Patent Publication Number: US-11026034-B2

Title: System and method for self-calibrating audio listening devices

Description:
TECHNICAL FIELD 
     The present disclosure generally relates to audio listening devices. More particularly, for example, it relates to systems and methods for self-calibrating audio listening devices. 
     BACKGROUND 
     Personal listening devices such as headphones, earphones, and headsets are calibrated during manufacturing at the production line to ensure such devices meet design specifications such as frequency responses, total harmonic distortion, uplink and down link noise reductions, and so forth. Audio devices with noise cancelling capabilities rely on the performance of embedded speakers and microphones to produce high quality noise cancellation. These audio devices can undergo changes during their lifespan, thus shifting the original specifications and affecting the user&#39;s listening experiences over time. The one-time calibration that is performed during production does not sufficiently ensure audio quality over an extended period. Thus, improved techniques for maintaining audio quality over the life of an audio device are desirable. 
     SUMMARY 
     Systems and methods providing improved calibration over the life of audio listening devices are disclosed herein. According to one or more embodiments, a system includes a housing including a first calibration circuit configured to coordinate with a second calibration circuit of an active noise cancelling (ANC) earphone to execute a calibration sequence for the earphone. The housing may further include a cavity configured to accommodate the ANC earphone, wherein the cavity is contoured to simulate the ANC earphone in a user&#39;s ear, a calibration microphone coupled with the first calibration circuit and configured to measure calibration sound waves from the ANC earphone, and a calibration speaker configured to emit calibration sound waves to the ANC earphone. 
     In various embodiments, a method for calibrating an active noise cancelling (ANC) earphone includes pairing a second calibration circuit of the ANC earphone with a first calibration circuit of a housing, and executing, by the second calibration circuit in communication with the first calibration circuit, a calibration sequence on the ANC earphone. The housing may include a first calibration circuit configured to coordinate with the second calibration circuit to execute a calibration sequence, a calibration microphone coupled with the first calibration circuit and configured to capture calibration sound waves from the ANC earphone, and a calibration speaker configured to emit calibration sound waves to the ANC earphone. 
     The scope of the invention is defined by the claims, which are incorporated into this section by reference. A more complete understanding of various embodiments will be afforded to those skilled in the art, as well as a realization of additional advantages thereof, by a consideration of the following detailed description. Reference will be made to the appended sheets of drawings that will first be described briefly. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a cross-sectional drawing of an example earphone with active noise cancellation, according to an embodiment of the present disclosure. 
         FIG. 2  is an illustration of an example self-calibration case, according to an embodiment of the present disclosure. 
         FIG. 3  is a system block diagram illustrating some features of an example earphone, according to an embodiment of the present disclosure. 
         FIG. 4  is a system block diagram illustrating an example earphone and self-calibration case, according to an embodiment of the present disclosure. 
         FIG. 5A  is a schematic diagram of an example self-calibrating system, according to an embodiment of the present disclosure. 
         FIG. 5B  is a flow chart illustrating one example of the self-calibration process, according to an embodiment of the present disclosure. 
         FIG. 6A  is a schematic diagram of another example self-calibrating system, according to an embodiment of the present disclosure. 
         FIG. 6B  is a flow chart illustrating another example of the self-calibration process, according to an embodiment of the present disclosure. 
         FIG. 7A  is a schematic diagram of an ANC self-calibration system, according to an embodiment of the present disclosure. 
         FIG. 7B  is a flow chart illustrating another example of the self-calibration process, according to an embodiment of the present disclosure. 
         FIG. 8A  is a schematic diagram of another example self-calibrating system, according to an embodiment of the present disclosure. 
         FIG. 8B  is a flow chart illustrating another example of the self-calibration process, according to an embodiment of the present disclosure. 
         FIG. 8C  is a flow chart illustrating another example of the self-calibration process, according to an embodiment of the present disclosure. 
     
    
    
     Embodiments of the present disclosure and their advantages are best understood by referring to the detailed description that follows. Unless otherwise noted, like reference numerals denote like elements throughout the attached drawings and the written description, and thus, descriptions thereof will not be repeated. In the drawings, the relative sizes of elements, layers, and regions may be exaggerated for clarity. 
     DETAILED DESCRIPTION 
     Various embodiments of the present disclosure will be described with reference to earphones. The term “earphone” as used herein is not intended to be limited to just earphones but may be interchangeable with the terms “headphone” or “earbud” among other audio listening devices that include at least a speaker configured to be used on-ear (supra-aural), over-the-ear (circum-aural), and/or in-ear. 
     Basic earphones generally include one or more speakers (e.g., micro-speaker) to generate and emit (e.g., playback) sound waves. Earphones with noise cancelling features such as active noise cancellation (ANC) features include one or more speakers and one or more embedded microphones (e.g., an external microphone and an internal microphone) to capture noise to enable the noise cancellation. To achieve a quality listening experience, the speaker and microphone are designed to perform according to certain operating specifications. 
