Patent Publication Number: US-8112273-B2

Title: Voice activity detection and silence suppression in a packet network

Description:
The present application is a continuation of U.S. patent application Ser. No. 11/773,699, filed Jul. 5, 2007, which is a continuation of U.S. patent application Ser. No. 10/330,957, filed Dec. 27, 2002, now U.S. Pat. No. 7,272,552, which are incorporated herein by reference in their entirety. 
     CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of the following application: System and Method for Improved Use of Voice Activity Detection, Ser. No. 10/331,013, filed Dec. 27, 2002, now U.S. Pat. No. 7,230,955, and Ser. No. 11/742,096, filed Apr. 30, 2007. 
    
    
     FIELD OF THE INVENTION 
     This invention relates generally to telecommunications. More particularly, this invention relates to the improved use of voice activity detection/silence suppression technology. 
     BACKGROUND OF THE INVENTION 
     Network providers, like AT&amp;T, are continually working to improve network efficiency. Consider a typical transmission from a calling party to called party in which voice signals, accompanied by noise, are transmitted. The noise component considered in this application is primarily the background noise of the speaking party. During this typical transmission there are periods of time when the calling party is not speaking but the background noise is still present. Even though no voice signal is being transmitted, the network is still committing the same amount of resources, and transmitting solely the noise signal. Conventional technology has made the network more efficient by reducing the amount of resources allocated to such a transmission during periods of “silence,” i.e., when only a noise signal is present, so that the bandwidth can be used for other transmissions. 
     Conventional technology detects a voice signal in a transmission. This technology, referred to as voice activity detection (VAD) or silence suppression (SS), determines whether an input signal is primarily a voice signal or a noise signal based on one or more parameters. This decision may be based on the current frame as well as a few of the preceding frames, to ensure that there is a significant break in the input voice signal. When the VAD/SS technology determines that no input voice signal is being transmitted, i.e., that just noise is present, instead of using a suitable amount of bandwidth for the particular transmission, the VAD/SS technology informs the receiving end that no signal is going to be transmitted. The VAD/SS technology sends one or more bits, referred to as silence insertion descriptors, that are noise characteristics. The VAD/SS technology, instead of transmitting the noise, or the “lack of voice” over the bandwidth, allocates the bandwidth to another use. At the receiving end, the silence insertion descriptors are converted into a representation of the background noise, also known as comfort noise, representation and transmitted to the called party. 
     In the event that the silence period continues for some time, and there is no significant change in the background noise, then the comfort noise is continually generated. However, if there is a change in the background noise, new silence insertion descriptors will be transmitted to the receiving end. This process avoids a comfort noise that is constant for the benefit of the listener. 
     Although there is bandwidth savings with this technology, suppressing silence in a transmission has another associated characteristic. Suppressing the silence “degrades” the quality of the connection. The parties participating in the transmission become familiar with each voice and the associated background noise. During periods of silence when the silence suppression system either transmits no signal or silence insertion descriptors, the parties will hear a difference in background noise, i.e., either no noise at all or a slightly different background noise. Noise pumping refers to the different sounds created when switching between the presence of noise and absence of noise. Noise contrast refers to the different sounds created when switching between the presence of actual noise and the presence of comfort noise. As noted above, the comfort noise results when the silence insertion descriptors are converted into a noise signal, and this noise is generally not identical to the actual noise. Both the noise pumping and the noise contrast yield audible distinctions that are apparent and undesirable to the parties. 
     Network providers, like AT&amp;T, are interested in using network bandwidth efficiently. This is especially important where bandwidth is limited, such as sub-oceanic fiber cable transmissions given the large cost to place the cable. Network providers are also interested in providing the best quality transmissions possible. Thus, given the foregoing, there is a need in the industry to maintain the bandwidth savings using silence suppression techniques while improving the quality of the signal to the users. 
     BRIEF SUMMARY OF THE INVENTION 
     Limitations of the prior art are overcome and a technical advance is made in accordance with the present invention, illustrative embodiments of which are described below. 
     In general, the present invention is a method and apparatus for improved silence suppression by packetizing voice signals received by an access gateway from a speaking party and transmitting these packetized voice signals via a network to an egress gateway. The egress gateway converts the packetized voice signal into voice signals suitable for output and transmits the output voice signals to a listening party. The invention also includes packetizing actual noise signals, typically background noise, received by an access gateway from a speaking party and transmitting these packetized noise signals via a network to an egress gateway. The egress gateway converts the packetized noise signal into noise signals suitable for output and transmits the output noise signals to a listening party. When the access gateway detects that no voice signal is being received and only a noise signal is being received for a predetermined period of time, the access gateway instructs the egress network to continually transmit output noise signals to the listening party and ceases to transmit packetized noise signals to the egress gateway. 
     In accordance with aspects of one illustrative embodiment, a silence suppression system is disclosed comprising an access gateway, including an access silence suppressor, a network, and an egress gateway, including an egress silence suppressor. The access gateway receives an input voice signal, that includes noise, and also received an input noise signal, that includes no voice. The access gateway packetizes the input voice signal and transmits the packetized voice signal over a network. The access gateway also packetizes the input noise signal and transmits the packetized noise signal over the network. An egress gateway receives the packetized voice signal, converts the packetized voice signal into an output voice signal, and outputs the output voice signal. The egress gateway also receives the packetized noise signal, converts the packetized noise signal into an output noise signal, and outputs the output noise signal. After a predetermined amount of time, if the access gateway continually receives the input noise signal, and not the input voice signal, the access gateway ceases to transmit the packetized noise signal through the network and instructs the egress gateway to continually output the output noise signal. 
