Patent Description:
Some devices that support health monitoring, however, can be obtrusive and uncomfortable. As such, people may choose to forego health monitoring if the device negatively impacts their movement or causes inconveniences while performing daily activities. It is therefore desirable for health-monitoring devices to be reliable, portable, and affordable to encourage more users to take advantage of these features.

<CIT> describes an apparatus for and a method of obtaining physiological measurements using ear-located sensors. <CIT> describes an apparatus for and a method of performing high-frequency audiometry. <CIT> describes a sensor on an earpiece being used to attempt to detect a signal corresponding to a heartbeat. In <CIT>, earphones for measuring and entraining respiration are being presented. <CIT> describes an apparatus and a method for detecting a physiological measurement from a physiological sound signal.

Techniques and apparatuses are described that implement audioplethysmography calibration.

Aspects described below include a method for audioplethysmography calibration. The method includes performing a calibration process that identifies at least one acoustic frequency suitable for audioplethysmography using at least one speaker and at least one microphone. The method also includes using the at least one frequency for performing the audioplethysmography at an ear of a user.

Some frequencies can be more sensitive for audioplethysmography than others. These frequencies can change over time based on the quality of an at least partial seal formed by a device at or around a user's ear. Also, these frequencies can vary for different ears of the user due to differences in the geometry of the ear canals. Techniques for audioplethysmography calibration as disclosed herein may therefore enable to dynamically select frequencies that improve the performance of audioplethysmography. With audioplethysmography calibration, different frequencies for different ears may be utilized, wherein these frequencies may change over time.

After calibration, an acoustic transmit signal that propagates within at least a portion of an ear canal of a user is transmitted by at least one speaker. An acoustic receive signal is then received by at least one microphone which acoustic receive signal represents a version of the acoustic transmit signal with one or more waveform characteristics modified due to the propagation within the ear canal. At least one physiological metric of the user is determined based on the one or more modified waveform characteristics of the acoustic receive signal. Example waveform characteristics include amplitude, phase, and/or frequency. Generally, the acoustic receive signal may result from the initially transmitted acoustic transmit signal that is influenced with respect to at least one of its amplitude, phase and frequency when propagating within the ear canal before being received via the at least one microphone.

Aspects described below include a device comprising at least one transducer and at least one processor. The device is configured to perform any of the described methods.

Aspects described below also include a system with means for performing audioplethysmography calibration.

Provided according to one or more preferred embodiments is a hearable, such as an earbud, that is capable of performing a novel physiological monitoring process termed herein audioplethysmography, an active acoustic method capable of sensing subtle physiologically-related changes observable at a user's outer and middle ear. To better perform audioplethysmography, the hearable may form at least a partial seal in or around the user's outer ear. This seal enables formation of an acoustic circuit, which includes the seal, at least one hearable, at least one ear canal, and at least one ear drum of at least one ear. By transmitting and receiving acoustic signals, the hearable can recognize changes in the acoustic circuit to monitor a user's biometrics, recognize facial behaviors, and/or sense an environment. The hearable can be a standalone device or can be integrated within another object or device, such as glasses, a hat, ear muffs, or a helmet.

Apparatuses for and techniques that facilitate audioplethysmography calibration are described with reference to the following drawings. The same numbers are used throughout the drawings to reference like features and components:.

Technological advances in medicine and healthcare are making it possible for people to live longer, healthier lives. To further achieve this, individuals have become interested in tracking their personal health. Health monitoring can motivate an individual to realize a particular fitness goal by tracking incremental improvements in the performance of the body's functions. Additionally, the individual can use health monitoring to observe changes in the body caused by chronic illnesses. With active feedback through health monitoring, the individual can live an active and full life with many chronic illnesses and recognize situations in which it is necessary to quickly seek medical attention.

Some health monitoring devices, however, can be obtrusive and uncomfortable. To measure carbon dioxide levels, for example, some devices take a sample of blood from the user. Other devices may utilize auxiliary sensors, including optical or electronic sensors, that add additional weight, cost, complexity, and/or bulk. Still other devices may require constant recharging of a battery due to relatively high power usage. As such, people may choose to forego health monitoring if the health monitoring device negatively impacts their movement or causes inconveniences while performing daily activities. It is therefore desirable for health monitoring devices to be reliable, portable, efficient, and affordable to expand accessibility to more users.

To address this challenge and provide new features, in particular for existing hearables, techniques are described that implement audioplethysmography calibration. Provided according to one or more preferred embodiments is a hearable, such as an earbud, that is capable of performing a novel physiological monitoring process termed herein audioplethysmography, an active acoustic method capable of sensing subtle physiologically-related changes observable at a user's outer and middle ear. To better perform audioplethysmography, the hearable may form at least a partial seal in or around the user's outer ear. This seal enables formation of an acoustic circuit, which includes the seal, at least one hearable, at least one ear canal, and at least one ear drum of at least one ear. By transmitting and receiving acoustic signals, the hearable can recognize changes in the acoustic circuit to monitor a user's biometrics, recognize facial behaviors, and/or sense an environment.

Some frequencies can be more sensitive for audioplethysmography than others. These frequencies can change over time, in particular based on the quality of a seal formed by a hearable at or around a user's ear. Also, these frequencies can vary for different ears of the user due to differences in the geometry of the ear canals. The techniques for audioplethysmography calibration therefore enable the dynamic selection of frequencies that improve the performance of audioplethysmography. With audioplethysmography calibration, different frequencies for different ears may be utilized, wherein these frequencies may change over time.

