Patent Publication Number: US-2023147222-A1

Title: Hotword detection on multiple devices

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This patent application is a continuation of, and claims priority under 35 U.S.C. § 120 from, U.S. patent application Ser. No. 17/137,157, filed on Dec. 29, 2020, which is a continuation of U.S. patent application Ser. No. 16/553,883, filed on Aug. 28, 2019, which is a continuation of U.S. patent application Ser. No. 16/171,495, filed on Oct. 26, 2018, which is a continuation of U.S. patent application Ser. No. 15/346,914, filed on Nov. 9, 2016, which is a continuation of U.S. patent application Ser. No. 15/088,477, filed on Apr. 1, 2016, which is a continuation of U.S. patent application Ser. No. 14/675,932, filed on Apr. 1, 2015, which claims priority under 35 U.S.C. § 119(e) from, U.S. Provisional Application No. 62/061,830, filed on Oct. 9, 2014. The disclosures of these prior applications are considered part of the disclosure of this application and are hereby incorporated by reference in their entireties. 
    
    
     TECHNICAL FIELD 
     This specification generally relates to systems and techniques for recognizing the words that a person is speaking, otherwise referred to as speech recognition. 
     BACKGROUND 
     The reality of a speech-enabled home or other environment — that is, one in which a user need only speak a query or command out loud and a computer-based system will field and answer the query and/or cause the command to be performed—is upon us. A speech-enabled environment (e.g., home, workplace, school, etc.) can be implemented using a network of connected microphone devices distributed throughout the various rooms or areas of the environment. Through such a network of microphones, a user has the power to orally query the system from essentially anywhere in the environment without the need to have a computer or other device in front of him/her or even nearby. For example, while cooking in the kitchen, a user might ask the system “how many milliliters in three cups?” and, in response, receive an answer from the system, e.g., in the form of synthesized voice output. Alternatively, a user might ask the system questions such as “when does my nearest gas station close,” or, upon preparing to leave the house, “should I wear a coat today?” 
     Further, a user may ask a query of the system, and/or issue a command, that relates to the user&#39;s personal information. For example, a user might ask the system “when is my meeting with John?” or command the system “remind me to call John when I get back home.” 
     SUMMARY 
     For a speech-enabled system, the users&#39; manner of interacting with the system is designed to be primarily, if not exclusively, by means of voice input. Consequently, the system, which potentially picks up all utterances made in the surrounding environment including those not directed to the system, must have some way of discerning when any given utterance is directed at the system as opposed, e.g., to being directed at an individual present in the environment. One way to accomplish this is to use a hotword, which by agreement among the users in the environment, is reserved as a predetermined word that is spoken to invoke the attention of the system. In an example environment, the hotword used to invoke the system&#39;s attention are the words “OK computer.” Consequently, each time the words “OK computer” are spoken, it is picked up by a microphone, conveyed to the system, which performs speech recognition techniques to determine whether the hotword was spoken and, if so, awaits an ensuing command or query. Accordingly, utterances directed at the system take the general form [HOTWORD] [QUERY], where “HOTWORD” in this example is “OK computer” and “QUERY” can be any question, command, declaration, or other request that can be speech recognized, parsed and acted on by the system, either alone or in conjunction with the server via the network. 
     According to one innovative aspect of the subject matter described in this specification, a user device receives an utterance that is spoken by a user. The user device determines whether the utterance includes a hotword and computes a hotword confidence score that indicates a likelihood that the utterance includes the hotword. The user device transmits this score to other user devices in the near vicinity. The other user devices likely received the same utterance. The other user devices compute a hotword confidence score and transmit their scores to the user device. The user device compares the hotword confidence scores. If the user device has the highest hotword confidence score, then the user device remains active and prepares to process additional audio. If the user device does not have the highest hotword confidence score, then the user device does not process the additional audio. 
     In general, another innovative aspect of the subject matter described in this specification may be embodied in methods that include the actions of receiving, by a first computing device, audio data that corresponds to an utterance; determining a first value corresponding to a likelihood that the utterance includes a hotword; receiving a second value corresponding to a likelihood that the utterance includes the hotword, the second value being determined by a second computing device; comparing the first value and the second value; and based on comparing the first value to the second value, initiating speech recognition processing on the audio data. 
     These and other embodiments can each optionally include one or more of the following features. The actions further include determining that the first value satisfies a hotword score threshold. The actions further include transmitting the first value to the second computing device. The actions further include determining an activation state of the first computing device based on comparing the first value and the second value. The action of determining an activation state of the first computing device based on comparing the first value and the second value further includes determining that the activation state is an active state. The actions further include receiving, by the first computing device, additional audio data that corresponds to an additional utterance; determining a third value corresponding to a likelihood that the additional utterance includes the hotword; receiving a fourth value corresponding to a likelihood that the utterance includes the hotword, the fourth value being determined by a third computing device; comparing the first value and the second value; and based on comparing the first value and the second value, determining that the activation state of the first computing device is an inactive state. 
