Patent Publication Number: US-2021183001-A1

Title: Power efficient detection of watermarks in media signals

Description:
RELATED APPLICATION(S) 
     This patent arises from a continuation of U.S. patent application Ser. No. 15/893,216 (now U.S. Pat. No. ______), entitled “POWER EFFICIENT DETECTION OF WATERMARKS IN MEDIA SIGNALS,” which was filed on Feb. 9, 2018, which is a continuation of U.S. patent application Ser. No. 15/495,584 (now U.S. Pat. No. 9,904,968), entitled “POWER EFFICIENT DETECTION OF WATERMARKS IN MEDIA SIGNALS,” which was filed on Apr. 24, 2017, which is a continuation of U.S. patent application Ser. No. 15/231,439 (now U.S. Pat. No. 9,641,857), entitled “POWER EFFICIENT DETECTION OF WATERMARKS IN MEDIA SIGNALS,” which was filed on Aug. 8, 2016, which is a continuation of U.S. patent application Ser. No. 14/587,995 (now U.S. Pat. No. 9,418,395), entitled “POWER EFFICIENT DETECTION OF WATERMARKS IN MEDIA SIGNALS,” which was filed on Dec. 31, 2014. Priority to each of U.S. patent application Ser. Nos. 14/587,995, 15/231,439, 15/495,584 and 15/893,216 is hereby claimed. U.S. patent application Ser. Nos. 14/587,995, 15/231,439, 15/495,584 and 15/893,216 are hereby incorporated by reference in their respective entireties. 
    
    
     FIELD OF THE DISCLOSURE 
     This disclosure relates generally to media watermarking and, more particularly, to power efficient detection of watermarks in media signals. 
     BACKGROUND 
     Watermarks can be embedded or otherwise included in media to enable additional information to be conveyed with the media. For example, audio watermarks can be embedded or otherwise included in the audio data/signal portion of a media stream, file and/or signal to convey data, such as media identification information, copyright protection information, etc., with the media. Such watermarks enable monitoring of the distribution and/or use of media, such as by detecting watermarks present in television broadcasts, radio broadcasts, streamed multimedia, etc., to identify the particular media being presented to viewers, listeners, users, etc. Such information can be valuable to advertisers, content providers, and the like. 
     Prior media monitoring systems employing watermarks typically include watermark decoders that run in a continuous fashion to ensure detection of the embedded watermarks in the monitored media signals. However, continuous operation of a watermark decoder can be undesirable in a portable meter. For example, such operation can quickly consume the available power of the portable meter and, thus, reduce the amount of time the portable meter is able to perform media monitoring. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram of an example media monitoring system including an example portable device implementing an example media device monitor supporting power efficient detection of watermarks in media signals in accordance with the teachings of this disclosure. 
         FIG. 2  illustrates an example watermark to be detected by the example media device monitor of  FIG. 1 . 
         FIG. 3  is a block diagram of an example implementation of the media device monitor of  FIG. 1 , which includes an example watermark detector controller to implement power efficient detection of watermarks in media signals in accordance with the teachings of this disclosure. 
         FIG. 4  is a block diagram illustrating an example implementation of the watermark detector controller of  FIG. 1 , which includes an example watermark verifier, an example watermark confirmer and an example search trigger evaluator. 
         FIG. 5  is a flowchart representative of first example machine readable instructions that may be executed to implement the example media device monitor of  FIGS. 1 and/or 3 , and/or the example watermark detector controller of  FIGS. 1, 3 and/or 4 . 
         FIG. 6  is a flowchart representative of first example machine readable instructions that may be executed to implement the example watermark verifier of  FIG. 4 . 
         FIG. 7  is a flowchart representative of first example machine readable instructions that may be executed to implement the example watermark confirmer of  FIG. 4 . 
         FIG. 8  is a flowchart representative of first example machine readable instructions that may be executed to implement the example search trigger evaluator of  FIG. 4 . 
         FIG. 9  is a flowchart representative of second example machine readable instructions that may be executed to implement the example media device monitor of  FIGS. 1 and/or 3 , and/or the example watermark detector controller of  FIGS. 1, 3 and/or 4 . 
         FIG. 10  is a flowchart representative of second example machine readable instructions that may be executed to implement the example watermark verifier of  FIG. 4 . 
         FIG. 11  is a flowchart representative of second example machine readable instructions that may be executed to implement the example watermark confirmer of  FIG. 4 . 
         FIG. 12  is a flowchart representative of second example machine readable instructions that may be executed to implement the example search trigger evaluator of  FIG. 4 . 
         FIG. 13  is a block diagram of an example processor platform structured to execute the example machine readable instructions of  FIGS. 5 and/or 9  to implement the example media device monitor of  FIGS. 1 and/or 3 . 
         FIG. 14  is a block diagram of an example processor platform structured to execute the example machine readable instructions of  FIGS. 5-11 and/or 12  to implement the example watermark detector controller of  FIGS. 1, 3 and/or 4 . 
     
    
    
     Wherever possible, the same reference numbers will be used throughout the drawing(s) and accompanying written description to refer to the same or like parts, elements, etc. As used herein, the phrase “in communication,” including variances thereof, encompasses direct communication and/or indirect communication through one or more intermediary components and does not require direct physical (e.g., wired) communication and/or constant communication, but rather additionally includes selective communication at periodic or aperiodic intervals, as well as one-time events. 
     DETAILED DESCRIPTION 
     Methods, apparatus, systems and articles of manufacture (e.g., physical storage media) to implement power efficient detection of watermarks in media signals are disclosed herein. Example watermark detection methods disclosed herein include operating a watermark detector in a first operating mode (e.g., such as a search mode) to search for a first watermark in a media signal. Such disclosed example methods also include, in response to detecting the first watermark, determining whether the first watermark satisfies a first condition. Such disclosed example methods further include, in response to determining the first watermark satisfies the first condition, operating the watermark detector in a second operating mode (e.g., such as a confirmation mode) in which the watermark detector cycles between a sleep interval and an active interval to detect a second watermark at a second location in the media signal relative to a first location of the first watermark in the media signal. 
     In some disclosed example methods, the first watermark includes a first group of symbols and a second group of symbols. In some such examples, the first group of symbols is repeated in the first watermark and the second watermark, whereas the second group of symbols differs between the first watermark and the second watermark. In some such disclosed example methods, detecting the first watermark includes detecting the first group of symbols in the media signal. Also, in some such disclosed example methods, the first watermark satisfies the first condition when the first group of symbols of the first watermark match a corresponding first group of symbols repeated in a third watermark detected by the watermark detector in the media signal within a first time period prior to detection of the first watermark. Additionally or alternatively, in some such disclosed example methods, the first watermark satisfies the first condition when respective ones of the first group of symbols of the first watermark satisfy respective symbol strength conditions. 
     Additionally or alternatively, in some such disclosed example methods, operating the watermark detector in the second operating mode includes operating the watermark detector to detect, in the media signal, the first group of symbols repeated in the second watermark. Additionally or alternatively, some such disclosed example methods further include continuing to operate the watermark detector in the second operating mode if at least one of (i) the first group of symbols repeated in the second watermark satisfies a first symbol strength condition or (ii) the first group of symbols repeated in the second watermark match at least a first number of the corresponding first group of symbols of the first watermark. Some such disclosed example methods also include transitioning operation of the watermark detector out of the second operating mode if (iii) the first group of symbols repeated in the second watermark does not satisfy the first symbol strength condition and (iv) the first group of symbols repeated in the second watermark does not match at least the first number of the corresponding first group of symbols of the first watermark. 
     In some such disclosed example methods, the sleep interval is a first sleep interval, and transitioning operation of the watermark detector out of the second operating mode transitioning operation of the watermark detector to the first operating mode if a second condition is met. Some such disclosed example methods also include, if the second condition is not met, transitioning operation of the operation of the watermark detector to a third operating mode (e.g., a sleep mode) in which the watermark detector is to (i) sleep for at least one of the first sleep interval or a second sleep interval different from the first sleep interval, and then (ii) transition operation to the first operating mode. 
     Additionally or alternatively, some example methods disclosed herein further include searching a buffer of prior watermark symbols evaluated by the watermark detector to detect a third watermark in the media signal in response to at least one of: (i) detecting the first watermark or (ii) detecting the second watermark at a third location in the media signal different from the second location. 
     Additionally or alternatively, some example methods disclosed herein further include, in response to not detecting the first watermark for a first time period of operating the watermark detector in the first operating mode, determining whether a second condition is met and, if the second condition is met, continuing to operate the watermark detector in the first operating mode. Some such disclosed example methods also include, if the second condition is not met, transitioning operation of the watermark detector to a third operating mode (e.g., a sleep mode) in which the watermark detector is to (i) sleep for at least one of the first sleep interval or a second sleep interval different from the first sleep interval then (ii) transition operation to the first operating mode. 
     These and other example methods, apparatus, systems and articles of manufacture (e.g., physical storage media) to implement power efficient detection of watermarks in media signals are disclosed in greater detail below. 
     As noted above, prior media monitoring systems employing watermarks typically include watermark decoders that run in a continuous fashion to ensure detection of the watermarks embedded in the media signals output from monitored media devices. However, when such watermark decoders are implemented by/in portable meters, their continuous operation can quickly consume the available power of the portable meter and, thus, reduce the amount of time the portable meter is able to perform media monitoring. Example methods, apparatus, systems and articles of manufacture (e.g., physical storage media) disclosed herein to implement power efficient detection of watermarks in media signals solve the technical problem of excessive power consumption associated with conventional watermark decoders in meters (e.g., portable meters). Power efficient detection of watermarks in media signals, as disclosed herein, is especially useful in watermarking systems in which a least of portion of a watermark is embedded repeatedly in the watermarked media at a given watermark repetition rate. For example, the watermark may include a first portion corresponding to media identification symbols and a second portion corresponding to timestamp symbols. In such examples, the media identification symbols remain the same across watermarks embedded in the media, whereas the timestamp symbols change with each successive watermark to, for example, identify a particular elapsed time within the watermarked media. In such examples, the media symbol portion of the watermark is repeated in the watermarked audio at the given watermark repetition rate. 