Wireless technology has become prevalent in everyday life, making communication and data readily accessible to users. One type of wireless technology are wireless hearables, examples of which include wireless earbuds and wireless headphones. Wireless hearables have allowed users freedom of movement while listening to audio content from music, audio books, podcasts, and videos. With the prevalence of wireless hearables, there is a market for adding additional features to existing hearables utilizing current hardware (e.g., without introducing any new hardware). Accordingly, the proposed solution may in particular implemented by a wireless hearable. The proposed solution may also be implemented by other objects or devices with one or more built-in hearables, such as glasses, a hat, ear muffs, or a helmet.

<FIG> is an illustration of an example environment <NUM> in which audioplethysmography calibration can be implemented. In the example environment <NUM>, a hearable <NUM> is connected to a smart device <NUM> using a physical or wireless interface. The hearable <NUM> is a device that can play audible content provided by the smart device <NUM> and direct the audible content into a user <NUM>'s ear <NUM>. In this example, the hearable <NUM> operates together with the smart device <NUM>. In other examples, the hearable <NUM> can operate or be implemented as a stand-alone device. Although depicted as a smartphone, the smart device <NUM> can include other types of devices, including those described with respect to <FIG>.

The hearable <NUM> is capable of performing audioplethysmography <NUM>, which is an acoustic method of sensing that occurs at the ear <NUM>. The hearable <NUM> can perform this sensing based on an evaluation of the transmitted and received acoustic signals alone and thus without the use of other auxiliary sensors, such as an optical sensor or an electrical sensor. Through audioplethysmography <NUM>, the hearable <NUM> can perform biometric monitoring <NUM>, facial behavior recognition <NUM>, and/or environment sensing <NUM>.

To use audioplethysmography <NUM>, the user <NUM> positions the hearable <NUM> in a manner that creates at least a partial seal <NUM> around or in the ear <NUM>. Some parts of the ear <NUM> are shown in <FIG>, including an ear canal <NUM> and an ear drum <NUM> (or tympanic membrane). Due to the seal <NUM>, the hearable <NUM>, the ear canal <NUM>, and the ear drum <NUM> couple together to form an acoustic circuit. Audioplethysmography <NUM> involves, at least in part, measuring properties associated with this acoustic circuit. The properties of the acoustic circuit can change due to a variety of different situations or actions.

For example, consider <FIG> in which a change occurs in a physical structure of the ear <NUM>. Example changes to the physical structure include a change in a geometric shape of the ear canal <NUM> and/or a change in a volume of the ear canal <NUM>. This change can be caused, at least in part, by subtle blood vessel deformations in the ear canal <NUM> caused by the user <NUM>'s heart pumping. Other changes can also be caused by movement in the ear drum <NUM> or movement of the user <NUM>'s jaw.

At <NUM>, for instance, the tissue around the ear canal <NUM> and the ear drum <NUM> itself are slightly "squeezed" due to blood vessel deformation. This squeeze causes a volume of the ear canal <NUM> to be slightly reduced at <NUM>. At <NUM>, however, the squeezing subsides and the volume of the ear canal <NUM> is slightly increased relative to <NUM>. The physical changes within the ear <NUM> can modulate an amplitude and/or phase of an acoustic signal that propagates through the ear canal <NUM>, as further described below.

During audioplethysmography <NUM>, the acoustic signal propagates through at least a portion of the ear canal <NUM>. The hearable <NUM> can receive an acoustic signal that represents a superposition of multiple acoustic signals that propagate along different paths within the ear canal <NUM>. Each path is associated with a delay (τ) and an amplitude (a). The delay and amplitude can vary over time due to the subtle changes that occur in the physical structure of the ear canal <NUM>. The received acoustic signal can be represented by Equation <NUM>: <MAT> where S(t) represents the received acoustic signal, n represents noise, φini represents a relative phase between the received acoustic signal and the transmitted acoustic signal, Ωfc represents a frequency of the transmitted acoustic signal, and t represents a time vector. Cardiac activities of the user <NUM> can modulate the amplitude and phase of the receive acoustic signal, so that the received acoustic signal can also be described as further shown in Equation <NUM>: <MAT> where hamp(t) represents an amplitude modulator and hphase(t) represents a phase modulator. For example, the two time-varying functions hamp(t) and hphase(t) can depend on interactions between the hearable <NUM> and the ear <NUM> as well as the physiological activities of the user <NUM>, in particular on cardiac activities. When relating to heart-rate-based modulations, one can, for example, assume that hamp(t) = kasin(φhr + + Ωhr(t)) and hphase(t) = kpsin(φhr + + Ωhr(t)), wherein ka and kp are modulation intensity coefficients and Ωhr is a frequency of a heart rate of the user. The interactions between the hearable <NUM> and the ear <NUM> as well as the physiological activities of the user <NUM> modulate the amplitude and phase of the received acoustic signal.

As another example, consider <FIG> in which a gas-composition change occurs in the ear canal <NUM>. This change is caused, at least in part, through breathing. As the user <NUM> breathes, the user <NUM>'s skin can exchange gas with its surroundings. For instance, at <NUM>, inhalation <NUM> occurs and the gas-cycling system within the ear canal <NUM> causes the carbon dioxide concentration <NUM> to decrease. At <NUM>, exhalation <NUM> occurs and the gas-cycling system within the ear canal <NUM> causes the carbon dioxide concentration <NUM> to increase. This change in the carbon dioxide concentration <NUM> impacts the speed of sound, which in turn impacts a speed at which acoustic signals propagate through the ear canal <NUM>.

