Abstract:
Methods and apparatus for detecting a channel change event are disclosed. An example method identifying at least one of a first muted audio condition or a first transient audio condition in a second portion of a media signal having first, second, and third portions, the first portion occurring earlier in time than the second portion and the second portion occurring earlier in time than the third portion, and identifying, using a processor, a channel change event in response to: 1) identifying the at least one of the first muted audio condition or the first transient audio condition; 2) failing to identify a second muted audio condition or a second transient audio condition in the first and third portions of the media signal; and 3) determining that a time domain length of the second portion of the media signal is greater than a first threshold and less than a second threshold.

Description:
RELATED APPLICATIONS 
     This patent arises from a continuation of U.S. patent application Ser. No. 12/832,812, filed Jul. 8, 2010, which is a continuation of U.S. patent application Ser. No. 10/570,567, filed Feb. 27, 2006 (now U.S. Pat. No. 7,765,564, issued Jul. 27, 2010), which is a non-provisional application of PCT Application Serial No. PCT/US03/27336, filed Aug. 29, 2003, the entireties of which are hereby incorporated by reference. 
    
    
     TECHNICAL FIELD 
     The present disclosure pertains to audience measurement systems and, more particularly, to methods and apparatus for detecting a channel change event. 
     BACKGROUND 
     Determining how many and what type of people are viewing which television programs helps television program producers improve their shows and determine a price for advertising slots during those shows. In addition, accurate television viewing demographics allow advertisers to target certain types and sizes of audiences. Similarly, radio listening demographics are also useful to producers and advertisers. 
     To collect these demographics, an audience measurement company, such as Nielsen Media Research, may enlist a plurality of television viewers, radio listeners, and/or any other type of audience member. The habits of the enlisted audience members are collected to statistically determine the demographics of the audiences and to develop ratings of those programs. Surveys may be used, but automatic measurement systems are preferred because of the increased accuracy of the statistics and the convenience for the viewers. 
     One aspect of automatic viewer measurement systems is to record information used to determine what television program is showing on a television or playing on a radio. Many automatic viewer measurement systems are non-invasive systems, which do not require installation of circuitry within the television or radio. Instead, external devices are used to determine what television program is showing or what radio program is playing. In contrast, invasive measurement systems install circuitry within the information presenting device (e.g., TV, radio, etc.) of the audience member. Invasive techniques are less desirable because of the possibility of damage to the information presentation device. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram illustrating an example television system. 
         FIG. 2  is a block diagram illustrating an example audio channel change detector. 
         FIG. 3  is a block illustrating another example audio channel change detector. 
         FIG. 4  is a flowchart representative of machine readable instructions that may be executed by a device to implement an example method of detecting a television channel change event. 
         FIG. 5  is a flowchart representative of machine readable instructions that may be executed by a device to implement another example method of detecting a television channel change event. 
         FIG. 6  is an example audio signal with a transient during a channel change event. 
         FIG. 7  is an example audio signal with a mute during a channel change event. 
     
    
    
     DETAILED DESCRIPTION 
     Although the following discloses example systems including, among other components, software executed on hardware, it should be noted that such systems are merely illustrative and should not be considered as limiting. For example, it is contemplated that any or all of the disclosed hardware and software components could be embodied exclusively in dedicated hardware, exclusively in software, exclusively in firmware or in some combination of hardware, firmware and/or software. 
     In addition, while the following disclosure is made with respect to example television systems, it should be understood that the disclosed system may be used in many other applications. For example, radio systems may employ the techniques described herein. Accordingly, while the following describes example systems and processes, persons of ordinary skill in the art will readily appreciate that the disclosed examples are not the only way to implement such systems. 
     In general, the methods and apparatus described herein detect a channel change event by monitoring an audio signal of an information presentation device such as a television system. The monitored audio signal is tested for certain characteristics indicative of a channel change event. In some television systems, changing channels produces an audible “pop” sound or transient. By detecting a normal television audio signal, followed by a transient television audio signal, followed by a normal television audio signal, the methods and apparatus described herein can signal when a channel change event has likely occurred. Normal and transient signals are defined using volume level thresholds and/or frequency thresholds. In other television systems, the “pop” sound produced when changing channels is muted by the television system. In such television systems, channel change events may be detected by detecting a normal television audio signal, followed by a muted television audio signal, followed by a normal television audio signal. Muted signals are defined using volume level thresholds and/or frequency thresholds. Once a channel change event is detected, an audience measurement system may automatically determine what program is on the information presentation device. Alternatively, an audience member may be prompted to manually enter what program is on the information presentation device. 