     In an alternative embodiment, the present invention is a silence suppression system for a telephone call that includes an access network, including an access silence suppressor, a network, and an egress network, including an egress silence suppressor. The access network receives an input voice signal (including noise) and converts the input voice signal into a packetized voice signal. The packetized voice signal is transmitted via a network to the egress network. The egress network receives the packetized voice signal, converts the packetized voice signal into an output voice signal, and outputs the output voice signal. The egress network also extracts and stores noise packets from the received packetized voice signal and converts the packetized noise signal into an output noise signal. When the access network ceases to receive the input voice signal while the call is still ongoing, the access network instructs the egress network to continually output the output noise signal. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
       The present invention will be more fully understood by reading the following detailed description in conjunction with the drawing, in which: 
         FIG. 1  is a block diagram of a telephone system illustrating the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  represents a telephone system  100  connecting a calling party  102  and a called party  104 . Calling party  102  places a telephone call to called party  104  by dialing a number as is well known in the art. The present invention is applicable for voice transmissions of a variety of different formats besides the traditional analog format, including Voice over Internet Protocol (VoIP), Voice over Frame, Voice over ATM and the like. Once the connection is complete, if appropriate given the particular telephone system, the voice signal from calling party  102  is packetized by access network or gateway  106 . The voice signal, in its packetized version, is transmitted through network  110  and is received at egress network or gateway  108 . Within egress network  108 , the voice signal is converted from a packetized signal into a voice signal. The voice signal is then transmitted to its termination point, called party  104 . 
     More specifically, calling party  102  places a telephone call to called party  104  and the connection is established. Calling party  102  speaks a voice signal that will be transmitted through network  110 . In addition to the voice signal, any noise, such as background noise, present in the calling party&#39;s vicinity is also transmitted through network  110 . Likewise, voice signals and noise signals are also transmitted through network  110  in the reverse direction, from called party  104  to calling party  102 . A conversation thus begins between calling party  102  and called party  104 . At certain times during the conversation, calling party  102  will not be sending a voice signal. The noise signal, however, is continually present and continues to be transmitted. 
     One embodiment of the present invention is as follows. Access network  106  and egress network  108  include a VAD/SS device. The VAD/SS device determines when a voice signal is present and when a voice signal is not present as is known in the art. For example, access network  106  monitors the energy of the input signal received. A certain energy pattern (e.g., level and frequency) is associated with a voice signal and a certain energy pattern is associated with a noise only signal. Vendors use proprietary methods for distinguishing between voice and noise only signals. 
     When the voice signal is not present, the VAD/SS device instructs a packet representing the noise signal to be created. The noise packet contains a sample of the actual noise signal, as opposed to approximate characteristics of the noise. The noise packet is transmitted through network  110  to egress network  108 . Egress network  108  is instructed to convert the noise packet into an output noise signal and to continually transmit the output noise signal to called party  104  until a voice signal is present. 
     In order to prevent clipping of the input voice signal, the VAD/SS method monitors the input signal for voice for a period of time after the voice input ceases, referred to as a hang-over time. In other words, when the voice signal is not present in the input signal, and noise is the only input signal, the VAD/SS device continues to transmit the packetized noise signal through network  110  for an extra period of time. This methodology ensures that there is no voice signal being input, as opposed to a small pause, for example. As a result, this methodology prevents the called party from hearing the calling party&#39;s voice cut in an out, so that called party does not miss the beginning portion of voice signals from the calling party. 
     In an alternate embodiment of the present invention, egress network  108  extracts and stores noise packets from the received voice signal. In a typical conversation, calling party  102  is not sending a continuous voice signal to called party  104 . There are natural breaks or pauses in the voice signal when only a noise signal is being transmitted. During these portions of time when no voice, and only noise is being transmitted to egress network  108 , egress network  108  extracts and stores noise packets. When egress network  108  is informed by access network  106  that there is no voice signal being transmitted through network  110 , egress network  108  converts the stored samples of the actual noise to an output noise signal and continually transmits the output noise signal to called party. When an input voice signal is again received at egress network  108 , the transmission of the stored noise signal to called party ceases and the input voice signal is transmitted to the called party as described above. 
     Although the present invention has been described as calling party  102  initiating the input voice signal and called party  104  received the voice signal, one skilled in the art will appreciate that called party  104  also initiates voice signals that are received by calling party  102 . 
     Although embodiments of the present invention are illustrated in the accompanying Figures and are described in this Detailed Description, it is understood that the present invention is not limited to these embodiments, but is capable of numerous arrangements, modifications, and substitutions without departing from the spirit or scope of the invention as defined in the claims. Various modifications and adaptations of the present invention will be apparent to persons skilled in the art.