Returning to <FIG>, the hearable <NUM> can detect aspects associated with biometric monitoring <NUM>, facial behavior recognition <NUM>, and/or environment sensing <NUM> using audioplethysmography <NUM>. In general, biometric monitoring <NUM> can include measuring the user <NUM>'s heart rate, respiration rate, blood pressure, body temperature, and/or carbon dioxide level. Additionally, biometric monitoring <NUM> can be used to measure a physical structure of the ear canal <NUM> and/or detect motions associated with concussive forces. Through biometric monitoring <NUM>, the hearable <NUM> can enable the user <NUM> to track a fitness goal or monitor overall health. This can be especially beneficial in caring for elderly patients or providing remote patient care. Some types of biometric monitoring <NUM> may require different qualities of the seal <NUM>. The heart rate, for instance, can be measured with relatively little seal <NUM> while the respiration rate may require a better seal <NUM>.

Audioplethysmography <NUM> can also be used for facial behavior recognition <NUM>, which can include detecting jaw clenching, recognizing the start of speech, and/or recognizing certain activities that involve the jaw (e.g., speaking or eating). Other types of facial behavior recognition <NUM> include recognizing facial expressions, tracking the user <NUM>'s gaze or head posture, and/or recognizing facial touch gestures. To provide some of these features, audioplethysmography <NUM> can analyze an acoustic channel formed between the left and right ears <NUM>. This acoustic channel can be modified by the user <NUM>'s facial expressions, gaze, head posture, or touch. Through facial behavior recognition <NUM>, the hearable <NUM> can facilitate communication with speech and hearing disabled persons and/or improve automatic speech recognition. Facial behavior recognition <NUM> also enables a more effortless user experience as a user <NUM> can control features of the hearable <NUM> and/or smart device <NUM> without touching the hearable <NUM>.

The hearable <NUM> can also support environment sensing <NUM>, which can include detecting a sports activity (e.g., walking or running). By detecting the sports activity, the hearable <NUM> can automatically increase the volume of audible content for the user <NUM> or play audible content from a playlist associated with a workout routine. As another example, the hearable <NUM> can also automatically detect when the user <NUM> places the hearable <NUM> proximate to their ear <NUM> and forms the seal <NUM>. As such, the hearable <NUM> can automatically determine when to play or pause the audible content for the user <NUM> or when to perform biometric monitoring <NUM> or facial behavior recognition <NUM>. The techniques for audioplethysmography <NUM> can be performed while the hearable <NUM> is playing audible content to the user <NUM>. The smart device <NUM> is further described with respect to <FIG>.

<FIG> illustrates an example smart device <NUM>. The smart device <NUM> is illustrated with various non-limiting example devices including a desktop computer <NUM>-<NUM>, a tablet <NUM>-<NUM>, a laptop <NUM>-<NUM>, a television <NUM>-<NUM>, a computing watch <NUM>-<NUM>, computing glasses <NUM>-<NUM>, a gaming system <NUM>-<NUM>, a microwave <NUM>-<NUM>, and a vehicle <NUM>-<NUM>. Other devices may also be used, such as a home service device, a smart speaker, a smart thermostat, a baby monitor, a Wi-Fi™ router, a drone, a trackpad, a drawing pad, a netbook, an e-reader, a home automation and control system, a wall display, and another home appliance. Note that the smart device <NUM> can be wearable, nonwearable but mobile, or relatively immobile (e.g., desktops and appliances).

The smart device <NUM> includes one or more computer processors <NUM> and at least one computer-readable medium <NUM>, which includes memory media and storage media. Applications and/or an operating system (not shown) embodied as computer-readable instructions on the computer-readable medium <NUM> can be executed by the computer processor <NUM> to provide some of the functionalities described herein. The computer-readable medium <NUM> also includes an audioplethysmography-based application <NUM>, which uses information provided by the hearable <NUM> to perform an action. Example actions can include displaying biometric data to the user <NUM> based on biometric monitoring <NUM>, providing touch-free control of the smart device <NUM> based on facial behavior recognition <NUM>, or changing the presentation of audible content based on environment sensing <NUM>.

The smart device <NUM> can also include a network interface <NUM> for communicating data over wired, wireless, or optical networks. For example, the network interface <NUM> may communicate data over a local-area-network (LAN), a wireless local-area-network (WLAN), a personal-area-network (PAN), a wire-area-network (WAN), an intranet, the Internet, a peer-to-peer network, point-to-point network, a mesh network, Bluetooth™, and the like. The smart device <NUM> may also include the display <NUM>. Although not explicitly shown, the hearable <NUM> can be integrated within the smart device <NUM>, or can connect physically or wirelessly to the smart device <NUM>. The hearable <NUM> is further described with respect to <FIG>.

<FIG> illustrates an example hearable <NUM>. The hearable <NUM> is illustrated with various non-limiting example devices, including wireless earbuds <NUM>-<NUM>, wired earbuds <NUM>-<NUM>, and headphones <NUM>-<NUM>. The earbuds <NUM>-<NUM> and <NUM>-<NUM> are a type of in-ear device that fits into the ear canal <NUM>. Each earbud <NUM>-<NUM> or <NUM>-<NUM> can represent a hearable <NUM>. Headphones <NUM>-<NUM> can rest on top of or over the ears <NUM>. The headphones <NUM>-<NUM> can represent closed-back headphones, open-back headphones, on-ear headphones, or over-ear headphones. Some headphones <NUM>-<NUM> include two hearables <NUM>, which are physically packaged together. In this case, there is one hearable <NUM> for each ear <NUM>. Other headphones <NUM>-<NUM>, such as single-ear headphones <NUM>-<NUM>, include one hearable <NUM>. In some implementations, one or more hearables <NUM> are implemented within (or as part of) another device, such as a pair of glasses, a hat, ear muffs, or a helmet.