     A block diagram of an example television system  100  is illustrated in  FIG. 1 . The television system  100  illustrated includes a television service provider  102 , a set-top box  104 , a signal splitter  106 , an analog-to-digital (A/D) converter  108 , a television  110 , and an audio channel change detector  112 . The components of the television system  100  may be connected as shown. 
     The television service provider  102  may be any television service provider  102  such as a cable television service provider, a satellite television service provider, and/or a radio frequency (RF) television service provider. The television service provider  102  may provide analog and/or digital television signals. For example, the television service provider  102  may provide analog and/or digital signals over a coaxial cable (e.g., AT&amp;T® cable). Similarly, the television service provider  102  may provide analog and/or digital signals over a wireless connection, such as a satellite connection (e.g., DIRECTV®) and/or a terrestrial broadcast tower (e.g., “free” TV). 
     The set-top box  104  may be any set-top box such as a cable television converter, a direct broadcast satellite (DBS) decoder, a digital video recorder (e.g., TiVo®), a digital video disc (DVD) player, or a video cassette recorder (VCR). The set-top box  104  receives a plurality of television channels from the television service provider  102 . Typically, the set-top box  104  selects one of the plurality of television channels based on a user input, and outputs an audio/video signal indicative of the selected television channel. In the case of an analog signal, the set-top box  104  tunes to a particular frequency to obtain the selected television channel. In the case of a digital signal, the set-top box  104  decodes certain packets of data to obtain the selected television channel. Of course, the set-top box  104  is optional. For example, receiving terrestrial broadcast television may not require a set-top box  104 . 
     The output from the set-top box  104  (if included) is fed to a signal splitter  106  such as a y-splitter. In one example, the signal splitter produces two signals indicative of the output from the set-top box  104 . One of the two signals is fed to the television  110 . The other signal is fed to the A/D converter  108 . The television  110  may be any type of television. For example, the television may be an NTSC (National Television Standards Committee) television, a high definition television (HDTV), etc. Of course, a person of ordinary skill in the art will readily appreciate that any number of signals may be produced by the signal splitter  106 . 
     The analog-to-digital converter  108  may be any type of analog-to-digital converter  108 . The analog-to-digital converter  108  converts a standard television audio signal into digital data. For example, the analog-to-digital converter  108  may convert NTSC audio signals to a digital representation of an audio wave. Alternatively or in addition, the analog-to-digital converter  108  may convert PAL (Phase Alternation Line) audio signals and/or SECAM (Sequential Couleur avec Memoire) audio signals to digital data. Regardless of the television broadcast standard converted, the digital data may be any size and may encode any number of data points. Alternatively, an analog sampling device may be used instead of the A/D converter  108 . 
     The analog-to-digital converter  108  periodically (e.g., at 200 MHz) takes a sample and passes the digital data representing the television audio to the audio channel change detector  112 . The audio channel change detector  112  scans the digital data it receives to determine if channel change events are occurring. 
     A block diagram of an example audio channel change detector  112  is illustrated in  FIG. 2 . The channel change detector  112  may be a personal computer (PC), an application specific device, and/or any other computing device. In an example, the channel change detector  112  includes a main processing unit  202  powered by a power supply  203 . The main processing unit  202  may include a processor  204  electrically coupled by a system interconnect  206  to a main memory device  208  and one or more interface circuits  210 . In an example, the system interconnect  206  is an address/data bus. Of course, a person of ordinary skill in the art will readily appreciate that interconnects other than busses may be used to connect the processor  204  to the main memory device  208 . For example, one or more dedicated lines and/or a crossbar may be used to connect the processor  204  to the main memory device  208 . 
     The processor  204  may include any type of well known central processing unit (CPU), such as a microprocessor from the Intel Pentium® family of microprocessors, the Intel Itanium® family of microprocessors, and/or the Intel XScale® family of processors. The processor  204  may include any type of well known cache memory, such as static random access memory (SRAM). The main memory device  208  may include dynamic random access memory (DRAM), but may also include non-volatile memory. In an example, the main memory device  208  stores a software program which is executed by processor  204  in a well known manner. 
     The interface circuit(s)  210  may be implemented using any type of well known interface standard, such as an analog cable interface, a digital cable interface, a satellite signal interface, an Ethernet interface, and/or a Universal Serial Bus (USB) interface. One or more input devices  212  may be connected to the interface circuits  210  for entering data and commands into the main processing unit  202 . For example, an input device  212  may be a keyboard, mouse, touch screen, track pad, track ball, isopoint, and/or a voice recognition system. In addition, the interface circuit(s)  210  handle digital data inputs from the analog-to-digital converter  108 . In an example, the analog-to-digital converter  108  is incorporated into the channel change detector  112 . 