     Power efficient detection of watermarks in media signals, as disclosed herein, takes advantage of such repeating watermarks. For example, and as disclosed in further detail below, a watermark detector operated in accordance with the teachings of the disclosure is operated in a first (e.g., search) mode to search for and detect a first watermark. Then, after a first watermark is detected, the watermark detector is operated in a second (e.g., confirmation) mode in which watermark detection is targeted at the locations in the media signal where other watermarks are expected based on the watermark repetition rate and the duration of the watermark. At other times, the watermark detector is placed in a low-power sleep mode to conserve power. In this way, portable meters utilizing power efficient detection of watermarks in media signals, as disclosed herein, can achieve increased operating times and/or more efficient operation relative to prior portable meters. For example, when a watermark detector is placed in a low-power sleep mode in accordance with the teachings disclosed herein, a device (e.g., a portable device) implementing the watermark detector may also be placed in a low power mode. Additionally or alternatively, when a watermark detector is placed in a low-power sleep mode in accordance with the teachings disclosed herein, the device (e.g., portable device) implementing the watermark detector may redirect the processing power (e.g., processor cycles) used for watermark detection to native and/or other functions implemented by the device. Further techniques for improving efficiency of such portable meters are also disclosed in detail below. 
     Turning to the figures, a block diagram of an example media monitoring system  100  implementing power efficient detection of watermarks in media signals as disclosed herein is illustrated in  FIG. 1 . The example media monitoring system  100  supports monitoring of media presented at one or more monitored sites, such as an example monitored site  105  illustrated in  FIG. 1 . The monitored site  105  includes an example media device  110 , which is also referred to herein as a media presentation device  110 . Although the example of  FIG. 1  illustrates one monitored site  105  and one media device  110 , power efficient detection of watermarks in media signals as disclosed herein can be implemented in media monitoring systems  100  supporting any number of monitored sites  105  having any number of media devices  110 . 
     The media monitoring system  100  of the illustrated example includes an example media device meter  125 , also referred to as a meter  125 , a site meter  125 , a site unit  125 , a home unit  125 , a portable device  125 , etc., to monitor media presented by the media device  110 . In the illustrated example, the media monitored by the media device meter  125  can correspond to any type of media presentable by the media device  110 . For example, monitored media can correspond to media content, such a television programs, radio programs, movies, Internet video, video-on-demand, etc., as well as commercials, advertisements, etc. In the illustrated example, the media device meter  125  determines metering data that may identify and/or be used to identify media presented by the media device (and, thus, infer media exposure) at the monitored site  105 . The media device meter  125  then stores and reports this metering data via an example network  135  to an example data processing facility  140 . The data processing facility  140  performs any appropriate post-processing of the metering data to, for example, determine audience ratings information, identify targeted advertising to be provided to the monitored site  105 , etc. In the illustrated example, the network  135  can correspond to any type(s) and/or number of wired and/or wireless data networks, or any combination thereof. 
     In the illustrated example, the media device  110  monitored by the media device meter  125  can correspond to any type of audio, video and/or multimedia presentation device capable of presenting media audibly and/or visually. For example, the media device  110  can correspond to a television and/or display device that supports the National Television Standards Committee (NTSC) standard, the Phase Alternating Line (PAL) standard, the Système Électronique pour Couleur avec Mémoire (SECAM) standard, a standard developed by the Advanced Television Systems Committee (ATSC), such as high definition television (HDTV), a standard developed by the Digital Video Broadcasting (DVB) Project, etc. As other examples, the media device  110  can correspond to a multimedia computer system, a personal digital assistant, a cellular/mobile smartphone, a radio, a tablet computer, etc. 
     In the media monitoring system  100  of the illustrated example, the media device meter  125  and the data processing facility  140  cooperate to perform media monitoring based on detecting media watermarks. Moreover, the media device meter  125  detects media watermarks in a power efficient manner as disclosed herein. Examples of watermarks include identification codes, ancillary codes, etc., that may be transmitted within media signals. For example, identification codes can be transmitted as watermarked data embedded or otherwise included with media (e.g., inserted into the audio, video, or metadata stream of media) to uniquely identify broadcasters and/or media (e.g., content or advertisements). Watermarks can additionally or alternatively be used to carry other types of data, such as copyright protection information, secondary data (e.g., such as one or more hyperlinks pointing to secondary media retrievable via the Internet and associated with the primary media carrying the watermark), commands to control one or more devices, etc. Watermarks are typically extracted using a decoding operation. 
     In contrast, signatures are a representation of some characteristic of the media signal (e.g., a characteristic of the frequency spectrum of the signal). Signatures can be thought of as fingerprints. They are typically not dependent upon insertion of data in the media, but instead preferably reflect an inherent characteristic of the media and/or the signal transporting the media. Systems to utilize codes and/or signatures for audience measurement are long known. See, for example, U.S. Pat. No. 5,481,294 to Thomas et al., which is hereby incorporated by reference in its entirety. 
     In the illustrated example of  FIG. 1 , the media device meter  125  is implemented by a portable device including an example watermark detector  145  and an example watermark detector controller  150 . In the illustrated example, the watermark detector  145  is configured to detect watermark(s) in media signal(s) output from a monitored media device, such as the example media device  110 . In the illustrated example, the watermark detector controller  150  is configured to control operation of the watermark detector  145  in a power efficient manner in accordance with the teachings of this disclosure. In some examples, the media device meter  125  corresponds to a special purpose portable device constructed to implement the example watermark detector  145  and the example watermark detector controller  150 . In other examples, the media device meter  125  corresponds to any portable device capable of being adapted (via hardware changes, software changes, firmware changes, etc., or any combination thereof) to implement the example watermark detector  145  and the example watermark detector controller  150 . As such, the media device meter  125  can be implemented by a smartphone, a tablet computer, a handheld device, a wrist-watch type device, other wearable devices, a special purpose device, etc. In some examples, the media device meter  125  can be implemented by a portable device that, although portable, is intended to be relatively stationary. Furthermore, in some examples, the media device meter  125  can be implemented by or otherwise included in the media device  110 , such as when the media device  110  corresponds to a portable device (e.g., a smartphone, a tablet computer, a handheld device, etc.) capable of presenting media. (This latter implementation can be especially useful in example scenarios in which a media monitoring application is executed on the media device  110  itself, but the media device  110  prevents, e.g., via digital rights management or other techniques, third-party applications, such as the media monitoring application, from accessing protected media data stored on the media device  110 .) An example implementation of the media device meter  125  is illustrated in  FIG. 3 , which is described in further detail below. 
       FIG. 2  illustrates an example watermark  200  that the example media device meter  125  may be configured to detect. The watermark  200  of the illustrated is embedded or otherwise included in media to be presented by media device(s), such as the example media device  110 . For example, the watermark  200  may be embedded in an audio portion (e.g., an audio data portion, an audio signal portion, etc.) of the media, a video portion (e.g., a video data portion, a video signal portion, etc.) of the media, or a combination thereof. The example watermark  200  of  FIG. 2  includes an example first group of symbols  205  and an example second group of symbols  210 . In the illustrated example of  FIG. 2 , the first group of symbols  205  is repeated in successive watermarks  200  embedded/included in the media, whereas the second group of symbols  210  differs between successive watermarks  200  embedded/included in the media. 
     In the example watermark of  FIG. 2 , the first group of symbols  205  conveys media identification data (e.g., a media identifier) identifying the media watermarked by the watermark  200 . For example, the media identification data conveyed by the first group of symbols  205  may include data identifying a broadcast station providing the media, a name (e.g., program name) of the media, a source (e.g., a website) of the media, etc. Thus, in the illustrated example of  FIG. 2 , the first group of symbols  205  is also referred to as a first group of media identification symbols  205  (or simply the media identification symbols  205 ). Furthermore, the media identification data conveyed by the first group of symbols  205  (e.g., the media identification symbols  205 ) is repeated in successive watermarks  200  embedded/included in the media. 
     In some examples, the first group of symbols  205  of the watermark  200  includes example marker symbols  215 A-B to assist the watermark detector  145  in detecting the start of the watermark  200  in the watermarked media, and example data symbols  220 A-F to convey the media identification data. Also, in some examples, corresponding symbols pairs in similar respective locations after the first marker symbol  215 A and the second marker symbol  215 B are related by an offset. For example, the value of data symbol  220 D may correspond to the value of data symbol  220 A incremented by an offset, the value of data symbol  220 E may correspond to the value of data symbol  220 B incremented by the same offset, and the value of data symbol  220 F may correspond to the value of data symbol  220 C incremented by the same offset, as well. In such examples, the symbols pairs  220 A/D,  220 B/E and  220 C/F are referred to as symbol offset pairs, or offset pairs, and the offset used to generate the symbol offset pairs forms an additional data symbol that can be used to convey the media identification data. 
     In the example watermark  200  of  FIG. 2 , the second group of symbols  210  conveys timestamp data (e.g., a timestamp) identifying, for example, a particular elapsed time within the watermarked media. Thus, in the illustrated example of  FIG. 2 , the second group of symbols  210  is also referred to as the second group of timestamp symbols  210  (or simply the timestamp symbols  210 ). Furthermore, the timestamp data conveyed by the second group of symbols  210  (e.g., the timestamp symbols  210 ) differs in successive watermarks  200  embedded/included in the media (e.g., as the elapsed time of the watermarked media increases with each successive watermark  200 ). 
     In the illustrated example of  FIG. 2 , the watermark  200  is embedded/included in the desired media at a repetition interval of T seconds (or, in other words, at a repetition rate of 1/T seconds), with the first group of symbols  205  remaining the same in successive watermarks  200 , and the second group of symbols  205  varying in successive watermarks  200 . For example, the repetition interval T may correspond to T=4.8 seconds. As there are 12 symbols in the example watermark  200  (e.g., 8 symbols in the first group of symbols  205  and 4 symbols in the second group of symbols  210 ) each watermark symbol in the illustrated example has a duration of 4.8/12=0.4 seconds. However, other values for the repetition interval T may be used in other examples. 
