Patent Publication Number: US-2022223137-A1

Title: Systems and methods for on ear detection of headsets

Description:
TECHNICAL FIELD 
     Embodiments generally relate to systems and methods for determining whether or not a headset is located on or in an ear of a user, and to headsets configured to determine whether or not the headset is located on or in an ear of a user. 
     BACKGROUND 
     Headsets are a popular device for delivering sound and audio to one or both ears of a user. For example, headsets may be used to deliver audio such as playback of music, audio files or telephony signals. Headsets typically also capture sound from the surrounding environment. For example, headsets may capture the user&#39;s voice for voice recording or telephony, or may capture background noise signals to be used to enhance signal processing by the device. Headsets can provide a wide range of signal processing functions. 
     For example, one such function is Active Noise Cancellation (ANC, also known as active noise control) which combines a noise cancelling signal with a playback signal and outputs the combined signal via a speaker, so that the noise cancelling signal component acoustically cancels ambient noise and the user only or primarily hears the playback signal of interest. ANC processing typically takes as inputs an ambient noise signal provided by a reference (feed-forward) microphone, and a playback signal provided by an error (feed-back) microphone. ANC processing consumes appreciable power continuously, even if the headset is taken off. 
     Thus in ANC, and similarly in many other signal processing functions of a headset, it is desirable to have knowledge of whether the headset is being worn at any particular time. For example, it is desirable to know whether on-ear headsets are placed on or over the pinna(e) of the user, and whether earbud headsets have been placed within the ear canal(s) or concha(e) of the user. Both such use cases are referred to herein as the respective headset being “on ear”. The unused state, such as when a headset is carried around the user&#39;s neck or removed entirely, is referred to herein as being “off ear”. 
     Previous approaches to on ear detection include the use of a sense microphone positioned to detect acoustic sound inside the headset when worn, on the basis that acoustic reverberation inside the ear canal and/or pinna will cause a detectable rise in power of the sense microphone signal as compared to when the headset is not on ear. However, the sense microphone signal power can be affected by noise sources such as the user&#39;s own voice, and so this approach can output a false negative that the headset is off ear when in fact the headset is on ear and affected by bone conducted own voice. 
     It is desired to address or ameliorate one or more shortcomings or disadvantages associated with prior systems and methods for determining whether or not a headset is in place on or in the ear of a user, or to at least provide a useful alternative thereto. 
     Throughout this specification the word “comprise”, or variations such as “comprises” or “comprising”, will be understood to imply the inclusion of a stated element, integer or step, or group of elements, integers or steps, but not the exclusion of any other element, integer or step, or group of elements, integers or steps. 
     In this document, a statement that an element may be “at least one of” a list of options is to be understood to mean that the element may be any one of the listed options, or may be any combination of two or more of the listed options. 
     Any discussion of documents, acts, materials, devices, articles or the like which has been included in the present specification is not to be taken as an admission that any or all of these matters form part of the prior art base or were common general knowledge in the field relevant to the present disclosure as it existed before the priority date of each of the appended claims. 
     SUMMARY 
     Some embodiments relate to a signal processing device for on ear detection for a headset, the device comprising:
         a first microphone input for receiving a microphone signal from a first microphone, the first microphone being configured to be positioned inside an ear of a user when the user is wearing the headset;   a second microphone input for receiving a microphone signal from a second microphone, the second microphone being configured to be positioned outside the ear of the user when the user is wearing the headset; and   a processor configured to:
           receive microphone signals from each of the first microphone input and the second microphone input;   pass the microphone signals through a first filter to remove low frequency components, producing first filtered microphone signals;   combine the first filtered microphone signals to determine a first on ear status metric;   pass the microphone signals through a second filter to remove high frequency components, producing second filtered microphone signals;   combine the second filtered microphone signals to determine a second on ear status metric; and   combine the first on ear status metric with the second on ear status metric to determine the on ear status of the headset.   
               

     According to some embodiments, the first filter is configured to filter the microphone signals to retain only frequencies that are likely to correlate to bone conducted speech of the user of the headset. In some embodiments, the first filter is a band pass filter. In some embodiments, the first filter is a bandpass filter configured to filter the microphone signals to frequencies between 2.8 and 4.7 kHz. 