     One or more displays, printers, speakers, and/or other output devices  214  may also be connected to the main processing unit  202  via one or more of the interface circuits  210 . The display  214  may be cathode ray tube (CRTs), liquid crystal displays (LCDs), or any other type of display. The display  214  may generate visual indications of data generated during operation of the main processing unit  202 . The visual displays may include prompts for human operator input, calculated values, detected data, etc. 
     The channel change detector  112  may also include one or more storage devices  216 . For example, the channel change detector  112  may include one or more hard drives, a compact disk (CD) drive, a digital versatile disk drive (DVD), and/or other computer media input/output (I/O) devices. 
     The channel change detector  112  may also exchange data with other devices via a connection to a network  218 . The network connection may be any type of network connection, such as an Ethernet connection, digital subscriber line (DSL), telephone line, coaxial cable, etc. The network  218  may be any type of network, such as the Internet, a telephone network, a cable network, and/or a wireless network. 
     A block diagram of another example audio channel change detector  112  is illustrated in  FIG. 3 . In this example, the channel change detector  112  includes a sampler  302 , a timer  304 , a threshold detector  306 , a buffer  308 , and a state machine  310  interconnected as shown. The audio channel change detector  112  of  FIG. 3  may be implemented using hardware and/or software, such as dedicated circuits and/or processor(s) executing instructions. 
     In operation, the sampler  302  periodically captures a portion of the audio signal from the television system  100 . The sampler  302  may be any type of sampler. For example, the sampler may an analog-to-digital converter. In such an event, the analog-to-digital converter  108  is not required. In another example, the sampler  302  may be a voltage and/or frequency measurement circuit. The frequency at which the sampler  302  captures portions of the audio signal is based on a signal from the timer  304 . The timer may be any type of timer such as a crystal oscillator or a resonator. 
     In this example, the output of the sampler  302  is passed to the threshold detector  306 . The output of the sampler  302  may be digital or analog. The threshold detector  306  compares the output of the sampler  302  to one or more predetermined thresholds. The threshold detector  306  may logically compare digital data indicative of the audio signal to one or more predetermined digital thresholds. Alternatively, the threshold detector  306  may compare one or more analog voltage levels indicative of the audio signal to a one or more predetermined voltage thresholds. For example, the threshold detector may be a digital comparator, an analog comparator, or a processor executing one or more comparison instructions. 
     Each time the threshold detector  306  makes a comparison of the audio signal to the predetermined thresholds, the threshold detector  306  outputs a signal to the buffer  308 . The signal indicates if the audio signal is greater than or less than a predetermined threshold. The buffer  308  stores data indicative of the series of signals coming form the threshold detector  306 . The buffer  308  may be any type of buffer such as a shift register or an addressable memory. 
     Data stored in the buffer  308  is then passed to the state machine  310 . The state machine  310  determines if a channel change event has occurred based on the sequence of threshold crossings reported by the audio channel change detector  112 . The state machine  310  may be implemented using any type of circuitry. For example, the state machine  310  may be a logic circuit or a processor executing instructions as described below. When the state machine  310  detects a channel change event, the state machine  310  outputs a signal indicative of the channel change event. For example, the signal may be a voltage level or a pulse. 
     An example process  400  for detecting a television channel change event is illustrated in  FIG. 4 . Preferably, the process  400  is embodied in one or more software programs that are stored in one or more memories and executed by one or more processors (e.g., processor  204 ) in a well known manner. However, some or all of the blocks of the process  400  may be performed manually and/or by another hardware device. For example, the process  400  may be executed by the audio channel change detector  112  of  FIG. 2  and/or the audio channel change detector  112  of  FIG. 3 . Although the process  400  is described with reference to the flowchart illustrated in  FIG. 4 , a person of ordinary skill in the art will readily appreciate that many other methods of performing the process  400  may be used. For example, the order of many of the blocks may be altered, the operation of one or more blocks may be changed, blocks may be combined, and/or blocks may be eliminated. 
     In general, the example process  400  detects a television channel change event by monitoring an audio signal of a television system  100 . The monitored audio signal is tested for certain characteristics indicative of a channel change event. In some television systems  100 , changing channels produces an audible “pop” sound or transient. By detecting a normal television audio signal, followed by a transient television audio signal, followed by a normal television audio signal, the methods and apparatus described herein can signal when a channel change event has likely occurred. Normal and transient signals are defined using volume level thresholds and/or frequency thresholds as described below. An example audio signal with a transient during a channel change event is illustrated in  FIG. 6 . 
     The example process  400  begins when the audio channel change detector  112  initializes a plurality of variables (block  402 ). The variables may be initialized based on a type of television equipment (e.g., a brand). For example, a variables “A”, “B”, and “C” may be initialized. Variable “A” may represent the number of samples (e.g., 60) of a group of samples (e.g., 100) that must be below a threshold (e.g., a volume level) during a first state in order to advance the process  400  to a second state. Variable “B” may represent the number of samples (e.g., 90) of a group of samples (e.g., 100) that must be above a threshold (e.g., a volume level) during the second state in order to advance the process  400  to a third state. Variable “C” may represent the number of samples (e.g., 60) of a group of samples (e.g., 100) that must be below a threshold (e.g., a volume level) during the third state in order to indicate that a channel change event occurred. Of course the values used herein are merely examples, and many other variables may be initialized. In addition, these variables may be dynamically updated. For example, transient audio signals may be identified by detecting energy peaks relative to a substantially stationary signal. In other words, the volume levels described herein may be relative volume levels, not absolute volume levels. 
     After initialization (block  402 ), the process  400  starts in a first state (block  404 ). In the first state, the process  400  looks for certain pre-channel change conditions. For example, the process  400  may look for normal audio signals, which may be characterized by one or more predetermined volume level thresholds and/or predetermined frequency thresholds. In one example, a predetermined number of audio signal samples being less than a predetermined threshold is indicative of a “normal” audio signal. 
     Accordingly, the process  400  periodically samples the audio signal (block  406 ). For example, the process  400  may take 100 samples that are 50 milliseconds (ms) apart. As described above, the samples may be analog samples and/or digital samples. Once a plurality of audio samples are taken (or after every sample), the example process  400  checks if a certain number of the audio samples are below a predetermined threshold (block  408 ). For example, the process  400  may determine if 60 out of 100 samples are below a certain volume level threshold. The threshold volume level may be a moving average threshold plus a margin constant (i.e., a band slightly above a historical average associated with the audio signal). If a sufficient number of the audio signal samples are not below the threshold, the example process  400  stays in the first state (block  404 ) and takes additional samples of the audio signal (block  406 ). If a sufficient number of the audio signal samples are below the threshold (i.e., normal audio is occurring), the example process  400  advances to a second state (block  410 ). 
     In the second state, the example process  400  looks for a transient condition (block  410 ). The transient condition may be characterized by one or more predetermined volume level thresholds and/or predetermined frequency thresholds. In one example, a transient audio signal is detected by finding a predetermined number of audio signal samples above a predetermined threshold for a predetermined time period. An example audio signal with a transient during a channel change event is illustrated in  FIG. 6 . 
     Accordingly, in the second state, the process  400  periodically samples the audio signal (block  412 ). For example, the process  400  may take 100 samples that are 50 milliseconds (ms) apart. Again, the samples may be analog samples and/or digital samples. Once a plurality of audio samples are taken (or after every sample), the example process  400  checks if a certain number of the audio samples are above a predetermined threshold (block  414 ). For example, the process  400  may determine if 30 out of 100 samples are above a certain volume level threshold. Again, the threshold volume level may be a moving average threshold plus a margin constant (i.e., a band slightly above a historical average associated with the audio signal). If a sufficient number of the audio signal samples are not above the threshold, the example process  400  reverts back to the first state (block  404 ) and takes additional samples of the audio signal (block  406 ). However, if a sufficient number of the audio signal samples are above the threshold (e.g., a transient spike occurred), the example process  400  advances to a third state (block  416 ). 
     In the third state, the process  400  looks for certain post-channel change conditions. For example, the process  400  may look for normal audio signals again. Accordingly, the process  400  periodically samples the audio signal (block  418 ). Once a plurality of audio samples are taken (or after every sample), the example process  400  determines if a certain number of the audio samples are below a predetermined threshold (block  420 ). For example, the process  400  may determine if 60 out of 100 samples are below a certain volume level threshold. If a sufficient number of the audio signal samples are not below the threshold, the example process  400  reverts back to the first state (block  404 ) and takes additional samples of the audio signal (block  406 ). However, if a sufficient number of the audio signal samples are below the threshold (i.e., normal audio is occurring again), the example process  400  indicates a channel change event has occurred (block  422 ). Subsequently, the process  400  may repeat in order to detect additional channel change events. 
