit or a storage-medium reader, such as a Hard Disk Drive HDD  303 ; a first interface  304  for communicating via the link  141 ; and a second interface  305  for communicating via the link  142 . 
     It should be noted that the acoustic processing device  102  can be implemented with a similar hardware architecture. 
     In the context of the architecture presented in  FIG. 3 , the FIFO  202  can be implemented within the second interface  305  or within the RAM  301 , for example in the form of a concatenated list. 
     The processor  300  is capable of executing instructions loaded into the RAM  301  from the ROM  302 , from an external memory (not shown), from a storage medium such as the hard disk drive HDD  303 , or from a communications network. When the source device  103  is powered up, the processor  300  is capable of reading instructions from the RAM  301  and executing them. These instructions form a computer program causing the implementation, by the processor  300 , of all or some of the algorithms and steps described hereafter. All or some of the algorithms and steps described hereafter can be implemented in software form by the execution of a set of instructions by a programmable machine, such as a DSP (Digital Signal Processor) or a microcontroller, or be implemented in hardware form by a machine or a dedicated component, such as an FPGA (Field-Programmable Gate Array) or an ASIC (Application-Specific Integrated circuit). 
       FIG. 4  schematically illustrates an algorithm implementing an initialisation phase  400  of the source device  103 . 
     In a step  401 , the source device  103  sends an audio signal via the interface  151 . This audio signal preferably corresponds to a predefined pattern. This audio signal may also a priori be unknown to the source device  103 , for example resulting from a demultiplexing and decoding of an audiovisual signal received by the source device  103  via a satellite link. In the architecture presented in  FIG. 2A , the source device  103  also sends the audio signal to the control unit  203 . 
     In a following step  402 , the source device  103  determines information representative of an instant at which the source device  103  has sent the audio signal via the interface  151 . The audio signal sent by the source device  103  is therefore intended to be reproduced by the reproduction device  101 . The reproduction device  101  decodes the audio signal transmitted by the source device  103  and generates a corresponding sound signal, the microphone(s)  111 ,  112  being adapted for capturing this sound signal. 
     In a following step  403 , the source device  103  performs, or requests, a sound-environment capture. To do so, the source device  103  instructs the acoustic processing device  102 , via the link  142 , to start a sound-environment capture thanks to the microphone(s)  111 ,  112 . During this initialisation phase, the source device  103  does not transmit any reference audio signal to the acoustic processing device  102  via the interface  153 . The acoustic processing device  102  then retransmits directly to the source device  103  the audio signal corresponding to the sound signal captured by the microphone(s)  111 ,  112 , no reference audio signal having to be suppressed from the sound signal captured by the microphone(s)  111 ,  112 . In the architecture presented in  FIG. 2A , the source device  103  sends the audio signal received from the acoustic processing device  102  to the control unit  203 . 
     In a following step  404 , the source device  103  determines information representative of an instant at which the acoustic processing device  102  has received the audio signal thanks to the microphone(s)  111 ,  112 . It can be considered that the instant at which the acoustic processing device  102  has received the audio signal thanks to the microphone(s)  111 ,  112  is the same as that at which the source device  103  has received the audio signal via the interface  153 . It is then considered that the processing operations performed by the acoustic processing device  102  have negligible latency. If such is not the case, the source device  103  has, by configuration, knowledge of this latency and can thus take it into account. 
     In order to determine the instant at which the acoustic processing device  102  received the audio signal thanks to the microphone(s)  111 ,  112 , the source device  103  detects an instant at which the audio signal received by the interface  153  is above a predefined threshold. The source device  103  then considers that this instant of crossing said predefined threshold is the one at which the acoustic processing device  102  received the audio signal thanks to the microphone(s)  111 ,  112 . According to a variant embodiment, the source device  103  makes a correlation between the audio signal sent via the interface  151  and the audio signal received via the interface  153 , in order to determine to which time window the audio signal sent corresponds in the received audio signal. To do so, a matched filter, also referred to as North filter, can be applied. The use of such a filter advantageously maximises the signal to noise ratio. Other correlation methods may be used. 