     According to some embodiments, the second filter is configured to filter the microphone signals to retain only frequencies that are likely to resonate within the ear of the user. In some embodiments, the second filter is a band pass filter. In some embodiments, the second filter is configured to filter the microphone signals to frequencies between 100 and 600 Hz. 
     In some embodiments, combining the first filtered signals comprises subtracting the first filtered signal derived from the microphone signal received from the second microphone from the first filtered signal derived from the microphone signal received from the first microphone. 
     According to some embodiments, combining the second filtered signals comprises subtracting the second filtered signal derived from the microphone signal received from the first microphone from the second filtered signal derived from the microphone signal received from the second microphone. 
     According to some embodiment, combining the first on ear status metric with the second on ear status metric comprises adding the metrics together, and comparing the result with a predetermined threshold. In some embodiments, the predetermined threshold is between 6 dB and 10 dB. According to some embodiments, the predetermined threshold is 8 dB. 
     Some embodiments relate to a method of on ear detection for an earbud, the method comprising:
         receiving microphone signals from each of a first microphone and a second microphone, wherein the first microphone is configured to be positioned inside an ear of a user when the user is wearing the earbud and the second microphone is configured to be positioned outside the ear of the user when the user is wearing the earbud;   passing the microphone signals through a first filter to remove low frequency components, producing first filtered microphone signals;   combining the first filtered microphone signals to determine a first on ear status value;   passing the microphone signals through a second filter to remove high frequency components, producing second filtered microphone signals;   combining the second filtered microphone signals to determine a second on ear status value; and   combining the first on ear status value with the second on ear status value to determine the on ear status of the headset.       

     According to some embodiments, the first filter is configured to filter the microphone signals to retain only frequencies that are likely to correlate to bone conducted speech of the user of the headset. In some embodiments, the first filter is a band pass filter. In some embodiments, the first filter is a band-pass filter configured to filter the microphone signals to frequencies between 100 and 600 Hz. 
     According to some embodiments, the second filter is configured to filter the microphone signals to retain only frequencies that are likely to resonate within the ear of the user. In some embodiments, the second filter is a band pass filter. According to some embodiments, the second filter is configured to filter the microphone signals to frequencies between 2.8 and 4.7 kHz. 
     According to some embodiments, combining the first filtered signals comprises subtracting the first filtered signal derived from the microphone signal received from the second microphone from the first filtered signal derived from the microphone signal received from the first microphone. 
     In some embodiments, combining the second filtered signals comprises subtracting the second filtered signal derived from the microphone signal received from the first microphone from the second filtered signal derived from the microphone signal received from the second microphone. 
     In some embodiments, combining the first on ear status metric with the second on ear status metric comprises adding the metrics together to produce a passive OED metric, and comparing the passive OED metric with a predetermined threshold. According to some embodiments, the predetermined threshold is between 6 dB and 10 dB. In some embodiments, the predetermined threshold is 8 dB. 
     Some embodiments further comprise incrementing an on ear variable if the passive OED metric exceeds the threshold, and incrementing an off ear variable if the passive OED metric does not exceed the threshold. Some embodiments further comprise determining that the status of the earbud is on ear if the on ear variable value is larger than a first predetermined threshold and the off ear variable value smaller than a second predetermined threshold; determining that the status of the earbud is off ear if the off ear variable value is larger than the first predetermined threshold and the on ear variable value smaller than the second predetermined threshold; and otherwise determining that the status of the earbud is unknown. 
     Some embodiments further comprise determining whether the microphone signals correspond to valid data, by comparing the power level of the microphone signals received from the second microphone exceed a predetermined threshold. In some embodiments, the threshold is 60 dB SPL. 
     Some embodiments relate to a non-transitory machine-readable medium storing instructions which, when executed by one or more processors, cause an electronic apparatus to perform the method of some other embodiments. 
     Some embodiments relate to an apparatus, comprising processing circuitry and a non-transitory machine-readable which, when executed by the processing circuitry, cause the apparatus to perform the method of some other embodiments. 