The hearable <NUM> includes a communication interface <NUM> to communicate with the smart device <NUM>, though this need not be used when the hearable <NUM> is integrated within the smart device <NUM>. The communication interface <NUM> can be a wired interface or a wireless interface, in which audio content is passed from the smart device <NUM> to the hearable <NUM>. The hearable <NUM> can also use the communication interface <NUM> to pass data measured using audioplethysmography <NUM> to the smart device <NUM>. In general, the data provided by the communication interface <NUM> is in a format usable by the audioplethysmography-based application <NUM>. The communication interface <NUM> also enables the hearable <NUM> to communicate with another hearable <NUM>. During bistatic sensing, for instance, the hearable <NUM> can use the communication interface <NUM> to coordinate with the other hearable <NUM> to support two-ear audioplethysmography <NUM>, as further described with respect to <FIG>. In particular, the transmitting hearable <NUM> can communicate timing and waveform information to the receiving hearable <NUM> to enable the receiving hearable <NUM> to appropriately demodulate a received acoustic signal.

The hearable <NUM> includes at least one speaker and at least one microphone, for example as parts of at least one transducer <NUM> that can convert electrical signals into sound waves. The same transducer <NUM> or a further transducer of the hearable <NUM> can also detect and convert sound waves into electrical signals. These sound waves may include ultrasonic frequencies and/or audible frequencies, either of which may be used for audioplethysmography <NUM>. In particular, a frequency spectrum (e.g., range of frequencies) that the transducer <NUM> uses to generate an acoustic signal can include frequencies from a low-end of the audible range to a high-end of the ultrasonic range, e.g., between <NUM> hertz (Hz) to <NUM> megahertz (MHz). Other example frequency spectrums for audioplethysmography <NUM> can encompass frequencies between <NUM> and <NUM> kilohertz (kHz), between <NUM> and <NUM>, between <NUM> and <NUM>, or between <NUM> and <NUM>.

In an example implementation, the transducer <NUM> has a monostatic topology. With this topology, the transducer <NUM> can convert the electrical signals into sound waves and convert sound waves into electrical signals (e.g., can transmit or receive acoustic signals). Example monostatic transducers may include piezoelectric transducers, capacitive transducers, and micro-machined ultrasonic transducers (MUTs) that use microelectromechanical systems (MEMS) technology.

Alternatively, the transducer <NUM> can be implemented with a bistatic topology, which includes multiple transducers that are physically separate. In this case, a first transducer converts the electrical signal into sound waves (e.g., transmits acoustic signals), and a second transducer converts sound waves into an electrical signal (e.g., receives the acoustic signals). An example bistatic topology can be implemented using at least one speaker <NUM> and at least one microphone <NUM>. The speaker <NUM> and the microphone <NUM> can be dedicated for audioplethysmography <NUM> or can be used for both audioplethysmography <NUM> and other functions of the smart device <NUM> (e.g., presenting audible content to the user <NUM>, capturing the user <NUM>'s voice for a phone call, or for voice control).

In general, the speaker <NUM> and the microphone <NUM> are directed towards the ear canal <NUM> (e.g., oriented towards the ear canal <NUM>). Accordingly, the speaker <NUM> can direct acoustic signals towards the ear canal <NUM>, and the microphone <NUM> is responsive to receiving acoustic signals from the direction associated with the ear canal <NUM>.

The hearable <NUM> includes at least one analog circuit <NUM>, which includes circuitry and logic for conditioning electrical signals in an analog domain. The analog circuit <NUM> can include analog-to-digital converters, digital-to-analog converters, amplifiers, filters, mixers, and switches for generating and modifying electrical signals. In some implementations, the analog circuit <NUM> includes other hardware circuitry associated with the speaker <NUM> or microphone <NUM>.

The hearable <NUM> also includes at least one system processor <NUM> and at least one system medium <NUM> (e.g., one or more computer-readable storage media). In the depicted configuration, the system medium <NUM> includes an audioplethysmography measurement module <NUM> (APG measurement module <NUM>) and optionally includes an audioplethysmography calibration module <NUM> (APG calibration module <NUM>). The audioplethysmography measurement module <NUM> and the audioplethysmography calibration module <NUM> can be implemented using hardware, software, firmware, or a combination thereof. In this example, the system processor <NUM> implements the audioplethysmography measurement module <NUM> and the audioplethysmography calibration module <NUM>. In an alternative example, the computer processor <NUM> of the smart device <NUM> can implement at least a portion of the audioplethysmography measurement module <NUM> and/or at least a portion of the audioplethysmography calibration module <NUM>. In this case, the hearable <NUM> can communicate digital samples of the acoustic signals to the smart device <NUM> using the communication interface <NUM>.

The audioplethysmography measurement module <NUM> analyzes receive acoustic signals to measure data associated with audioplethysmography <NUM>. The audioplethysmography measurement module <NUM> can be implemented using at least one biometric monitor <NUM> for biometric monitoring <NUM>, at least one facial behavior detector <NUM> for facial behavior recognition <NUM>, and/or at least one environment detector <NUM> for environment sensing <NUM>. Example audioplethysmography measurement modules <NUM> are further described with respect to <FIG> and <FIG>.