     The action of transmitting the first value to the second computing device further includes transmitting, to a server, through a local network, or through a short range radio, the first value. The action of receiving a second value corresponding to a likelihood that the utterance includes the hotword, the second value being determined by a second computing device further includes receiving, from the server, through the local network, or through the short range radio, a second value that was determined by a second computing device. The actions further include identifying the second computing device; and determining that the second computing device is configured to respond to utterances that include the hotword. The action of transmitting the first value to the second computing device further includes transmitting a first identifier for the first computing device. The action of receiving a second value corresponding to a likelihood that the utterance includes the hotword, the second value being determined by a second computing device further includes receiving a second identifier for the second computing device. The action of determining that the activation state is an active state further includes determining that a particular amount of time has elapsed since receiving the audio data that corresponds to the utterance. The actions further include continuing, for a particular amount of time, to transmit the first value based on determining that the activation state is an active state. 
     Other embodiments of this aspect include corresponding systems, apparatus, and computer programs recorded on computer storage devices, each configured to perform the operations of the methods. 
     Particular embodiments of the subject matter described in this specification can be implemented so as to realize one or more of the following advantages. Multiple devices can detect a hotword and only one device will respond to the hotword. 
     The details of one or more embodiments of the subject matter described in this specification are set forth in the accompanying drawings and the description below. Other features, aspects, and advantages of the subject matter will become apparent from the description, the drawings, and the claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a diagram of an example system for hotword detection. 
         FIG.  2    is a diagram of an example process for hotword detection. 
         FIG.  3    shows an example of a computing device and a mobile computing device. 
     
    
    
     Like reference numbers and designations in the various drawings indicate like elements. 
     DETAILED DESCRIPTION 
     In the not too distant future, it is possible that many devices may be continuously listening for hotwords. When a single user has multiple devices trained to respond to their voice (e.g., a phone, tablet, TV, etc), it may be desirable to suppress responding to hotwords on devices that are not likely to be the ones a user intends to address. For example, when a user speaks the hotword toward one device, if any of their other devices are nearby, it is likely that they will also trigger a voice search. In many cases, this is not the user&#39;s intention. Thus, it may be advantageous if only a single device should trigger, specifically the device the user is speaking to. The present specification addresses the problem of selecting the correct device for reacting to a hotword, and suppressing reaction to the hotword on other devices. 
       FIG.  1    is a diagram of an example system  100  for hotword detection. In general, system  100  illustrates a user  102  speaking an utterance  104  that is detected by microphones of computing devices  106 ,  108 , and  110 . The computing devices  106 ,  108 , and  110  process the utterance  104  to determine a likelihood that the utterance  104  includes a hotword. The computing devices  106 ,  108 , and  110  each transmit data to each other that indicates the likelihood that the utterance  104  includes a hotword. The computing devices  106 ,  108 , and  110  each compare the data, and the computing device that computed the highest likelihood that the utterance  104  included a hotword initiates speech recognition on the utterance  104 . The computing devices that did not compute the highest likelihood that the utterance  104  includes a hotword do not initiate speech recognition on the speech following the utterance  104 . 
     Before transmitting, to another computing device, data that indicates a likelihood that the utterance  104  corresponds to a hotword, the computing devices that are located near each other identify each other. In some implementations, the computing devices identify each other by searching the local network for other devices that are configured to respond to the hotword. For example, computing device  106  may search the local area network for other devices that are configured to respond to the hotword and identify computing device  108  and computing device  110 . 
     In some implementations, the computing devices identify other nearby computing devices that are configured to respond to the hotword by identifying the user who is logged into each device. For example, user  102  is logged into computing devices  106 ,  108 , and  110 . The user  102  has the computing device  106  is the user&#39;s hand. The computing device  108  is sitting on the table, and the computing device  110  is located on a nearby wall. Computing device  106  detects computing devices  108  and  110  and each computing device shares information that is related to the user who is logged into the computing device, such as a user identifier. In some implementations, the computing devices may identify other near computing devices that are configured to respond to the hotword by identifying computing devices that are configured to respond when the hotword is spoken by the same user through speaker identification. For example, the user  102  configured the computing devices  106 ,  108 , and  110  each to respond to the voice of user  102  when user  102  speaks the hotword. The computing devices share the speaker identification information by providing a user identifier for user  102  to each other computing device. In some implementations, the computing devices may identify other computing devices that are configured to respond to the hotword through short range radio. For example, the computing device  106  may transmit a signal through short range radio searching for other computing devices that are configured to respond to the hotword. The computing devices may employ one of these techniques or a combination of them to identify other computing devices that are configured to respond to the hotword. 
     Once the computing devices  106 ,  108 , and  110  have identified other computing devices that are configured to respond to the hotword, the computing devices  106 ,  108 , and  110  share and store device identifiers for the identified computing devices. The identifiers may be based on a type of device, an IP address of the device, a MAC address, a name given to the device by a user, or any similar unique identifier. For example, the device identifier  112  for computing device  106  may be “phone.” The device identifier  114  for computing device  108  may be “tablet.” The device identifier  116  for computing device  110  may be “thermostat.” The computing devices  106 ,  108 , and  110  store the device identifier for the other computing devices that are configured to respond to the hotword. Each computing device has a device group where the computing device stores the device identifiers. For example, computing device  106  has device group  118  that lists “tablet” and “thermostat” as the two devices that will receive the likelihood that the audio data includes the hotword as computed by the computing device  106 . The computing device  108  has device group  120  that lists “phone” and “thermostat” as the two devices that will receive the likelihood that the audio data includes the hotword as computed by the computing device  108 . The computing device  110  has device group  122  that lists “phone” and “tablet” as the two devices that will receive the likelihood that the audio data includes the hotword as computed by the computing device  110 . 