     Some embodiments relate to a system for on ear detection for an earbud, the system comprising a processor and a memory, the memory containing instructions executable by the processor and wherein the system is operative to perform the method of some other embodiments. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       Embodiments are described in further detail below, by way of example and with reference to the accompanying drawings, in which: 
         FIG. 1  illustrates a signal processing system comprising a headset in which on ear detection is implemented according to some embodiments; 
         FIG. 2  shows a block diagram illustrating the hardware components of an earbud of the headset of  FIG. 1  according to some embodiments; 
         FIG. 3  shows a block diagram illustrating the earbud of  FIG. 2  in further detail according to some embodiments; 
         FIG. 4  shows a block diagram showing a passive on ear detection process performed by the earbud of  FIG. 2  according to some embodiments; 
         FIG. 5  shows a block diagram showing the software modules of the earbud of the headset of  FIG. 1 ; 
         FIG. 6  shows a flowchart illustrating a method of determining whether or not a headset is in place on or in an ear of a user, as performed by the system of  FIG. 1 ; 
         FIGS. 7A and 7B  show graphs illustrating level differences measured by internal and external microphones according to some embodiments; and 
         FIGS. 8A and 8B  show graphs illustrating level differences of filtered signals measured by internal and external microphones according to some embodiments. 
     
    
    
     DETAILED DESCRIPTION 
     Embodiments generally relate to systems and methods for determining whether or not a headset is located on or in an ear of a user, and to headsets configured to determine whether or not the headset is located on or in an ear of a user. 
     Some embodiments relate to a passive on ear detection technique that reduces, or mitigates the likelihood of, false negative results that may arise from an earbud detecting the user&#39;s own voice via bone conduction, by filtering signals received from internal and external microphones by two different filters and comparing these in parallel, with the results of each comparison being added to result in a final on ear status being determined. 
     Specifically, some embodiments relate to a passive on ear detection technique that uses a first algorithm to filter the internal and external microphones to a band that excludes most bone conducted speech, which tends to be of a lower frequency, and to determine whether the external microphone senses louder sounds than the internal microphone. In parallel, the technique uses a second algorithm to filter the internal and external microphones to a band that would include most bone conducted speech, and determines whether bone conduction exists by determining whether the internal microphone senses louder sounds than the external microphone. The outcomes of the first and second algorithms are combined to determine the on ear status of the earbud. 
     As bone conduction only occurs when an earphone is located inside an ear, this technique allows for the on-ear on ear status of the earbud to be determined regardless of whether own voice is present or not. 
       FIG. 1  illustrate a headset  100  in which on ear detection is implemented. Headset  100  comprises two earbuds  120  and  150 , each comprising two microphones  121 ,  122  and  151 ,  152 , respectively. Headset  100  may be configured to determine whether or not each earbud  120 ,  150  is located in or on an ear of a user. 
       FIG. 2  is a system schematic showing the hardware components of earbud  120  in further detail. Earbud  150  comprises substantially the same components as earbud  120 , and is configured in substantially the same way. Earbud  150  is thus not separately shown or described. 
     As well as microphones  121  and  122 , earbud  120  comprises a digital signal processor  124  configured to receive microphone signals from earbud microphones  121  and  122 . Microphone  121  is an external or reference microphone and is positioned to sense ambient noise from outside the ear canal and outside of the earbud when earbud  120  is positioned in or on an ear of a user. Conversely, microphone  122  is an internal or error microphone and is positioned inside the ear canal so as to sense acoustic sound within the ear canal when earbud  120  is positioned in or on an ear of the user. 
     Earbud  120  further comprises a speaker  128  to deliver audio to the ear canal of the user when earbud  120  is positioned in or on an ear of a user. When earbud  120  is positioned within the ear canal, microphone  122  is occluded to at least some extent from the external ambient acoustic environment, but remains well coupled to the output of speaker  128 . In contrast, microphone  121  is occluded to at least some extent from the output of speaker  128  when earbud  120  is positioned in or on an ear of a user, but remains well coupled to the external ambient acoustic environment. Headset  100  may be configured to deliver music or audio to a user, to allow a user to make telephone calls, and to deliver voice commands to a voice recognition system, and other such audio processing functions. 
     Processor  124  is further configured to adapt the handling of such audio processing functions in response to one or both earbuds  120 ,  150  being positioned on the ear, or being removed from the ear. For example, processor  124  may be configured to pause audio being played through headset  100  when processor  124  detects that one or more earbuds  120 ,  150  have been removed from a user&#39;s ear(s). Processor  124  may be further configured to resume audio being played through headset  100  when processor  124  detects that one or more earbuds  120 ,  150  have been placed on or in a user&#39;s ear(s). 