     In a following step  405 , the source device  103  determines information representative of a propagation latency, which is the difference between the instant at which the acoustic processing device  102  received the audio signal thanks to the microphone(s)  111 ,  112  and the instant at which the source device  103  sent the audio signal via the interface  151 . This propagation latency is determined thanks to the information determined in steps  404  and  402  respectively. 
     In a following step  406 , the source device  103  determines information representative of a triggering threshold of the FIFO  202 , to be implemented during the nominal operating phase of the source device  103 . This triggering threshold of the FIFO  202  is determined according to the propagation latency determined at the step  405 , and enables applying a delay to the reference audio signal to be transmitted to the acoustic processing device  102  via the interface  153 . If the propagation time between the source device  103  and the acoustic processing device  102  is neglected, this delay is equal to the propagation latency determined at the step  405 . Otherwise this delay is equal to the propagation latency determined at the step  405  from which a predefined value of the propagation time between the source device  103  and acoustic processing device  102  is subtracted. 
     Then, the source device  103  configures the FIFO  202  so that, in the nominal operating phase, the triggering threshold determined at the step  405  is applied. The initialisation phase is then ended and the nominal operating phase can begin. 
     The source device  103  may supply to the user an indication that the initialisation phase is under way, for example by means of an LED (Light Emitting Diode) of a user interface. This can enable the user to know whether he must limit any ambient noise in order to facilitate the detection of the audio signal expected in return by the source device  103 . 
     In the architecture presented in  FIG. 2A , the steps  402 ,  404 ,  405  and  406  are performed by the control unit  203 . 
       FIG. 5  schematically illustrates an algorithm of nominal operating of the source device  103 , once the initialisation phase has been executed. 
     In a step  501 , the source device  103  activates the filling of the FIFO  202 . No data item is then present in the FIFO  202 . 
     In a following step  502 , the source device  103  activates the sound signal capture thanks to the microphone(s)  111 ,  112 . To do this, the source device  103  sends to the acoustic processing device  102  an instruction to trigger such a capture. An audio signal corresponding to the sound signal captured by the microphone(s)  111 ,  112  is then received by the acoustic processing unit  201 . 
     In a following step  503 , the source device  103  activates the sending of an audio signal to the reproduction device  101  via the interface  151 . This audio signal results for example from a demultiplexing and decoding of an audiovisual content received or read by the source device  103 . The source device  103  having activated the filling of the FIFO  202 , the audio signal is also stored in the FIFO  202 . 
     In a following step  504 , the source device  103  checks whether the filling threshold of the FIFO  202  determined at the step  406  is reached. If such is the case, a step  505  is performed; otherwise the step  504  is reiterated. 
     In the step  505 , the source device  103  activates the reading of the FIFO  202 . The data stored in the FIFO  202  are then transmitted as a reference audio signal to the acoustic processing device  102  via the interface  153 . This reading of the FIFO  202  takes place at the rate at which the data of the audio signal are written in the FIFO  202 . A time delay, the duration of which is adapted so as to compensate for the propagation latency determined at the step  405 , is thus applied to the audio signal supplied by the source device  103  to the acoustic processing device  102 . 
     Thus, thanks to the application of this delay, the audio signals input to the acoustic processing unit  201  are sufficiently synchronised to enable the acoustic processing unit  202  to suppress the reference audio signal from the audio signal corresponding to the sound signal captured by the microphone(s)  111 ,  112 . In this way, the audio signal supplied to the processing unit  212  is filtered and substantially devoid of the sound signal corresponding to the audio signal reproduced by the reproduction device  101 . A slight noise may however remain through the distortions in the sound signal captured by the microphone(s)  111 ,  112  with respect to the reference audio signal. Then, when the user wishes to use voice commands or participate in a teleconference, his voice can be clearly distinguished in the audio signal, even if the sound volume of the reproduction device  101  is high. 