     When the user  102  speaks the utterance  104 , “OK computer,” each computing device that has a microphone in the vicinity of the user  102  detects and processes the utterance  104 . Each computing device detects the utterance  104  through an audio input device such as a microphone. Each microphone provides audio data to a respective audio subsystem. The respective audio subsystem buffers, filters, and digitizes the audio data. In some implementations, each computing device may also perform endpointing and speaker identification on the audio data. The audio subsystem provides the processed audio data to a hotworder. The hotworder compares the processed audio data to known hotword data and computes a confidence score that indicates the likelihood that the utterance  104  corresponds to a hotword. The hotworder may extract audio features from the processed audio data such as filterbank energies or mel-frequency cepstral coefficients. The hotworder may use classifying windows to process these audio features such as by using a support vector machine or a neural network. Based on the processing of the audio features, the hotworder  124  computes a confidence score of 0.85, hotworder  126  computes a confidence score of 0.6, and hotworder  128  computes a confidence score of 0.45. In some implementations, the confidence score may be normalized to a scale of zero to one, with a higher number indicating a greater confidence that the utterance  104  includes a hotword. 
     Each computing device transmits a respective confidence score data packet to the other computing devices in the device group. Each confidence score data packet includes a respective confidence score and the respective device identifier for the computing device. For example, the computing device  106  transmits the confidence score data packet  130  that includes the confidence score of 0.85 and the device identifier “phone” to computing devices in device group  118 , computing devices  108  and  110 . The computing device  108  transmits the confidence score data packet  132  that includes the confidence score of 0.6 and the device identifier “tablet” to computing devices in device group  120 , computing devices  106  and  110 . The computing device  110  transmits the confidence score data packet  134  that includes the confidence score of 0.45 and the device identifier “thermostat” to computing devices in device group  118 , computing device  106  and  108 . 
     In some implementations, a computing device may transmit the confidence score data packet if the confidence score satisfies a hotword score threshold. For example, if the hotword score threshold is 0.5, then the computing device  110  would not transmit the confidence score data packet  134  to the other computing devices in device group  122 . The computing devices  106  and  108  would still transmit the confidence score data packets  130  and  132  to computing devices in device groups  118  and  120 , respectively. 
     In some implementations, the computing device that transmit a confidence score data packet may transmit the confidence score data packet to other computing devices directly. For example, computing device  106  may transmit the confidence score data packet  130  to computing devices  108  and  110  through a short range radio. The communication protocol used between two computing devices may be universal plug and play. In some implementations, a computing device that transmits a confidence score data packet may broadcast the confidence score data packet. In this instance, the confidence score data packet may be received by the computing devices in the device group and by other computing devices. In some implementations, a computing device that transmits a confidence score data packet may transmit the confidence score data packet to a server and then the server transmits the confidence score data packet to the computing devices in the data group. The server may be located within the local area network of the computing devices or accessible through the Internet. For example, the computing device  108  sends the confidence score data packet  132  and the list of computing devices in device group  120  to a server. The server transmits the confidence score data packet  132  to computing device  106  and  110 . In instances where a computing device that is transmitting the confidence score data packet to another computing device, the receiving computing device may send back a confirmation that the receiving computing device received the confidence score data packet. 
     Each computing device uses a score comparer to compare the hotword confidence scores that the computing device has received. For example, the computing device  106  computed a hotword confidence score of 0.85 and received hotword confidence scores of 0.6 and 0.45. In this instance, the score comparer  136  compares the three scores and identifies the score of 0.85 as the highest. For computing devices  108  and  110 , the score comparers  138  and  140  reach similar conclusions, identifying the score of 0.85, which corresponds to computing device  106 , as the highest. 
     The computing device that determines that its own hotword confidence score is the highest initiates speech recognition on speech data the follows the hotword utterance. For example, the user may speak “OK computer” and computing device  106  may determine that it has the highest hotword confidence score. The computing device  106  will initiate speech recognition on audio data received after the hotword. If the user speaks “call Alice,” then the computing device  106  will process the utterance and execute the appropriate command. In some implementations, receiving a hotword may cause the computing devices that receive the hotword to activate from a sleep state. In this instance, the computing device with the highest hotword confidence score remains in an awake state while the other computing devices that do not have the highest hotword confidence score do not process speech data that follows the hotword utterance and enter a sleep state. 