     To ensure quality, earphones may be calibrated by the manufacturer during production. After the earphones leave the manufacturing facility and are in the hands of a consumer, the earphones are usually not calibrated again because most users do not have the ability or capability to perform such calibration. Various parameters of the earphone may be affected (e.g., reduced sensitivity/gain, especially at the lower frequencies) as the earphones undergo wear and tear, for example, from the user putting them in his/her pocket or bag, being dropped or thrown, debris accumulation (e.g., dust, sweat, oil, moisture, etc.) on the speaker and the microphones, and/or degradation of the coupling caused by fatigue of rubber/silicone earpads and wings/tips. Over time, the wear and tear eventually shifts earphone properties such as the frequency response, total harmonic distortion, and/or uplink and downlink noise reductions, etc. Recalibration is desirable to ensure the earphones continue to produce quality audio and appropriate anti-noise for noise cancellation. In some instances, software or firmware updates to the earphones may include newly calibrated parameters but such parameters are generic across all earphones receiving the update and not necessarily specific to an individual earphone. Moreover, it may be difficult and cost prohibitive to recall used earphones back to the manufacturer for recalibration. 
     The embodiments of the present disclosure provide systems and methods to maintain specification parameters of the earphones through self-calibration, for example, by the consumer, without having to send the earphones back to the manufacturer and through techniques that improve performance over standardized firmware updates. According to the embodiment, a controlled environment may be provided to enclose the earphone and perform calibration, which may be repeated as often as desired and/or needed by the user. In one embodiment, the enclosure may be a storage case such as, for example, a charging case that may be used for charging the earphone batteries. Such a case can include an embedded calibration speaker, an embedded calibration microphone, and a processor to execute programmed calibration instructions, which together with a calibration processor of the earphone, can self-calibrate the earphones. 
       FIG. 1  is a cross-sectional drawing of an example earphone  100  with embedded active noise cancellation (ANC) features. In accordance with an embodiment, the earphone  100  is an in-ear audio device that is configured to transmit sound waves (e.g., voice or music playback) to a user&#39;s ear. The earphone  100  may have an eartip  108  that is configured to fit on or just inside the user&#39;s ear canal. The eartip  108  may be configured to substantially seal the user&#39;s ear canal to reduce ambient external noise from directly entering the user&#39;s ear canal. The earphone  100  includes a speaker  102  (e.g., micro-speaker) for emitting the sound waves that propagate through a channel  110  in the earphone and toward the user&#39;s eardrum. The earphone  100  includes an external microphone  104  that is utilized by the ANC circuitry, and is arranged such that it is exposed to noises that are external to the earphone  100  when the user wears the earphone  100 . As such, the external microphone  104  is configured to pick up the external noise and the ANC circuitry of the earphone (e.g., embedded inside the earphone) generates anti-noise waves that are used to cancel at least some or a substantial amount of the detected noise that is external to the earphone  100 . 
     An internal microphone  106  is disposed inside of the earphone and, in some embodiments, is positioned close to the speaker  102 . The sound waves measured by the internal microphone  106  are used to measure the performance of the noise cancellation. While the eartip  108  is configured to substantially seal the user&#39;s ear canal, it does not form a perfect seal and some external noise may enter the ear canal by way of one or more paths, such as a primary path  112 . Meanwhile, the external noise is captured by the external microphone  104  and corresponding anti-noise is generated and outputted from the speaker  102  via the second path  114 . The ANC circuitry is configured to generate anti-noise to substantially cancel out the detected external noise (e.g., which may correspond to the noise that enters the user&#39;s ear canal via the primary path  112 ). The internal microphone  106  captures the anti-noise generated by the speaker  102 , the external noise received at the internal microphone  106 , and/or a playback signal generated by the speaker  102  (e.g., music or speech played through the speaker  102 ) and provides a feedback/error signal to the ANC circuitry for use in adjusting the anti-noise signal to improve performance. The embodiments of the present disclosure will describe techniques to calibrate an exemplary earphone like the one illustrated in  FIG. 1  to optimize the speaker performance and noise cancellation quality. 
       FIG. 2  is an illustration of an example self-calibration case  200 , according to an embodiment of the present disclosure. The self-calibration case  200  (“case”) is an acoustically controlled environment that accommodates the earphones  214 ,  212  inside to acoustically isolate the earphones  214 ,  212  from the external environment and perform a calibration process. The case  200  may include an acoustically sealable cover  204  to completely enclose the earphones  214 ,  212  inside to reduce interference during the calibration process. The cover  204  may have, for example, a gasket or other like material to form a sound dampening seal when the cover  204  is closed. 