     Earbud  120  further comprises a memory  125 , which may in practice be provided as a single component or as multiple components. The memory  125  is provided for storing data and program instructions readable and executable by processor  124 , to cause processor  124  to perform functions such as those described above. 
     Earbud  120  further comprises a transceiver  126 , which allows the earbud  120  to communicate with external devices. According to some embodiments, earbuds  120 ,  150  may be wireless earbuds, and transceiver  126  may facilitate wireless communication between earbud  120  and earbud  150 , and between earbuds  120 ,  150  and an external device such as a music player or smart phone. According to some embodiments, earbuds  120 ,  150  may be wired earbuds, and transceiver  126  may facilitate wired communications between earbud  120  and earbud  150 , either directly such as within an overhead band, or via an intermediate device such as a smartphone. According to some embodiments, earbud  120  may further comprise a proximity sensor  129  configured to send signals to processor  124  indicating whether earbud  120  is located in proximity to an object, and/or to measure the proximity of the object. Proximity sensor  129  may be an infrared sensor or an infrasonic sensor in some embodiments. According to some embodiments, earbud  120  may have other sensors, such as movement sensors or accelerometers, for example. Earbud  120  further comprises a power supply  127 , which may be a battery according to some embodiments. 
       FIG. 3  is a block diagram showing earbud  120  in further detail, and illustrating a process of passive on ear detection in accordance with some embodiments.  FIG. 3  shows microphones  121  and  122 . Reference microphone  121  generates passive signal X RP  based on detected ambient sounds when no audio is being played via speaker  128 . Error microphone  122  generates passive signal X EP  based on detected ambient sounds when no audio is being played via speaker  128 . 
     Reference signal own voice filter  310  is configured to filter the passive signal X RP  generated by reference microphone  121  to frequencies that are likely to correlate to bone conducted user&#39;s speech or own voice. According to some embodiments, filter  310  may be configured to filter the passive signal X RP  to frequencies between 100 and 600 Hz. According to some embodiments, filter  310  may be a 4 th  order infinite impulse response (IIR) filter. Error signal own voice filter  315  is configured to filter the passive signal X EP  generated by error microphone  122  to frequencies that are likely to correlate to bone conducted user&#39;s speech or own voice. According to some embodiments, filter  315  may be configured with the same parameters as filter  310 . According to some embodiments, filter  315  may be configured to filter the passive signal X EP  to frequencies between 100 and 600 Hz. According to some embodiments, filter  315  may be a 4 th  order infinite impulse response (IIR) filter. 
     In order to avoid analysing unstable signals and as the output of band pass filters  310  and  315  may take a while to stabilise, the outputs of filters  310  and  315  may be passed through hold-off switches  312  and  317 . Switches  312  and  317  may be configured to close after a predetermined time period has elapsed after receiving a signal via microphones  121  or  122 . According to some embodiments, the predetermined time period may be between 10 ms and 60 ms. According to some embodiments, the predetermined time period may be around 40 ms. 
     Once the hold-off switches  312  and  317  have closed, the output of filter  310  may be subtracted from the output of filter  315  by subtraction node  330  to generate an own voice OED metric. As own voice is likely to be louder in ear than out of ear due to bone conduction, a positive own voice OED metric is likely to be generated when earbud  120  is located in or on an ear of a user, and a negative own voice OED metric is likely to be generated when earbud  120  is off the ear of the user. 
     Error signal resonance filter  320  is configured to filter the passive signal X EP  generated by error microphone  122  to frequencies that are likely to resonate within the user&#39;s ear. According to some embodiments, these may also be frequencies that are unlikely to correlate to the user&#39;s speech or own voice. According to some embodiments, filter  320  may be configured to filter the passive signal X EP  to frequencies between 2.8 and 4.7 kHz. According to some embodiments, filter  320  may be a 6th order infinite impulse response (IIR) filter. Reference signal resonance filter  325  is configured to filter the passive signal X RP  generated by reference microphone  121  to frequencies that are likely to resonate within the user&#39;s ear. According to some embodiments, these may also be frequencies that are unlikely to correlate to the user&#39;s speech or own voice. According to some embodiments, filter  325  may be configured with the same parameters as filter  320 . According to some embodiments, filter  325  may be configured to filter the passive signal X RP  to frequencies between 2.8 and 4.7 kHz. According to some embodiments, filter  325  may be a 6th order infinite impulse response (IIR) filter. 