     Another example process  500  for detecting a television channel change event is illustrated in  FIG. 5 . Preferably, the process  500  is embodied in one or more software programs that are stored in one or more memories and executed by one or more processors (e.g., processor  204 ) in a well known manner. However, some or all of the blocks of the process  500  may be performed manually and/or by another hardware device. For example, the process  500  may be executed by the audio channel change detector  112  of  FIG. 2  and/or the audio channel change detector  112  of  FIG. 3 . Although the process  500  is described with reference to the flowchart illustrated in  FIG. 5 , a person of ordinary skill in the art will readily appreciate that many other methods of performing the process  500  may be used. For example, the order of many of the blocks may be altered, the operation of one or more blocks may be changed, blocks may be combined, and/or blocks may be eliminated. 
     In general, the example process  500  detects a television channel change event by monitoring an audio signal of a television system  100 . The monitored audio signal is tested for certain characteristics indicative of a channel change event. In some television systems  100 , the “pop” sound produced by changing channels is muted by the television system  100 . In such television systems  100 , channel change events may be detected by detecting a normal television audio signal, followed by a muted television audio signal, followed by a normal television audio signal. Normal and muted signals are defined using volume level thresholds and/or frequency thresholds as described below. An example audio signal with a mute during a channel change event is illustrated in  FIG. 7 . 
     The example process  500  begins when the audio channel change detector  112  initializes a plurality of variables (block  502 ). These variables may be initialized based on a type of television equipment (e.g., a brand). For example, variables “A”, “B”, “C” and “X” may be initialized. Variable “A” may represent the number of samples (e.g., 60) of a group of samples (e.g., 100) that must be above a threshold (e.g., a volume level) during a first state in order to advance the process  400  to a second state. Variable “B” may represent the number of samples (e.g., 90) of a group of samples (e.g., 100) that must be below a threshold (e.g., a volume level) during the second state in order to advance the process  400  to a third state. Variable “C” may represent the number of samples (e.g., 60) of a group of samples (e.g., 100) that must be above a threshold (e.g., a volume level) during the third state in order to indicate that a channel change event occurred. Variable “X” may represent a time period (e.g., 15 seconds) after which a muted condition is treated as a television off condition or a “user mute” condition. Of course the values used herein are merely examples, and many other variables may be initialized. In addition, these variables may be dynamically updated. For example, muted audio signals may be identified by detecting energy lows relative to a substantially stationary signal. In other words, the volume levels described herein may be relative volume levels, not absolute volume levels. 
     After initialization (block  502 ), the process  500  starts in a first state (block  504 ). In the first state, the process  500  looks for certain pre-channel change conditions. For example, the process  500  may look for normal audio signals. Normal audio signals may be characterized by one or more predetermined volume level thresholds and/or predetermined frequency thresholds. In one example, a predetermined number of audio signal samples being less than a predetermined threshold is indicative of a “normal” audio signal. 
     Accordingly, the process  500  periodically samples the audio signal (block  506 ). For example, the process  500  may take 100 samples that are 50 milliseconds (ms) apart. As described above, the samples may be analog samples and/or digital samples. Once a plurality of audio samples are taken (or after every sample), the example process  500  checks if a certain number of the audio samples are above a predetermined threshold (block  508 ). For example, the process  500  may determine if 60 out of 100 samples are above a certain volume level threshold. The threshold volume level may be a moving average threshold minus a margin constant (i.e., a band slightly below historically averaged audio signals). If a sufficient number of the audio signal samples are not above the threshold, the example process  500  stays in the first state (block  504 ) and takes additional samples of the audio signal (block  506 ). If a sufficient number of the audio signal samples are above the threshold (i.e., normal audio is occurring), the example process  500  advances to a second state (block  410 ). 
     In the second state, the example process  500  looks for a muted condition (block  510 ). The muted condition may be characterized by one or more predetermined volume level thresholds and/or predetermined frequency thresholds. In one example, a muted audio signal is detected by finding a predetermined number of audio signal samples below a predetermined threshold for a predetermined time period. An example audio signal with a mute during a channel change event is illustrated in  FIG. 7 . 