     In some embodiments, the case  200  includes a housing  202  having at least one cavity  222  that is substantially contoured to the shape of the earphones  214 ,  212  to accommodate and hold the earphones  214 ,  212  in place. In some embodiments, the contour of the cavity  222  may have the form of a standard coupler  264 ,  248  (e.g., an industry standard coupler such as IEC 711) to simulate the earphones  214 ,  212  being fitted in an earphone user&#39;s ear. In this manner, earphone speakers  228 ,  226  are pointed to or face into the coupler. The case  200  includes an embedded case calibration circuit  220  configured to communicate wirelessly (e.g., Bluetooth, Wi-Fi, other wireless connection) with an earphone ANC/calibration circuit  216 ,  218  embedded within each of the earphones  214 ,  212  to facilitate the self-calibration process. In this manner, the earphones  214 ,  212  may be calibrated inside the case  200  (e.g., when placed in the case to charge the batteries between use). 
     To perform the self-calibration, the case includes a case calibration speaker  206 , configured to emit calibration noises. The case calibration speaker  206  may be positioned on the case  200 , for example, in the cover  204  facing the earphones  214 ,  212 , such that the emitted noise is directed toward the earphone  214 ,  212 . The earphones  214 ,  212  include external microphones  230 ,  232  and internal microphones  236 ,  234  that measure the calibration noises that propagate from the case calibration speaker  206  depending on the calibration process that is being performed. Thus, the case  200  enclosure contains a noise propagation space  246 ,  262  for the calibration noise to propagate, simulating an external noise environment for the earphones  214 ,  212 . The external microphones  230 ,  232  measure the calibration noise from the case calibration speaker  206 , and the internal microphones  236 ,  234  measure the error inside the earphone based on the calibration noise and the anti-noise generated by the ANC earphones. 
     In some embodiments, the case  200  may further include calibration microphones (e.g., left calibration microphone  208  and right calibration microphone  210 ) to measure calibration noises that are emitted by the left earphone speaker  228  and the right earphone speaker  226 , respectively, simulating the earphones  214 ,  212  being inside a user&#39;s ear. More specifically, the earphones  214 ,  212  are positioned such that the earphone speakers  228 ,  226  face in a direction toward the left and right calibration microphones, respectively (e.g., which may be positioned to simulate the sound received at a user&#39;s left and right eardrums, respectively). Accordingly, when the earphones  214 ,  212  are placed in their respective slots in the case  200  and the cover  204  is closed, a calibration acoustic environment is created that simulates the earphones  214 ,  212  being fitted in a person&#39;s ear with a primary path and a secondary path for the calibration noises to propagate and perform the calibration procedures accordingly. 
     Together, the earphone ANC/calibration circuits  216 ,  218  and the case calibration circuit  220  coordinate to execute the calibration process, for example, by emitting a calibration noise (e.g., a tone of a certain frequency, a sweeping range of tones of various frequencies, or pink noise) from the case calibration speaker  206  while listening (and thereby measuring) the calibration noise with the earphones  214  and  212  according to a calibration process. According to another calibration process, the left earphone speaker  228  and the right earphone speaker  226  may emit the calibration noise, and the left calibration microphone  208  and the right calibration microphone  210  may listen to the calibration noise. The measured calibration information may be processed by the case calibration circuit  220  and/or the earphone ANC/calibration circuit  216 ,  218  to update the earphone calibration parameters (e.g., speaker calibration gain, microphone calibration gain, etc.). Accordingly, a self-calibration process may be performed on the earphones by inserting the earphones in the self-calibration case  200 . 
     In some embodiments, the self-calibration case  200  may also include charging contacts  256  that are configured to make contact with corresponding earphone charging contacts  250  to charge the batteries of the earphones  214 ,  212  when they are inserted in to the cavity  222 . 
     In some embodiments, the walls of the housing  202  and the cover  204  may be insulated with sound absorbing or sound proofing material or other techniques to further reduce sound leakage between the interior and the exterior of the self-calibration case  200 . In some embodiments, the housing  202  and the cover  204  may be a hard-shell case such as a hard plastic or polymer that maintains its shape and does not deform during its intended use, even when compressed or after repeated use. 
       FIG. 3  is a system block diagram illustrating some features of an exemplary ANC earphone, according to an embodiment of the present disclosure. The system may include a left earphone  214  that includes an embedded left speaker  228 , a left internal microphone  236 , a left external microphone  230 , and a left earphone ANC/calibration circuit  216 , and a right earphone  212  that includes an embedded right speaker  226 , a right internal microphone  234 , a right external microphone  232 , and a right earphone ANC/calibration circuit  218 . Each of the left and right earphone ANC/calibration circuits  216 ,  218  includes a logic device and/or circuitry configured to facilitate active noise cancellation during operation of the left and right earphones  214 ,  212  respectively, and facilitate calibration of the ANC system as described herein. In some embodiments, each of the left and right earphone ANC/calibration circuits  216 ,  218  includes at least a processor  324 ,  325 , a memory  326 ,  327 , a wireless interface  328 ,  329 , and an audio codec  330 ,  331 . In some embodiments where the ANC earphone is a wired ANC earphone, the left earphone calibration circuit  216  and right earphone ANC/calibration circuit  218  may be combined into a single circuit and embedded in just one of either the left earphone  214  or the right earphone  212 . That is, the single circuit is able to control the calibration process for both the left and the right earphones via a wired connection. The following will be described for the left earphone  214  and the left earphone calibration circuit  216  but the description is also applicable with reference to the right earphone  212 . 