     In some examples, a watermark symbol included in the watermark  200  is able to take on one of several possible symbol values. For example, if a symbol in the watermark  200  represents 4 bits of data, then the symbol is able to take on one of 16 different possible values. For example, each possible symbol value may correspond to a different signal amplitude, a different set of code frequencies, etc. In some such examples, to detect a watermark symbol embedded/included in watermarked media, the example watermark detector  145  processes monitored media data/signals output from the example media device  110  to determine measured values (e.g., signal-to-noise ratio (SNR) values) corresponding to each possible symbol value the symbol may have. The watermark detector  145  then selects the symbol value corresponding to the best (e.g., strongest, largest, etc.) measured value (possibly after averaging across multiple samples of the media data/signal) as the detected symbol value for that particular watermark symbol. 
     An example implementation of the media device meter  125  (e.g., which may be a portable device) of  FIG. 1  is illustrated in  FIG. 3 . In the illustrated example of  FIG. 3 , the media device meter  125  includes one or more example sensor(s)  305  to detect media data/signal(s) emitted or otherwise output by the example media device  110 . In some examples, the sensor(s)  305  include an audio sensor to monitor audio data/signal(s) output by the media device  110 . Such an audio sensor may be implemented using any type of audio sensor or audio interface, such as a microphone, a transducer, a cable/wire, etc., capable of receiving and processing audio signals (e.g., such as in the form of acoustic and/or electrical signals). Additionally or alternatively, in some examples, the sensor(s)  305  include a video sensor to monitor video data/signal(s) output by the media device  110 . Such a video sensor may be implemented using any type of video sensor or video interface, such as a camera, a light detector, a cable/wire, etc., capable of receiving and processing video signals (e.g., such as in the form of optical images and/or electrical signals). 
     The example media device meter  125  of  FIG. 3  also includes the example watermark detector  145 . In the illustrated example of  FIG. 3 , the watermark detector  145  is configured to detect watermarks, such as the example watermark  200  of  FIG. 2 , in the media data/signal(s) detected by the example sensor(s)  305 . In some examples, the watermark detector  145  of  FIG. 3  is structured to process audio data/signal(s) obtained by the sensor(s)  305  to detect symbols of instances of the watermark  200  that are encoded in one or more frequencies of the sensed audio data/signal(s), or otherwise encoded in the frequency domain of the sensed audio data/signal(s). Examples of encoding watermarks in the frequency domain of an audio signal, and corresponding example watermark detection techniques that may be implemented by the example watermark detector  145 , are described in U.S. Pat. No. 8,359,205, entitled “Methods and Apparatus to Perform Audio Watermarking and Watermark Detection and Extraction,” which issued on Jan. 22, 2013, U.S. Pat. No. 8,369,972, entitled “Methods and Apparatus to Perform Audio Watermarking Detection and Extraction,” which issued on Feb. 5, 2013, U.S. Publication No. 2010/0223062, entitled “Methods and Apparatus to Perform Audio Watermarking and Watermark Detection and Extraction,” which was published on Sep. 2, 2010, U.S. Pat. No. 6,871,180, entitled “Decoding of Information in Audio Signals,” which issued on Mar. 22, 2005, U.S. Pat. No. 5,764,763, entitled “Apparatus and Methods for Including Codes in Audio Signals and Decoding,” which issued on Jun. 9, 1998, U.S. Pat. No. 5,574,962, entitled “Method and Apparatus for Automatically Identifying a Program Including a Sound Signal,” which issued on Nov. 12, 1996, U.S. Pat. No. 5,581,800, entitled “Method and Apparatus for Automatically Identifying a Program Including a Sound Signal,” which issued on Dec. 3, 1996, U.S. Pat. No. 5,787,334, entitled “Method and Apparatus for Automatically Identifying a Program Including a Sound Signal,” which issued on Jul. 28, 1998, and U.S. Pat. No. 5,450,490, entitled “Apparatus and Methods for Including Codes in Audio Signals and Decoding,” which issued on Sep. 12, 1995, all of which are hereby incorporated by reference in their entireties. U.S. Pat. Nos. 8,359,205, 8,369,972, U.S. Publication No. 2010/0223062, U.S. Pat. Nos. 6,871,180, 5,764,763, 5,574,962, 5,581,800, 5,787,334 and 5,450,490 describe example watermarking systems in which a watermark is included in an audio signal by manipulating a set of frequencies of the audio signal. 
     In some examples, the watermark detector  145  of  FIG. 3  is structured to process audio data/signal(s) obtained by the sensor(s)  305  to detect symbols of instances of the watermark  200  that are encoded in one or more time domain characteristics of the sensed audio signal, such as by modulating the amplitude and/or phase of the audio signal in the time domain. Examples of encoding watermarks in the time domain of an audio signal, and corresponding example watermark detection techniques that may be implemented by the example watermark detector  145 , include, but are not limited to, examples in which spread spectrum techniques are used to include a watermark in an audio signal. For example, such a watermark can be encoded in the audio signal by (1) spreading the watermark by modulating the watermark with a pseudo-noise sequence and then (2) combining the spread watermark with the audio signal. Detection of such a watermark involves correlating the audio signal (after being watermarked) with the pseudo-noise sequence, which de-spreads the watermark, thereby permitting the watermark to be detected after the correlation. 
     The example media device meter  125  of  FIG. 3  also includes the example watermark detector controller  150 . In the illustrated example of  FIG. 3 , the watermark detector controller  150  is configured to take advantage of watermarks, such as the example watermark  200 , that are embedded repeatedly in media by initially configuring the example watermark detector  145  to search for and detect a first watermark, and then configuring the watermark detector  145  to target watermark detection at the locations in the media (e.g., in the media audio signal) where other watermarks are expected based on the watermark repetition rate and the duration of the watermark. At other times, the watermark detector controller  150  of the illustrated example places the watermark detector  145  in a low-power sleep mode to conserve power (e.g., by disabling power to the watermark detector  145 , by asserting a control input/signal to place the watermark detector  145  in a low-power mode, by causing the watermark detector  145  to not be invoked by a processor, etc.). 
     In some examples, the watermark detector controller  150  causes the watermark decoder to operate in one of at least three modes, such as a search mode, a confirmation mode and a sleep mode. In the search mode, the watermark detector controller  150  activates the watermark detector  145  to begin detecting a watermark in a monitored media (e.g., audio) signal. This mode of operation is referred to herein as the search mode and, in some examples, the watermark detector controller  150  causes the watermark detector  145  to continue operating in the search mode until (1) a watermark is detected and/or one or more trigger conditions, which indicate conditions are determined to be conducive for watermark detection, is/are met, or (2) a search interval has expired. If the search interval expires before a watermark is detected or the trigger condition is met, the watermark detector controller  150  causes the watermark detector  145  to transition to a sleep mode to conserve power for a sleep interval, after which watermark detector controller  150  causes the watermark detector  145  to again reenter search mode. 
     In some examples, if a watermark is detected during search mode, the watermark detector controller  150  verifies detection of the watermark (e.g., to reduce the likelihood that a false watermark detection will cause the watermark detector controller  150  to transition the watermark detector  145  out of the search mode prematurely). In examples in which the watermark being detected by the watermark detector  145  corresponds to the example watermark  200 , the watermark detector controller  150  may verify that a valid watermark was detected if the first group of media identification symbols  205  of the detected watermark  200  match the corresponding first group of media identification symbols  205  of a prior detected watermark  200  (e.g., as this portion is embedded repeatedly in the media signal). If the watermark detector controller  150  is unable to validate the detected watermark, and the search interval expires with no other watermarks being detected and validated, and with the trigger condition no longer being met, the watermark detector controller  150  causes the watermark detector  145  to transition to the sleep mode to conserve power for the sleep interval, after which the watermark detector controller  150  wakes the watermark detector  145  and causes it to reenter search mode. However, if the watermark detector controller  150  is unable to validate the detected watermark, but the search interval has not expired or the trigger condition is still being met, the watermark detector controller  150  causes the watermark detector  145  to remain enabled and continue to operate to perform watermark detection. 
     In some examples, if a watermark is detected during search mode, and the watermark detector controller  150  verifies that the detected watermark is valid, the watermark detector controller  150  causes the watermark detector to transition to a confirmation mode. In the confirmation mode, the watermark detector controller  150  reduces the operation interval of the watermark detector  145  to cause a corresponding reduction in power consumption. For example, in the confirmation mode, the watermark detector controller  150  places the watermark detector  145  in the sleep mode for a sleep interval (which may be the same or different from the sleep interval used for a transition from search mode into sleep mode). The watermark detector controller  150  then wakes the watermark detector  145  to perform watermark detection and to store detected watermark symbols in a watermark symbol buffer. The watermark detector controller  150  examines the watermark symbol buffer at a location where an embedded watermark is expected to be present in the media signal (e.g., due to the watermark repetition rate). If watermark confirmation is successful (e.g., if a valid watermark is detected), the watermark detector controller  150  places the watermark detector  145  in the sleep mode to conserve power for the sleep interval, after which watermark detector controller  150  causes the watermark detector  145  to reenter confirm mode. However, if a valid watermark is not detected, the watermark detector controller  150  searches the watermark symbol buffer to determine if a watermark is present in the media signal, but at a different location than expected (e.g., which may be due to a change in the media being presented). If a new watermark is detected, the watermark detector controller  150  places the watermark detector  145  back in the sleep mode to conserve power for the sleep interval, after which the watermark detector controller  150  causes the watermark detector  145  to reenter confirm mode. However, if no watermark is detected after expiration of a time interval (which may be the same or different from the search interval), the watermark detector controller  150  places the watermark detector  145  into the search mode and the process repeats. 
