Abstract:
In one embodiment, earphones with bimodally fitting earbuds enable accurate reproduction of music while exposing a wearer to environmental noises on one side of the wearer. More specifically, an open earbud is designed to create a substantially open (i.e., unsealed) sound chamber around one ear while a closed earbud is designed to create a substantially closed sound chamber around the other ear. Because the open earbud is associated with sound leakage that alters both the intended level and the bass content of the music, the earphones include a signal redistribution subsystem that perspicaciously replaces at least a portion of this lost signal energy. Advantageously, such earphones expose the wearer to useful localized sounds, such as noises from an auto lane adjacent to a bike lane, while conveying the intended mix of music more accurately than conventional earphones with two open earbuds.

Description:
BACKGROUND 
       [0001]    Field of the Various Embodiments 
         [0002]    The various embodiments relate generally to acoustics technology and, more specifically, to earphones with bimodally fitting earbuds and bass preservation capabilities. 
         [0003]    Description of the Related Art 
         [0004]    Users of a variety of listening and communications systems employ personal hearing devices to experience transmitted music and other desired sounds. For example, to listen to recorded music transmitted via MP3 players, CD players, streaming audio players, etc., users may wear wired or wireless earphones that include two earbuds. Each earbud includes a speaker that transmits sounds targeted toward an ear of the user. In operation, the user places each earbud proximate to or within an ear—the left earbud forming a sound chamber around the left ear, and the right earbud forming a sound chamber around the right ear. Subsequently, the earphones deliver sounds directly to the ears of the user via the earbuds. Notably, the design of the earbuds (e.g., the shape of the eartips, the number and type of vents included in the earbuds, etc.) defines the acoustical characteristics of the earbuds, such as the quality of the transmitted sound. 
         [0005]    To optimize the quality of the listening experience, some earphones include earbuds that provide a “closed” fit with the ears of the user. When these types of earphones are worn by a user, each of the earbuds creates a relatively sealed sound chamber relative to the ear of the user that minimizes the amount of sound leaked to the external environment during operation. However, while sealed earbuds deliver sound to the user without excessive sound degradation due to leakage, sealed earbuds also isolate the user from important environmental sounds, such as traffic noise, alerts, speech, etc. 
         [0006]    To allow users to hear environmental sounds when wearing earphones, other earphones provide an “open” fit with the ears of the user. When these types of earphones are worn by a user, neither of the earbuds creates a sealed sound chamber and, consequently, the earphones provide acoustic transparency that enable the user to hear sounds from the outside environment during operation. However, a major drawback of open earphones is the amount of sound lost to leakage into the environment during operation. In particular, the bass content of the transmitted sound may be significantly attenuated. 
         [0007]    In general, both earphones with closed earbuds and earphones with open earbuds have advantages and disadvantages depending on the particular task being performed by the user. Consequently, users are forced to select earphones that optimize a given aspect of the listening experience at the expense of another aspect of the listening experience. For example, to increase the quality of the sound transmitted by the earphones, a user may resort to wearing earphones with closed earbuds in a situation where the isolation caused by closed earbuds is unsafe. Alternatively, to maximize safety, a user may choose to wear earphones with open earbuds, thereby sacrificing quality of the sound transmitted by the earphones. 
         [0008]    As the foregoing illustrates, what is needed in the art are more effective techniques for transmitting sound to users via earphones. 
       SUMMARY 
       [0009]    One embodiment sets forth an audio device. The audio device includes a first earbud configured to create a substantially open sound chamber around a first ear of a user; a second earbud configured to create a substantially closed sound chamber around a second ear of the user; and a signal redistribution subsystem that is coupled to both the first earbud and the second earbud and configured to perform one or more compensation operations on a first audio input signal that is targeted for output via the first earbud, where the one or more compensation operations produce a compensated signal that mitigates sound leakage associated with the substantially open sound chamber. 
         [0010]    Further embodiments provide, among other things, a computer-implemented method and a non-transitory computer-readable medium configured to implement the system set forth above. 
         [0011]    At least one advantage of the disclosed audio device is that it enables an optimized listening experience. More specifically, by leveraging both an open earbud and a closed earbud included in audio device, the audio device enables tradeoffs between sound quality and environmental isolation that are not supported by conventional earphones. In particular, a signal redistribution subsystem included in the audio device may configure the audio device to provide exposure to important environmental sounds, such as traffic noise, while preserving bass frequencies. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]    So that the manner in which the above recited features of the various embodiments can be understood in detail, a more particular, briefly summarized above, may be had by reference to embodiments, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only typical embodiments and are therefore not to be considered limiting of scope, for the various embodiments may admit to other equally effective embodiments. 
           [0013]      FIG. 1  illustrates an earphone system configured to implement one or more aspects of the various embodiments; 
           [0014]      FIG. 2  is a more detailed illustration of the compensation unit of  FIG. 1 , according to various embodiments; 
           [0015]      FIG. 3  illustrates the signal redistribution subsystem of  FIG. 1  configured to mitigate sound energy losses associated with an open earbud, according to various embodiments; 
           [0016]      FIG. 4  illustrates a computing device within which one or more aspects of the signal redistribution subsystem of  FIG. 1  may be implemented, according to various embodiments; and 
           [0017]      FIG. 5  is a flow diagram of method steps for delivering sound via earphones that include bimodally fitting earbuds, according to various embodiments. 
       
    
    
     DETAILED DESCRIPTION 
       [0018]    In the following description, numerous specific details are set forth to provide a more thorough understanding of the various embodiments. However, it will be apparent to one of skill in the art that the various embodiments may be practiced without one or more of these specific details. 
         [0019]    Overview of Earphone System 
         [0020]      FIG. 1  illustrates an earphone system  100  configured to implement one or more aspects of the various embodiments. As shown, the earphone system  100  includes, without limitation, a closed earbud  170 , an open earbud  160 , and a signal redistribution subsystem  120 . In alternate embodiments, without limitation, the earphone system  100  may include other types of sensory equipment, such as a microphone, and/or control devices (e.g., a volume control). 
         [0021]    In some embodiments, without limitation, the earphone system  100  may be implemented as integrated earphones. In some such embodiments, the signal redistribution subsystem  120  may be embedded in or mounted on the closed earbud  170 , the open earbud  160 , or on a physical connection (e.g., a plastic headband) between the closed earbud  170  and the open earbud  160 . In other embodiments, without limitation, the earphone system  100  may be implemented as earphones that include the closed earbud  170  and the open earbud  160 , and the earphone system  100  may be driven by an independently deployed signal redistribution subsystem  120 . For example, and without limitation, the signal redistribution subsystem  120  could be implemented in a computer system included in a smartphone that communicates with the closed earbud  170  and the open earbud  160  using any wired or wireless communication protocol. 
         [0022]    The closed earbud  170  includes a miniature speaker that converts a closed earbud signal  155  to sound. When worn correctly by the user, the closed earbud  170  forms a relatively sealed sound chamber in the ear of the user. In general, the correct usage of the closed earbud  170  depends on the design of the closed earbud  170 . For example, and without limitation, in some embodiments, the closed earbud  170  is designed to be inserted into an ear canal. The closed earbud  170  may be manufactured in any technically feasible fashion, such as including an ear tip with form fitting material that adjusts to the contours of the ear canal. 
         [0023]    In general, the physical characteristics of the closed earbud  170 , including providing a sealed acoustic chamber and close fit via the ear tip, enable the closed earbud  170  to deliver relatively high sound quality. Further, these physical characteristics also substantially isolate the associated ear of the user from ambient sounds, such as distracting conversations, traffic noises, construction sounds, etc. While such sound isolation is acceptable and/or desirable in some circumstances, in other situations it is desirable to hear such ambient sounds. For example, and without limitation, for safety reasons, a bicyclist or a pedestrian travelling on a busy road may desire to hear traffic noises. 
         [0024]    For this reason, the earphone system  100  also includes the open earbud  160 . The open earbud  160  enables the user to hear sounds on one side of the user. For example, and without limitation, if a bicyclist travelling on the right side of the road in the United States were to insert the closed earbud  170  in their right ear and the open earbud  160  in their left ear, then the bicyclist would be able to hear the traffic noises of the cars travelling adjacent to (i.e., on the left hand side of) the bicyclist. 
         [0025]    Analogously to the closed earbud  170 , the open earbud  160  contains a miniature speaker that converts an open earbud signal  145  to sound. However, in contrast to the closed earbud  170 , when worn correctly by the user, the open earbud  160  permits ambient sound to leak through to the ear. For example, and without limitation, in some embodiments the open earbud  160  may include an ear tip that is shaped to provide a relatively loose fit around an ear of the user and/or may include vents that support audio transparency. 
         [0026]    Since the open earbud  160  does not provide a tight audio seal, the open earbud  160  allows sound to leak outwards (away from the ear). Consequently, the sound received by the user via the open earbud  160  is typically degraded relative to a prototypical sound that is specified by the open earbud signal  145 . More specifically, signal energy is lost before the sound is received by the user via the open earbud  160 , undesirably altering the level (i.e., volume) and mix from the intended sound as specified by the open earbud signal  145 . In general, the lower the frequency of the component included in the open earbud signal  145 , the greater the attenuation of the open earbud signal  145 . As a result, the open earbud  160  often unacceptably weakens the bass components of the open earbud signal  145 . 
         [0027]    To compensate for the signal energy lost via the open earbud  160 , the earphone system  100  includes the signal redistribution subsystem  120 . In operation, the signal redistribution subsystem  120  receives two signals: an open earbud target signal  105  and a closed earbud target signal  115 . The open earbud target signal  105  and the closed earbud target signal  115  may be generated in any technically feasible fashion. For example, an MP3 player may transmit the open earbud target signal  105  and the closed earbud target signal  115  to the earphone system  100 . 
         [0028]    Ideally, when translated to sound and transmitted without noticeably signal energy loss to the ears of the user, the open earbud target signal  105  and the closed earbud target signal  115  provide an overall “target” listening experience. In some embodiments, without limitation, a monophonic target listening experience may be specified. In such embodiments, without limitation, the open earbud target signal  105  and the closed earbud target signal  115  may be replaced with a single target signal that is intended to be received by both ears of the user. In other embodiments, without limitation, a stereo target listening experience may be specified—the content of the open earbud target signal  105  and the closed earbud target signal  115  differ. 
         [0029]    In a stereo target listening experience, the desired sounds may be allocated between the open earbud  160  and the closed earbud  170  in any technically feasible fashion. For example, in some embodiments, without limitation, the open earbud target signal  105  may include vocal sounds but not instrumental sounds and the closed earbud target signal  115  may include instrumental sounds but not vocal sounds. In other embodiments, without limitation, signal components may be distributed (i.e., panned) between the open earbud target signal  105  and the closed earbud target signal  115  to provide “hints” regarding the location of the source of the sound (i.e., footsteps to the left of the user). 
         [0030]    Because an “optimized” listening experience may entail preserving the distribution of the sounds between the ears, minimizing the sound energy loss via the open earbud  160 , or any combination thereof, the signal redistribution subsystem  120  implements a configurable variety of compensation mechanisms. More specifically, the signal redistribution subsystem  120  may be configured to leverage the open earbud  160  and/or the closed earbud  170  to replace any portion of the signal energy lost as the open earbud  160  transforms the open earbud signal  145  to sounds that are received by the user. The signal redistribution subsystem  120  may perform compensation in any technically feasible fashion. For example and without limitation, in some embodiments, the signal redistribution subsystem  120  may perform a variety of equalization and repanning operations. 
         [0031]    As also shown in  FIG. 1 , the signal redistribution subsystem  120  includes, without limitation, a compensation unit  130 , an open earbud mixing unit  140 , and a closed earbud mixing unit  150 . To compensate for the typically frequency-dependent attenuation associated with the open earbud  160 , the signal redistribution subsystem  120  performs compensation operations in a frequency-dependent fashion. In alternate embodiments, without limitation, the signal redistribution subsystem  120  may not differentiate between frequency components and may instead apply signal compensation on a more granular basis. 
         [0032]    In operation the compensation unit  130  splits the components of the open earbud target signal  105  into signal partitions, where each signal partition is associated with a separate frequency band. Subsequently, for each of the signal partitions, based on the signal energy loss associated with delivery of the included frequencies via the open earbud  160 , the compensation unit  130  generates an open earbud compensated signal partition  133  and a closed earbud compensation signal partition  135 . Together, the open earbud compensated signal partitions  133  and the closed earbud compensation signal partitions  135  enable the user to receive a listening experience that is similar to the listening experience specified by the open earbud target signal  105 . 
         [0033]    To provide this target listening experience, the compensation unit  130  tailors the open earbud compensated signal partitions  133  to supplant the open earbud target signal  105  and the closed earbud compensation signal partitions  135  to supplement the listening experience provided by the open earbud  160  using the closed earbud  170 . Accordingly, the open earbud mixing unit  140  combines the open earbud compensated signal partitions  133  to form the open earbud signal  145 . By contrast, the closed earbud mixing unit  150  combines the closed earbud compensation signal partitions  135  with the closed earbud target signal  115 . Such a combination configures the closed earbud  170  to supplement the listening experience received via the open earbud  160  without compromising the listening experience specified by the closed earbud target signal  115 . 
         [0034]      FIG. 2  is a more detailed illustration of the compensation unit  130  of  FIG. 1 , according to various embodiments. As shown, the compensation unit  130  includes, without limitation, a crossover unit  210  and one or more equalization/repanning units  240 . In alternate embodiments, any number of units may provide the functionality included in the crossover unit  210  and/or the equalization/repanning units  240 , in any combination. 
         [0035]    Upon receiving the open earbud target signal  105 , the crossover unit  210  splits the open earbud target signal  105  into one or more signal partitions  233 . Each of the signal partitions  233  is associated with a frequency band  212 , and the crossover unit  210  ensures that the signal partition  233 ( i ) includes the components of the open earbud target signal  105  that are included in the frequency band  212 ( i ). Together, the signal partitions  233 ( 1 ) through  233 (N) include all the components of the open earbud target signal  105 . The number of frequency bands  212  and the distribution of frequencies between the frequency bands  212  may be determined in any technically feasible fashion. In general, the signal redistribution subsystem  120  is configured such that the frequency bands  212  are consistent with both the frequency-dependent signal attenuation associated with the open earbud  160  and the compensation that the headphone system  100  is designed to provide. 
         [0036]    The crossover unit  210  may be implemented in any technically feasible fashion. For example, and without limitation, in a software implementation, the crossover unit  210  could be an application executed by a processing unit. Alternatively, and without limitation, in a hardware implementation, the crossover unit  210  could include any number and combination of digital signal processing units, such as high-pass filters, band-pass filters, low-pass filters, shelf filters, filterbank, etc. 
         [0037]    After the crossover unit  210  subdivides the open earbud target signal  105 , the compensation unit  130  routes each of the signal partitions  233 ( i ) to an associated equalization/trepanning unit  240 ( i ). As shown, each of the equalization/repanning units  240  includes a compensation parameter  242 , a translation parameter  244 , and open earbud gain  246 , and a closed earbud gain  248 . The compensation parameter  242  and the translation parameter  244  customize the operation of the equalization/repanning unit  240  and may be set or determined in any technically feasible fashion. 
         [0038]    The compensation parameter  242 ( i ) specifies the amount of overall compensation that the equalization/repanning unit  240 ( i ) generates for the signal partition  233 ( i ) (i.e., the total gain that the equalization/repanning unit  240 ( i ) applies to the signal partition  233 ( i )). The translation parameter  244 ( i ) specifies the percentage of this overall compensation that the equalization/repanning unit  240 ( i ) provides via the closed earbud  170  instead of the open earbud  160 . In operation, each of the equalization/repanning units  240 ( i ) calculates the open earbud gain  246 ( i ) and the closed earbud gain  248 ( i ) based on the compensation parameter  242 ( i ) and the translation parameter  244 ( i ). 
         [0039]    In general, the semantics and values of the compensation parameters  242  and the translation parameters  244  may be determined in any consistent and technically feasible fashion. In some embodiments, without limitation, the compensation parameter  242 ( i ) may be expressed in terms of a transfer function H open  that reflects the response of the open earbud  160  relative to the closed earbud  170 . In other embodiments, without limitation, the compensation parameters  242  and the translation parameters  244  may be omitted and the equalization/repanning unit  240 ( i ) may determine the open earbud gain  246 ( i ) and the closed earbud gain  248 ( i ) in any technically feasible fashion that reflects the processing of the open earbud target signal  105  to provide a desired listening experience. 
         [0040]    Upon receiving the signal partition  233 ( i ), the equalization/repanning unit  240 ( i ) applies the open earbud gain  246 ( 1 ) to the signal partition  233 ( 1 ) to create the open earbud compensated signal partition  133 ( i ). Similarly, the equalization/repanning unit  240 ( i ) applies the closed earbud gain  248 ( i ) to the signal partition  233 ( i ) to create the closed earbud compensation signal partition  135 ( i ). The equalization/repanning unit  240 ( i ) may apply the open earbud gain  246 ( i ) and the closed earbud gain  248 ( i ) in any technically feasible fashion, such as performing one or more signal amplification operations. 
         [0041]    The compensation parameters  242  and the translation parameter  244  included in the equalization/repanning units  240  may be set independently. Consequently, the compensation units  130  may be configured to provide compensation that is customized for each of the frequency bands  212  via the open earbud compensated signal partitions  133  and the closed earbud compensation signal partitions  135 . In general, the compensation provided by each of the equalization/repanning units  240  ranges from none (i.e., passing through the received signal partition  233  without alteration) to full compensation. As used herein, providing “full compensation” refers to providing a listening experience substantially similar to one that would be provided were the user to receive both the open ear bud target signal  105  and the closed earbud target signal  115  via closed earbuds (i.e., the closed earbud  170  and a second closed earbud). 
       Optimizing Sound Delivered Via Bimodally Fitting Earbuds 
       [0042]      FIG. 3  illustrates the signal redistribution subsystem  120  of  FIG. 1  configured to mitigate sound energy losses associated with the open earbud  160 , according to various embodiments. As shown, the signal redistribution subsystem  120  is configured to independently process three separate frequency bands (a high frequency band, a middle frequency band, and a low frequency band) and then perform compensation operations that are tailored to each frequency band. 
         [0043]    The signal redistribution subsystem  120  may be configured as shown in any technically feasible fashion. For example, and without limitation, in some embodiments each equalization/repanning unit  240 ( i ) may be configured via the compensation parameter  242 ( i ) and the translation parameter  244 ( i ) as described in  FIG. 2 . In other embodiments, without limitation, each equalization/repanning unit  240 ( i ) may omit the compensation parameter  242 ( i ) and the translation parameters  244 ( i ) and reflect the desired equalization and/or translation directly via the open earbud gain  246   i ( ) and the closed earbud gain  248 ( i ). 
         [0044]    As shown, the crossover unit  210  includes, without limitation, a high-pass filter  310 , a band-pass filter  320 , and a low-pass filter  330 . In alternate embodiments, the crossover unit  210  may include any number and type of filters and/or the filters may be replaced with any other mechanism for extracting signal components. Upon receiving the open earbud target signal  105 , the high-pass filter  310 , the band-pass filter  320 , and the low-pass filter  330  work together to divide the signal components of the open earbud target signal  105  into the signal partitions  233 ( 1 ),  233 ( 2 ), and  233 ( 3 ). 
         [0045]    The signal partition  233 ( 1 ) includes the relatively high frequency components of the open earbud target signal  105 . In operation, the equalization/repanning unit  240 ( 1 ) processes the signal partition  233 ( 1 ). Because the signal energy loss of high frequency components via the open earbud  160  is relatively low and typically does not compromise the listening experience, the equalization/repanning unit  240 ( 1 ) is configured to “pass through” the signal partition  233 ( 1 ). 
         [0046]    More specifically, the equalization/repanning unit  240 ( 1 ) includes a value of “1” or “unity” for the open earbud gain  246 ( 1 ) and a value of “0” for the closed earbud gain  248 ( 1 ). Accordingly, the equalization/repanning unit  240 ( 1 ) does not perform any equalization or repanning operations and does not target any portion of the signal partition  233 ( 1 ) for delivery via the closed earbud  170 . Consequently, the open earbud compensated signal partition  133 ( 1 ) matches the signal partition  233 ( 1 ) and the equalization/repanning unit  240 ( 1 ) does not generate a closed earbud compensation signal partition. Since the equalization/repanning unit  240 ( 1 ) does not alter the signal partition  233 ( 1 ), in alternate embodiments, without limitation, the equalization/repanning unit  240 ( 1 ) may be omitted from the compensation unit  130 . 
         [0047]    The equalization/repanning unit  240 ( 2 ) processes the signal partition  233 ( 2 )—the “middle” frequency components of the open earbud target signal  105 . Because the signal energy loss of middle frequency components via the open earbud  160  may noticeably compromise the listening experience, the equalization/repanning unit  240 ( 2 ) is configured to mitigate the signal energy loss via both equalization and repanning operations. 
         [0048]    The configuration of the equalization/repanning unit  240 ( 2 ) is specified by the open earbud gain  246 ( 2 )“G open ” and the closed earbud gain  248 ( 2 ) “G closed .” The equalization/repanning unit  240 ( 2 ) applies the open earbud gain  246 ( 2 ) to the signal partition  233 ( 2 ) to generate the open earbud compensated signal partition  133 ( 2 ) and applies the closed earbud gain  248 ( 2 ) to the signal partition  233 ( 2 ) to generate the closed earbud compensation signal partition  135 ( 2 ). In this fashion, the equalization/repanning unit  240 ( 2 ) leverages both the open earbud  160  and the closed earbud  170  to produce a sound experience for the user that is acceptably similar to the ideal sound experience specified by the signal partition  233 ( 2 ). 
         [0049]    Gain calculations  250  illustrate the relationship of the values G open  and G closed  to each other and to a transfer function H open  that reflects the response of the open earbud  160  relative to the closed earbud  170 . In alternate embodiments, the values G open  and G closed  may be determined in any technically feasible fashion. Further, the values G open  and G closed  may be calculated off-line as part of the design of the equalization/repanning unit  240 ( 2 ) or dynamically in response to user input, such as values of the compensation parameter  242 ( 2 ) and the translation parameter  244 ( 2 ). 
         [0050]    The signal partition  233 ( 3 ) includes the low frequency components of the open earbud target signal  105 , and the equalization/repanning unit  240 ( 3 ) processes the signal partition  233 ( 3 ). Because the signal energy loss of low frequency components via the open earbud  160  is relatively high and typically noticeably compromises the listening experience, the equalization/repanning unit  240 ( 3 ) is configured to repan (i.e., redirect) the signal partition  233 ( 3 ) from the open earbud  160  to the closed earbud  170 . 
         [0051]    Accordingly, the equalization/repanning unit  240 ( 3 ) includes a value of “0” for the open earbud gain  246 ( 3 ) and a value of “1” for the closed earbud gain  248 ( 3 ). Upon receiving the signal partition  233 ( 3 ), the equalization/repanning unit  240 ( 3 ) does not perform any equalization operations, but retargets the signal partition  233 ( 3 ) for delivery via the closed earbud  170 . Consequently, the equalization/repanning unit  240 ( 3 ) does not generate an open earbud compensated signal partition, and the equalization/repanning unit  240 ( 3 ) ensures that the closed earbud compensation signal partition  135 ( 3 ) matches the signal partition  233 ( 3 ). In this fashion, the equalization/repanning unit  240 ( 3 ) leverages the closed earbud  170  to fully preserve the bass components of the open earbud target signal  105 . 
         [0052]    The open earbud mixing unit  140  receives the open earbud compensated signal partitions  133 ( 1 ) and  133 ( 2 ). The open earbud mixing unit  140  then performs compositing operations that generate the open earbud signal  145  based on the open earbud compensated signal partitions  133 ( 1 ) and  133 ( 2 ). The open earbud mixing unit  140  neither receives nor processes any portion of the signal partition  233  (the bass components of the open earbud target signal  105 ). 
         [0053]    In a complementary fashion, the closed earbud mixing unit  150  receives the closed earbud compensation signal partitions  135 ( 2 ) and  135 ( 3 ). The closed earbud mixing unit  150  also receives the closed earbud target signal  115 . The closed earbud mixing unit  150  then performs compositing operations that generate the closed earbud signal  155  based on the open earbud compensation signal partitions  135 ( 2 ) and  135 ( 3 ) and the closed earbud target signal  115 . In this fashion, the closed earbud mixing unit  150  supplements the closed earbud target signal  115  with a portion of the middle frequency components and all the low frequency components included in the open earbud target signal  105 . 
         [0054]    Upon delivery of the open earbud signal  145  via the open earbud  160  and the closed earbud signal  155  via the closed earbud signal  170 , the headphone system  100  provides a listening experience that optimally reflects the open earbud target signal  105  and the closed earbud target signal  115 . Importantly, the listening experience is substantially similar to a listening experience that would be provided via a conventional headset with two closed earbuds, but the headphone system  100  also allows the user to hear outside sounds, such as traffic, via the open earbud  160 . 
         [0055]    In alternate embodiments, the compensation unit  130  may be configured to divide the open target earbud signal  105  into any number of signal partitions  133 . Further, and without limitation, in some embodiments, the compensation unit  130  may not divide the target earbud signal  105  and may process the target earbud signal  105  as a single signal partition  133 . In such embodiments, the crossover unit  210  may be omitted and replaced with a filterbank. 
         [0056]    In various embodiments, each of the equalization/repanning units  240  may be independently configured to generate any amount of compensation for signal energy lost via the open earbud  160  for transmission by the open earbud  160 , the closed earbud  170 , or any combination thereof. For example, and without limitation, in some embodiments, the equalization/repanning unit  240 ( i ) may be configured to provide compensation via the open earbud  160  but not the closed earbud  170 . In such embodiments, the equalization/repanning unit  240 ( i ) would not produce the closed earbud compensation signal partition  135 ( i ). Further, in some embodiments, without limitation, the equalization/repanning unit  240 ( i ) may be configured to provide compensation via the closed earbud  170  but not the open earbud  160 . In such embodiments, the equalization/repanning unit  240 ( i ) would relay the signal partition  233 ( i ) to the open earbud  160  without alteration, but would generate the closed earbud compensation signal partition  135 ( i ) to compensate for signal energy lost via the open earbud  160 . 
         [0057]    In alternate embodiments, the functionality included in the signal redistribution subsystem  120  may be distributed between any number and types of units. For example, and without limitation, multiple equalization/repanning units  240  may be combined into a single equalization/repanning unit. Further, the signal redistribution subsystem  120  may be implemented in any technically feasible fashion using any combination of software, firmware, and hardware. For example, and without limitation, in an entirely software implementation, the signal redistribution subsystem  120  could be an application executed by a processing unit. 
         [0058]      FIG. 4  illustrates a computing device  400  within which one or more aspects of the signal redistribution subsystem  120  of  FIG. 1  may be implemented, according to various embodiments. The computing device  400  may be any type of device capable of executing application programs including, and without limitation, application programs included in the signal redistribution subsystem  120 . As shown, the computing device  400  includes, without limitation, a processing unit  410 , a memory unit  420 , and input/output (I/O) devices  430 . 
         [0059]    The processing unit  410  may be implemented as a central processing unit (CPU), digital signal processing unit (DSP), graphics processor unit (GPU), and so forth. Among other things, and without limitation, the processing unit  410  executes one or more application programs that implement the signal redistribution subsystem  120  and are stored in the memory unit  420 . The memory unit  420  may include a memory module or collection of memory modules that provide storage space accessible by the processing unit  410 . The I/O devices  430  may include input devices, output devices, and devices capable of both receiving input and providing output and may enable any communication protocols. For example, and without limitation, the I/O devices  430  may include Smart WiFi and Bluetooth interfaces. 
         [0060]    In alternate embodiments, the computing device  400  may be replaced and/or supplemented with any number of signal processing components that facilitate the operation of the earphone system  100 . For example, and without limitation, instead of the computing device  400 , the earphone system  100  may include components that implement a variety of filters, digital to analog converters, dynamic amplifiers, etc. that are configured to implement the functionality included in the signal redistribution subsystem  120 . 
         [0061]    The computing device  400  may be incorporated into the earphone system  100  of  FIG. 1  in any technically feasible fashion and as any number of discrete or integrated units. For example, each of the processing unit  410 , the memory unit  420 , and the I/O devices  430  may be embedded in or mounted on the open earbud  160 , the closed earbud  170 , and/or a physical connection between the open earbud  160  and the closed earbud  170 . In some embodiments, without limitation, the computing device  400  may be implemented as a stand-alone chip or as part of a more comprehensive solution that is implemented as an application-specific integrated circuit (ASIC), a system-on-a-chip (SoC), and so forth. 
         [0062]    In alternate embodiments, any portion, including all, of the computing device  400  may be external to the physical earphones (i.e., the portions of the earphone system  100  that are worn by the user). For example and without limitation, the computing device  400  may be a laptop, a tablet, a smartphone, or the like that executes the signal redistribution subsystem  120  and transmits data to the physical earphones. In general, the embodiments disclosed herein contemplate any technically feasible system configured to implement the functionality included in various components of the signal redistribution subsystem  120  in any combination. 
         [0063]      FIG. 5  is a flow diagram of method steps for delivering sound via earphones that include befitted earbuds, according to various embodiments. Although the method steps are described in conjunction with the systems of  FIGS. 1-4  persons skilled in the art will understand that any system configured to implement the method steps, in any order, falls within the scope of the various embodiments. 
         [0064]    As shown, a method  500  begins at step  504 , where the earphone system  100  receive the open earbud target signal  105  and the closed earbud target signal  115 . The earphone system  100  may receive the open earbud target signal  105  and the closed earbud target signal  115  in any technically feasible fashion. For example, the earphone system  100  may include a wireless receiver that receives transmissions from an MP3 player. At step  506 , the crossover unit  210  divides the open earbud target signal  105  into the signal partitions  233  based on frequency. More specifically, each of the signal partitions  233  is associated with a separate frequency band  212 , and the crossover unit  210  distributes the components of the open earbud target signal  105  to the signal partitions  233  according to the frequency of the components. 
         [0065]    At step  508 , for each of the signal partitions  233 ( i ), the signal equalizing/repanning unit  240 ( i ) calculates the open earbud gain  246 ( i ) and the closed earbud gain(i). More specifically, signal equalizing/repanning unit  240 ( i ) determines the open earbud gain  246 ( i ) and the closed earbud gain(i) based on the compensation parameter  242 ( i ) and the translation parameter  244 ( i ). For example, and without limitation, the crossover unit  210  could divide the open earbud target signal  105  into the signal partitions  233  of “high,” “medium,” and “low.” In such a scenario, three separate signal equalization/repanning units  240  would calculate three separate open earbud gains  246  and three separate closed earbud gains  248  based on three compensation parameters  242  and three translation parameters  244 . 
         [0066]    The compensation parameters  242  and the translation parameters  244  may be any values that are consistent with the desired acoustic characteristics of the earphone system  100 . For example, and without limitation, the compensation parameter  242 ( 1 ) could be zero and the translation parameter  244 ( 1 ) could be 0.0 to specify, respectively, no “high” frequency compensation and no redistribution of “high” frequencies from the open earbud  160  to the closed earbud  170 . Further, and without limitation, the compensation parameter  242 ( 1 ) could be 1.0 and the translation parameter  244 ( 3 ) could be 1.0 to provide full “low” frequency compensation via the closed earbud  170 . In such a configuration, the signal redistribution subsystem  120  could redirect all the low frequencies from the open earbud  160  to the closed earbud  170 , thereby providing a sound experience that is substantially similar to the sound experience that would typically be provided by conventional headphones with two closed earbuds. 
         [0067]    In some embodiments, without limitation, the compensation parameters  242  may be based signal energy lost via the open earbud  160 . For example, and without limitation, the compensation parameter  242  could be the reciprocal of the open earbud transfer function that represents the response to a signal delivered via the open earbud  160  versus the closed earbud  170 . In general, the pairs of the compensation parameters  242  and the translation parameters  244  across the various frequency bands of the signal partitions  233  tailor the performance characteristic of the earphone system  100  to provide the desired listening experience. In alternate embodiments, without limitation, the compensation parameters  242  and the translation parameters  244  are omitted and the open earbud gain  246  and the closed earbud gain  248  are directly configured to control the listening experience. 
         [0068]    At step  510 , for each of the signal partitions  233 ( i ), the signal equalizing/repanning unit  240 ( i ) applies the open earbud gain  246 ( i ) to the signal partition  233 ( i ), thereby generating the open earbud compensated signal partition  133 ( 1 ). Notably, the open earbud compensated signal partition  133 ( i ) represents the strategically modified (e.g., amplified) signal components within the frequency band  212 ( i ) in the open earbud target signal  105  that are to be delivered via the open earbud  160 . 
         [0069]    In some embodiments, without limitation, the equalization/repanning unit  240 ( i ) may be configured to provide compensation via the closed earbud  170  but not the open earbud  160 . In such embodiments, the equalization/repanning unit  240 ( i ) would relay the signal partition  233 ( i ) to the open earbud  160  without alteration. If all the equalization/repanning units  240  were configured to provide compensation using the closed earbud  170  but not the open earbud  160 , then step  510  could be omitted. 
         [0070]    At step  512 , the open earbud mixing unit  140  combines the open earbud compensated signal partitions  133  to create the open earbud signal  145 . Subsequently, the open earbud mixing unit  140  delivers the open earbud signal  145  to the speakers included in the open earbud  160  for delivery as sounds to the proximally located ear of the user. In this fashion, the earphone system  100  conveys a listening experience via the open earbud  160  that may compensate for any portion of the signal loss attributable to the open design of the open earbuds  160 . 
         [0071]    At step  514 , for each of the signal partitions  233 ( i ), the signal equalizing/repanning unit  240 ( i ) applies the closed earbud gain  248 ( i ) to the signal partition  233 ( i ), thereby generating the closed earbud compensation signal partition  135 ( i ). In a complementary fashion to the open earbud compensated signal partition  133 ( i ), the closed earbud compensated signal partition  133 ( i ) represents processed signal components within the frequency band  212 ( i ) in the open earbud target signal  105  that are to be delivered via the closed earbud  170 . 
         [0072]    In alternate embodiments, the equalization/repanning unit  240 ( i ) may be configured to provide compensation via the open earbud  160  but not the closed earbud  170 . In such embodiments, the equalization/repanning unit  240 ( i ) would not produce the closed earbud compensation signal partition  135 ( i ). If all the equalization/repanning units  240  were configured to provide compensation using the closed earbud  170  but not the open earbud  160 , then step  514  could be omitted. 
         [0073]    At step  516 , the closed earbud mixing unit  150  combines the entire frequency range of the closed earbud target signal  115  with the closed earbud compensation signal partitions  135  to create the closed earbud signal  155 . In this fashion, the closed earbud mixing unit  150  supplements the closed earbud target signal  115  with processed portions of the open earbud target signal  105 . The closed earbud mixing unit  150  then delivers this closed earbud signal  155  to the speakers included in the closed earbud  170  for delivery as sound to the proximately located ear of the user. In this fashion, the closed earbud  170  provides a listening experience as specified by the closed earbud target signal  155  that is, optionally, supplemented to compensate for portions of the signal loss attributable to the open design of the open earbud  160 . Together, the open earbud  160  and the closed earbud  170  provide a comprehensive listening experience that mitigates signal degradation associated with the open earbuds  160 , without isolating the user from the outside environment. 
         [0074]    In sum, the disclosed techniques may be used to optimize the personal listening experience of users. Notably, earphones leverage a signal redistribution subsystem, an open earbud, and a closed earbud to deliver high-fidelity sounds directly to the ears of users without undesirably isolating the user from external sounds. In operation, the signal redistribution subsystem analyzes an open earbud signal intended for transmission via the open earbud and performs one or more equalization and/or panning operations that compensate for signal degradation attributable to the design of the open earbud. 
         [0075]    First, the signal redistribution subsystem divides the open earbud signal based on frequency—creating a low frequency signal partition, a middle frequency signal partition, and a high frequency signal partition. Because the sound loss associated with an open earbud inversely correlates to the frequency of the signal delivered via the open earbud, the signal redistribution subsystem retargets the low frequency signal partition for delivery via the closed earbud (bypassing the low frequency signal corruption associated with the open earbud). The signal redistribution subsystem then divides the middle frequency signal, targeting a portion for delivery via the open earbud and the remaining for delivering via the closed earbud. As part of dividing the middle frequency signal partition, the signal redistribution subsystem applies gains to each portion that, together, compensate for signal energy lost via the open earbud. Finally, the signal redistribution subsystem routes the high frequency signal partition for delivery via the open earbud. 
         [0076]    At least one advantage of the disclosed approach is that it provides optimized, flexible listening experiences for users. By exploiting the advantages of both open earbuds and closed earbuds, the disclosed earphones enable tradeoffs between sound quality and environmental isolation that are not supported by conventional earphones. Notably, the user may optimally perform activities, such as bicycling, that benefit from exposure to external noises without unacceptable sacrificing the fidelity of sound delivered via the earphones. More specifically, a bicyclist may wear earphones with an open earbud inserted in the ear that is closer to the road and a closed earbud inserted in the ear that is further from the road. In operation, such earphones expose the user to traffic noises via the open earbud while delivering higher fidelity sound than is typically delivered via conventional earphones that include two open earbuds. 
         [0077]    The descriptions of the various embodiments have been presented for purposes of illustration, but are not intended to be exhaustive or limited to the embodiments disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the described embodiments. 
         [0078]    Aspects of the present embodiments may be embodied as a system, method or computer program product. Accordingly, aspects of the present disclosure may take the form of an entirely hardware embodiment, an entirely software embodiment (including firmware, resident software, micro-code, etc.) or an embodiment combining software and hardware aspects that may all generally be referred to herein as a “circuit,” “module” or “system.” Furthermore, aspects of the present disclosure may take the form of a computer program product embodied in one or more computer readable medium(s) having computer readable program code embodied thereon. 
         [0079]    Any combination of one or more computer readable medium(s) may be utilized. The computer readable medium may be a computer readable signal medium or a computer readable storage medium. A computer readable storage medium may be, for example, but not limited to, an electronic, magnetic, optical, electromagnetic, infrared, or semiconductor system, apparatus, or device, or any suitable combination of the foregoing. More specific examples (a non-exhaustive list) of the computer readable storage medium would include the following: an electrical connection having one or more wires, a portable computer diskette, a hard disk, a random access memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM or Flash memory), an optical fiber, a portable compact disc read-only memory (CD-ROM), an optical storage device, a magnetic storage device, or any suitable combination of the foregoing. In the context of this document, a computer readable storage medium may be any tangible medium that can contain, or store a program for use by or in connection with an instruction execution system, apparatus, or device. 
         [0080]    Aspects of the present disclosure are described above with reference to flowchart illustrations and/or block diagrams of methods, apparatus (systems) and computer program products according to embodiments of the disclosure. It will be understood that each block of the flowchart illustrations and/or block diagrams, and combinations of blocks in the flowchart illustrations and/or block diagrams, can be implemented by computer program instructions. These computer program instructions may be provided to a processor of a general purpose computer, special purpose computer, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, enable the implementation of the functions/acts specified in the flowchart and/or block diagram block or blocks. Such processors may be, without limitation, general purpose processors, special-purpose processors, application-specific processors, or field-programmable gate arrays. 
         [0081]    The flowchart and block diagrams in the figures illustrate the architecture, functionality, and operation of possible implementations of systems, methods and computer program products according to various embodiments of the present disclosure. In this regard, each block in the flowchart or block diagrams may represent a module, segment, or portion of code, which comprises one or more executable instructions for implementing the specified logical function(s). It should also be noted that, in some alternative implementations, the functions noted in the block may occur out of the order noted in the figures. For example, two blocks shown in succession may, in fact, be executed substantially concurrently, or the blocks may sometimes be executed in the reverse order, depending upon the functionality involved. It will also be noted that each block of the block diagrams and/or flowchart illustration, and combinations of blocks in the block diagrams and/or flowchart illustration, can be implemented by special purpose hardware-based systems that perform the specified functions or acts, or combinations of special purpose hardware and computer instructions. 
         [0082]    The various embodiments have been described above with reference to specific embodiments. Persons of ordinary skill in the art, however, will understand that various modifications and changes may be made thereto without departing from the broader spirit and scope of the various embodiments as set forth in the appended claims. For example, and without limitation, although many of the descriptions herein refer to specific types of audiovisual equipment and sensors, persons skilled in the art will appreciate that the systems and techniques described herein are applicable to other types of performance output devices (e.g., lasers, fog machines, etc.) and sensors. The foregoing description and drawings are, accordingly, to be regarded in an illustrative rather than a restrictive sense. 
         [0083]    While the preceding is directed to embodiments of the present disclosure, other and further embodiments of the disclosure may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.