     The processor  324  may comprise one or more of a processor, a microprocessor, a single-core processor, a multi-core processor, a microcontroller, a programmable logic device (PLD) (e.g., field programmable gate array (FPGA)), a digital signal processing (DSP) device, or other logic device that may be configured, by hardwiring, executing software instructions, or a combination of both, to perform various operations discussed herein for embodiments of the disclosure. The left earphone ANC/calibration circuit  216  is operable to interface and communicate with the self-calibration case  200  via the wireless interface  328  or via physical connections, such as through a contact or other electronic communications interface. 
     It will be appreciated that although the earphone ANC/calibration circuit  216  and the earphone  214  is shown as incorporating a combination of hardware components, circuitry, and software, in some embodiments, at least some or all of the functionalities that the hardware components and circuitries are operable to perform may be implemented as software modules being executed by the processor  324  in response to software instructions and/or configuration data, stored in the memory  326  or firmware of the earphone ANC/calibration circuit  216 . 
     The memory  326  may be implemented as one or more memory devices operable to store an operating system and other data and information such as audio data and program instructions. Memory  326  may comprise one or more various types of memory devices including volatile and non-volatile memory devices, such as RAM (Random Access Memory), ROM (Read-Only Memory), EEPROM (Electrically-Erasable Read-Only Memory), flash memory, and/or other types of non-transitory memory. 
     The processor  324  may be operable to execute software instructions stored in the memory  326 . Applications stored on the memory  326  may be software applications executable by the processor  324  to perform operations with or without user inputs from a user interface. In some embodiments, the application may be a calibration processing application where a user may initiate through the user interface. The user interface may be a button, or a switch located on the earphone  214 , an interface integrated into the case, and/or it may be an interface on a remote device such as a smartphone, tablet, or a computer in communication with the earphone and/or the self-calibration case. 
     The wireless interface  328  facilitates communication between the left earphone ANC/calibration circuit  216  and the self-calibration case  200  and/or other external devices such as a smartphone, tablet or a computer. For example, the wireless interface  328  may enable Wi-Fi (e.g., 802.11) or Bluetooth connections between the self-calibration case  200  and/or other local devices, such as a smartphone, tablet, or laptop computer. In various embodiments, the wireless interface  328  may include other wired and wireless communications components facilitating direct or indirect communications between the case calibration circuit  220  and the earphone  214 . 
     The audio codec  330  may comprise one or more of a processor, a microprocessor, a single-core processor, a multi-core processor, a microcontroller, a programmable logic device (PLD) (e.g., field programmable gate array (FPGA)), a digital signal processing (DSP) device, or other logic device that may be configured, by hardwiring, executing software instructions, or a combination of both, to process audio signals, including but not limited to converting analog audio to digital audio, or converting digital audio to analog audio. The audio codec  330  may therefore take audio data that is stored in the memory  326 , convert from digital to analog and transmit that analog audio information to the speaker  228 . Similarly, the audio codec  330  may take analog audio captured by the external microphone  230  or internal microphone  236  and convert the analog audio signal to digital and process, such as calibrate or store in memory  326 . 
       FIG. 4  is a system block diagram illustrating the exemplary ANC earphone block diagram of  FIG. 3  with an exemplary block diagram of the self-calibration case  200 , according to an embodiment of the present disclosure. The self-calibration case  200  includes a case calibration circuit  220  that includes at least a processor  424 , a memory  426 , a wireless interface  428 , and an audio codec  430 . In some embodiments, the self-calibrating case  200  may use similar hardware components as described above with reference to the left earphone ANC/calibration circuit  216  of  FIG. 3 . 
     The processor  424  may comprise one or more of a processor, a microprocessor, a single-core processor, a multi-core processor, a microcontroller, a programmable logic device (PLD) (e.g., field programmable gate array (FPGA)), a digital signal processing (DSP) device, or other logic device that may be configured, by hardwiring, executing software instructions, or a combination of both, to perform various operations discussed herein for embodiments of the disclosure. The case calibration circuit  220  is operable to interface and communicate with the earphones  214 ,  212  via the wireless interface  428  or via physical connections, such as through contacts or other electronic communications interface. 