     A block diagram of an example implementation of the watermark detector controller  150  of  FIGS. 1 and/or 3  is illustrated in  FIG. 4 . The example watermark detector controller  150  of  FIG. 4  includes an example symbol buffer  405  to store measured watermark symbol values determined by the example watermark detector  145  when the watermark detector  145  is active. In some examples, to detect a watermark symbol, the watermark detector  145  determines measured watermark symbol values corresponding to each possible symbol value the watermark symbol may have. For example, to detect the symbol  220 A in the example watermark  200 , the watermark detector  145  determines, for each symbol interval (e.g., 0.4 seconds in the example of  FIG. 2 ) corresponding to the symbol  220 A, measured watermark signal-to-noise (SNR) values corresponding to each of the  16  possible symbol values the symbol  220 A may have. The symbol buffer  405  stores the measured watermark symbol values provided by the watermark detector  145  for further processing. The example symbol buffer  405  may be implemented by any appropriate memory, storage device, etc., such as one or more of the volatile memory  1414  and/or the mass storage device  1428  of the example processor platform  1400  of  FIG. 14 , which is described in further detail below. 
     The example watermark detector controller  150  of  FIG. 4  also includes an example watermark verifier  410  to operate the example watermark detector  145  in a first (e.g., search) mode and to verify watermarks detected by the watermark detector  145 , as described above. In some examples, the watermark verifier  410  operates the watermark detector  145  in a first (e.g., search) operating mode to search for a first watermark in a media signal output from the example media device  110 . Then, in response to the watermark detector  145  detecting the first watermark, the watermark verifier  410  determines whether the detected watermark satisfies one or more verification conditions. If the verification condition(s) is(are) satisfied, the watermark verifier  410  indicates that the detected watermark is verified. 
     In examples in which the watermark detector  145  is configured to detect the example watermark  200  of  FIG. 2 , the watermarks to be detected by the watermark detector  145  in the first (e.g., search) mode include the first group of media identification symbols  205 , which are repeated in successive watermarks, and the second group of timestamp symbols  210 , which vary among successive watermarks. In some such examples, the watermark verifier  410  operates the watermark detector  145  in the first (e.g., search) operating mode to detect the first group of media identification symbols  205 . Furthermore, if the watermark verifier  410  determines that the watermark detector  145  has detected a first watermark, which includes the first group of media identification symbols  205 , in the monitored media signal (e.g., by detecting the first group of media identification symbols  205  in the symbol buffer  405 ), the watermark verifier  410  then determines whether the first group of media identification symbols  205  satisfy a verification condition to verify the detected watermark. For example, the watermark verifier  410  may determine that the verification condition is satisfied when the first group of media identification symbols  205  detected by the watermark detector  145  during the first (e.g., search) operating mode match a corresponding first group of media identification symbols  205  repeated in a prior watermark detected by the watermark detector  145  during a time period prior to detection of the current watermark. Additionally or alternatively, in some examples, the watermark verifier  410  may determine that the verification condition is satisfied when the symbols in the first group of media identification symbols  205  satisfy one or more symbol strength conditions individually or collectively. 
     The watermark detector controller  150  of  FIG. 4  also includes an example watermark confirmer  415  to operate the example watermark detector  145  in a second (e.g., confirmation) mode in response to the watermark verifier  410  verifying a first watermark detected by the watermark detector  145  during the first (e.g., search) mode. In the second (e.g., confirmation) mode, the watermark confirmer  415  causes the watermark detector  145  to cycle between a sleep interval and an active interval to detect subsequent watermarks at expected locations in the monitored media signal relative to the location of the first watermark detected and verified during the first (e.g., search) operating mode. For example, if the watermarks to be detected by the watermark detector  145  correspond to the example watermark  200  of  FIG. 2 , the watermark confirmer  415  may operate the watermark detector  145  to detect, in the monitored media signal, the first group of media identification symbols  205  repeated in a second watermark at a second location in the monitored media signal that is determined relative to the location of the first watermark based on the repetition interval and duration of the watermarks  200  embedded in the monitored media signal. 
     Furthermore, in some examples, the watermark confirmer  415  continues to operate the watermark detector  145  in the second (e.g., confirmation) operating mode if the first group of media identification symbols  205  repeated in a second watermark detected during the second (e.g., confirmation) mode satisfy one or more symbol strength conditions. Additionally or alternatively, in some examples, the watermark confirmer  415  continues to operate the watermark detector  145  in the second (e.g., confirmation) operating mode if the first group of media identification symbols  205  repeated in the second watermark detected during the second (e.g., confirmation) mode match at least a threshold number of the first group of media identification symbols  205  included in a prior watermark detected by the watermark detector  145 . The prior watermark may correspond to, for example, the first watermark detected by the watermark detector  145  during the first (e.g., search) operating mode, or another watermark previously detected by the watermark detector  145  during the second (e.g., confirmation) mode. However, in some such examples, the watermark confirmer  415  transitions operation of the watermark detector  145  out of the second (e.g., confirmation) operating mode if, for example, the first group of media identification symbols  205  repeated in the second watermark does not satisfy the symbol strength condition(s) and/or the first group of media identification symbols  205  repeated in the second watermark does not match at least the threshold number of the corresponding first group of media identification symbols  205  included in a prior detected watermark. 
     In some examples, the watermark detector controller  150  of  FIG. 4  includes an example search trigger evaluator  420  to evaluate one or more trigger conditions to determine whether to continue operating the watermark detector  145  in the first (e.g., search), or cause the watermark detector  145  to be placed in a third (e.g., sleep) operating mode. For example, in response to a watermark not being detected for a first time period of operating the watermark detector  145  in the first (e.g., search) operating mode, the search trigger evaluator  420  may evaluate whether one or more trigger conditions have been met. If, for example, a trigger condition is met, the search trigger evaluator  420  may continue to operate the watermark detector  145  in the first (e.g., search) operating mode. However, if the trigger condition is not met, the search trigger evaluator  420  may transition operation of the watermark detector  145  to a third (e.g., sleep) operating mode in which the watermark detector  145  sleeps for a sleep interval, and then is woken and transitioned back to operating in the first (e.g., search) operating mode. The sleep interval used during the third (e.g., sleep) operating mode may be the same as, or different from, the sleep interval used during the second (e.g., confirmation) mode. 
     Additionally or alternatively, when the watermark confirmer  415  decides to transition operation of the watermark detector  145  out of the second (e.g., confirmation) operating mode, in some examples the search trigger evaluator  420  determines how the watermark detector  145  is to be transitioned out of the second (e.g., confirmation) operating mode. For example, the search trigger evaluator  420  may cause operation of the watermark detector  145  to transition from the second (e.g., confirmation) operating mode to the first (e.g., search) operating mode discussed above if a trigger condition is met. However, if the trigger condition is not met, the search trigger evaluator  420  may transition operation of the watermark detector  145  to the third (e.g., sleep) operating mode in which the watermark detector  145  sleeps for a sleep interval, and then is woken and transitioned back to operating in the first (e.g., search) operating mode. As noted above, the sleep interval used during the third (e.g., sleep) operating mode may be the same as, or different from, the sleep interval used during the second (e.g., confirmation) mode. 
     In some examples, the trigger condition(s) evaluated by the search trigger evaluator  420  include watermark symbol strength conditions, which are described in further detail below. Additionally or alternatively, in some examples, the trigger condition(s) evaluated by the search trigger evaluator  420  include a quiet level condition evaluated by an example quiet level evaluator  425  included in the example watermark detector controller  150  of  FIG. 4 . The quiet level evaluator  425  of the illustrated example processes audio samples received from, for example, the example sensor(s)  305  of the example media device meter  125  to determine whether the strength (e.g., amplitude, power, energy, etc.) of the audio samples obtained from the sensor(s)  305  indicates that the measured audio is quiet. For example, the quiet level evaluator  425  may compare the strength of the sensed audio samples to a quiet threshold which, if not met, indicated the measured audio is quiet. In such examples, if the measured audio is determined to be quiet, the trigger condition is not satisfied and the watermark detector  145  is placed in the third (e.g., sleep) mode. However, if the measured audio is determined to not be quiet, the trigger condition is satisfied and the watermark detector  145  is placed in the first (e.g., search) mode. 
     The example watermark detector controller  150  of  FIG. 4  also includes an example timer  430  to, for example, track the sleep interval(s) employed in the second (e.g., confirmation) and the third (e.g., sleep) modes. For example, the timer  430  may be configured to track a first sleep interval when the watermark detector controller  150  is causing the watermark detector  145  to operate in the second (e.g., confirmation) operating mode Additionally or alternatively, the timer  430  may be configured to track a second sleep interval (e.g., which may be the same as, or different from, the first sleep interval) when the watermark detector controller  150  is causing the watermark detector  145  to operate in the third (e.g., sleep) operating mode. The time  430  may be implemented by any type(s) and/or number(s) of timing sources, clocks, oscillators, etc. 
     In some examples, the watermark detector controller  150  of  FIG. 4  includes an example back confirmer  435  to process the measured watermark symbol values stored in the example symbol buffer  405  to search for watermark(s) in addition to those watermarks detected directly in the first (e.g., search) and/or the second (e.g., confirmation) operating modes. For example, when transitioning operation of the watermark detector  145  from the first (e.g., search) operating mode to the second (e.g., confirmation) operating mode, the watermark verifier  410  may invoke the back confirmer  435  to search measured watermark symbol values stored in the symbol buffer  405  and corresponding to a given time period (e.g., 15 minutes or some other value) prior to detection of the first watermark during the first (e.g., search) operating mode. If the back confirmer  435  detects any other watermarks, the back confirmer  435  invokes the watermark verifier  410  to verify the detected watermark. In such examples, the watermark confirmer  415  uses the location(s) of any other detected and verified watermarks to determine other period(s) during which the watermark detector  145  is to be activated during the second (e.g., confirmation) mode to detect subsequent instances of these watermarks in the monitored media signal. 
