Combining signals at a conference bridge

Combining signals includes receiving signals from communication devices, where each signal is associated with a content describing the signal. The following is repeated for each signal: the content associated with a signal is examined, whether the signal is a voice signal is determined in accordance with the content, and the signals are sent to a signal combiner in accordance with the determination of whether the signal is a voice signal. The signals are combined at the signal combiner.

TECHNICAL FIELD OF THE INVENTION

This invention relates generally to the field of telecommunications and more specifically to combining signals at a conference bridge.

BACKGROUND OF THE INVENTION

Conference calls involve combining audio or video signals from multiple communication devices while maintaining the quality of the signals. Signal quality may be affected by, for example, music on hold, ambient noise from a cell phone, or someone typing in the background. Known techniques for avoiding this type of signal degradation involve muting or dropping a particular participant. These known techniques, however, require the intervention of a user. Consequently, known techniques for combining signals may not be suitable in certain situations.

SUMMARY OF THE INVENTION

In accordance with the present invention, disadvantages and problems associated with previous techniques for combining signals at a conference bridge may be reduced or eliminated.

According to one embodiment of the present invention, combining signals includes receiving signals from communication devices, where each signal is associated with a content describing the signal. The following is repeated for each signal: the content associated with a signal is examined, whether the signal comprises a voice signal is determined in accordance with the content, and the signals are sent to a signal combiner in accordance with the determination of whether the signal comprises a voice signal. The signals are combined at the signal combiner.

Certain embodiments of the invention may provide one or more technical advantages. A technical advantage of one embodiment may be that the content of the signals is examined in order to determine whether signals are voice signals. The signals that are voice signals are combined at the conference bridge. By using the content to determine whether the signals are voice signals, the conference bridge may more effectively combine signals while maintaining signal quality.

DETAILED DESCRIPTION OF THE DRAWINGS

Embodiments of the present invention and its advantages are best understood by referring toFIGS. 1 through 5of the drawings, like numerals being used for like and corresponding parts of the various drawings.

FIG. 1is a block diagram of a system10for combining signals. System10includes a conference bridge that has a speech recognition module. The speech recognition module examines the content of signals received from multiple communication devices to determine whether the signals comprise voice signals. The conference bridge combines the signals in accordance with the determination in order to generate a combined signal that is sent to the communication devices.

According to the illustrated embodiment, system10includes communication devices20a-cthat communicate with a conference bridge30through communication networks22a-c. A communication device20a-cmay send and receive audio signals, video signals, or any combination of the preceding. The signals may communicate information such as data, video, multimedia, any other suitable type of information, or any combination of the preceding. Communication device20a-cmay comprise, for example, a telephone, a cellular telephone, a mobile handset, or any other device suitable for communicating signals to and from system10. Communication device20a-cmay support, for example, simple Internet Protocol (IP), mobile IP, or any other suitable communication protocol. Communication device20a-cmay utilize, for example, Global System for Mobile communications (GSM) technology or any other suitable communication technology.

Communication network22a-callows communication device20a-cto communicate with other networks or devices. Communication network22a-cmay comprise a public switched telephone network (PSTN), a public or private data network, the Internet, a wireline or wireless network, a local, regional, or global communication network, an enterprise intranet, other suitable communication link, or any combination of the preceding.

Conference bridge30determines whether the content of signals received from communication devices20a-ccomprises voice signals, combines the signals that are determined to comprise voice signals to generate a combined signal, and sends the combined signal to communication devices20a-c. Conference bridge30includes automatic gain control (AGC) circuits32a-c, vector generators33a-c, speech recognition modules34a-c, weighting modules36a-c, and a signal combiner38. Automatic gain control circuits32a-ccontrol the amplitude of signals received from communication devices20a-c. Automatic gain control circuits32may be used to bring the amplitude of the signals to the same level to equalize the signals.

Vector generator33a-cgenerates a feature vector that describes the features of a signal. Speech recognition module34a-bmay use the feature vector to determine whether the signal comprises a voice signal. Each feature vector may comprise values for variables that describe certain features of a signal. For example, a feature vector may comprise a frequency value for a variable that represents the frequency of the signal. “Each” as used in this document refers to each member of a set or each member of a subset of a set. Other features may be represented by a frequency vector, for example, the duration and energy level at a given frequency. Fast Fourier transforms, discrete cosine transforms, wavelet techniques, or other suitable technique may be used to determine the feature vector of a signal.

Speech recognition module34a-cexamines the content of a signal to determine whether the signal comprises a voice signal. Content may include, for example, the frequency spectrum of the signal with respect to time. Example frequency spectrums of music and voice signals are described with reference toFIGS. 2 and 3, respectively. Content, however, may include any feature suitable for determining whether a signal comprises a voice signal. The content may be provided by feature vectors generated by vector generators33a-c.

Speech recognition module34a-cmay perform speech recognition for a signal in any suitable manner. For example, speech recognition module34a-cmay compare a feature vector for the signal to a voice signal vector that describes the ranges of typical feature values for voice signals. If the values of the feature signal fall within the ranges of the typical values, the signal may be designated as comprising a voice signal. Other suitable procedures for performing speech recognition, however, may be used.

Speech recognition may be performed at any suitable time or for any suitable signals. For example, speech recognition module34a-cmay continuously or periodically check whether a signal comprises a voice signal. As another example, speech recognition may be performed only for streams that are designated as active. Active streams may comprise, for example, signals that have amplitude greater than a threshold amplitude.

Speech recognition module34a-cmay be located at any part of system10where there is access to the signal and processing power for determining whether the signal comprises a voice signal. For example, speech recognition module34may be located at communication device20a-c, a gateway or node that communicates a signal between communication device20a-cand conference bridge30, at conference bridge30, or at any other point where speech recognition module30can determine whether the signal comprises a voice signal.

Weighting modules36a-cweight the signals in response to instructions from speech recognition modules34a-c. According to one embodiment, a weighting module36a-cassigns weights to the signals that indicate the contribution of the signal to the combined signal. A higher weight indicates a greater contribution and a lower weight indicates a lesser contribution. The weight may influence a signal in any suitable manner, such as by adjusting the signal gain or volume of the signal. If a speech recognition module34a-cindicates that a signal comprises a voice signal, weighting module36a-cprovides the signal with a higher weight. If speech recognition module34a-cindicates that a signal does not comprise a voice signal, weighting module36a-cprovides the signal with a lower weight.

According to another embodiment, weighting module36a-cmay comprise a switch that transmits or blocks the signals in response to an instruction from speech recognition module34a-c. If speech recognition module34a-cindicates that the signal comprises a voice signal, the switch may be said to transmit the signal to signal combiner38by assigning the signal a maximum weight. If speech recognition module38a-cindicates that the signal is not a voice signal, the switch may be said to block the signal from being transmitted to signal combiner38by assigning the signal a minimum weight.

Along with speech recognition module34a-c, weighting module36a-cmay be located at any part of system10where there is access to the signal and processing power for weighting the signal. For example, weighting module36a-cmay be located at communication device20a-c, a gateway or node that communicates a signal between communication device20a-cand conference bridge30, at conference bridge30, or at any other point where weighting module36a-ccan weight the signal.

Signal combiner38combines the signals received from weighting modules36a-c. The signals comprising voice signals have a higher weight than that of the signals that do not comprise voice signals. Accordingly, the combined signals include more voice signals than other types of signals. The combined signals are transmitted back to communication devices20a-c.

Modifications, additions, or omissions may be made to the system without departing from the scope of the invention. For example, vector generators33a-cmay be omitted, and speech recognition module34a-cmay use other procedures for determining whether the signal comprises a voice signal. Additionally, functions may be performed using any suitable logic comprising software, hardware, other logic, or any suitable combination of the preceding.

FIGS. 2 and 3are example graphs illustrating the differences between an example voice frequency spectrum and an example music frequency spectrum.FIG. 2is a graph50illustrating an example voice frequency f spectrum with respect to time t. The shaded regions indicate significant energy present at frequency f at time t. Voice signals typically have frequencies that fall within a range of approximately 100 to 2,500 Hz. As illustrated by graph50, frequencies f of voice signals at a time t typically fall within a small number of frequency ranges, each with a spread of approximately 50 Hz. As time t increases, the frequencies f may smoothly shift to another a small range of frequencies.

FIG. 3is a graph52illustrating an example music frequency spectrum with respect to time t. Signals other than voice signals have frequencies f that often do not fall within the range of voice signal frequencies. Moreover, other types of signals have frequencies that typically do not smoothly shift as time t increases. For example, graph52illustrates music signals that have frequencies f that fall outside of the typical range of voice signal frequencies. Moreover, the frequencies f do not smoothly shift as time t increases.

FIG. 4is a graph70illustrating an example latency situation. Graph70illustrates a received signal72and a speech recognition signal74with respect to time t. Received signal72is received from a communication device20a-c. Speech recognition signal74indicates whether received signal72comprises a voice signal, and may be generated by speech recognition module34a-c.

Received signal72includes segments76a-cof voice and music signals. Segment76acomprises a voice signal, segment76bcomprises a music signal, and segment76ccomprises a voice signal. Speech recognition signal74includes segments78a-cthat indicate whether received signal72includes voice signals. Segment78aindicates that received signal72comprises a voice signal, segment78bindicates that received signal72does not include a voice signal, and segment78cindicates that received signal72comprises a voice signal.

As illustrated by graph70, there is a delay time between when received signal72changes to a voice signal or to an other type of signal and the time at which speech recognition signal74indicates whether received signal72is a voice signal or an other type of signal. The delay time, however, is relatively short such as approximately 100 milliseconds. The short delay time is typically acceptable for telephone conferences since speakers often make an initial sound such as “uh” or “excuse me” before interjecting into a conversation.

FIG. 5is a flowchart illustrating one embodiment of a method for combining a plurality of signals. The method begins at step100, where conference bridge30receives signals from communication devices20a-c. A signal from a communication device20a-cis selected at step102. Automatic gain control circuits32a-ccondition the signal at step104. Vector generator33a-cgenerates a feature vector for the signal at step106. The feature vector describes features that may be used to determine whether the signal comprises a voice signal.

Speech recognition module34a-cdetermines whether the signal comprises a voice signal at step108. Speech recognition module34a-cmay generate a speech recognition signal that indicates whether the signal comprises a voice signal. If the signal does not comprise a voice signal, the method proceeds to step110, where the contribution of the signal to the combined signal is decreased. Weighting module36a-cmay decrease the contribution of the signal by assigning the signal a low or zero weight. The method then proceeds to step112. If the signal comprises a voice signal at step108, the method proceeds directly to step112.

Weighting module36a-csends the signal, if any, to signal combiner38at step112. If there is a next signal at step114, the method returns to step102to select the next signal. If there is no next signal at step114, the method proceeds to step116. Signal combiner38combines the signals at step116. Signals that have been determined to comprise voice signals contribute more to the combined signal than signals that have been determined to comprise other types of signals. The combined signal is output at step118. After outputting the combined signal, the method terminates.

Modifications, additions, or omissions may be made to the method without departing frog the scope of the invention. Additionally, steps may be performed in any suitable order without departing from the scope of the invention.

Certain embodiments of the invention may provide one or more technical advantages. A technical advantage of one embodiment may be that the content of the signals is examined in order to determine whether signals are voice signals. The signals that are voice signals are combined at the conference bridge. By using the content to determine whether the signals are voice signals, the conference bridge may more effectively combine signals while maintaining signal quality.

Although an embodiment of the invention and its advantages are described in detail, a person skilled in the art could make various alterations, additions, and omissions without departing from the spirit and scope of the present invention as defined by the appended claims.