     In order to avoid analysing unstable signals and as the output of band pass filters  320  and  325  may take a while to stabilise, the outputs of filters  320  and  325  may be passed through hold-off switches  335  and  340 . Switches  335  and  340  may be configured to close after a predetermined time period has elapsed after receiving a signal via microphones  121  or  122 . According to some embodiments, the predetermined time period may be between 10 ms and 60 ms. According to some embodiments, the predetermined time period may be around 40 ms. 
     Once the hold-off switches  335  and  340  have closed, the outputs of filters  320  and  325  are passed to power meters  345  and  350 . Error signal power meter  345  determines the power of the filtered output of filter  320 , while reference signal power meter  350  determines the power of the filtered output of filter  325 . The reference signal power determined by meter  350  is passed to passive OED decision module  365  for analysis. According to some embodiments, in order to further avoid instability in the data, power meters  345  and  350  may be primed to a predetermined power level, so that the power of the filtered signals can be more quickly determined. According to some embodiments, power meters  345  and  350  may be primed to start at a power threshold, which may be between 50 and 80 dB SPL in some embodiments. According to some embodiments, the power threshold may be 60 to 70 dB SPL. 
     The error signal power as determined by meter  345  is then subtracted from the reference signal power as determined by meter  350  at subtraction node  355  to generate a passive loss OED metric. As ambient noise is likely to be louder out of ear than in ear due to obstruction of error microphone  122  when earbud  120  is in ear, a large degree of attenuation or passive loss is likely to be generated when earbud  120  is located in or on an ear of a user, and a passive loss close to zero is likely to be generated when earbud  120  is off the ear of the user. 
     The own voice OED metric generated by node  330  and the passive loss OED metric generated by node  355  are both passed to addition node  360 . Addition node  360  adds the two metrics together to produce a passive OED metric, which is passed to passive OED decision module  365  for analysis. The decision process performed by OED decision module  365  is described in further detail below with reference to  FIG. 4 . 
       FIG. 4  is a flowchart illustrating a method  400  of passive on ear detection using earbud  120 . Method  400  is performed by processor  124  executing passive OED decision module  365  stored in memory  125 . 
     Method  400  starts at step  410 , at which a reference signal power calculated by reference signal power meter  350  is received by passive OED decision module  365 . At step  420 , processor  124  determines whether or not the reference signal power exceeds a predetermined power threshold, which may be between 50 and 80 dB SPL in some embodiments. According to some embodiment, the power threshold may be 60 to 70 dB SPL. 
     If the power does not exceed the threshold, this indicates that the data is invalid, as there is are not enough sounds captured by reference microphone  121  to make an accurate OED determination. Processor  124  causes method  400  to restart at step  410 , waiting for further data to be received. If the power does exceed the threshold, processor  124  determines that the data is valid and continues executing method  400  at step  430 . 
     At step  430 , the passive OED metric determined by node  360  is received by passive OED decision module  365 . At step  440 , processor  124  determines whether or not the metric exceeds a predetermined threshold, which may be between 6 dB and 10 dB, and may be 8 dB according to some embodiments. If processor  124  determines that the metric does exceed the threshold, indicating that earbud  120  is likely to be on or in the ear of a user, an “on ear” variable is incremented by processor  124  at step  450 . If processor  124  determines that the metric does not exceed the threshold, indicating that earbud  120  is likely to be off the ear of a user, an “off ear” variable is incremented by processor  124  at step  460 . 
     Method  400  then moves to step  470 , at which processor  124  determines whether enough data has been received. According to some embodiments, processor  124  may make this determination by incrementing a counter, and determining if the counter exceeds a predetermined threshold. For example, the predetermined threshold may be between 100 and 500, and may be 250 in some embodiments. If processor  124  determines that enough data has not been received, such as by determining that the threshold has not been reached, processor  124  may continue executing method  400  from step  410 , waiting for further data to be received. According to some embodiments, data may be received at regular intervals. According to some embodiments, the regular intervals may be intervals of 4 ms. 
     If processor  124  determines that enough data has been received, such as by determining that the threshold has been reached, processor  124  may continue executing method  400  from step  480 . According to some embodiments, processor  124  may also be configured to execute a time out process, where if enough data is not received within a predefined time period, processor  124  continues executing method  400  from step  480  once the predetermined time has elapsed. According to some embodiments, in this case processor  124  may determine that the OED status is unknown. 