     In some examples, the back confirmer  435  is additionally or alternatively invoked by the watermark confirmer  415  during the second (e.g., confirmation) mode to search measured watermark symbol values stored in the symbol buffer  405  and corresponding to a given time period (e.g., 1 minute or some other value) prior to detection of the watermark at the expected location in the media signal corresponding to when the watermark detector  145  is configured to be active. For example, during the second (e.g., confirmation) mode, the watermark confirmer  415  may wake the watermark detector  145  prior to the expected location of the next watermark to be detected in the monitored media signal. In such examples, the back confirmer  435  may be invoked to search the measured watermark symbol values stored in the symbol buffer  405  for watermark(s) occurring prior to the expected location of the next watermark. In this way, the back confirmer  435  permits the example watermark detector controller  150  to quickly adjust to watermarks being embedded at different locations in the media signal, and/or to new media being presented by the monitored media device  110 . 
     The example watermark detector controller  150  of  FIG. 4  also includes an example watermark logger  440  to log the watermarks detected by the watermark detector  145  during the first (e.g., search) and/or second (e.g., confirmation) operating modes. In the illustrated example of  FIG. 4 , the watermark logger  440  reports the logged watermarks via the example network  135  to the example data processing facility  140  for further processing, as described above. For example, the watermark logger  440  may report the logged watermarks periodically (e.g., at specified reporting intervals), based on one or more events (e.g., such as when a log storage threshold is satisfied, when a query from the data processing facility  140  is received, etc.), etc. 
     While example manners of implementing the media device meter  125  are illustrated in  FIGS. 1-4 , one or more of the elements, processes and/or devices illustrated in  FIGS. 1-4  may be combined, divided, re-arranged, omitted, eliminated and/or implemented in any other way. Further, the example watermark detector  145 , the example watermark detector controller  150 , the example sensor(s)  305 , the example symbol buffer  405 , the example watermark verifier  410 , the example watermark confirmer  415 , the example search trigger evaluator  420 , the example quiet level evaluator  425 , the example timer  430 , the example back confirmer  435 , the example watermark logger  440  and/or, more generally, the example media device meter  125  of  FIGS. 1-4  may be implemented by hardware, software, firmware and/or any combination of hardware, software and/or firmware. Thus, for example, any of the example watermark detector  145 , the example watermark detector controller  150 , the example sensor(s)  305 , the example symbol buffer  405 , the example watermark verifier  410 , the example watermark confirmer  415 , the example search trigger evaluator  420 , the example quiet level evaluator  425 , the example timer  430 , the example back confirmer  435 , the example watermark logger  440  and/or, more generally, the example media device meter  125  could be implemented by one or more analog or digital circuit(s), logic circuits, programmable processor(s), application specific integrated circuit(s) (ASIC(s)), programmable logic device(s) (PLD(s)) and/or field programmable logic device(s) (FPLD(s)). When reading any of the apparatus or system claims of this patent to cover a purely software and/or firmware implementation, at least one of the example media device meter  125 , the example watermark detector  145 , the example watermark detector controller  150 , the example sensor(s)  305 , the example symbol buffer  405 , the example watermark verifier  410 , the example watermark confirmer  415 , the example search trigger evaluator  420 , the example quiet level evaluator  425 , the example timer  430 , the example back confirmer  435  and/or the example watermark logger  440  is/are hereby expressly defined to include a tangible computer readable storage device or storage disk such as a memory, a digital versatile disk (DVD), a compact disk (CD), a Blu-ray disk, etc. storing the software and/or firmware. Further still, the example media device meter  125  may include one or more elements, processes and/or devices in addition to, or instead of, those illustrated in  FIGS. 1-4 , and/or may include more than one of any or all of the illustrated elements, processes and devices. 
     Flowcharts representative of example machine readable instructions for implementing the example media device meter  125 , the example watermark detector  145 , the example watermark detector controller  150 , the example sensor(s)  305 , the example symbol buffer  405 , the example watermark verifier  410 , the example watermark confirmer  415 , the example search trigger evaluator  420 , the example quiet level evaluator  425 , the example timer  430 , the example back confirmer  435  and/or the example watermark logger  440  are shown in  FIGS. 5-12 . In these examples, the machine readable instructions comprise one or more programs for execution by a processor, such as the processors  1312  and/or  1412  shown in the example processor platforms  1300  and  1400  discussed below in connection with  FIGS. 13 and 14 . The one or more programs, or portion(s) thereof, may be embodied in software stored on a tangible computer readable storage medium such as a CD-ROM, a floppy disk, a hard drive, a digital versatile disk (DVD), a Blu-ray Disk™, or a memory associated with the processors  1312  and/or  1412 , but the entire program or programs and/or portions thereof could alternatively be executed by a device other than the processors  1312  and/or  1412 , and/or embodied in firmware or dedicated hardware (e.g., implemented by an ASIC, a PLD, an FPLD, discrete logic, etc.). Further, although the example program(s) is(are) described with reference to the flowcharts illustrated in  FIGS. 5-12 , many other methods of implementing the example media device meter  125 , the example watermark detector  145 , the example watermark detector controller  150 , the example sensor(s)  305 , the example symbol buffer  405 , the example watermark verifier  410 , the example watermark confirmer  415 , the example search trigger evaluator  420 , the example quiet level evaluator  425 , the example timer  430 , the example back confirmer  435  and/or the example watermark logger  440  may alternatively be used. For example, with reference to the flowcharts illustrated in  FIGS. 5-12 , the order of execution of the blocks may be changed, and/or some of the blocks described may be changed, eliminated, combined and/or subdivided into multiple blocks. 
     As mentioned above, the example processes of  FIGS. 5-12  may be implemented using coded instructions (e.g., computer and/or machine readable instructions) stored on a tangible computer readable storage medium such as a hard disk drive, a flash memory, a read-only memory (ROM), a compact disk (CD), a digital versatile disk (DVD), a cache, a random-access memory (RAM) and/or any other storage device or storage disk in which information is stored for any duration (e.g., for extended time periods, permanently, for brief instances, for temporarily buffering, and/or for caching of the information). As used herein, the term tangible computer readable storage medium is expressly defined to include any type of computer readable storage device and/or storage disk and to exclude propagating signals and to exclude transmission media. As used herein, “tangible computer readable storage medium” and “tangible machine readable storage medium” are used interchangeably. Additionally or alternatively, the example processes of  FIGS. 5-12  may be implemented using coded instructions (e.g., computer and/or machine readable instructions) stored on a non-transitory computer and/or machine readable medium such as a hard disk drive, a flash memory, a ROM, a CD, a DVD, a cache, a RAM and/or any other storage device or storage disk in which information is stored for any duration (e.g., for extended time periods, permanently, for brief instances, for temporarily buffering, and/or for caching of the information). As used herein, the term non-transitory computer readable medium is expressly defined to include any type of computer readable storage device and/or storage disk and to exclude propagating signals and to exclude transmission media. As used herein, when the phrase “at least” is used as the transition term in a preamble of a claim, it is open-ended in the same manner as the term “comprising” is open ended. Also, as used herein, the terms “computer readable” and “machine readable” are considered equivalent unless indicated otherwise. 
     A first example program  500  that may be executed to implement the example media device meter  125  of  FIGS. 1 and/or 3 , and/or the example watermark detector controller  150  of  FIGS. 1, 3 and/or 4 , is represented by the flowchart shown in  FIG. 5 . With reference to the preceding figures and associated written descriptions, the example program  500  of  FIG. 5  begins execution at block  505  at which the example timer  430  of the example watermark detector controller  150  wakes the example watermark detector  145  at the end of the current sleep interval. At block  510 , the watermark detector controller  150  determines the current operating mode in which the watermark detector  145  has been configured to operate. If the current operating mode is the search operating mode (block  510 ), then at block  515  the example watermark verifier  410  of the watermark detector controller  150  causes the watermark detector  145  to operate (or continue to operate) in the search operating mode to detect watermarks in a monitored media signal output by the media device  110 , and store the resulting measured watermark symbol values in the example symbol buffer  405 , as described above. If a watermark is detected (block  520 ), processing proceeds to block  525 . Otherwise, the watermark verifier  410  continues to operate the watermark detector  145  in the search mode. 
     If a watermark is detected during search mode (block  520 ), at block  525  the watermark verifier  410  verifies the detected watermark, as described above. Example machine readable instructions that may be used to implement the processing at block  525  are illustrated in  FIG. 6 , which is described in further detail below. If the watermark verifier  410  determines the detected watermark is verified (block  530 ), processing proceeds to block  535  at which the watermark verifier  410  sets the operating mode of the watermark detector to the confirmation mode. Otherwise, processing proceeds to block  540  at which the example search trigger evaluator  420  of the example watermark detector controller  150  evaluates one or more search trigger conditions, as described above. Example machine readable instructions that may be used to implement the processing at block  540  are illustrated in  FIG. 8 , which is described in further detail below. 
     If the search trigger condition(s) evaluated at block  540  is(are) satisfied (block  545 ), processing returns to block  515  and blocks subsequent thereto at which the watermark verifier  410  continues to operate the watermark detector  145  in the search mode. Otherwise, processing proceeds to block  550  at which the watermark detector controller  150  places the watermark detector  145  in a sleep mode (e.g., or other low power operating mode, such as a standby mode, etc.) for a sleep interval (e.g., such as for a duration of 1 minute or some other duration). After the sleep interval expires, processing returns to block  505  and blocks subsequent thereto. 
     Returning to block  530 , if the watermark verifier  410  determines the detected watermark is verified (block  530 ), processing proceeds to block  555  at which the watermark verifier  410  sets the operating mode of the watermark detector to the confirmation mode. At block  560 , the example back confirmer  435  of the watermark detector controller  150  performs a backconfirm operation to search through the example symbol buffer  405  of the watermark detector controller  150  to detect other watermarks detected by the watermark detector  145  during the current active interval, as described above. At block  565 , the example watermark logger  440  of the watermark detector controller  150  logs (and reports, if appropriate) the watermark(s) detected during the current active interval. Processing then proceeds to block  550  and blocks subsequent thereto, which are described in detail above. 