       FIG. 6  schematically illustrates a simplified perspective view of a shell of a box  600  in which the acoustic processing device  102  may be installed. 
     The shell of the box  600  comprises a first part  601  and a second part  602 . The two parts  601  and  602  are intended to be connected to each other, for example by adhesive bonding, or by means of assembly screws, or using clips. 
     Preferably, said first part  601  serves as a cover for said second part  602 . The external thickness of this first part is shown in broken lines in  FIG. 6 . The acoustic processing device  102  consists of an electronic board on which components fulfilling the previously described functions are mounted. The electronic board is mounted on the internal face of said first part  601 . The electronic board may be assembled with said first part  601  by means of assembly screws, rivets or clips. 
     The microphones  111 ,  112  are also integrated in the box  600 , the shell of which comprises, for each microphone  111 ,  112 , a first slot  610  and a second slot  611 . These slots  610 ,  611  enable the microphones  111 ,  112  to capture the sound environment, as described hereafter in relation to  FIGS. 7A and 7B . In the illustration in  FIG. 6 , the slots  610 ,  611  are formed in said second part  602  of the shell. 
       FIG. 7A  schematically illustrates a perspective view of a microphone support  701  intended to be placed in the box  600 . Each microphone  111 ,  112  is then unidirectional and has an associated support  701 . 
     The support  701  intended to receive the microphone  111  or  112  in an adjusted manner is preferably manufactured from rubber, so as to isolate the microphone  111  or  112  from vibrations transmitted by mechanical parts of the box  600 . Microphones with the reference CM1045RFH-35BL-C56F1K-LF from the company MWM Acoustics are for example used. 
     On one face of the support  701 , two slots  710 ,  711  are formed, intended to be respectively placed so as to match the slots  610 ,  611  formed in the shell of the box  600 , when the support  701  is installed in the box  600 . 
     The support  701  has a cavity  702  emerging on the slots  710 ,  711 , and intended to receive the microphone  111  or  112 . Once installed in the cavity  702 , the microphone  111  or  112  is disposed so that a face of the microphone  111  or  112  in the direction of the sound signal to be favoured is inline with the slot  711  and therefore with the slot  611 ; furthermore, the microphone  111  or  112  is disposed so that the face of the microphone  111  or  112  opposite to the direction of the sound signal to be favoured is inline with the slot  710  and therefore the slot  610 . In typical designs of unidirectional microphones this face opposite to the direction of the sound signal to be favoured comprises a hole that enables the sounds other than those to be favoured to enter through the rear, i.e. those that come from directions other than the one from which the sound signal to be favoured comes. In other words, this hole attenuates the ambient noise without eliminating it. To do so, it is however necessary for the propagation times of the sound signal from the slots made in the shell of the box  600  and the aforementioned two faces of the microphone  111 ,  112  to be substantially identical, i.e. for the distances between these slots and these faces to be substantially identical. The arrangement of the support  701  enables achieving this objective. The term “substantially” means that any difference existing is negligible with regard to the reactivity of the microphone. 
     The combination of the support  701  as presented and at least one microphone  111 ,  112  thus enables highlighting the sound signal (the voice of the user in the system of  FIG. 1 ) in the direction favoured by the unidirectional microphone(s)  111 ,  112 . “Highlighting” means bringing out the voice of the user with respect to the other sounds in the sound environment. This facilitates the processing carried out by the acoustic processing device  102 . 
       FIG. 7B  schematically illustrates another view of the microphone support  701 . It is clear, more prominently in this view, that the slot  711  is preferably formed by a step, or recess. The slot  711  is thus definitively formed when the support  701  is mounted in abutment on the internal face of the first part  601  of the shell of the box  600 . 
     It should be noted that the support  701  can be used to install a unidirectional microphone in a box without implementing the processing operations implemented by the source  103  and acoustic processing  102  devices. This enables improving the prominence of the voice of the user.