     At step  480 , processor  124  may determine the OED status based on the on ear and off ear variables. According to some embodiments, if the on ear variable exceeds a first threshold and the off ear variable if less than a second variable, processor  124  may determine that earbud  120  is on or in the ear of a user. If the off ear variable exceeds the first threshold and the on ear variable is less than the second variable, processor  124  may determine that earbud  120  is off the ear of a user. If neither of these criteria are met, processor  124  may determine that the on ear status of earbud  120  is unknown. According to some embodiments, the first threshold may be between 50 and 200, and may be 100 according to some embodiments. According to some embodiments, the second threshold may be between 10 and 100, and may be 50 according to some embodiments. 
     According to some embodiments, the method of  FIG. 4  may be executed as part of a broader process for on ear detection, as described below with reference to  FIGS. 5 and 6 . 
       FIG. 5  is a block diagram showing executable software modules stored in memory  125  of earbud  120  in further detail, and further illustrating a process for on ear detection in accordance with some embodiments.  FIG. 5  shows microphones  121  and  122 , as well as speaker  128  and proximity sensor  129 . Proximity sensor  129  may be an optional component in some embodiments. Reference microphone  121  generates passive signal X RP  based on detected ambient sounds when no audio is being played via speaker  128 . When audio is being played via speaker  128 , reference microphone  121  generates active signal X RA  based on detected sounds, which may include ambient sounds as well as sounds emitted by speaker  128 . Error microphone  122  generates passive signal X EP  based on detected ambient sounds when no audio is being played via speaker  128 . When audio is being played via speaker  128 , error microphone  122  generates active signal X EA  based on detected sounds, which may include ambient sounds as well as sounds emitted by speaker  128 . 
     Memory  125  stores passive on ear detection module  510  executable by processor  124  to use passive on ear detection to determine whether or not earbud  120  is located on or in an ear of a user. Passive on ear detection refers to an on ear detection process that does not require audio to be emitted via speaker  128 , but instead uses the sounds detected in the ambient acoustic environment to make an on ear determination, such as the process described above with reference to  FIGS. 3 and 4 . Module  510  is configured to receive signals from proximity sensor  129 , as well as passive signals X RP  and X EP  from microphones  121  and  122 . The signal received from proximity sensor  129  may indicate whether or not earbud  120  is in proximity to an object. If the signal received from proximity sensor  129  indicates that earbud  120  is in proximity to an object, passive on ear detection module  510  may be configured to cause processor  124  to process passive signals X RP  and X EP  to determine whether earbud  120  is located in or on an ear of a user. According to some embodiments where earbud  120  does not comprise a proximity sensor  129 , earbud  120  may instead perform passive on ear detection constantly or periodically based on a predetermined time period, or based on some other input signal being received. 
     Processor  124  may perform passive on ear detection by performing method  400  as described above with reference to  FIGS. 3 and 4 . 
     If a determination cannot be made by passive on ear detection module  510 , passive on ear detection module  510  may send a signal to active on ear detection module  520  to indicate that passive on ear detection was unsuccessful. According to some embodiments, even where passive on ear detection module  510  can make a determination, passive on ear detection module  510  may send a signal to active on ear detection module  520  to initiate active on ear detection, which may be used to confirm the determination made by passive on ear detection module  510 , for example. 
     Active on ear detection module  520  may be executable by processor  124  to use active on ear detection to determine whether or not earbud  120  is located on or in an ear of a user. Active on ear detection refers to an on ear detection process that requires audio to be emitted via speaker  128  to make an on ear determination. Module  520  may be configured to cause speaker  128  to play a sound, to receive active signal X EA  from error microphone  122  in response to the played sound, and to cause processor  124  to process active signal X EA  with reference to the played sound to determine whether earbud  120  is located in or on an ear of a user. According to some embodiments, module  520  may also optionally receive and process active signal X RA  from reference microphone  121 . 
     Processor  124  executing active on ear detection module  520  may first be configured to instruct signal generation module  530  to generate a probe signal to be emitted by speaker  128 . According to some embodiments, the generated probe signal may be an audible probe signal, and may be a chime signal, for example. According to some embodiments, the probe signal may be a signal of a frequency known to resonate in the human ear canal. For example, according to some embodiments, the signal may be of a frequency between 100 Hz and 2 kHz. According to some embodiments, the signal may be of a frequency between 200 and 400 Hz. According to some embodiments, the signal may comprise the notes C, D and G, being a Csus2 chord. 