     Returning to block  510 , if the current operating mode is the confirmation operating mode, then at block  570  the example watermark confirmer  415  of the watermark detector controller  150  operates (or continues to operate) the watermark detector  145  in the confirmation mode. In the confirmation mode, the watermark confirmer  415  causes the watermark detector  145  to cycle between a sleep interval and an active interval to detect subsequent watermarks at expected locations in the monitored media signal relative to the location of the first watermark detected and verified during the search operating mode, and store the resulting measured watermark symbol values in the example symbol buffer  405 , as described above. As also noted above, the duration of the sleep interval employed in the confirmation mode may be the same as, or different from, the duration of the sleep interval employed in the sleep mode. Also, in some examples, the watermark detector controller  150  varies the duration of the sleep interval employed in the sleep mode and/or the confirmation mode depending on one or more criteria, such as based on time-of-day (e.g., with longer sleep intervals utilized during nighttime hours), detected media activity (e.g., with longer sleep intervals utilized when media signals have not be detected for a given interval of time). Additionally or alternatively, in some examples, the watermark detector controller  150  varies the sleep interval in a random or pseudo-random manner (e.g., by utilizing a random or pseudo-random number generator to determine the duration of the sleep interval). Example machine readable instructions that may be used to implement the processing at block  570  are illustrated in  FIG. 7 , which is described in further detail below. 
     At block  575 , the watermark confirmer  415  determines whether a watermark was detected at block  570  (e.g., during the confirmation operating mode) and, thus, watermark confirmation was successful. If watermark confirmation was successful (block  575 ), processing proceeds to block  555  at which the operating mode remains as the confirmation mode. Processing then proceeds to block  560  and blocks subsequent thereto, which are described in detail above. However, if watermark confirmation was not successful (block  575 ), processing proceeds to block  580  at which the watermark confirmer  415  sets the operating mode of the watermark detector  145  back to the search operating mode. In some examples, at block  575  the watermark confirmer  415  causes the operating mode to remain in the confirmation mode (and, thus, does not proceed to block  580 ) for at least a given confirmation time period (e.g., 5 minutes or some other time period). In such examples, if the given confirmation time period elapses without watermark confirmation being successful, then processing proceeds to block  580  at which the watermark confirmer  415  sets the operating mode of the watermark detector  145  back to the search operating mode at block. Processing then proceeds to block  540  and blocks subsequent thereto, which are described in detail above. 
     A first example program P 525  that may be executed to implement the example watermark verifier  410  of  FIG. 4 , and/or that may be used to perform the processing at block  525  of  FIG. 5 , is represented by the flowchart shown in  FIG. 6 . With reference to the preceding figures and associated written descriptions, the example program P 525  of  FIG. 6  begins execution at block  605  at which the watermark verifier  410  begins verifying a watermark, such as the example watermark  200 , detected by the example watermark detector  145  during the search operating mode. For example, at block  605 , the watermark verifier  410  determines whether all symbols in the current detected watermark are valid (e.g., have no errors). If all detected watermark symbols are not valid, control proceeds to block  610  at which the watermark verifier  410  indicates that the watermark has not been verified. However, if all detected watermark symbols are valid, control proceeds to block  615  at which the watermark verifier  410  determines whether the detected watermark matches a prior watermark detected within a verification time interval (e.g., which may be 5 minutes or some other duration). If at block  615  the detected watermark matches a prior watermark detected within the verification time interval (e.g., or if at least their repeating groups of media identification symbols  205  match), at block  620  the watermark verifier  410  indicates that the watermark has been verified. Otherwise, at block  625  the watermark verifier  410  determines whether the symbols of the watermark being verified satisfy one or more symbol strength condition(s). If the symbol strength condition(s) is(are) satisfied, at block  620  the watermark verifier  410  indicates that the watermark has been verified. Otherwise, at block  610  the watermark verifier  410  indicates that the watermark has not been verified. 
     A first example program P 570  that may be executed to implement the example watermark confirmer  415  of  FIG. 4 , and/or that may be used to perform the processing at block  570  of  FIG. 5 , is represented by the flowchart shown in  FIG. 7 . With reference to the preceding figures and associated written descriptions, the example program P 570  of  FIG. 7  begins execution at block  705  at which the watermark confirmer  415  examines the example symbol buffer  405  to determine whether, when the watermark detector  145  was active, a valid watermark (e.g., an instance of the watermark  200  having a first group of code symbols  205  matching the first group of code symbols  205  in a prior detected instance of the watermark  200 ) was detected at the expected location in the monitored media signal. If a valid watermark was not detected (block  705 ), at block  710  the watermark confirmer  415  examines the example symbol buffer  405  to determine whether any valid watermark (e.g., at any location in the monitored media signal) was detected while the watermark detector  145  was active. If a valid watermark was identified at block  705  or block  710 , processing proceeds to block  715  at which the watermark confirmer  415  evaluates a first set of one or more symbol strength conditions for the symbols of the valid watermark. For example, the first set of one or more symbol strength conditions may correspond to a first symbol strength threshold that is compared against the symbols of the valid watermark. 
     However, if a valid watermark was not identified at block  705  or block  710 , processing proceeds to block  720  at which the watermark confirmer  415  evaluates a second set of one or more symbol strength conditions for the measured watermark symbols at the expected location in the media signal. For example, the second set of one or more symbol strength conditions may correspond to a second symbol strength threshold that is compared against the symbols of the valid watermark, with the second symbol strength threshold being higher than the first symbol strength threshold. At block  725 , the watermark confirmer  415  determines whether the symbol strength condition(s) evaluated at blocks  715  or  720  was(were) satisfied by the watermark symbols examined. If the symbol strength condition(s) was(were) satisfied (block  725 ), at block  735  the watermark confirmer  415  determines watermark confirmation was successful. However, if the symbol strength condition(s) was(were) satisfied (block  725 ), at block  730  the watermark confirmer  415  determines whether at least a threshold number of the watermark symbols at the expected location (e.g., the first group of symbols  205  for an instance of the watermark  200  at the expected location) match the corresponding symbols in a prior valid watermark detected in the monitored media signal. If at least the threshold number of the watermark symbols match (block  730 ), processing proceeds to block  735  at which the watermark confirmer  415  determines watermark confirmation was successful. Otherwise, at block  740  the watermark confirmer  415  determines watermark confirmation was not successful. 
     A first example program P 540  that may be executed to implement the example search trigger evaluator  420  of  FIG. 4 , and/or that may be used to perform the processing at block  540  of  FIG. 5 , is represented by the flowchart shown in  FIG. 8 . With reference to the preceding figures and associated written descriptions, the example program P 540  of  FIG. 8  begins execution at block  805  at which the search trigger evaluator  420  determines whether the current active interval in which the watermark detector  145  is to be active has expired. For example, the active interval may have a duration of 1 minute or some other value. If the active interval has expired, at block  810  the search trigger evaluator  420  indicates that the search trigger condition(s) has(have) not been satisfied. However, if the active interval has not expired, (block  805 ), at block  815  the search trigger evaluator  420  evaluates one or more search trigger conditions, as described above. If the search trigger condition(s) is(are) satisfied (block  820 ), at block  825  the search trigger evaluator  420  indicates that the search trigger condition(s) has(have) been satisfied. Otherwise, processing proceeds to block  810  at which the search trigger evaluator  420  indicates that the search trigger condition(s) has(have) not been satisfied. 
     A second example program  900  that may be executed to implement the example media device meter  125  of  FIGS. 1 and/or 3 , and/or the example watermark detector controller  150  of  FIGS. 1, 3 and/or 4 , is represented by the flowchart shown in  FIG. 9 . The second example program  900  is tailored for scenarios in which the watermark detector  145  is to detect watermarks corresponding to the example watermark  200  of  FIG. 2 . With reference to the preceding figures and associated written descriptions, the example program  900  of  FIG. 9  begins execution at block  905  at which the watermark detector controller  150  activates the example watermark detector  145  of the media device meter  125 , which causes the watermark detector  145  to store measured watermark symbol values in the example symbol buffer  405 . At block  910 , the example watermark verifier  410  determines whether a verified watermark was detected, as described above. If a verified watermark was detected (block  910 ), processing proceeds to block  915  at which, if the current operating mode is the search mode, the watermark verifier  410  transitions the operating mode to the confirmation mode. Otherwise, if the current operating mode is the confirmation mode, at block  915  the operating mode remains in the confirmation mode. As such, in the illustrated example of  FIG. 9 , the watermark verifier  410  performs watermark verification in both the search and confirmation operating modes, and processing proceeds to block  920  if watermark verification is successful in either the search or confirmation operating modes. 
     At block  920 , the example back confirmer  435  of the watermark detector controller  150  performs a backconfirm operation to search through the example symbol buffer  405  of the watermark detector controller  150  to detect other watermarks detected by the watermark detector  145  during the current active interval, as described above. At block  925 , the example watermark logger  440  of the watermark detector controller  150  logs (and reports, if appropriate) the watermark(s) detected during the current active interval. Processing then proceeds to block  930  at which the watermark detector controller  150  places the watermark detector  145  in a sleep mode (e.g., or other low power operating mode, such as a standby mode, etc.) for a sleep interval (e.g., such as for a duration of 1 minute or some other duration), after which the watermark detector  145  is woken and processing returns to block  905  and blocks subsequent thereto. 
     Returning to block  910 , if a verified watermark was not detected, processing proceeds to block  935 . At block  935 , the example watermark confirmer  415  determines whether the current operating mode is the confirmation mode and, if so, whether a watermark confirmation was successful. If the current operating mode is the confirmation mode and watermark confirmation was successful (block  935 ), processing proceeds to block  940 . At block  940 , the watermark confirmer  415  examines the location of the most recent watermark detected during the confirmation operating mode. If the watermark occurred at the expected location in the media signal (e.g., based on the duration and repetition interval of the watermark  200 ), processing proceeds from block  940  to block  925  at which the example watermark logger  440  of the watermark detector controller  150  logs (and reports, if appropriate) the watermark(s) detected during the current active interval. Otherwise, if the location of the detected watermark has changed from the expected location (block  940 ), processing proceeds to block  920  at which the back confirmer  435  performs the backconfirm operation described above before processing then proceeds to block  925 . Processing then proceeds to block  930  and blocks subsequent thereto, which are described above. 