     As illustrated in  FIG.  1   , the score comparer  136  identified the hotword confidence score corresponding to computing device  106  to be the highest. Therefore, the device status  142  is “awake.” The score comparers  138  and  140  also identified the hotword confidence score corresponding to computing device  106  to be the highest. Therefore, the device statuses  138  and  140  are “asleep.” In some implementations, the activation state of the computing device may be unaffected. For example, the user  102  may be watching a movie on the computing device  108  and have the computing device  106  in the user&#39;s hand. When the user  102  speaks “OK computer,” the computing device  106 , by virtue of having the highest hotword confidence score, initiates speech recognition on the audio data following the hotword. The computing device  108  does not initiate speech recognition on the audio data following the hotword, and continues to play the movie. 
     In some implementations, the computing device that determines that it has the highest hotword confidence score waits for a particular amount of time before beginning to perform speech recognition on speech following the hotword. Doing so allows a computing device that computed the highest hotword confidence score to begin performing speech recognition on speech that follows the hotword without waiting for a higher hotword confidence score. To illustrate, the score comparer  136  of computing device  106  received hotword confidence scores of 0.6 and 0.45 from computing device  108  and  110 , respectively, as well as the hotword confidence score of 0.85 from the hotworder  124 . From the time that the hotworder  124  computes a hotword confidence score of the “Ok computer” audio data, the computing device  106  waits five hundred milliseconds before performing speech recognition on speech that follows the hotword. In instances where the score comparer receives a higher score, the computing device may not wait for a particular amount of time before setting the device status to “sleep.” For example, the hotworder  126  of computing device  108  computes a hotword confidence score of 0.6 and receives hotword confidence scores of 0.85 and 0.45. Once the computing device  108  receives the hotword confidence score of  0 . 85 , then the computing device  108  can set the device status  144  to “sleep.” This assumes that the computing device  108  receives the hotword confidence score of  0 . 85  within the particular amount of time after the hotworder  126  computes the hotword confidence score of 0.6. 
     In some implementations, when a computing device has the highest hotword confidence score, the computing device may continue to broadcast the confidence score data packet for a particular amount of time to ensure that other computing devices receive the confidence score data packet. This strategy would be most applicable in instances where a computing device does send back a confirmation once it receives a confidence score data packet from another computing device. Therefore, if the computing device  106  transmits the confidence score data packet  130  to computing devices in data group  118  and receives a confirmation before a particular amount of time such as five hundred milliseconds, then the computing device  106  may begin to perform speech recognition on speech following the hotword. In instances where computing devices broadcast their confidence score data packets and do not expect confirmation, the computing device may continue to broadcast their hotword confidence scores for a particular amount of time, such as five hundred milliseconds, or until the computing device receives a higher hotword confidence score, whichever comes first. For example, computing device  110  computes a hotword confidence score of 0.45 and begins to broadcast the confidence score data packet  134 . After three hundred milliseconds, the computing device  110  receives confidence score data packet  130  and stops broadcasting the confidence score data packet  134  because the hotword confidence score of  0 . 85  from confidence score data packet  130  is higher than the hotword confidence score of forty five. As another broadcast example, computing device  106  computes a hotword confidence score of 0.45 and begins to broadcast the confidence score data packet  130 . After five hundred milliseconds, the computing device  106  stops broadcasting confidence score data packet  130  and begins to perform speech recognition on speech following the hotword. The computing device  106  may receive the confidence score data packets  132  and  134  before five hundred milliseconds has elapsed, but because the hotword confidence scores in the confidence score data packets  132  and  134  are lower than 0.85, the computing device continues to wait until after the five hundred milliseconds has elapsed. 
     In some implementations, the computing device may begin to perform speech recognition on speech following the hotword until the computing device receives a higher hotword confidence score. The hotworder computes a hotword confidence score and if the hotword confidence score satisfies a threshold, then the computing device performs speech recognition on speech following the hotword. The computing device may perform the speech recognition without displaying any indication of the speech recognition to the user. This may be desirable because doing so gives the user the impression that the computing device is not active while also allowing the computing device to display results based on the speech recognition to the user quicker than if the computing device had waited until the computing device confirmed that it computed the highest hotword score. As an example, the computing device  106  computes a hotword confidence score of 0.85 and begins to perform speech recognition on speech following the hotword. The computing device  106  receives confidence score data packets  132  and  134  and determines that the hotword confidence score of 0.85 is the highest. The computing device  106  continues to perform speech recognition on speech following the hotword and presents the results to the user. For computing device  108 , the hotworder  126  computes a hotword confidence score of 0.6 and the computing device  108  begins to perform speech recognition on speech following the hotword without displaying data to the user. Once the computing device  108  receives the confidence score data packet  130  that includes the hotword confidence of 0.85, the computing device stops performing speech recognition. No data is displayed to the user, and the user is likely under the impression that the computing device  108  has remained in a “sleep” state. 
     In some implementations, to avoid any latency after a hotword is spoken, scores could be reported from the hotworder before the end of the hotword, e.g. for a partial hotword. For example, as a user is speaking “Ok computer,” a computing device could compute a partial hotword confidence score once the user has finished speaking “OK comp.” The computing device can then share the partial hotword confidence score with other computing devices. The computing device with the highest partial hotword confidence score can continue to process the user&#39;s speech. 