     Microphone  122  may generate active signal X EA  during the period that speaker  128  is emitting the probe signal. Active signal X EA  may comprise a signal corresponding at least partially to the probe signal emitted by speaker  128 . 
     Once speaker  128  has emitted the signal generated by signal generation module  530 , and microphone  122  has generated active signal X EA , being the signal generated based on audio sensed by microphone  122  during the emission of the generated signal by speaker  128 , signal X EA  is processed by processor  124  executing active on ear detection module  520  to determine whether earbud  120  is on or in an ear of a user. Processor  124  may perform active on ear detection by detecting whether or not error microphone  122  detected resonance of the probe signal emitted by speaker  128 , by comparing the probe signal with active signal X EA . This may comprise determining whether a resonance gain of the detected signal exceeds a predetermined threshold. If processor  124  determines that active signal X EA  correlates with resonance of the probe signal, processor  124  may determine that microphone  122  is located within an ear canal of a user, and that earbud  120  is therefore located on or in an ear of a user. If processor  124  determines that active signal X EA  does not correlate with resonance of the probe signal, processor  124  may determine that microphone  122  is not located within an ear canal of a user, and that earbud  120  is therefore not located on or in an ear of a user. The results of this determination may be sent to decision module  540  for further processing. 
     Once an on ear decision has been generated by one of passive on ear detection module  510  and active on ear detection module  520  and passed to decision module  540 , processor  124  may execute decision module  540  to determine whether any action needs to be performed as a result of the determination. According to some embodiments, decision module  540  may also store historical data of previous states of earbud  120  to assist in determining whether any action needs to be performed. For example, if the determination is that earbud  120  is now in an in-ear position, and previously stored data indicates that earbud  120  was previously in an out-of-ear position, decision module  540  may determine that audio should now be delivered to earbud  120 . 
       FIG. 6  is a flowchart illustrating a method  600  of on ear detection using earbud  120 . Method  600  is performed by processor  124  executing code modules  510 ,  520 ,  530  and  540  stored in memory  125 . 
     Method  600  starts at step  605 , at which processor  124  receives a signal from proximity sensor  129 . At step  610 , processor  124  analyses the received signal to determine whether or not the signal indicates that earbud  120  is in proximity to an object. This analysis may include comparing the received signal to a predetermined threshold value, which may be a distance value in some embodiments. If processor  124  determines that the received signal indicates that earbud  120  is not in proximity to an object, processor  124  determines that earbud  120  cannot be located in or on an ear of a user, and so proceeds to wait for a further signal to be received from proximity sensor  129 . 
     If, on the other hand, processor  124  determines from the signal received from proximity sensor  129  that earbud  120  is in proximity to an object, processor  124  continues to execute method  600  by proceeding to step  615 . In embodiments where earbud  120  does not include a proximity sensor  129 , steps  605  and  610  of method  600  may be skipped, and processor  124  may commence executing the method from step  615 . According to some embodiments, a different sensor, such as a motion sensor, may be used to trigger the performance of method  600  from step  615 . 
     At step  615 , processor  124  executes passive on ear detection module  510  to determine whether earbud  120  is located in or on an ear of a user. As described in further detail above with references to  FIGS. 3 and 4 , executing passive on ear detection module  510  may comprise processor  124  receiving and comparing the power of passive signals X RP  and X EP  generated by microphones  121  and  122  in response to received ambient noise. 
     At step  620 , processor  124  checks whether the passive on ear detection process was successful. If processor  124  was able to determine whether earbud  120  is located in or on an ear of a user based on passive signals X RP  and X EP , then at step  625  the result is output to decision module  540  for further processing. If processor  124  was unable to determine whether earbud  120  is located in or on an ear of a user based on passive signals X RP  and X EP , then processor  124  proceeds to execute an active on ear detection process by moving to step  630 . 