     Returning to block  935 , if the current operating mode is not the confirmation mode, or watermark confirmation was not successful, processing proceeds to block  945 . At block  945 , the example search trigger evaluator  420  evaluates one or more search trigger conditions, as described above. If the search trigger condition(s) is(are) not satisfied (block  945 ), at block  950  the search trigger evaluator  420  determines whether a time period (e.g., Y minutes, where Y is equal to 5 or some other value) has elapsed since the last watermark was detected. If the time period has elapsed, the search trigger evaluator  420  disables confirmation mode (if it was enabled), and causes the operating mode to transition to (or remain in) the search operating mode. As no watermarks have been detected, nothing is logged for the current active interval (block  955 ). Processing then proceeds to block  930  and blocks subsequent thereto, which are described above. 
     Returning to block  945 , if the search trigger condition(s) is(are) satisfied (block  945 ), processing returns to block  905  and blocks subsequent thereto at which the watermark detector controller  150  evaluates the watermark symbols detected during the next active period. As indicated in the illustrated example of  FIG. 9 , if the search trigger condition(s) is(are) satisfied, subsequent processing iterations will continue every X seconds, where X corresponds to, for example, the duration of the example watermark  200  (e.g., X=4.8 seconds, or some other value). 
     A second example program  910 P that may be executed to implement the example watermark verifier  410  of  FIG. 4 , and/or that may be used to perform the processing at block  910  of  FIG. 9 , is represented by the flowchart shown in  FIG. 10 . The second example program  910 P is tailored for scenarios in which the watermark detector  145  is to detect watermarks corresponding to the example watermark  200  of  FIG. 2 . With reference to the preceding figures and associated written descriptions, the example program  910 P of  FIG. 9  begins execution at block  1005  at which the watermark verifier  410  determines whether a valid watermark (e.g., a watermark with no symbol errors) was detected. For example, the watermark detector  145  may indicate that a detected watermark is valid when the detected watermark satisfies an error detection test. As described above, if the watermark detector  145  outputs a valid detected watermark, the watermark verifier  410  performs further processing to verify the validity of the watermark before permitting power efficient watermark detection, as disclosed herein, to proceed further. Conversely, if a valid watermark was not detected by the watermark detector  145  (block  1005 ), at block  1010  the watermark verifier  410  indicates that watermark verification was unsuccessful as there is no valid watermark to verify. 
     However, if a valid watermark was detected (block  1005 ), then at block  1015  the watermark verifier  410  determines whether the first group of media identification symbols  205  of the currently detected watermark match the first group of media identification symbols  205  of a prior watermark detected within a verification time interval (e.g., such as Z minutes, where Z=5 or some other value). If the first group of media identification symbols  205  match (block  1015 ), then at block  1020  the watermark verifier  410  indicates that watermark verification was successful. If, however, the first group of media identification symbols  205  do not match (block  1015 ), the watermark verifier  410  evaluates three symbol strength conditions in the illustrated example. 
     For example, at block  1025 , the watermark verifier  410  determines whether the signal-to-noise ratios (SNRs) of the detected first group of media identification symbols  205  satisfy a first validation threshold. For example, the first validation threshold at block  1025  can be a multiple (e.g., A, where A=2 or some other value) of the average SNR for all possible symbol values measured by the watermark detector  145  when decoding the watermark. At block  1030 , the watermark verifier  410  determines whether the average of the combined SNR of each offset pair (see above for a description of offset pairs) in the first group of media identification symbols  205  satisfy a second validation threshold, which may be the same or different from the first validation threshold used at block  1025 . For example, the second validation threshold at block  1030  can be a multiple (e.g., B, where B=4.2 or some other value) of the average SNR for all possible symbol values measured by the watermark detector  145  when decoding the watermark. At block  1035 , the watermark verifier  410  determines whether the average of the combined SNR of each offset pair (see above for a description of offset pairs) in the first group of media identification symbols  205  satisfy a third validation threshold, which may be the same or different from the first and/or second validation thresholds. For example, the third validation threshold at block  1030  can be fixed value (e.g., not a function of the symbol SNRs), which is preset, programmable, etc. 
     In the illustrated example, if all three symbol strength conditions evaluated at block  1025 ,  1030  and  1035  are satisfied, processing proceeds to block  1020  at which the watermark verifier  410  indicates that watermark verification was successful. Otherwise, processing proceeds to block  1010  at which the watermark verifier  410  indicates that watermark verification was unsuccessful. However, in other examples, processing proceeds to block  1020 , at which the watermark verifier  410  indicates that watermark verification was successful, if a subset of one or more of the conditions evaluated at block  1025 ,  1030  and  1035  are satisfied. 
     A second example program  935 P that may be executed to implement the example watermark confirmer  415  of  FIG. 4 , and/or that may be used to perform the processing at block  935  of  FIG. 9 , is represented by the flowchart shown in  FIG. 11 . The second example program  935 P is tailored for scenarios in which the watermark detector  145  is to detect watermarks corresponding to the example watermark  200  of  FIG. 2 . With reference to the preceding figures and associated written descriptions, the example program  935 P of  FIG. 11  begins execution at block  1105  at which the watermark confirmer  415  determines whether the current operating mode is the confirmation mode. If the current operating mode is not the confirmation mode (block  1105 ), then at block  1110  the watermark confirmer  415  indicates that watermark confirmation was unsuccessful. However, if the current operating mode is the confirmation mode (block  1105 ), then at block  1115  the watermark confirmer  415  determines whether a verified watermark was detected within a confirmation time interval (e.g., such as within the past W minutes, where W=5 or some other value). If a verified watermark was detected within the confirmation time interval (block  1115 ), then at block  1120  the watermark confirmer  415  evaluates a first symbol strength condition. Otherwise, at block  1125 , the watermark confirmer  415  evaluates a second symbol strength condition 
     For example, at block  1120 , the watermark confirmer  415  determines whether the first group of media identification symbols  205  detected at the expected location in the monitored media signal satisfy a first confirmation threshold. For example, the first confirmation threshold at block  1120  can be a multiple (e.g., C, where C=1.9 or some other value) of the average SNR for all possible symbol values measured by the watermark detector  145  when decoding the watermark at the expected location. At block  1125 , the watermark confirmer  415  determines whether the first group of media identification symbols  205  detected at the expected location in the monitored media signal satisfy a second confirmation threshold, which may be larger than the first confirmation threshold. For example, the second confirmation threshold at block  1120  can be a multiple (e.g., D, where D=2.7 or some other value) of the average SNR for all possible symbol values measured by the watermark detector  145  when decoding the watermark at the expected location. 
     In the illustrated example, if either of the symbol strength conditions evaluated at blocks  1120  or  1125  are satisfied, processing proceeds to block  1030  at which the watermark confirmer  415  indicates that watermark confirmation was successful. Otherwise, processing proceeds to block  1035  at which the watermark confirmer  415  determines whether at least a threshold number of the first group of media identification symbols  205  detected at the expected location in the monitored media signal match the first group of media identification symbols  205  of a prior instance of the watermark  200  detected in the media signal. If at least the threshold number of the first group of media identification symbols  205  match (block  1035 ), then processing proceeds to block  1030  at which the watermark confirmer  415  indicates that watermark confirmation was successful. Otherwise, proceeds to block  1010  at which the watermark confirmer  415  indicates that watermark confirmation was unsuccessful. 
     A second example program  945 P that may be executed to implement the example search trigger evaluator  420  of  FIG. 4 , and/or that may be used to perform the processing at block  945  of  FIG. 9 , is represented by the flowchart shown in  FIG. 12 . The second example program  945 P is tailored for scenarios in which the watermark detector  145  is to detect watermarks corresponding to the example watermark  200  of  FIG. 2 . With reference to the preceding figures and associated written descriptions, the example program  945 P of  FIG. 12  begins execution at block  1205  at which the search trigger evaluator  420  determines whether the current active interval has expired. If the current active interval has expired (block  1205 ), at block  1210  the search trigger evaluator  420  indicates that the search trigger is not satisfied. 
     However, if the current active interval has not expired (block  1205 ), at block  1215  the search trigger evaluator  420  determines whether a valid watermark was detected by the watermark detector  145 , but did not satisfy the verification condition(s). If a valid watermark was detected, but did not satisfy the verification condition(s) (block  1215 ), at block  1220  the search trigger evaluator  420  indicates that the search trigger is satisfied. 
     However, if a valid watermark was not detected by the watermark detector  145  (block  1215 ), processing proceeds to block  1225  at which the search trigger evaluator  420  determines whether a first number (N 1 =10 or some other value) of symbols from adjacent watermark locations have been accumulated. Because in the illustrated example the instances of the watermark  200  are repeatedly embedded in the media signal for particular media such that the first group of the media identification symbols  205  in each embedded watermark instance is the same, the first group of the media identification symbols  205  from different watermark locations can be accumulated to increase the likelihood of successful detection. If the first number of symbols from adjacent watermark locations has already been accumulated (block  1225 ), then at block  1210  the search trigger evaluator  420  indicates that the search trigger is not satisfied. 
     However, if the first number of symbols from adjacent watermark locations has not already been accumulated (block  1225 ), then at block  1230  the search trigger evaluator  420  determines whether the SNRs for the detected watermark symbols satisfy a first trigger threshold. For example, the first trigger threshold at block  1230  can be a multiple (e.g., E, where E=1.9 or some other value) of the average SNR for all possible symbol values measured by the watermark detector  145  when decoding the watermark. If the symbol strength condition evaluated at block  1230  is satisfied, processing proceeds to block  1220  at which the search trigger evaluator  420  indicates that the search trigger is satisfied. 
     However, if the symbol strength condition evaluated at block  1230  is not satisfied, at block  1235  the search trigger evaluator  420  determines whether a watermark was detected within a search trigger interval (e.g., such as V minutes, where V=5 or some other value). If a watermark was detected within the search trigger interval (block  1235 ), then at block  1240  the search trigger evaluator  420  determines whether no more than a second number (N 2 =3 or some other value) of symbols from adjacent watermark locations have been accumulated. If no more than the second number of symbols from adjacent watermark locations have been accumulated (block  1240 ), then processing proceeds to block  1220  at which the search trigger evaluator  420  indicates that the search trigger is satisfied. Otherwise, at blocks  1245  or block  1250 , the search trigger evaluator  420  configures either a first threshold or a second threshold to be used by the quiet level evaluator  425 . For example, the first threshold configured at block  1245  when there has been no watermark detected within the search trigger interval may be higher than the second threshold configured at block  1250  when more than the second number of symbols from adjacent watermark locations have been accumulated. 
     At block  1255 , the quiet level evaluator  425  processes audio samples received from, for example, the example sensor(s)  305  of the example media device meter  125  to determine whether the strength (e.g., amplitude, power, energy, etc.) of the audio samples obtained from the sensor(s)  305  indicates that the measured audio is quiet, as described above. If the quiet level evaluator  425  determines that the measured audio is quiet, at block  1260  the search trigger evaluator  420  increases the threshold used by the quiet level evaluator  425 . At block  1265 , the search trigger evaluator  420  determines whether a ratio (e.g., division) of the SNRs for the detected watermark symbols to an average SNR for all possible symbol values measured by the watermark detector  145  when decoding the watermark satisfies a threshold. If the threshold is satisfied (block  1265 ), processing proceeds to block  1220  at which the search trigger evaluator  420  indicates that the search trigger is satisfied. Otherwise, processing proceeds to block  1210  at which the search trigger evaluator  420  indicates that the search trigger is not satisfied. 
       FIG. 13  is a block diagram of an example processor platform  1300  structured to execute the instructions of  FIGS. 5 and/or 9  to implement the example media device meter  125  of  FIGS. 1 and/or 3 . The processor platform  1300  can be, for example, a server, a personal computer, a mobile device (e.g., a cell phone, a smart phone, a tablet such as an iPad™), a personal digital assistant (PDA), an Internet appliance, a DVD player, a CD player, a digital video recorder, a Blu-ray player, a gaming console, a personal video recorder, a set top box a digital camera, or any other type of computing device. 
     The processor platform  1300  of the illustrated example includes a processor  1312 . The processor  1312  of the illustrated example is hardware. For example, the processor  1312  can be implemented by one or more integrated circuits, logic circuits, microprocessors or controllers from any desired family or manufacturer. In the illustrated example of  FIG. 13 , the processor  1312  is configured via example instructions  1332  to implement the example media device meter  125 , the example watermark detector  145  and/or the example watermark detector controller  150  of  FIGS. 1 and/or 3 . 
     The processor  1312  of the illustrated example includes a local memory  1313  (e.g., a cache). The processor  1312  of the illustrated example is in communication with a main memory including a volatile memory  1314  and a non-volatile memory  1316  via a link  1318 . The link  1318  may be implemented by a bus, one or more point-to-point connections, etc., or a combination thereof. The volatile memory  1314  may be implemented by Synchronous Dynamic Random Access Memory (SDRAM), Dynamic Random Access Memory (DRAM), RAMBUS Dynamic Random Access Memory (RDRAM) and/or any other type of random access memory device. The non-volatile memory  1316  may be implemented by flash memory and/or any other desired type of memory device. Access to the main memory  1314 ,  1316  is controlled by a memory controller. 
     The processor platform  1300  of the illustrated example also includes an interface circuit  1320 . The interface circuit  1320  may be implemented by any type of interface standard, such as an Ethernet interface, a universal serial bus (USB), and/or a PCI express interface. 
     In the illustrated example, one or more input devices  1322  are connected to the interface circuit  1320 . The input device(s)  1322  permit(s) a user to enter data and commands into the processor  1312 . The input device(s) can be implemented by, for example, an audio sensor, a microphone, a camera (still or video), a keyboard, a button, a mouse, a touchscreen, a track-pad, a trackball, a trackbar (such as an isopoint), a voice recognition system and/or any other human-machine interface. Also, many systems, such as the processor platform  1300 , can allow the user to control the computer system and provide data to the computer using physical gestures, such as, but not limited to, hand or body movements, facial expressions, and face recognition. In the illustrated example of  FIG. 13 , the input device(s)  1322  include the example sensor(s)  305 . 
     One or more output devices  1324  are also connected to the interface circuit  1320  of the illustrated example. The output devices  1324  can be implemented, for example, by display devices (e.g., a light emitting diode (LED), an organic light emitting diode (OLED), a liquid crystal display, a cathode ray tube display (CRT), a touchscreen, a tactile output device, a printer and/or speakers). The interface circuit  1320  of the illustrated example, thus, typically includes a graphics driver card, a graphics driver chip or a graphics driver processor. 
     The interface circuit  1320  of the illustrated example also includes a communication device such as a transmitter, a receiver, a transceiver, a modem and/or network interface card to facilitate exchange of data with external machines (e.g., computing devices of any kind) via a network  1326  (e.g., an Ethernet connection, a digital subscriber line (DSL), a telephone line, coaxial cable, a cellular telephone system, etc.). 
     The processor platform  1300  of the illustrated example also includes one or more mass storage devices  1328  for storing software and/or data. Examples of such mass storage devices  1328  include floppy disk drives, hard drive disks, compact disk drives, Blu-ray disk drives, RAID (redundant array of independent disks) systems, and digital versatile disk (DVD) drives. 
     Coded instructions  1332  corresponding to the instructions of  FIGS. 5 and/or 9  may be stored in the mass storage device  1328 , in the volatile memory  1314 , in the non-volatile memory  1316 , in the local memory  1313  and/or on a removable tangible computer readable storage medium, such as a CD or DVD  1336 . 
       FIG. 14  is a block diagram of an example processor platform  1400  structured to execute the instructions of  FIGS. 5-11 and/or 12  to implement the example watermark detector controller  150  of  FIGS. 1, 3 and/or 4 . The processor platform  1400  can be, for example, a server, a personal computer, a mobile device (e.g., a cell phone, a smart phone, a tablet such as an iPad™), a PDA, an Internet appliance, a DVD player, a CD player, a digital video recorder, a Blu-ray player, a gaming console, a personal video recorder, a set top box a digital camera, or any other type of computing device. 
     The processor platform  1400  of the illustrated example includes a processor  1412 . The processor  1412  of the illustrated example is hardware. For example, the processor  1412  can be implemented by one or more integrated circuits, logic circuits, microprocessors or controllers from any desired family or manufacturer. In the illustrated example of  FIG. 14 , the processor  1412  is configured via example instructions  1432  to implement the example watermark detector controller  150 , the example watermark verifier  410 , the example watermark confirmer  415 , the example search trigger evaluator  420 , the example quiet level evaluator  425 , the example timer  430 , the example back confirmer  435 , the example watermark logger  440  of  FIGS. 1, 3 and/or 4 . 
     The processor  1412  of the illustrated example includes a local memory  1413  (e.g., a cache). The processor  1412  of the illustrated example is in communication with a main memory including a volatile memory  1414  and a non-volatile memory  1416  via a link  1418 . The link  1418  may be implemented by a bus, one or more point-to-point connections, etc., or a combination thereof. The volatile memory  1414  may be implemented by SDRAM, DRAM, RDRAM and/or any other type of random access memory device. The non-volatile memory  1416  may be implemented by flash memory and/or any other desired type of memory device. Access to the main memory  1414 ,  1416  is controlled by a memory controller. 
     The processor platform  1400  of the illustrated example also includes an interface circuit  1420 . The interface circuit  1420  may be implemented by any type of interface standard, such as an Ethernet interface, a USB, and/or a PCI express interface. 
     In the illustrated example, one or more input devices  1422  are connected to the interface circuit  1420 . The input device(s)  1422  permit(s) a user to enter data and commands into the processor  1412 . The input device(s) can be implemented by, for example, an audio sensor, a microphone, a camera (still or video), a keyboard, a button, a mouse, a touchscreen, a track-pad, a trackball, a trackbar (such as an isopoint), a voice recognition system and/or any other human-machine interface. Also, many systems, such as the processor platform  1400 , can allow the user to control the computer system and provide data to the computer using physical gestures, such as, but not limited to, hand or body movements, facial expressions, and face recognition. 
     One or more output devices  1424  are also connected to the interface circuit  1420  of the illustrated example. The output devices  1424  can be implemented, for example, by display devices (e.g., a LED, an OLED, a liquid crystal display, a CRT display, a touchscreen, a tactile output device, a printer and/or speakers). The interface circuit  1420  of the illustrated example, thus, typically includes a graphics driver card, a graphics driver chip or a graphics driver processor. 
     The interface circuit  1420  of the illustrated example also includes a communication device such as a transmitter, a receiver, a transceiver, a modem and/or network interface card to facilitate exchange of data with external machines (e.g., computing devices of any kind) via a network  1426  (e.g., an Ethernet connection, a DSL, a telephone line, coaxial cable, a cellular telephone system, etc.). 
     The processor platform  1400  of the illustrated example also includes one or more mass storage devices  1428  for storing software and/or data. Examples of such mass storage devices  1428  include floppy disk drives, hard drive disks, compact disk drives, Blu-ray disk drives, RAID systems, and DVD drives. In some examples, the mass storage device  1428  may implement the example symbol buffer  405 . Additionally or alternatively, in some examples the volatile memory  1414  may implement the example symbol buffer  405 . 
     Coded instructions  1432  corresponding to the instructions of  FIGS. 5-11 and/or 12  may be stored in the mass storage device  1428 , in the volatile memory  1414 , in the non-volatile memory  1416 , in the local memory  1413  and/or on a removable tangible computer readable storage medium, such as a CD or DVD  1436 . 
     Although certain example methods, apparatus and articles of manufacture have been disclosed herein, the scope of coverage of this patent is not limited thereto. On the contrary, this patent covers all methods, apparatus and articles of manufacture fairly falling within the scope of the claims of this patent.