     It will be appreciated that although the case calibration circuit  220  is shown as incorporating a combination of hardware components, circuitry, and software, in some embodiments, at least some or all of the functionalities that the hardware components and circuitries are operable to perform may be implemented as software modules being executed by the processor  424  in response to software instructions and/or configuration data, stored in the memory  426  or firmware of the case calibration circuit  220 . 
     The memory  426  may be implemented as one or more memory devices operable to store an operating system and other data and information such as audio data and program instructions. Memory  426  may comprise one or more various types of memory devices including volatile and non-volatile memory devices, such as RAM (Random Access Memory), ROM (Read-Only Memory), EEPROM (Electrically-Erasable Read-Only Memory), flash memory, hard disk drive, and/or other types of non-transitory memory. 
     The processor  424  may be operable to execute software instructions stored in the memory  426 . Applications stored on the memory  426  may be software applications executable by the processor  424  to perform operations with user. In some embodiments, the application may be a calibration processing application where a user may initiate through the user interface. The user interface may be a button, or a switch disposed on the self-calibration case  200  or it may be an interface to a remote device such as a smartphone, tablet, or a computer that is wirelessly connected to the case calibration circuit  220 . 
     The wireless interface  428  facilitates communication between the case calibration circuit  220  and the left earphone ANC/calibration circuit  216 , the right earphone ANC/calibration circuit  218 , and external devices such as a smartphone, tablet or a computer. For example, the wireless interface  428  may enable Wi-Fi (e.g., 802.11) or Bluetooth connections between the case calibration circuit  220  and/or other local devices, such as a smartphone, tablet, or laptop computer. In various embodiments, the wireless interface  428  may include other wired and wireless communications components facilitating direct or indirect communications between the left and right earphone ANC/calibration circuits  216 ,  218  and the case calibration circuit  220 . 
     The audio codec  430  may comprise one or more of a processor, a microprocessor, a single-core processor, a multi-core processor, a microcontroller, a programmable logic device (PLD) (e.g., field programmable gate array (FPGA)), a digital signal processing (DSP) device, or other logic device that may be configured, by hardwiring, executing software instructions, or a combination of both, to process audio signals, including but not limited to converting analog audio to digital audio, or converting digital audio to analog audio. The audio codec  430  may therefore take audio data that is stored in the memory  426 , convert from digital to analog and transmit that analog audio information to the case calibration speaker  206 . Similarly, the audio codec  430  may take analog audio captured by the calibration microphones  208 ,  210 , and convert the analog audio signal to digital and process, such as calibrate or store in memory  426 . 
       FIGS. 5-8  illustrate and describe example calibration processes that may be executed and performed on the earphone  100  using the self-calibration case  200  according to various embodiments of the present disclosure. Various examples may be described with reference to just one earphone, for example, just the left earphone or just the right earphone. However, the embodiments may also be applicable to both the left and the right earphone. 
       FIG. 5A  is a schematic diagram of an example self-calibrating system according to an embodiment of the present disclosure. According to an embodiment, the sensitivities  552 ,  554  may be a fixed, nominal value of the speaker  228  and microphone  208 , respectively, and gain  550  of the earphone speaker  228  may be set for optimal performance by the speaker calibration process. In some embodiments, the gain  550  may be a filter that is set during manufacturing, but it may also be updatable post-manufacturing by a user, according to various calibration processes described in the present disclosure. Thus, by executing the self-calibration procedure in the case  200 , an updated filter value may be determined to adjust the gain  550  to improve optimal performance by the earphone speaker  228 . 
       FIG. 5B  is a flow chart illustrating one example of the self-calibration process, according to an embodiment of the present disclosure. In accordance with this embodiment, techniques for performing self-calibration of the earphone speaker  228  are described. First, the earphone ANC is turned off ( 502 ). Next, the earphone  214  is inserted into the cavity  222  and the cover  204  is closed, isolating the earphone  214  inside of the self-calibration case  200  ( 504 ). When the earphone  214  is inserted into the case  200 , a pairing process may be executed to wirelessly connect the case calibration circuit  220  with the left earphone ANC/calibration circuit  216 , e.g., a Bluetooth connection ( 506 ). In some embodiments, the left earphone ANC/calibration circuit  216  may verify that the earphone  214  is in a sufficiently controlled environment where ambient noise is quiet enough such that it does not interfere with the calibration process ( 508 ). For example, if a user attempted to run the self-calibration system inside of a loud airplane, then the ambient noise may be too loud to properly perform calibration. Thus, the calibration process will not run until the environment is quieter. In various embodiments, audio signals received from one or more of the microphones  230 ,  236  and  208  may be monitored to verify that the intensity of the received signal(s) is below an acceptable silence threshold for performing calibration (e.g., close to 0 decibels). After it is verified that the earphone is in an environment that is suitable for performing calibration, the user may initiate the calibration process by manually starting the calibration through a user interface on the calibration case and/or an external device (e.g., a phone, tablet, personal computer, etc.). In some embodiments, the calibration process may automatically begin after the earphone  214  is inserted in the case and the cover  204  is closed ( 510 ). For example, a calibration initiation process may initiate the calibration process after determining that each earphone is charging, and the earphone is in a sufficiently quiet environment. 