The audioplethysmography calibration module <NUM> can determine appropriate waveform characteristics for transmitting acoustic signals to improve audioplethysmography <NUM> performance. For example, the audioplethysmography calibration module <NUM> can take into account the quality of the seal <NUM> and the physical structure of the ear canal <NUM> to determine a transmission frequency that can enable the hearable <NUM> to detect the user <NUM>'s heart rate and/or respiration rate with an accuracy of <NUM>% or less. With the audioplethysmography calibration module <NUM>, the hearable <NUM> can dynamically adjust the transmission frequency each time the seal <NUM> is formed and based on the unique physical structure of each ear <NUM>. Through this calibration process, the hearables <NUM> on different ears may operate with one or more different acoustic frequencies. An example implementation of the audioplethysmography calibration module <NUM> is further described with respect to <FIG>.

Some hearables <NUM> include an active-noise-cancellation circuit <NUM>, which enables the hearables <NUM> to reduce background or environmental noise. In this case, the microphone <NUM> used for audioplethysmography <NUM> can be implemented using a feedback microphone <NUM> of the active-noise-cancellation circuit <NUM>. During active noise cancellation, the feedback microphone <NUM> provides feedback information regarding the performance of the active noise cancellation. During audioplethysmography <NUM>, the feedback microphone <NUM> receives an acoustic signal, which is provided to the audioplethysmography measurement module <NUM> and/or the audioplethysmography calibration module <NUM>. In some situations, active noise cancellation and audioplethysmography <NUM> are performed simultaneously using the feedback microphone <NUM>. In this case, the acoustic signal received by the feedback microphone <NUM> can be provided to at least one of the audioplethysmography modules <NUM> or <NUM> and can be provided to the active-noise-cancellation circuit <NUM>. Different types of audioplethysmography <NUM> are further described with respect to <FIG> and <FIG>.

<FIG> illustrates example operations of two hearables <NUM>-<NUM> and <NUM>-<NUM> performing single-ear audioplethysmography <NUM>. In environment <NUM>-<NUM>, the hearables <NUM>-<NUM> and <NUM>-<NUM> independently perform audioplethysmography <NUM> on different ears <NUM> of the user <NUM>. In this case, the first hearable <NUM>-<NUM> is proximate to the user <NUM>'s right ear <NUM>, and the second hearable <NUM>-<NUM> is proximate to the user <NUM>'s left ear <NUM>. Each hearable <NUM>-<NUM> and <NUM>-<NUM> includes a speaker <NUM> and a microphone <NUM>. The hearables <NUM>-<NUM> and <NUM>-<NUM> can operate in a monostatic manner during the same time period or during different time periods. In other words, each hearable <NUM>-<NUM> and <NUM>-<NUM> can independently transmit and receive acoustic signals.

For example, the first hearable <NUM>-<NUM> uses the speaker <NUM> to transmit a first acoustic transmit <NUM>-<NUM>, which propagates within at least a portion of the user <NUM>'s right ear canal <NUM>. The first hearable <NUM>-<NUM> uses the microphone <NUM>, which can be the feedback microphone <NUM>, to receive a first acoustic receive signal <NUM>-<NUM>. In this example, an acoustic circuit is formed that includes the seal <NUM>, the hearable <NUM>-<NUM>, the right ear canal <NUM>, and the ear drum <NUM> of the right ear <NUM>. The first acoustic receive signal <NUM>-<NUM> represents a version of the first acoustic transmit signal <NUM>-<NUM> that is modified, at least in part, by the acoustic circuit associated with the right ear canal <NUM>. This modification can change an amplitude, phase, and/or frequency of the first acoustic receive signal <NUM>-<NUM> relative to the first acoustic transmit signal <NUM>-<NUM>.

Similarly, the second hearable <NUM>-<NUM> uses the speaker <NUM> to transmit a second acoustic transmit signal <NUM>-<NUM>, which propagates within at least a portion of the user <NUM>'s left ear canal <NUM>. The second hearable <NUM>-<NUM> uses the microphone <NUM>, which can be the feedback microphone <NUM>, to receive a second acoustic receive signal <NUM>-<NUM>. The second acoustic receive signal <NUM>-<NUM> represents a version of the second acoustic transmit signal <NUM>-<NUM> that is modified, at least in part, by the acoustic circuit associated with the left ear canal <NUM>. This modification can change an amplitude, phase, and/or frequency of the second acoustic receive signal <NUM>-<NUM> relative to the second acoustic transmit signal <NUM>-<NUM>.

In this example, the hearables <NUM>-<NUM> and <NUM>-<NUM> both operate as a transmitter and a receiver. More specifically, the hearable <NUM>-<NUM> represents a transmitter (or a source) of the acoustic transmit signal <NUM>-<NUM> and also represents a receiver (or destination) of the acoustic receive signal <NUM>-<NUM>. Likewise, the hearable <NUM>-<NUM> represents a transmitter (or a source) of the acoustic transmit signal <NUM>-<NUM> and also represents a receiver (or destination) of the acoustic receive signal <NUM>-<NUM>.

The techniques of single-ear audioplethysmography <NUM> can be particularly beneficial for biometric monitoring <NUM>, environment sensing <NUM>, and at least some aspects of facial behavior recognition <NUM>. This also enables the smart device <NUM> to compile information from both hearables <NUM>-<NUM> and <NUM>-<NUM>, which can further improve measurement confidence. For some aspects of audioplethysmography <NUM>, it can be beneficial to analyze the acoustic channel between two ears <NUM>, as further described with respect to <FIG>.

<FIG> illustrates an example joint operation of two hearables <NUM>-<NUM> and <NUM>-<NUM> performing two-ear audioplethysmography <NUM>. In the environment <NUM>-<NUM>, the hearables <NUM>-<NUM> and <NUM>-<NUM> jointly perform audioplethysmography <NUM> across two ears <NUM> of the user <NUM>. In this case, at least one of the hearables <NUM> (e.g., the first hearable <NUM>-<NUM>) includes the speaker <NUM>, and at least one of the other hearables <NUM> (e.g., the second hearable <NUM>-<NUM>) includes the microphone <NUM>. The hearables <NUM>-<NUM> and <NUM>-<NUM> operate together in a bistatic manner during the same time period.

During operation, the first hearable <NUM>-<NUM> transmits a first acoustic transmit <NUM> using the speaker <NUM>. The acoustic transmit signal <NUM> propagates through the user <NUM>'s right ear canal <NUM>. The acoustic transmit signal <NUM> also propagates through an acoustic channel that exists between the right and left ears <NUM>. In the left ear <NUM>, the acoustic transmit signal <NUM> propagates through the user <NUM>'s left ear canal <NUM> and is represented as an acoustic receive signal <NUM>. The second hearable <NUM>-<NUM> receives the acoustic receive signal <NUM> using the microphone <NUM>. In this example, an acoustic circuit is formed that includes the seals <NUM> associated with the hearables <NUM>-<NUM> and <NUM>-<NUM>, the hearable <NUM>-<NUM>, the right ear canal <NUM>, the ear drum <NUM> of the right ear <NUM>, the acoustic channel between the right and left ears <NUM>, the ear drum <NUM> of the left ear <NUM>, the left ear canal <NUM>, and the hearable <NUM>-<NUM>. The acoustic receive signal <NUM> represents a version of the acoustic transmit signal <NUM> that is modified by the acoustic circuit associated with the right ear canal <NUM>, modified by the acoustic channel associated with the user <NUM>'s face, and modified by the acoustic circuit associated with the left ear canal <NUM>. This modification can change an amplitude, phase, and/or frequency of the acoustic receive signal <NUM> relative to the acoustic transmit signal <NUM>. In some cases, the hearable <NUM>-<NUM> measures the time-of-flight (ToF) associated with the propagation from the first hearable <NUM>-<NUM> to the second hearable <NUM>-<NUM>. Sometimes a combination of single-ear and two-ear audioplethysmography <NUM> are applied to further improve measurement confidence. The single-ear and two-ear audioplethysmography <NUM> can occur during a same time period or during different time periods.

In this example, the hearable <NUM>-<NUM> operates as a transmitter, and the hearable <NUM>-<NUM> operates as a receiver. More specifically, the hearable <NUM>-<NUM> represents a transmitter (or a source) of the acoustic transmit signal <NUM>. The hearable <NUM>-<NUM>, in contrast, represents a receiver (or a destination) of the acoustic receive signal <NUM>.

The acoustic transmit signal <NUM> of <FIG> and <FIG> can represent a variety of different types of signals. As described above with respect to <FIG>, the acoustic transmit signal <NUM> can be an ultrasonic signal and/or an audible signal. Also, the acoustic transmit signal <NUM> can be a continuous-wave signal or a pulsed signal. Some acoustic transmit signals <NUM> can have a particular tone or frequency. Other acoustic transmit signals <NUM> can have multiple tones or multiple frequencies. A variety of modulations can be applied to generate the acoustic transmit signal <NUM>. Example modulations include linear frequency modulations, triangular frequency modulations, stepped frequency modulations, phase modulations, or amplitude modulations. The acoustic transmit signal <NUM> can be transmitted during an operational or mission mode, as further described with respect to <FIG> and <FIG>. Also, the acoustic transmit signal <NUM> can be transmitted during a calibration mode, as further described with respect to <FIG>. An example audioplethysmography measurement module <NUM> is further described with respect to <FIG>.

<FIG> illustrates an example scheme implemented by the audioplethysmography measurement module <NUM>. In the depicted configuration, the audioplethysmography measurement module <NUM> includes at least one audioplethysmography pre-processing pipeline <NUM> and at least one biometric monitor <NUM>. The audioplethysmography pre-processing pipeline <NUM> processes digital samples of the acoustic receive signal <NUM> and outputs data in a format that is usable by the biometric monitor <NUM>. The biometric monitor <NUM> determines one or more physiological metrics (e.g., one or more biometrics) of the user <NUM> for biometric monitoring <NUM>. In this example, the biometric monitor <NUM> includes a heart rate detector <NUM> and/or a respiration rate detector <NUM>. The heart rate detector <NUM> measures a heart rate of the user <NUM>. The respiration rate detector <NUM> measures a respiration rate of the user <NUM>.

Other implementations are also possible in which the audioplethysmography measurement module <NUM> includes the facial behavior detector <NUM> and/or the environment detector <NUM> coupled to an output of the audioplethysmography pre-processing pipeline <NUM>. In general, the audioplethysmography measurement module <NUM> can include any combination of the biometric monitor <NUM>, the facial behavior detector <NUM> and/or the environment detector <NUM>.

The audioplethysmography pre-processing pipeline <NUM> includes at least one demodulator <NUM>, at least one filter <NUM>, and at least one autocorrelation module <NUM>. The demodulator <NUM> can operate as a mixer and perform a multiplication operation. The filter <NUM>, which can be implemented as a low-pass filter, is designed to attenuate spurious or undesired frequencies. Example spurious frequencies include harmonic frequencies generated through operation of the demodulator <NUM>. The audioplethysmography pre-processing pipeline <NUM> can optionally include a clutter cancellation module <NUM>. The clutter cancellation module <NUM> can attenuate other undesired frequencies that are passed by the filter <NUM>.

During audioplethysmography <NUM>, the audioplethysmography pre-processing pipeline <NUM> accepts a digital transmit signal <NUM>, which represents a version of the acoustic transmit signal <NUM>. In some implementations, the system processor <NUM> generates the digital transmit signal <NUM> in the digital domain and passes the digital transmit signal <NUM> to the analog circuit <NUM> to enable transmission of the acoustic transmit signal <NUM> via the transducer <NUM>. The audioplethysmography pre-processing pipeline <NUM> also accepts a digital receive signal <NUM> from the analog circuit <NUM>. The digital receive signal <NUM> represents a digital version of the acoustic receive signal <NUM>.

Using the digital transmit signal <NUM>, the demodulator <NUM> demodulates the digital receive signal <NUM> to generate a mixed signal <NUM>. As an example, the demodulator <NUM> can multiply or perform a beating operation to combine the digital transmit signal <NUM> with the digital receive signal <NUM>. For example, the demodulator <NUM> may apply an In-phase and Quadrature (IQ) mixing for the digital receive signal <NUM> using the digital transmit signal <NUM>. Referring to Equation <NUM> above, an in-phase digital transmit signal <NUM> may be given by SI(t) = cos(Ωfc(t)) and the demodulator <NUM> may then perform a multiplication of S(t) and SI(t). The filter <NUM> filters the mixed signal <NUM> to generate a filtered signal <NUM>. Due to the operation of the filter <NUM>, some higher-frequency components of the filtered signal <NUM> can be attenuated relative to the mixed signal <NUM>. Based on filtering, for example when applying an IQ mixing for the digital receive signal <NUM>, an in-phase part I(t) and a quadrature-phase part Q(t) may be determined as well as an amplitude <MAT> or a phase <MAT> of the digital receive signal <NUM>.

In a first example implementation, the autocorrelation module <NUM> accepts the filtered signal <NUM> and applies an autocorrelation function to generate autocorrelation <NUM>. The biometric monitor <NUM> analyzes the autocorrelation <NUM> to measure a physiological metric of the user <NUM>. For example, the heart rate detector <NUM> detects peaks <NUM> of the autocorrelation <NUM> and measures the time interval between the peaks <NUM>. This time interval, or period of the autocorrelation <NUM>, represents the heart rate. At <NUM>, a graph of an example autocorrelation <NUM> is shown having peaks <NUM>-<NUM> and <NUM>-<NUM>, which can be used to determine the heart rate. A similar process can occur for measuring the respiration rate using the respiration rate detector <NUM>.

Sometimes frequencies associated with other physiological metrics or noise can make it harder to accurately measure the desired physiological metric. To address this, the audioplethysmography pre-processing pipeline <NUM> can apply the clutter cancellation module <NUM>. Instead of directly sending the filtered signal <NUM> to the autocorrelation module <NUM>, the clutter cancellation module <NUM> operates on the filtered signal <NUM> and generates a modified filtered signal <NUM>. For example, the clutter cancellation module <NUM> can attenuate frequencies that are outside of a range associated with the heart rate. These can include slower frequencies associated with a respiration rate of the user <NUM> and/or frequencies associated with movement of the hearable <NUM>.

In an example implementation, the clutter cancellation module <NUM> applies a curve fitting (e.g., a fifth-order polynomial curve fit) onto the filtered signal <NUM> to generate a fitted curve. The fitted curve has a frequency that incorporates, at least in part, the frequency associated with noise or other physiological metrics that are not of interest. The clutter cancellation module <NUM> then subtracts the fitted curve from the filtered signal <NUM> to generate the modified filtered signal <NUM>. The modified filtered signal <NUM> is passed to the autocorrelation module <NUM> and the measurement process can continue as described above.

Some transmission frequencies can be better for audioplethysmography <NUM> than others. The desired frequency can depend, at least in part, on the quality of the seal <NUM> and the physical structure of the ear canal <NUM>. To determine the desired frequency, the hearable <NUM> can optionally perform a calibration process using the audioplethysmography calibration module <NUM>, which is further described with respect to <FIG>.

<FIG> illustrates an example scheme implemented by the audioplethysmography calibration module <NUM>. In the depicted configuration, the audioplethysmography calibration module <NUM> includes the demodulator <NUM>, the filter <NUM>, and at least one frequency selector <NUM>. The frequency selector <NUM> selects one or more acoustic frequencies for audioplethysmography <NUM>. In an example implementation, the frequency selector <NUM> includes a derivative module <NUM>, a zero-crossing detector <NUM>, and an evaluator <NUM>. The operations of these components are further described below.

During a calibration mode, the hearable <NUM> transmits the acoustic transmit signal <NUM> and receives the acoustic receive signal <NUM>. The acoustic transmit signal <NUM> can have a particular bandwidth on the order of several kilohertz. For example, the acoustic transmit signal <NUM> can have a bandwidth of approximately <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, or <NUM> kilohertz. The audioplethysmography calibration module <NUM> accepts the digital transmit signal <NUM>, which represents a version of the acoustic transmit signal <NUM>. Also, the audioplethysmography calibration module <NUM> accepts the digital receive signal <NUM>, which represents a digital version of the acoustic receive signal <NUM>.

Using the digital transmit signal <NUM>, the demodulator <NUM> demodulates the digital receive signal <NUM> to generate the mixed signal <NUM>, as described above with respect to <FIG>. The filter <NUM> filters the mixed signal <NUM> to attenuate spurious or undesired frequencies and to generate the filtered signal <NUM>.