     Accordingly, the process  500  periodically samples the audio signal (block  512 ) and checks if a certain number of the audio samples are below a predetermined threshold (block  514 ). Again, the threshold volume level may be a band slightly below historically averaged audio signals. If a sufficient number of the audio signal samples are not below the threshold, the example process  500  reverts back to the first state (block  504 ) and takes additional samples of the audio signal (block  506 ). However, if a sufficient number of the audio signal samples are below the threshold (i.e., a mute occurred), the example process  500  checks if the muted condition has lasted longer than a predetermined amount of time (block  516 ). If the muted condition has lasted longer than a predetermined amount of time, the process  500  reverts back to the first state (block  504 ). For example, if a muted condition exists for 30 minutes, the example process  500  may assume the television has been turned off. In another example, if the muted condition lasts 15 seconds, it may be assumed that the viewer intentionally muted the television rather than the muting having been caused by a channel change event. If a sufficient number of the audio signal samples are below the threshold (i.e., a mute occurred), and the muted condition has not lasted longer than a predetermined amount of time (e.g., the television is not intentionally muted or turned off), the process  500  advances to a third state (block  518 ). 
     In the third state, the process  500  looks for certain post-channel change conditions. For example, the process  500  may look for normal audio signals again. Accordingly, the process  500  periodically samples the audio signal (block  520 ) and checks if a certain number of the audio samples are above a predetermined threshold (block  522 ). If a sufficient number of the audio signal samples are not above the threshold, the example process  500  reverts back to block  514  to determine if audio is still muted. If the audio is still muted, the process  500  determines if the mute condition has lasted long enough to assume the television has been turned off (block  516 ). However, if a sufficient number of the audio signal samples are above the threshold (i.e., normal audio is occurring again), the example process  500  indicates a channel change event has occurred (block  524 ). 
     In addition to each of the separate processes  400  and  500 , a person of ordinary skill in the art will readily appreciate that process  400  and process  500  may be combined. For example, when looking for normal audio, the combined process may look for volume levels that are both (i) above a first predetermined threshold like process  400  and (ii) below a second predetermined threshold like process  500 . Similarly, the combined process may accept either a transient condition or a muted condition as satisfying the conditions of the second state. 
     An example audio signal  600  generated during a channel change event is illustrated in  FIG. 6 . In this example, a transient signal  602  is generated during the channel change event. The portion  604  of the audio which occurs before the transient  602  is normal or stationary audio because a certain percentage (e.g., &gt;80%) of the audio before the channel change has a volume (or energy) level below a threshold  606 . The threshold may be a moving average plus some constant  608  (i.e., a horizontal line slightly above an average peak line  610 ). Similarly, the portion  612  of the audio which occurs after the transient  602  is “normal” or “stationary” audio because a certain percentage (e.g., &gt;80%) of the audio after the channel change also has a volume (or energy) level below the threshold  606 . 
     In the portion  604  of the audio before the channel change, some of the audio peaks  614  may go above the threshold  606 , but most of the audio peaks  616  fall below the threshold  606 . Similarly, in the portion  612  of the audio after the channel change, most of the audio peaks  618  fall below the threshold  606 . Conversely, in the portion  602  of the audio during the channel change, some of the audio peaks  620  may fall below the threshold  606 , but most of the audio peaks  622  reach above the threshold  606 . 
     Another example audio signal  700  generated during a channel change event is illustrated in  FIG. 7 . In this example, a mute signal  702  is generated during the channel change event. The portion  704  of the audio which occurs before the mute  702  is normal or stationary audio because a certain percentage (e.g., &gt;80%) of the audio before the channel change has a volume (or energy) level above a threshold  706 . The threshold may be a moving average plus some constant  708  (i.e., a horizontal line slightly below an average peak line  710 ). Similarly, the portion  712  of the audio which occurs after the mute  702  is normal or stationary audio because a certain percentage (e.g., &gt;80%) of the audio after the channel change also has a volume (or energy) level above the threshold  706 . 
     In the portion  704  of the audio before the channel change, some of the audio peaks  714  may fall below the threshold  706 , but most of the audio peaks  716  go above the threshold  706 . Similarly, in the portion  712  of the audio after the channel change, most of the audio peaks  718  reach above the threshold  706 , even though some peaks  720  may fall below the threshold  706 . In the example illustrated in  FIG. 7 , the portion  702  of the audio that is muted falls entirely below the threshold  706 . However, a person of ordinary skill in the art will readily appreciate that the portion  702  of the audio that is muted need not fall entirely below the threshold  706 . 
     Although certain apparatus have been described herein, the scope of coverage of this patent is not limited thereto. On the contrary, this patent covers all apparatuses, methods and articles of manufacture fairly falling within the scope of the appended claims either literally or under the doctrine of equivalents.