     In some embodiments, the calibration process is synchronized or otherwise coordinated between the left earphone  214 , right earphone  212  and self-calibration case  200  through the wireless interface components  328 ,  329  and  428 . For example, the case calibration circuit  220  may facilitate communications with the left earphone  214  and right earphone  212  to initiate a calibration process, set a calibration mode, communicate calibration results, etc. In some embodiments, the ANC/calibration circuit, via the earphone audio codec  330 , causes the earphone speaker to play a calibration noise (e.g., a tone of a certain frequency, a sweeping range of various frequencies, or pink noise) ( 512 ), and the case calibration microphone  208  listens to the calibration tone ( 514 ). The case calibration circuit  220  measures the calibration tone that is captured with the case microphone  208  and computes the earphone speaker  228  response (if any) based on reference noise ( 516 ). The information may used to compute the earphone speaker  228  gain and this information may be written to memory to update the earphone speaker gain ( 518 ), thus optimizing the speaker performance. This process may be repeated if desired or the calibration process may end here ( 520 ). 
       FIG. 6A  is a schematic diagram of an example self-calibrating system according to another embodiment of the present disclosure. According to an embodiment, gain  654 ,  656  of the earphone external and internal microphones  230 ,  236  may be set for optimal performance. The sensitivities  650 ,  652  may be a fixed value that is set during production. In some embodiments, the gain  654 ,  656  may be a filter that is set during manufacturing and it may also be updatable post-manufacturing by a user, according to various calibration processes described in the present disclosure. Thus, by executing the self-calibration procedure in the case  200 , an updated filter value may be determined to adjust the gain  654 ,  656  to achieve optimal performance by the earphone microphones. 
       FIG. 6B  is a flow chart illustrating another example of the self-calibration process, according to an embodiment of the present disclosure. In accordance with this embodiment, techniques for performing self-calibration of the earphone microphone  230  is described. In some embodiments, the self-calibration is performed on each of the left earphone external microphone  230  and the left earphone internal microphone  236 . According to an embodiment, the earphone ANC is turned off ( 602 ). Next, the earphones  214 ,  212  are inserted in to the cavity  222  and the cover  204  is closed, isolating the earphones  214 ,  212  inside of the self-calibration case  200  ( 604 ). When the earphones  214 ,  212  are inserted into the case  200 , a pairing process may be executed to wirelessly connect the case calibration circuit with the earphone ANC/calibration circuits  216 ,  218 , e.g., a Bluetooth connection. ( 606 ). In some embodiments, the ANC/earphone calibration circuits  216 ,  218  may verify that the earphones  214 ,  212  are in a sufficiently controlled environment where ambient noise is quiet enough such that it does not interfere with the calibration process ( 608 ). 
     In some embodiments, the user may initiate the calibration process by manually starting the calibration through a user interface. In some embodiments, the calibration process may automatically begin the calibration process after the earphones  214 ,  212  are inserted in the case  200  and the cover  204  is closed ( 610 ). In some embodiments, the calibration process is synchronized or otherwise coordinated between the left earphone  214 , right earphone  212  and self-calibration case  200  through the wireless interface components  328 ,  329  and  428 . In some embodiments, the case calibration circuit  220 , via case audio codec  430 , causes the case calibration speaker  206  to output a calibration noise ( 612 ) (e.g., a reference tone), and the earphone microphones  230 ,  236  listen and measure the calibration noise ( 614 ). The earphone ANC/calibration circuits  216 ,  218  measure the calibration sound that is captured with the earphone microphones  230 ,  236  and computes the microphones&#39; responses (if any) based on the reference tone ( 616 ). The information may be used to compute the earphone microphone gain and this information may be written to memory to update the microphone gain ( 618 ), thus improving the earphone microphone parameters to optimal operation (e.g., noise cancellation). This process may be repeated if desired and/or necessary or the calibration process may end here ( 620 ). 
       FIG. 7A  is a schematic diagram of an ANC system according to an embodiment of the present disclosure. In some embodiments, ANC may be performed in a feedforward mode as illustrated. In the feedforward mode, the earphone external microphone  230  is used to detect external noise and the detected noise may be processed through ANC feedforward filters B ff (z) and W ff (z) to generate anti-noise in an effort to cancel the noise level experienced by the user. The sensitivity  752 ,  756  of the external microphone  230  and the speaker  228  may be fixed values. In some embodiments, the calibration gain  754  of the anti-noise may also be set during manufacturing through various filters but may also be updated by the user over time by using the calibration case  200 , described according to various embodiments of the present disclosure to optimize ANC performance. 
     In other embodiments, ANC may be performed in feedback mode as illustrated. In the feedback mode, the earphone internal microphone  236  is used to detect error noise. The error is processed through ANC feedback filter B fb (z) to generate anti-noise to reduce the error. The calibration gain  760  may be adjusted to more precisely reduce the error. Such gain may also be determined by performing the self-calibration process according to the embodiments of the present disclosure. 
       FIG. 7B  is a flow chart illustrating another example of the self-calibration process, according to an embodiment of the present disclosure. Active noise cancellation relies on the performance of the earphone speakers  228  and the earphone microphones (e.g., internal microphone  236  and external microphone  230 ) for quality noise cancellation. Thus, calibration is performed with the ANC turned off and then performed again with the ANC turned on, and the results are compared to measure the ANC performance. According to the embodiment, the earphone ANC is initially turned off ( 702 ). Next, the earphone  214  is inserted in to the cavity  222  and the cover  204  is closed, isolating the earphone  214  inside the self-calibration case  200  ( 704 ). When the earphone  214  is inserted in to the case  200 , a pairing process may be executed to wirelessly connect the case calibration circuit  220  with the earphone ANC/calibration circuit  216 , e.g., a Bluetooth connection ( 706 ). In some embodiments, the earphone ANC/calibration circuit  216  may verify that the earphone  214  is in a sufficiently controlled environment where ambient noise is quiet enough that it does not interfere with the calibration process ( 708 ). The user may initiate the calibration process by manually starting the calibration through a user interface or the calibration circuit may be configured to automatically begin the calibration process after the earphone  214  is inserted in the case and the cover  204  is closed ( 710 ). 
     In some embodiments, the case calibration circuit  220 , via the audio codec  430 , causes the case speaker  206  to sweep a wide-band calibration noise (e.g., pink noise) ( 712 ), and the case calibration microphone  208  measures the frequency response and stores this information in the earphone memory  326  ( 714 ). Next, the ANC is turned on ( 718 ) and the wide-band calibration noise is swept again ( 720 ) while the case calibration microphone  208  measures the frequency response and stores this information in the earphone memory  326  ( 722 ) and compares with the calibration information that was previously stored in the memory  326  with the ANC turned off to determine the performance of the noise cancellation ( 726 ). Based on this determination, the feedforward gain  754  and feedback gain  760  may be adjusted thus improving the overall quality of ANC ( 728 ). 
       FIG. 8A  is a schematic diagram of an ANC system according to an embodiment of the present disclosure. In some cases, a user may turn on ANC when listening to audio (e.g., music playback) in noisy environments to reduce the background noise. In this case, the earphone speaker  228  is used not only for music playback but also for generating anti-noise in the secondary path. Thus, the user can listen to the music with the background noise substantially cancelled out. The internal earphone microphone  236  is positioned on the earphone  214  near the earphone speaker  228  to measure the noise cancelled music playback to determine the error. In some embodiments, a playback cancellation calibration filter  852  may be used. In this case, the playback cancellation algorithm Ŝ(z)  850  stays on, and the earphone speaker  228  parameters is compared with the ANC turned off and with the ANC turned on. The difference is then calibrated against their desired masks and the calibration gain  852  is updated in the memory. 
     In some embodiments, the ANC may be kept turned off, and the earphone speaker playback  102  parameters may be compared with the playback cancellation algorithm Ŝ(z)  850  turned off and on. The difference may be calibrated against their desired masks and the calibration gain  852  is updated in the memory. 
       FIG. 8B  is a flow chart illustrating another example of the self-calibration process, according to an embodiment of the present disclosure. Accordingly, the earphone ANC is first turned off ( 802 ). Next, the earphone  214  are inserted in to the cavity  222  and the cover  204  is closed, completely sealing the earphones  100  inside of the self-calibration case  200  ( 804 ). When the earphone  214  is inserted in to the case  200 , a pairing process may be executed to wirelessly connect the case calibration circuit with the earphone calibration circuit, e.g., a Bluetooth connection. ( 806 ). In some embodiments, the left earphone ANC/calibration circuit  216  may verify that the earphone  214  is in a sufficiently controlled environment where ambient noise is quiet enough that it does not interfere with the calibration process ( 808 ). The user may initiate the calibration process by manually starting the calibration through a user interface or the calibration circuit may be configured to automatically begin the calibration process once the earphone  214  is inserted in the case and the cover  204  is closed ( 810 ). According to an embodiment of the present disclosure, the playback path is turned on for playback cancellation calibration by playing an audio, e.g., music, from the earphone speaker  228  and the playback is measured by the case microphone  208  ( 812 ). Next, the ANC is turned on ( 814 ) and the audio is played back again from the earphone speaker  228  while being measured again by the case microphone  208  ( 816 ). The difference between the measured playback with the ANC on (e.g., enabled) and off (e.g., disabled) are computed and then compared against their desired mask, and their calibration gain is stored in memory ( 818 ). This process may be repeated if necessary or the calibration process may be complete ( 820 ). 
       FIG. 8C  is a flow chart illustrating another example of the self-calibration process, according to an embodiment of the present disclosure. Accordingly, the earphone ANC is turned off ( 902 ). Next, the earphone  214  are inserted in to the cavity  222  and the cover  204  is closed, completely sealing the earphones  100  inside of the self-calibration case  200  ( 904 ). When the earphone  214  is inserted in to the case  200 , a pairing process may be executed to wirelessly connect the case calibration circuit with the earphone calibration circuit, e.g., a Bluetooth connection. ( 906 ). In some embodiments, the left earphone ANC/calibration circuit  216  may verify that the earphone  214  is in a sufficiently controlled environment where ambient noise is quiet enough that it does not interfere with the calibration process ( 908 ). The user may initiate the calibration process by manually starting the calibration through a user interface or the calibration circuit may be configured to automatically begin the calibration process once the earphone  214  is inserted in the case and the cover  204  is closed ( 910 ). According to an embodiment of the present disclosure, the playback cancellation path is turned off by playing an audio, e.g., music, from the earphone speaker  228  and the playback is measured by the case microphone  208  ( 912 ). Next, the ANC remains off and the playback cancellation path is turned on by playing an audio, e.g., music, from the earphone speaker  228  and the playback is measured by the case microphone  208  ( 914 ). The difference between the measured playback with the playback path off and on are computed and then compared against their desired mask, and their calibration gain is stored in memory ( 918 ). This process may be repeated if necessary or the calibration process may be complete ( 920 ). 
     In this manner, earphones may be calibrated and re-calibrated by a consumer at home or wherever they choose for the life of the earphones to assure quality audio playback and quality noise cancellation, thereby extending the overall life of the earphones. The above described calibration processes are provided only as examples of calibrations and it not intended to be limited to just the described calibrations. Instead, other audio calibrations using the described calibration case  200  may be envisaged. 
     The systems and methods of the present disclosure may be embodied in various forms and should not be construed as being limited to only the illustrated embodiments. Rather, these embodiments are provided as examples to convey the aspects and features of the present disclosure to those skilled in the art. Accordingly, processes, elements, and techniques that are not necessary to those having ordinary skill in the art for a complete understanding of the aspects and features of the present disclosure may not be described. 
     The terminology used herein is for the purpose of describing particular embodiments and is not intended to be limiting of the present disclosure. It will be understood that when an element is referred to as being “on,” “connected to,” or “coupled to” another element, it can be directly on, connected to, or coupled to the other element, or one or more intervening elements may be present. In addition, it will also be understood that when an element is referred to as being “between” two elements, it can be the only element or layer between the two elements or layers, or one or more intervening elements or layers may also be present. 
     As used herein, the terms “substantially,” “about,” and similar terms are used as terms of approximation and not as terms of degree, and are intended to account for the inherent deviations in measured or calculated values that would be recognized by those of ordinary skill in the art. Further, the use of “may” when describing embodiments of the present disclosure refers to “one or more embodiments of the present disclosure.” As used herein, the terms “use,” “using,” and “used” may be considered synonymous with the terms “utilize,” “utilizing,” and “utilized,” respectively. 
     The electronic or electric devices and/or any other relevant devices or components according to embodiments of the present disclosure described herein may be implemented utilizing any suitable hardware, firmware (e.g. an application-specific integrated circuit), software, or a combination of software, firmware, and/or hardware. For example, the various components of these devices may be formed on one integrated circuit (IC) chip or on separate IC chips. Further, the various components of these devices may be implemented on a flexible printed circuit film, a tape carrier package (TCP), a printed circuit board (PCB), or formed on one substrate. Further, the various components of these devices may be a process or thread, running on one or more processors, in one or more computing devices, executing computer program instructions and interacting with other system components for performing the various functionalities described herein. The computer program instructions are stored in a memory which may be implemented in a computing device using a standard memory device, such as, for example, a random-access memory (RAM). The computer program instructions may also be stored in other non-transitory computer readable media such as, for example, a CD-ROM, flash drive, or the like. Also, a person of skill in the art should recognize that the functionality of various computing devices may be combined or integrated into a single computing device, or the functionality of a particular computing device may be distributed across one or more other computing devices without departing from the spirit and scope of the example embodiments. 
     Embodiments described herein are exemplary only. One skilled in the art may recognize various alternative embodiments from those specifically disclosed. Those alternative embodiments are also intended to be within the scope of this disclosure. As such, the embodiments are limited only by the following claims and their equivalents.