     In some implementations, a computing device may emit an audible or inaudible sound, e.g., of a particular frequency or frequency pattern, when the computing device determines that a hotword confidence score satisfies a threshold. The sound would signal to other computing devices that the computing device will continue to process the audio data following the hotword. Other computing devices would receive this sound and cease processing of the audio data. For example, a user speaks “Ok computer.” One of the computing devices computes a hotword confidence score that is greater than or equal to a threshold. Once the computing device determines that the hotword confidence score is greater than or equal two a threshold, the computing device emits a sound of eighteen kilohertz. The other computing devices in the vicinity of the user may also be computing a hotword confidence score and may be in the middle of computing a hotword confidence score when the other computing devices receive the sound. When the other computing devices receive the sound, the other computing devices cease processing of the user&#39;s speech. In some implementations, the computing device may encode the hotword confidence score in the audible or inaudible sound. For example, if the hotword confidence score is  0 . 5 , then the computing device may generate an audible or inaudible sound that includes a frequency pattern that encodes the score of 0.5. 
     In some implementations, the computing devices may use different audio metrics to select a computing device to continue processing the user&#39;s speech. For example, the computing devices may use loudness to determine which computing device will continue to process the user&#39;s speech. The computing device that detects the loudest speech may continue to process the user&#39;s speech. As another example, the computing device that is currently in use or has an active display may notify the other computing devices that it will continue to processes the user&#39;s speech upon detecting a hotword. 
     In some implementations, each computing device that is in the vicinity of the user while the user is speaking receives the audio data and sends the audio data to a server to improve speech recognition. Each computing device can receive the audio data that corresponds to the user&#39;s speech. While only one computing device will appear to the user to be processing the user&#39;s speech, each computing device can transmit the audio data to a server. The server can then use the audio data that is received from each computing device to improve speech recognition because the server can compare different audio samples that correspond to the same utterance. For example, a user says “Ok computer, remind me to buy milk.” Once the user finishes speaking “Ok computer,” the nearby computing devices will have likely determined which computing device has the highest hotword confidence score and that computing device will process and respond “remind me to buy milk” as the user speaks those words. The other computing devices will also receive “remind me to buy milk.” While the other computing device will not respond to the “remind me to buy milk” utterance, the other computing devices can send audio data corresponding to “remind me to buy milk” to a server. The computing devices responding to “remind me to buy milk” can also send its audio data to the server. The server can process the audio data to improve speech recognition because the server has different audio samples from different computing devices that correspond to the same “remind me to buy milk” utterance. 
       FIG.  2    is a diagram of an example process  200  for hotword detection. The process  200  may be performed by a computing device such as the computing device  108  from  FIG.  1   . The process  200  computes a value that corresponds a likelihood that an utterance includes a hotword and compares the value to other values computed by other computing devices to determine whether or not to perform speech recognition on the portion of the utterance after the hotword. 
     The computing device receives audio data that corresponds to an utterance ( 210 ). A user speaks the utterance and a microphone of the computing device receives the audio data of the utterance. The computing device processes the audio data by buffering, filtering, endpointing, and digitizing the audio data. As an example, the user may utter “Ok, computer” and the microphone of the computing device will receive the audio data that corresponds to “Ok, computer.” An audio subsystem of the computing device will sample, buffer, filter, and endpoint the audio data for further processing by the computing device. 
     The computing device determines a first value corresponding to a likelihood that the utterance includes a hotword ( 220 ). The computing device determines the first value, which may be referred to as a hotword confidence score, by comparing the audio data of the utterance to a group of audio samples that include the hotword or by analyzing the audio characteristics of the audio data of the utterance. The first value may be normalized to a scale from zero to one where one indicates the highest likelihood that the utterance includes a hotword. In some implementations, the computing device identifies a second computing device and determines that the second computing device is configured to respond to utterances that include the hotword and is configured by the user to be responsive to the hotword. The user may be logged into both the computing device and the second computing device. Both the computing device and the second computing device may be configured to respond to the user&#39;s voice. The computing device and the second computing device may be connected to the same local area network. The computing device and the second computing device may both be located within a particular distance of each other, such as ten meters, as determined by GPS or signal strength. For example, the computing devices may communicate by a short range radio. The computing device may detect a strength of a signal being transmitted by the second computing device as five dBm and translate that a corresponding distance such as five meters. 
     The computing device receives a second value corresponding to a likelihood that the utterance includes the hotword, the second value being determined by a second computing device ( 230 ). The second computing device receives the utterance through a microphone of the second computing device. The second computing device processes the received audio data that corresponds to the utterance and determines a second value or a second hotword confidence score. The second hotword confidence score reflect the likelihood, as calculated by the second computing device, that the utterance includes a hotword. In some implementations, the computing device transmits the first value to the second computing device using one or more of the following techniques. The computing device may transmit the first value to the second computing device through a server accessible through the Internet, through a server that is located on the local area network, or directly through the local area network or a short range radio. The computing device may transmit the first value only to the second computing device or the computing device may broadcast the first value so that other computing devices may also receive the first value. The computing device may receive the second value from the second computing device using the same or different technique as the computing device transmitted the first value. 
     In some implementations, the computing device may compute a loudness score for the utterance or a signal to noise ratio for the utterance. The computing device may combine the loudness score, the signal to noise ratio, and the hotword confidence score to determine a new value for comparing to similar values from other computing devices. For example, the computing device may compute a hotword confidence score and a signal to noise ratio. The computing device may then combine those two scores and compare to similarly computed scores from other computing devices. In some implementations, the computing device may compute different scores and transmit each score to other computing devices for comparison. For example, the computing device may compute a loudness score for the utterance and a hotword confidence score. The computing device may then transmit those scores to other computing devices for comparison. 
     In some implementations, the computing device may transmit a first identifier with the first value. The identifier may be based on one or more of an address of the computing device, a name of the computing device given by the user, or a location of the computing device. For example, an identifier may be “ 69 . 123 . 132 . 43 ” or “phone.” Similarly, the second computing device may transmit a second identifier with the second value. In some implementations, the computing device may transmit the first identifier to particular computing devices that the computing device previously identified as configured to respond to the hotword. For example, the computing device may have previously identified the second computing device as configured to respond to the hotword because, in addition to being able to respond to a hotword, the same user was logged into the second computing device as the computing device. 
     The computing device compares the first value and the second value ( 240 ). The computing device then initiates, based on the result of the comparison, speech recognition processing on the audio data ( 250 ). In some implementations, for example, the computing device initiates speech recognition when the first value is greater than or equal to the second value. If the user spoke “ok computer, call Carol,” then the computing device would begin to process “call Carol” by performing speech recognition on “call Carol” because the first value is greater than or equal to second value. In some implementations, the computing device sets an activation state. In instances where the first value is greater than or equal to the second value, then the computing device sets the activation state as active or “awake.” In the “awake” state, the computing device displays results from the speech recognition. 
     In some implementations, the computing device compares the first value and the second value and determines that the first value is less than the second value. The computing device, based on determining that the first value is less than the second value, sets the activation state as inactive or “sleep.” In the “sleep” state, the computing device does not appear, to the user, to be active or processing the audio data. 
     In some implementations, when the computing device determines that the first value is greater than or equal to the second value, the computing device may wait for a particular amount of time before setting the activation state to active. The computing device may wait for the particular amount of time to increase the probability that the computing device will not receive a higher value from another computing device. The particular amount of time may be fixed or may vary depending on the technique that the computing devices transmit and receive values. In some implementations, when the computing device determines that the first value is greater than or equal to the second value, the computing device may continue to transmit the first value for a particular amount of time. By continuing to transmit the first value for a particular amount of time, the computing device increases the probability that the first value is received by the other computing devices. In instances where the computing device determines that the first value is less than the second value, the computing device may stop transmitting the first value. 
     In some implementations, the computing device may consider additional information in determining whether to execute the command following the hotword. One example of the additional information may be the portion of the utterance that follows the hotword. Typically, the audio data that follows the hotword corresponds to a command for the computing device such as “call Sally,” “play Halloween Movie,” or “set heat to 70 degrees.” The computing device may identify a typical device that handles the type of request or that is capable of handling the request. A request to call a person would be typically handled by a phone based on pre-programed typical usages or based on usage patterns of a user of the device. If the user typically watches movies on a tablet, then the tablet may handle a request to play a movie. If the thermostat is capable of adjusting the temperature, then the thermostat may handle temperature adjustments. 
     For the computing device to consider the portion of the utterance that follows the hotword, the computing device would have to initiate speech recognition on the audio data once it likely identifies a hotword. The computing device may categorize the command portion of the utterance and compute a frequency of commands in that category. The computing device may transmit the frequency along with the hotword confidence score to other computing devices. Each computing device may use the frequencies and the hotword confidence scores to determine whether to execute the command following the hotword. 
     For example, if the user utters “OK computer, play Michael Jackson,” then if the computing device is a phone that the user use&#39;s twenty percent of the time to listen to music, then the computing device may transmit that information along with the hotword confidence score. A computing device such as a tablet that the user uses five percent of the time to listen to music may transmit that information along with the hotword confidence score to other computing devices. The computing devices may use a combination of the hotword confidence score and the percentage of time playing music to determine whether to execute the command. 
       FIG.  3    shows an example of a computing device  300  and a mobile computing device  350  that can be used to implement the techniques described here. The computing device  300  is intended to represent various forms of digital computers, such as laptops, desktops, workstations, personal digital assistants, servers, blade servers, mainframes, and other appropriate computers. The mobile computing device  350  is intended to represent various forms of mobile devices, such as personal digital assistants, cellular telephones, smart-phones, and other similar computing devices. The components shown here, their connections and relationships, and their functions, are meant to be examples only, and are not meant to be limiting. 
     The computing device  300  includes a processor  302 , a memory  304 , a storage device  306 , a high-speed interface  308  connecting to the memory  304  and multiple high-speed expansion ports  310 , and a low-speed interface  312  connecting to a low-speed expansion port  314  and the storage device  306 . Each of the processor  302 , the memory  304 , the storage device  306 , the high-speed interface  308 , the high-speed expansion ports  310 , and the low-speed interface  312 , are interconnected using various busses, and may be mounted on a common motherboard or in other manners as appropriate. The processor  302  can process instructions for execution within the computing device  300 , including instructions stored in the memory  304  or on the storage device  306  to display graphical information for a GUI on an external input/output device, such as a display  316  coupled to the high-speed interface  308 . In other implementations, multiple processors and/or multiple buses may be used, as appropriate, along with multiple memories and types of memory. Also, multiple computing devices may be connected, with each device providing portions of the necessary operations (e.g., as a server bank, a group of blade servers, or a multi-processor system). 
     The memory  304  stores information within the computing device  300 . In some implementations, the memory  304  is a volatile memory unit or units. In some implementations, the memory  304  is a non-volatile memory unit or units. The memory  304  may also be another form of computer-readable medium, such as a magnetic or optical disk. 
     The storage device  306  is capable of providing mass storage for the computing device  300 . In some implementations, the storage device  306  may be or contain a computer-readable medium, such as a floppy disk device, a hard disk device, an optical disk device, or a tape device, a flash memory or other similar solid state memory device, or an array of devices, including devices in a storage area network or other configurations. Instructions can be stored in an information carrier. The instructions, when executed by one or more processing devices (for example, processor  302 ), perform one or more methods, such as those described above. The instructions can also be stored by one or more storage devices such as computer- or machine-readable mediums (for example, the memory  304 , the storage device  306 , or memory on the processor  302 ). 
     The high-speed interface  308  manages bandwidth-intensive operations for the computing device  300 , while the low-speed interface  312  manages lower bandwidth-intensive operations. Such allocation of functions is an example only. In some implementations, the high-speed interface  308  is coupled to the memory  304 , the display  316  (e.g., through a graphics processor or accelerator), and to the high-speed expansion ports  310 , which may accept various expansion cards (not shown). In the implementation, the low-speed interface  312  is coupled to the storage device  306  and the low-speed expansion port  314 . The low-speed expansion port  314 , which may include various communication ports (e.g., USB, Bluetooth, Ethernet, wireless Ethernet) may be coupled to one or more input/output devices, such as a keyboard, a pointing device, a scanner, or a networking device such as a switch or router, e.g., through a network adapter. 
     The computing device  300  may be implemented in a number of different forms, as shown in the figure. For example, it may be implemented as a standard server  320 , or multiple times in a group of such servers. In addition, it may be implemented in a personal computer such as a laptop computer  322 . It may also be implemented as part of a rack server system  324 . Alternatively, components from the computing device  300  may be combined with other components in a mobile device (not shown), such as a mobile computing device  350 . Each of such devices may contain one or more of the computing device  300  and the mobile computing device  350 , and an entire system may be made up of multiple computing devices communicating with each other. 
     The mobile computing device  350  includes a processor  352 , a memory  364 , an input/output device such as a display  354 , a communication interface  366 , and a transceiver  368 , among other components. The mobile computing device  350  may also be provided with a storage device, such as a micro-drive or other device, to provide additional storage. Each of the processor  352 , the memory  364 , the display  354 , the communication interface  366 , and the transceiver  368 , are interconnected using various buses, and several of the components may be mounted on a common motherboard or in other manners as appropriate. 
     The processor  352  can execute instructions within the mobile computing device  350 , including instructions stored in the memory  364 . The processor  352  may be implemented as a chipset of chips that include separate and multiple analog and digital processors. The processor  352  may provide, for example, for coordination of the other components of the mobile computing device  350 , such as control of user interfaces, applications run by the mobile computing device  350 , and wireless communication by the mobile computing device  350 . 
     The processor  352  may communicate with a user through a control interface  358  and a display interface  356  coupled to the display  354 . The display  354  may be, for example, a TFT (Thin-Film-Transistor Liquid Crystal Display) display or an OLED (Organic Light Emitting Diode) display, or other appropriate display technology. The display interface  356  may comprise appropriate circuitry for driving the display  354  to present graphical and other information to a user. The control interface  358  may receive commands from a user and convert them for submission to the processor  352 . In addition, an external interface  362  may provide communication with the processor  352 , so as to enable near area communication of the mobile computing device  350  with other devices. The external interface  362  may provide, for example, for wired communication in some implementations, or for wireless communication in other implementations, and multiple interfaces may also be used. 
     The memory  364  stores information within the mobile computing device  350 . The memory  364  can be implemented as one or more of a computer-readable medium or media, a volatile memory unit or units, or a non-volatile memory unit or units. An expansion memory  374  may also be provided and connected to the mobile computing device  350  through an expansion interface  372 , which may include, for example, a SIMM (Single In Line Memory Module) card interface. The expansion memory  374  may provide extra storage space for the mobile computing device  350 , or may also store applications or other information for the mobile computing device  350 . Specifically, the expansion memory  374  may include instructions to carry out or supplement the processes described above, and may include secure information also. Thus, for example, the expansion memory  374  may be provide as a security module for the mobile computing device  350 , and may be programmed with instructions that permit secure use of the mobile computing device  350 . In addition, secure applications may be provided via the SIMM cards, along with additional information, such as placing identifying information on the SIMM card in a non-hackable manner. 
     The memory may include, for example, flash memory and/or NVRAM memory (non-volatile random access memory), as discussed below. In some implementations, instructions are stored in an information carrier. that the instructions, when executed by one or more processing devices (for example, processor  352 ), perform one or more methods, such as those described above. The instructions can also be stored by one or more storage devices, such as one or more computer- or machine-readable mediums (for example, the memory  364 , the expansion memory  374 , or memory on the processor  352 ). In some implementations, the instructions can be received in a propagated signal, for example, over the transceiver  368  or the external interface  362 . 
     The mobile computing device  350  may communicate wirelessly through the communication interface  366 , which may include digital signal processing circuitry where necessary. The communication interface  366  may provide for communications under various modes or protocols, such as GSM voice calls (Global System for Mobile communications), SMS (Short Message Service), EMS (Enhanced Messaging Service), or MMS messaging (Multimedia Messaging Service), CDMA (code division multiple access), TDMA (time division multiple access), PDC (Personal Digital Cellular), WCDMA (Wideband Code Division Multiple Access), CDMA2000, or GPRS (General Packet Radio Service), among others. Such communication may occur, for example, through the transceiver  368  using a radio-frequency. In addition, short-range communication may occur, such as using a Bluetooth, WiFi, or other such transceiver (not shown). In addition, a GPS (Global Positioning System) receiver module  370  may provide additional navigation- and location-related wireless data to the mobile computing device  350 , which may be used as appropriate by applications running on the mobile computing device  350 . 
     The mobile computing device  350  may also communicate audibly using an audio codec  360 , which may receive spoken information from a user and convert it to usable digital information. The audio codec  360  may likewise generate audible sound for a user, such as through a speaker, e.g., in a handset of the mobile computing device  350 . Such sound may include sound from voice telephone calls, may include recorded sound (e.g., voice messages, music files, etc.) and may also include sound generated by applications operating on the mobile computing device  350 . 
     The mobile computing device  350  may be implemented in a number of different forms, as shown in the figure. For example, it may be implemented as a cellular telephone  380 . It may also be implemented as part of a smart-phone  382 , personal digital assistant, or other similar mobile device. 
     Various implementations of the systems and techniques described here can be realized in digital electronic circuitry, integrated circuitry, specially designed ASICs (application specific integrated circuits), computer hardware, firmware, software, and/or combinations thereof. These various implementations can include implementation in one or more computer programs that are executable and/or interpretable on a programmable system including at least one programmable processor, which may be special or general purpose, coupled to receive data and instructions from, and to transmit data and instructions to, a storage system, at least one input device, and at least one output device. 
     These computer programs (also known as programs, software, software applications or code) include machine instructions for a programmable processor, and can be implemented in a high-level procedural and/or object-oriented programming language, and/or in assembly/machine language. As used herein, the terms machine-readable medium and computer-readable medium refer to any computer program product, apparatus and/or device (e.g., magnetic discs, optical disks, memory, Programmable Logic Devices (PLDs)) used to provide machine instructions and/or data to a programmable processor, including a machine-readable medium that receives machine instructions as a machine-readable signal. The term machine-readable signal refers to any signal used to provide machine instructions and/or data to a programmable processor. 
     To provide for interaction with a user, the systems and techniques described here can be implemented on a computer having a display device (e.g., a CRT (cathode ray tube) or LCD (liquid crystal display) monitor) for displaying information to the user and a keyboard and a pointing device (e.g., a mouse or a trackball) by which the user can provide input to the computer. Other kinds of devices can be used to provide for interaction with a user as well; for example, feedback provided to the user can be any form of sensory feedback (e.g., visual feedback, auditory feedback, or tactile feedback); and input from the user can be received in any form, including acoustic, speech, or tactile input. 
     The systems and techniques described here can be implemented in a computing system that includes a back end component (e.g., as a data server), or that includes a middleware component (e.g., an application server), or that includes a front end component (e.g., a client computer having a graphical user interface or a Web browser through which a user can interact with an implementation of the systems and techniques described here), or any combination of such back end, middleware, or front end components. The components of the system can be interconnected by any form or medium of digital data communication (e.g., a communication network). Examples of communication networks include a local area network (LAN), a wide area network (WAN), and the Internet. 
     The computing system can include clients and servers. A client and server are generally remote from each other and typically interact through a communication network. The relationship of client and server arises by virtue of computer programs running on the respective computers and having a client-server relationship to each other. 
     Although a few implementations have been described in detail above, other modifications are possible. For example, while a client application is described as accessing the delegate(s), in other implementations the delegate(s) may be employed by other applications implemented by one or more processors, such as an application executing on one or more servers. In addition, the logic flows depicted in the figures do not require the particular order shown, or sequential order, to achieve desirable results. In addition, other actions may be provided, or actions may be eliminated, from the described flows, and other components may be added to, or removed from, the described systems. Accordingly, other implementations are within the scope of the following claims.