     At step  630 , processor  124  executes signal generation module  530  to cause a probe signal to be generated and sent to speaker  128  for emission. At step  635 , processor  124  further executes active on ear detection module  520 . As described in further detail above with references to  FIG. 5 , executing active on ear detection module  520  may comprise processor  124  receiving active signal X EA  generated by microphone  122  in response to the emitted probe signal, and determining whether the received signal corresponds to resonance of the probe signal. According to some embodiments, executing active on ear detection module  520  may further comprise processor  124  receiving active signal X RA  generated by microphone  121  in response to the emitted probe signal, and determining whether the received signal corresponds to resonance of the probe signal. At step  625 , the result of the active on ear detection process is output to decision module  540  for further processing. 
       FIGS. 7A and 7B  are graphs illustrating the level differences between signals measured by internal and external microphones. 
       FIG. 7A  shows a graph  700  having an X-axis  705  and a Y-axis  710 . X-axis  705  displays two conditions, being a 60 dBA ambient environment with no own speech and a 70 dBA environment with no speech. Y-axis  710  shows the level differences between signals recorded by reference microphone  121  and error microphone  122  in each environment. 
     Data points  720  relate to level differences for signals captured while earbud  120  was on or in an ear of a user, while data points  730  relate to level differences for signals captured while earbud  120  was off ear. As visible from graph  700 , there is a significant gap between data points  720  and data points  730 , indicating that calculating the level difference is an effective way to determine on ear status of earbud  120  in an environment with no own speech. 
       FIG. 7B  shows a graph  750  having an X-axis  755  and a Y-axis  760 . X-axis  755  displays two conditions, being a 60 dBA ambient environment with own speech and a 70 dBA environment with own speech. Y-axis  760  shows the level differences between signals recorded by reference microphone  121  and error microphone  122  in each environment. 
     Data points  770  relate to level differences for signals captured while earbud  120  was on or in an ear of a user, while data points  780  relate to level differences for signals captured while earbud  120  was off ear. As visible from graph  750 , there is no longer a significant gap between data points  770  and data points  780 , and instead these data points overlap, indicating that calculating the level difference is not always an effective way to determine on ear status of earbud  120  in an environment where own speech is present. 
       FIGS. 8A and 8B  are graphs illustrating the level differences between signals measured by internal and external microphones, where those signals have been filtered and processed as described above with reference to  FIGS. 3 and 4 . 
       FIG. 8A  shows a graph  800  having an X-axis  805  and a Y-axis  810 . X-axis  805  displays two conditions, being a 60 dBA ambient environment with own speech and a 70 dBA environment with own speech. Y-axis  810  shows the level differences between signals recorded by reference microphone  121  and error microphone  122  and filtered by a 100 to 700 Hz band-pass filter in each environment. 
     Data points  820  relate to level differences for signals captured while earbud  120  was on or in an ear of a user, while data points  830  relate to level differences for signals captured while earbud  120  was off ear. As visible from graph  800 , there is a significant gap between data points  820  and data points  830  for the 60 dBA environment and a small gap between data points  820  and data points  830  for the 70 dBA environment, with no overlap between data points  820  and  830 . This indicates that calculating the level difference of filtered signals can be an effective way to determine on ear status of earbud  120  in an environment when own speech is present. 
       FIG. 8B  shows a graph  850  having an X-axis  855  and a Y-axis  860 . X-axis  855  displays two conditions, being a 60 dBA ambient environment with own speech and a 70 dBA environment with own speech. Y-axis  850  shows the level differences between signals recorded by reference microphone  121  and error microphone  122  and processed to combine level differences with the level differences filtered by a 100 to 700 Hz band-pass filter in each environment. Specifically, graph  850  uses the larger of the level difference being the signal recorded by error microphone  122  subtracted from the signal recorded by reference microphone  121  filtered by a 2.8 to 4.7 kHz band-pass filter; and the level difference being the signal recorded by reference microphone  121  subtracted from the signal recorded by error microphone  122  filtered by a 100 to 700 Hz band-pass filter for each environment. 
     Data points  870  relate to level differences for signals captured while earbud  120  was on or in an ear of a user, while data points  880  relate to level differences for signals captured while earbud  120  was off ear. As visible from graph  850 , there is a significant gap between data points  870  and data points  880 , indicating that a combined metric including both level differences with and without own voice can be an effective way to determine on ear status of earbud  120  in an environment where own speech is present. 
     It will be appreciated by persons skilled in the art that numerous variations and/or modifications may be made to the above-described embodiments, without departing from the broad general scope of the present disclosure. The present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive.