Patent Publication Number: US-8117033-B2

Title: System and method for automatic verification of the understandability of speech

Description:
PRIORITY CLAIM 
     The present application is a continuation of U.S. patent application Ser. No. 12/644,802, filed Dec. 22, 2009, which is a continuation of U.S. patent application Ser. No. 11/866,648, filed Oct. 3, 2007, now U.S. Pat. No. 7,660,716, which is a continuation of U.S. patent application Ser. No. 09/992,988 filed Nov. 19, 2001, now U.S. Pat. No. 7,295,982, the contents of which are incorporated herein by reference in their entirety. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to the field of communications. More specifically, the present invention relates to a speech verification system to verify the intelligibility of a user&#39;s message in real time. 
     BACKGROUND OF THE INVENTION 
     Automated voice messaging systems are known in the art and used extensively for rapid and convenient communication. The recording of telephone voice messages is a convenience to both the calling and called parties. The caller may leave a message for the called party during off-hours, or when the called party is unable to answer the call. The called party may be a person or may be a machine or system such as an automatic voice recognition system or a voice message system. The call may occur over traditional telephone exchange lines, a switched network, a mobile-based network, the Internet, and the like. The called party may retrieve the stored message when desired. The caller&#39;s message is delivered to the called party and the information within the message is not lost. One problem with this process is, however, inaudible or unintelligible voice messages. 
     Callers attempt to speak clearly and audibly, but voice messages may include voice content that is difficult to understand or is subjected to noise levels that make comprehension difficult. The called party may directly listen to the message or the message may be processed through, for example, a voice recognition system. Further, messages may be converted to text or stored for archival purposes. All of these actions require that the person or system receiving the message understand the information within the message. 
     Partially unintelligible messages can be inconvenient to the called party, especially if names or numbers are inaudible. The called party may lose the information within the message and the caller is typically unaware that the message was not understood or processed. If the identity of the caller is unknown or unintelligible, the called party may not have any recourse in resolving the information or content of the message. In other words, neither the caller nor the called party may take any action that is efficient or on a real time basis when an incomprehensible message is left. 
     SUMMARY OF THE INVENTION 
     The present invention relates to a system and method for automatically verifying that a message received from a user is intelligible. In an exemplary embodiment, a message is received from the user. A speech level of the user&#39;s message may be measured and compared to a pre-determined speech level threshold to determine whether the measured speech level is below the pre-determined speech level threshold. A signal-to-noise ratio of the user&#39;s message may be measured and compared to a pre-determined signal-to-noise ratio threshold to determine whether the measured signal-to-noise ratio of the message is below the pre-determined signal-to-noise ratio threshold. An estimate of intelligibility for the user&#39;s message may be calculated and compared to an intelligibility threshold to determine whether the calculated estimate of intelligibility is below the intelligibility threshold. If any of the measured speech level, measured signal-to-noise ratio and calculated estimate of intelligibility of the user&#39;s message are determined to be below their respective thresholds, the user may be prompted to repeat at least a portion of the message. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Embodiments of the present invention are illustrated by way of example, and not limitation, in the accompanying figures in which like references denote similar elements, and in which: 
         FIG. 1  is a block diagram of a speech verification system in accordance with an embodiment of the present invention; 
         FIG. 2  illustrates a block diagram of a speech verification device in accordance with an embodiment of the present invention; and 
         FIGS. 3 and 4  illustrate flowcharts showing speech verification methods in accordance with an exemplary embodiment of the present invention. 
     
    
    
     DESCRIPTION OF THE INVENTION 
       FIG. 1  is a block diagram of a speech verification system  100  according to an exemplary embodiment of the present invention. The speech verification system  100  may include an automatic speech verification device (SVD)  150  in accordance with an embodiment of the present invention. 
     The SVD  150  may monitor, in real time, a message received from a user for various characteristics of the user&#39;s message to verify that the message will be sufficiently intelligible when played back and/or processed by a human and/or a machine. For example, the SVD  150  may determine whether there is sufficient level of speech energy in the message such that the message is potentially intelligible. SVD  150  may also determine whether the signal-to-noise ratio of the user&#39;s message is sufficient such that the message is intelligible. 
     In embodiments of the present invention, the SVD  150  may further employ other or additional techniques to verify that the message is intelligible. For example, the SVD may establish an estimate of intelligibility for the entire message or a portion of the user&#39;s message. In embodiments of the present invention, the SVD  150  may establish the estimate of intelligibility based on recognizable or identifiable phonemes. The SVD  150  may recognize phonemes in the user&#39;s message to verify that the message contains a normal phoneme distribution for a given language such that the message may be recognizable. If the SVD  150  determines that the message does not contain phonemes from an expected language, the SVD  150  may determine that the user&#39;s message is unintelligible. Alternatively, if the SVD  150  determines that the spoken message does not contain phonemes from an expected language, the SVD  150  may attempt to determine whether the spoken message is in another language. The SVD  150  may employ an extended set of phonemes to determine whether the spoken message is potentially intelligible in the other language. 
     In alternative embodiments of the present invention, the SVD may use grammars and/or word spotting techniques to verify that important and/or critical information—for example, names, bank account numbers, credit card numbers, telephone numbers, etc.—included in the user&#39;s message will be intelligible when played back and/or processed by a human and/or a machine. The estimate of intelligibility may indicate the degree to which the recognized important information is intelligible. 
     In further alternative embodiments of the present invention, the SVD  150  may employ context-specific or domain-specific libraries or databases to verify that the message contains words that match with the vocabulary words included in the domain-specific libraries. The SVD may establish an estimate of intelligibility based on—for example—the numbers of words included in the user&#39;s message that appear in the vocabulary of the domain-specific libraries. If a certain number of words included in the message do not appear in the database, the SVD  150  may determine that the entire message or a portion of the message is unintelligible. 
     In the above examples, if the speech level of the user&#39;s message, the signal-to-noise ratio of the user&#39;s message and/or an established estimate of intelligibility is below a predetermined probability threshold, the SVD  150  may determine that the entire message or a portion of the message is unintelligible. The SVD  150  may prompt the user to repeat either the entire message or the portion of the message that is determined to be unintelligible. In other words, the system may specify how much speech the user may need to repeat. Additionally or optionally, the system may specify how the repeated speech should be spoken. For example, based on the characteristics of the speech that may have caused the message to be possibly unintelligible, the SVD may request that the user&#39;s message be repeated with, for example, a higher volume, a slower speed, with the background noise eliminated, etc. SVD  150  may make such requests to repeat either after the entire message including the unintelligible portion has been received or immediately after recognizing the unintelligible portion of the message. 
     Referring again to  FIG. 1 , speech verification system  100  shows a terminal device  110  that may be a calling party&#39;s terminal device. The terminal device  110  can communicate with an originating communication switch (not shown) that may be located within a local exchange carrier&#39;s central office  120  (hereinafter referred to as originating-side local exchange carrier (LEC)  120 ). The LEC  120  is typically connected to a transit network  130 . Another terminal device  160 , for example, a called party&#39;s terminal device, can communicate with a terminating communication switch (not shown). The terminating communication switch may be located within, for example, a local exchange carrier&#39;s central office  140  (hereinafter referred to as terminating-side LEC  140 ) that may also be connected to transit network  130 . In embodiments of the present invention, the terminating-side LEC  140  may be further coupled to the SVD  150 . 
     Although the SVD  150  is shown connected to the terminating-side LEC  140 , it is recognized that the SVD  150  may be connected to originating-side LEC  120 . The SVD  150  may be located within the LECs (e.g., 120, 140) or may be located external to the LECs. 
     Terminal devices  110 ,  160  can be any of a variety of communication devices such as wired or wireless telephones, one way or two-way pagers, Personal Digital Assistants (PDAs), personal computers (PC), a Voice Recognition System, a Voice Response Unit (VRU), an Interactive Voice Response Unit (IVRU), a paging unit, intelligent switches, private branch exchanges (PBX), or any other devices used for and/or in communications. 
     In alternative embodiments of the present invention, SVD  150  may be externally coupled to or located within terminal devices  110 ,  160 . 
     Terminal device  110  (also referred to herein as user device  110 ) may communicate with terminal device  160  (also referred to herein user device  160 ) through LEC  120 , transit network  130 , and LEC  140 . 
     Although SVD  150 , as shown in  FIG. 1 , is configured in a telecommunications system, it is recognized that embodiments of the SVD  150  as described herein can be incorporated into any device or system that receives audio messages from users. For example, the SVD  150  or a similarly configured device may be incorporated within a dictation machine, a personal computer, a PDA, an IVR, a phone, voice messaging system, a tape recorder, or other suitable device or system that can record or store user messages. The SVD  150  may verify that an intelligible message is received or recorded in real time. If the SVD  150  determines that any portion of the message is unintelligible, the SVD  150  may automatically request that the user repeat the entire message or the portion of the message that is determined to be unintelligible. 
     LEC  120  and LEC  140  may be central offices or switching centers of local phone companies that receive and deliver calls. In the example illustrated in  FIG. 1 , LEC  120  may receive, for example, a call from terminal device  110 . The call may be routed via the transit network  130  to LEC  140 . LEC  140  may route the call to the called party&#39;s terminal device  160 . In embodiments of the present invention, speech verification as provided by the SVD  150  may be a feature or service that is provided by the local phone companies. If the calling party and/or the called party is a subscriber of the speech verification service or feature, one of the LECs may process the call using the speech verification technique employed by the SVD  150  as discussed herein. 
     LEC  120  and/or LEC  140  may contain originating and/or terminating communication switches (not shown) that may include a processor, computer readable memory, a computer-readable medium, a data port, a network port and a data bus (all not shown). The data port permits communications with devices such as the terminal devices  110 ,  160  and/or the SVD  150 . As indicated above, the SVD  150  or similarly configured device may be configured external to or internal to such originating and/or terminating communication switches. The network port of the communication switches can be connected to transit network  130 . The data bus located within the originating and/or terminating communications switch connects the processor, the computer readable memory, computer-readable medium, the data port and the network port and permits communication between the various components of the switch. 
     Communication switches located with the LECs  120 ,  140  may operate special software to perform functions associated with toll calls and/or local calls. Originating and/or terminating communication switches that may be located within LECs  120 ,  140  may contain a dual tone modulated frequency (DTMF) detection unit to receive the DTMF signals. Alternatively, the communication switches may contain a VRU or an IVRU to recognize and/or process voice responses. The 4ESS® and 5ESS® switches manufactured by Lucent Technologies, Inc. of Murray Hill, N.J. are examples of the hardware that can perform the functions of communications switches that may be used by LECs. 
     In embodiments of the present invention, communication switches may be Mobile Telephone Switching Office (MTSO) switches to handle calls from mobile telephones. As used herein, MTSO switch refers generally to any type of switch that can handle analog, cellular, digital or personal communication services (PCS) calls. 
     Note that while  FIG. 1  merely shows LECs  120 ,  140  coupled to the transit network  130 , additional LECs including additional switches may also be coupled to the transit network  130 . 
     Transit network  130  may be a communications network that may include, for example, a public switched telephone network (PSTN), an Integrated Services Digital Network (ISDN), a cellular network, a digital mobile network, a Personal Communication Systems (PCS) network, an Internet, an intranet, a signaling system 7 (SS7) network, a local area network (LAN), a satellite network, an advanced intelligent network (AIN), any suitable digital or analog network, a broadband network such as a cable network, any other suitable national and/or international communications network or any suitable combination thereof. 
     Although  FIG. 1  only shows terminal devices  110 ,  160  connected to the LECs  120 ,  140 , respectively, of course any number of additional terminal devices may be connected to the transit network  130 . 
       FIG. 2  is a block diagram of SVD  150  that may contain intelligence to monitor, in real time, an incoming message from a user and to verify that message is intelligible. The SVD  150  may be a stand-alone device or, as indicated above, the SVD  150  may be coupled external to or incorporated within the user&#39;s terminal device. It is recognized that any suitable hardware and/or software may be used by one of ordinary skill in the art to configure and/or implement an SVD in accordance with embodiments of the present invention. 
     The SVD  150  may include a receiver  210  that receives audio or speech messages from users. For example, the receiver  210  may be a network interface that interfaces with a switch located in the LEC or other type of interface that can receive the user&#39;s messages. In embodiments of the present invention, the receiver  210  may support a coaxial interface, twisted pair interface, optical interface, wireless interface and/or any other interface to permit the receiver  210  to receive messages. In alternative embodiments of the present invention, the receiver  210  may be a microphone or other device that can receive, for example, audio messages from users. 
     Embodiments of the present invention may further include an analog-to-digital converter  220  (A/D converter). The A/D converter  220  may receive a user&#39;s message that may be represented as an analog signal from the receiver  210 . The A/D converter  220  can convert the analog message to a digitized signal. The digitized signal may be processed in accordance with embodiments of the present invention to verify that the user&#39;s message represented by the digitized signal is intelligible. It is recognized that the A/D converter  220  can be omitted if the message is received in a digital format at the receiver  210 . In alternative embodiments of the present invention, some processing—such as determining the speech level or determining the intelligibility of the message—may be done directly using the analog signal. In this case, the receiver  210  may pass the analog message signal directly to the understandability evaluator  280  for processing. 
     In embodiments of the present invention, the user&#39;s message may be forwarded to an understandability evaluator  280  that may evaluate the message for understandability and/or may determine the intelligibility level of the message. The understandability evaluator  280  may look at various characteristics of the user&#39;s message to evaluate whether the user&#39;s message will be sufficiently intelligible or understandable. The understandability evaluator  280  may include, for example, a speech level monitor  230 , a signal-to-noise ratio monitor  240  and/or an intelligibility monitor  250 . 
     The understandability evaluator  280  may be coupled to dialog manager  260  that may manage a dialog with the user if the user&#39;s message is determined not to be sufficiently intelligible by the understandability evaluator  280 . The understandability evaluator  280  may be further coupled to an output interface  290  that may output the user&#39;s communication for storage and/or processing, if the user&#39;s message is determined to be sufficiently intelligible by the understandability evaluator  280 . 
     In embodiments of the present invention, the speech level monitor  230  measures the speech level of the user&#39;s message. The speech level is typically defined as the speech signal power or intensity that may be measured over a portion of the speech, such as a phrase or sentence. The speech level monitor  230  may be configured with a pre-determined speech level threshold that may indicate the minimum intensity of the speech signal that may be desirable for the speech to be sufficiently intelligible. Any speech level above the threshold may be considered potentially intelligible and any speech below the threshold may be considered unintelligible. The speech level threshold may be a variable or fixed value that is typically measured in decibels as referenced to 1 milliwatt (dBm). The speech level threshold may be varied or adjusted by an operator of the SVD  150  as desired. 
     The speech level monitor  230  may compare the measured speech level of the user&#39;s message with the pre-determined speech level threshold to determine whether the speech level of the user&#39;s message is above or below the pre-determined threshold. If the speech level of the user&#39;s message is above the pre-determined speech level threshold, the user&#39;s message may be considered potentially intelligible and may be forwarded to the output interface  290  for storage and/or processing. However, if the speech level of the user&#39;s message is below the pre-determined speech level threshold, the understandability monitor  280  may consider this characteristic of the user&#39;s message alone and/or may consider this characteristic in combination with other characteristics to determine whether the user&#39;s message should be considered unintelligible. 
     If the understandability monitor  280  determines that the user&#39;s message is unintelligible based on the measured speech level, the dialog manager  260  may begin a dialog with the user to repeat the entire message or a portion of the message. After the user repeats the message, the understandability monitor  280  reevaluates the repeated message to determine intelligibility. 
     In embodiments of the present invention, the SVD  150  may include a signal-to-noise monitor  240  that measures the signal-to-noise ratio of the user&#39;s message. Typically, the signal-to-noise ratio is defined as the ratio of the usable signal being transmitted or received to the noise or undesirable signal. The signal-to-noise monitor  240  may be configured with a pre-determined signal-to-noise ratio threshold that may indicate the minimum signal-to-noise ratio that may be desirable for the speech to be sufficiently intelligible. Any signal representing the user&#39;s message above the signal-to-noise ratio threshold may be considered potentially intelligible and any signal below the threshold may be considered potentially unintelligible. The signal-to-noise ratio threshold may be a variable or fixed value that is typically measured in decibels (dB). The signal-to-noise ratio threshold may be varied or adjusted by an operator of the SVD  150  as desired. 
     The signal-to-noise monitor  240  may compare the measured signal-to-noise ratio of the user&#39;s message with the pre-determined signal-to-noise ratio threshold to determine whether the speech signal representing the user&#39;s message is above or below the pre-determined signal-to-noise ratio threshold. If the speech signal representing the user&#39;s message is above the pre-determined signal-to-noise ratio threshold, the user&#39;s message may be considered potentially intelligible and may be forwarded to the output interface  290  for storage and/or processing. However, if the speech signal representing the user&#39;s message is below the pre-determined signal-to-noise ratio threshold, the understandability monitor  280  may consider this characteristic of the user&#39;s message alone and/or may consider this characteristic with other characteristics to determine whether the user&#39;s message should be considered unintelligible. 
     If the understandability monitor  280  determines that the user&#39;s message is unintelligible based on the measured signal-to-noise ratio, the dialog manager  260  may begin a dialog with the user to repeat the entire message or a portion of the message. After the user repeats the message, the understandability monitor  280  reevaluates the repeated message to determine intelligibility. 
     In embodiments of the present invention, the intelligibility monitor  250  may further calculate an estimate of intelligibility based on the user&#39;s message. In embodiments of the present invention, the estimate of intelligibility may be calculated based on, for example, the number of identifiable phonemes included in the user&#39;s message, the intelligibility of critical words or information detected in the user&#39;s message and/or the number of words detected in the user&#39;s message that are contained in a domain library. It is recognized that other parameters may be used to calculate the estimate of intelligibility. For example, natural language understanding techniques may be used to calculate the estimate of intelligibility. 
     In embodiments of the present invention, the estimate of intelligibility based on phonemes may be calculated first, followed by the estimate of intelligibility based on the critical words, which may be followed by the estimate of intelligibility based on the number of words contained in the domain library. Alternatively, the estimates of intelligibility may be calculated in any other order. 
     In embodiments of the present invention, the estimate of intelligibility can be computed by determining whether probabilities calculated by the recognizer fall below their respective intelligibility threshold levels. For example, the estimate of intelligibility calculated based on phonemes may be compared to a phoneme estimate of intelligibility threshold. The intelligibility monitor  250  may be configured with one or more such intelligibility thresholds that may indicate the minimum intelligibility level that may be desirable for the speech to be sufficiently intelligible. Thus, any message or a portion thereof from the user having a calculated estimate of intelligibility above its corresponding intelligibility threshold may be considered potentially intelligible. Conversely, any message or a portion thereof from the user having a calculated estimate of intelligibility below its respective intelligibility threshold may be considered unintelligible. The intelligibility threshold may be a fixed or variable value that may be varied or adjusted by an operator of the SVD  150  as desired. The intelligibility monitor  250  may establish an estimate of intelligibility and/or an overall estimate of intelligibility for the entire or for a portion of the user&#39;s message. 
     In alternate embodiments of the present invention, one or more individual estimates of intelligibility (e.g., for phonemes, for critical words, for domain-based words, etc.) may be used to determine an overall estimate of intelligibility for the user&#39;s message. The overall estimate of intelligibility may be compared with respective overall intelligibility thresholds. Thus, any message or a portion thereof from the user having an overall estimate of intelligibility above its corresponding overall intelligibility threshold may be considered potentially intelligible, while any message or a portion thereof from the user having an overall estimate of intelligibility below its respective overall intelligibility threshold may be considered unintelligible. 
     In an embodiment of the present invention, the intelligibility monitor  250  may establish the estimate of intelligibility based on recognizable or identifiable phonemes in the user&#39;s message. The intelligibility monitor  250  may verify that the user&#39;s message contains a normal phoneme distribution so that the message is potentially intelligible. A phoneme is typically the smallest phonetic unit in a language capable of conveying a distinction in meaning There are approximately 64 total phonemes for all human languages. The English language contains approximately 48 of the total 64 phonemes. The intelligibility monitor  250  may contain a recognizer (not shown) that may determine that phonemes contained in the user&#39;s message do not correspond to those from English, possibly indicating that the message is unintelligible. 
     In embodiments of the present invention, the intelligibility monitor  250  may attempt to recognize the most likely phoneme or phonemes from the complete set of phonemes that are expected from a particular language. The intelligibility monitor  250  may calculate a phoneme estimate of intelligibility based on the recognizable phoneme distribution for the expected language, such as English. The intelligibility monitor  250  may compare the calculated phoneme estimate of intelligibility with an estimate of intelligibility threshold for phonemes. If the calculated phoneme estimate of intelligibility is lower than the corresponding threshold for phonemes, this may indicate that the intelligibility monitor  250  is consistently having trouble determining which phoneme or phonemes in, for example, the English language are being spoken. Accordingly, the intelligibility monitor  250  may conclude that the user&#39;s message is unintelligible based on the phoneme calculation. 
     In alternative embodiments of the present invention, if the intelligibility monitor is unable to recognize phonemes contained in the English language, the intelligibility monitor may conclude that the most likely phonemes being spoken by the user are from a language other than English (e.g., Spanish, French, German, Hindi, etc.). In this case, the intelligibility monitor may employ an extended set of phonemes (e.g., including those phonemes that are not usually found in the English language). By analyzing the phoneme distribution based on the extended set of phonemes, the intelligibility monitor  250  may determine which language may be spoken by the user and then may consider the normal phoneme distribution for that language. After the intelligibility monitor  250  determines the language spoken by the user, it may know which phonemes to look for as well as which words to look for. The intelligibility monitor  250  may calculate a phoneme estimate of intelligibility based on the extended set of phonemes. The intelligibility monitor  250  may compare the calculated phoneme estimate of intelligibility based on the extended set of phonemes with a corresponding estimate of intelligibility threshold. If the calculated phoneme estimate of intelligibility is lower than the corresponding threshold, the intelligibility monitor  250  may conclude that the user&#39;s message is unintelligible based on this extended phoneme calculation. 
     After phonemes are recognized, the intelligibility monitor  250  may attempt to determine the actual words being spoken by the user. In an embodiment of the present invention, the intelligibility monitor  250  may recognize the words being spoken by combining the recognized phonemes together and trying to parse the results into recognizable words. If the intelligibility monitor is unable to recognize the words or if the recognized words do not form sentences that seem to make sense (e.g., using known natural language understanding technology), then the speech can be considered potentially unintelligible. The intelligibility monitor may employ pre-determined thresholds to determine whether the words are recognizable and/or to determine whether the sentences formed by the words seem sensible. 
     If the calculated estimate of intelligibility based on recognizable phonemes is above the intelligibility threshold for phonemes, the user&#39;s message may be considered potentially intelligible and may be forwarded to the output interface  290  for storage and/or processing. However, if the calculated estimate of intelligibility based on recognizable phonemes is below the intelligibility threshold for phonemes, the dialog manager  260  may begin a dialog with the user to repeat the entire message or a portion of the message. After the user repeats the message, the understandability monitor  280  may reevaluate the repeated message to determine intelligibility. 
       FIG. 4  illustrates several features discussed next. In an alternative embodiment of the present invention, the intelligibility monitor  250  may calculate an estimate of intelligibility based on the user&#39;s message containing critical or important information ( 402 ). Critical or important information may be, for example, names, bank account numbers, credit card numbers, telephone numbers, etc. that may be a critical portion of the user&#39;s message and need to be sufficiently intelligible when played back and/or processed by a human and/or a machine. The intelligibility monitor  250  may use known grammars and/or word spotting techniques to detect or identify words or segments of the user&#39;s message that may contain important and/or critical information. 
     If the intelligibility monitor  250  recognizes or identifies important information in the user&#39;s message, the intelligibility monitor  250  may calculate an estimate of intelligibility for the recognized important information ( 404 ). The calculated estimate of intelligibility may indicate the degree to which the important information is intelligible. The intelligibility monitor  250  may compare the calculated estimate of intelligibility for the recognized important information with an intelligibility threshold. In this case, the intelligibility threshold may indicate the minimum intelligibility level that may be desirable for the recognized important information to be sufficiently intelligible. 
     If the calculated estimate of intelligibility for the recognized important information is above the intelligibility threshold, the user&#39;s message may be considered potentially intelligible and may be forwarded to the output interface  290  for storage and/or processing. However, if the calculated estimate of intelligibility for the recognized important information is below the intelligibility threshold, the dialog manager  260  may begin a dialog with the user to repeat the entire message or a portion of the message. After the user repeats the message, the understandability monitor  280  may reevaluates the repeated message to determine intelligibility. 
     In a further alternative embodiment of the present invention, the intelligibility monitor  250  may employ one or more context-specific or domain-specific libraries or databases (not shown) to verify that the user&#39;s message contains words that match with the vocabulary words included in the domain-specific libraries or databases. In this embodiment, the intelligibility monitor  250  may establish an estimate of intelligibility ( 404 ) based on, for example, the number of words included in the user&#39;s message that appear in the vocabulary of the one or more domain-specific libraries. 
     In embodiments of the present invention, after receiving the user&#39;s message, the intelligibility monitor  250  may determine the domain of the user&#39;s message based on the words included in the user&#39;s message. The intelligibility monitor  250  may access the database of vocabulary words from the various context-specific or domain-specific libraries. As the user message is received, the intelligibility monitor  250  may attempt to determine the domain or domains of the message by determining the number of words from each of the domain vocabularies occur in the message. The intelligibility monitor  250  may determine the domain or domains of the message based on the predetermined or maximum number of words in that domain that occur in the message. For example, the intelligibility monitor  250  may be configured such that if four ( 4 ) words in the user&#39;s message appear in one or more of the domain libraries, then those domain libraries may be classified as the domain or domains of the message. The domain or domains of the message may be used to process the user&#39;s message. In alternative embodiments of the present invention, the domain of the message may be determined by prompting the user for information that may be used to specify the domain. 
     After the intelligibility monitor  250  determines the domain for the user&#39;s message, the intelligibility monitor  250  may access the one or more domain libraries (not shown) determined to be the domain of the user&#39;s message. The intelligibility monitor  250  may calculate an estimate of intelligibility ( 404 ) based on the number of words in the user&#39;s message that appear or correlate to terms in the one or more domain libraries ( 406 ). The calculated estimate of intelligibility may be compared to a domain-related intelligibility threshold ( 408 ). In this case, the domain-related intelligibility threshold may indicate the minimum number of words of the message that also occur in the one or more accessed domain-libraries for the message to be sufficiently intelligible. 
     If the calculated estimate of intelligibility based on the number of words that appear in the one or more accessed domain libraries is above the domain-related intelligibility threshold, then the user&#39;s message may be considered potentially intelligible and may be forwarded to the output interface  290  for storage and/or processing. However, if the calculated estimate of intelligibility based on the number of words that appear in the one or more accessed domain libraries is below the domain-related intelligibility threshold, then the dialog manager  260  may begin a dialog with the user to repeat the entire message or a portion of the message. After the user repeats the message, the understandability monitor  280  may reevaluate the repeated message to determine intelligibility. 
     The above techniques for determining whether a user&#39;s message is intelligible are given by example only and other methods may be used to determine whether the user&#39;s message is sufficiently intelligible. 
     If the understandability evaluator  280  determines that the user&#39;s message is potentially unintelligible, the understandability monitor may notify the dialog manager  260 . The dialog manager  260  may engage in an interactive dialog with the user to repeat the entire or a portion of the user&#39;s message. The dialog manager  260  may prompt the user to repeat the message based on which measured and/or calculated value of the message is determined to be below its threshold value. For example, if the speech level is determined to be below its respective threshold, the dialog manager  260  may request the user to repeat the message with a higher volume. On the other hand, if the signal-to-noise ratio is determined to be below its respective value, the dialog manager  260  may request the user to hold the microphone closer to her mouth when repeating the message. As another example, if the estimate of intelligibility is determined to be below its respective threshold, the dialog manager may request the user to repeat the message slowly. It is recognized that the dialog manager  260  can engage in any number of specific dialogs to notify the user of the manner in which to repeat the message. In embodiments of the present invention, during the interactive dialog with the user, the dialog manager  260  may replay the unintelligible portion of the user&#39;s message so that the user may hear what the system determined to be unintelligible. 
       FIG. 3  is a flowchart illustrating an exemplary manner in which a user&#39;s messages may be verified for intelligibility according to an embodiment of the present invention. A user or calling party places a call to a called party&#39;s terminal device  160  using, for example, terminal device  110  (also referred to herein as called party  110 ). The call is received at the originating-side LEC  120  that may route the call through the transit network  130 . Based on the dialed number, the call is received at, for example, the LEC  140 . The LEC  140  further routes the call to the called party&#39;s terminal device  160  (also referred to herein as the called party  160 ). In this example, the called party  160  may be unavailable, thus an answering machine or service may pick up the call. After a greeting is played to the calling party  110 , the calling party  110  is invited to leave a message for a called party  160 . 
     As the calling party  110  is recording a message for the called party  160 , the SVD  150  may monitor the message to verify that the recorded message is sufficiently intelligible. As indicated above, the SVD  150  may be coupled to one of the LECs or may be located internal to the terminal device  160 . As the message for the called party  160  is being recorded by the answering machine or service, the message from the user is received by the SVD  150  and forwarded to understandability evaluator  280  ( 3000 ). The speech level monitor  230  of the understandability evaluator  280  may receive the message. The speech level monitor  230  may measure the speech level of the user&#39;s message ( 3010 ). The speech level monitor  230  may determine whether the measured speech level of the user&#39;s message is below a pre-determined speech level threshold ( 3020 ). 
     After the speech level monitor  230  processes the user&#39;s message, the signal-to-noise ratio monitor  240  receives the message. The signal-to-noise ratio monitor  240  may measure a signal-to-noise ratio for the user&#39;s message and determine whether the measured signal-to-noise ratio of the message is below a pre-determined signal-to-noise ratio threshold ( 3030 - 3040 ). After the signal-to-noise ratio monitor  240  processes the user&#39;s message, the message is forwarded to the intelligibility monitor  250  for processing. 
     The intelligibility monitor  250  receives the message and may calculate an estimate of intelligibility for the user&#39;s message ( 3050 ). The intelligibility monitor  250  may determine whether the calculated estimate of intelligibility is below an intelligibility threshold ( 3060 ). 
     In embodiments of the present invention, if the measured speech level, the measured signal-to-noise ratio, and/or the calculated estimate of intelligibility are determined to be below the respective thresholds, the dialog manager  260  may prompt the user to repeat the entire message or a portion of the message ( 3070 - 3080 ). Alternatively, if the measured speech level, the measured signal-to-noise ratio, and the calculated estimate of intelligibility are all determined to be above their respective thresholds, the process may end ( 3070 ). In embodiments of the present invention, after the process is completed, the user&#39;s message may be forwarded to the output interface  290  for storage and/or processing. 
     In alternative embodiments of the present invention, the understandability evaluator  280  may receive the measured speech level, the measured signal-to-noise ratio, and/or the calculated estimate of intelligibility and compare each to its respective threshold. The understandability evaluator  280  may evaluate the difference between the measured and/or calculated values and their respective thresholds and determine whether the user&#39;s message is intelligible or unintelligible. For example, the understandability evaluator may determine that even though one of the measured and/or calculated values is below its respective threshold, another of the measured and/or calculated values is well above its respective threshold and so the user&#39;s message should be classified as intelligible. It is recognized that the understandability evaluator  280  may perform other calculations and/or computations based on the measured and/or calculated values and/or their respective thresholds to determine whether the user&#39;s message is intelligible. 
     Several embodiments of the present invention are specifically illustrated and/or described herein. However, it will be appreciated that modifications and variations of the present invention are covered by the above teachings and within the purview of the appended claims without departing from the spirit and intended scope of the invention.