The derivative module <NUM> calculates a second-order derivative of the frequency response of the filtered signal <NUM> to generate derivative <NUM>. The zero-crossing detector <NUM> identifies frequencies within the derivative <NUM> that are associated with zero crossings. These zero-crossing frequencies <NUM> represent frequencies that are particularly sensitive to changes in the acoustic channel or the acoustic circuit. The zero-crossing frequencies <NUM> are passed to the evaluator <NUM>.

The evaluator <NUM> identifies one or more zero-crossing frequencies <NUM> for audioplethysmography <NUM>, which are represented by selected frequency <NUM>. To determine the selected frequency <NUM>, the evaluator <NUM> can take into account the difference between adjacent zero-crossing frequencies <NUM> and/or an amount of energy within the filtered signal <NUM> at the zero-crossing frequencies <NUM>. In general, the evaluator <NUM> selects frequencies that are sufficiently far apart to reduce interference and have a sufficient amount of energy to perform audioplethysmography <NUM>. The resulting selected frequency <NUM> (or selected frequencies <NUM>) can be used to achieve accurate results for audioplethysmography <NUM>. As an example, the evaluator <NUM> can select <NUM>, <NUM>, <NUM>, <NUM>, <NUM> or <NUM> different frequencies.

In some cases, the evaluator <NUM> can apply an autocorrelation function to evaluate the performance of each selected frequency <NUM>. Selected frequencies <NUM> that produce an autocorrelation function having a peak-to-average ratio that is greater than a predetermined threshold can be candidates for selection.

The hearable <NUM> can use at least one of the selected frequencies <NUM> to transmit subsequent acoustic transmit signals <NUM> for audioplethysmography110. This calibration process can be performed as often as desired to account for changes in the seal <NUM> and/or changes in the physical structure of the ear canal <NUM>. In some implementations, the hearable <NUM> detects the formation of the seal <NUM> and performs the calibration process based on this detection. The hearable <NUM> can detect the formation of the seal <NUM> using audioplethysmography <NUM> or using another sensor that performs on-head (or in-ear) detection. Also, the calibration process can be performed for each ear <NUM>. In some cases, the hearable <NUM> uses multiple selected frequencies <NUM> to transmit a subsequent acoustic transmit signal <NUM>. In this case, the audioplethysmography measurement module <NUM> can execute multiple audioplethysmography pre-processing pipelines <NUM>, as further described with respect to <FIG>.

<FIG> illustrates another example scheme implemented by the audioplethysmography measurement module <NUM>. In this case, the hearable <NUM> transmits an acoustic transmit signal <NUM> with multiple tones or frequencies, which can be based on the selected frequencies <NUM> determined during a calibration mode. As shown in <FIG>, the audioplethysmography measurement module <NUM> includes multiple audioplethysmography pre-processing pipelines <NUM>-<NUM> to <NUM>-N. Each audioplethysmography pre-processing pipelines <NUM>-<NUM> to <NUM>-N is designed to process information associated with one of the selected frequencies <NUM> and generate a corresponding autocorrelation <NUM>-<NUM> to <NUM>-N.

The audioplethysmography measurement module <NUM> also includes a rank selector <NUM>, which evaluates the autocorrelations <NUM>-<NUM> to <NUM>-N and selects the autocorrelation with the highest quality factor. For example, the rank selector <NUM> can select one of the autocorrelations <NUM>-<NUM> to <NUM>-N with a highest peak-to-average ratio in the frequency domain of the autocorrelation. This selected autocorrelation <NUM> is passed to other modules, such as the biometric monitor <NUM>, the facial behavior detector <NUM>, or the environment detector <NUM>, for further processing. This selection process enables the audioplethysmography measurement module <NUM> to achieve a higher level of accuracy for performing audioplethysmography <NUM>, including for measuring at least one physiological metric as part of biometric monitoring <NUM>. <FIG> further graphically illustrate example signals associated with a calibration process implemented by an audioplethysmography calibration module <NUM> and as explained with respect to <FIG>.

<FIG> illustrates graphs <NUM> and <NUM> of an example mixed signal <NUM> and an example filtered signal <NUM>. The graphs <NUM> and <NUM> depict amplitude over frequency. The graph <NUM> represents an enlarged view of a section of the graph <NUM>. As shown in <NUM>, the mixed signal <NUM> has at least some noise. The filtered signal <NUM> represents a smoother version of the mixed signal <NUM>.

<FIG> illustrates a graph <NUM> of an example derivative <NUM> of the filtered signal <NUM> of <FIG>. In this example, the derivative <NUM> represents a second-order derivative as calculated by the derivative module <NUM>. Dashed line <NUM> represents a zero amplitude. The zero-crossing detector <NUM> calculates and identifies frequencies at which the derivative <NUM> crosses the zero amplitude represented by <NUM>. Based on these zero-crossings, several frequencies are identified. These frequencies can be particularly sensitive to changes in the acoustic channel or the acoustic circuit. The frequencies are further described with respect to <FIG>.

<FIG> illustrates a graph <NUM> in which frequencies <NUM>-<NUM> to <NUM>-<NUM> associated with the zero-crossings of <FIG> are shown relative to the mixed signal <NUM> and the filtered signal <NUM> of <FIG>. The evaluator <NUM> evaluates the zero-crossing frequencies <NUM>-<NUM> to <NUM>-<NUM> and (pre-)selects a subset of the frequencies <NUM> taking into account the difference between the adjacent zero-crossing frequencies and/or an amount of energy within the filtered signal <NUM> at a zero-crossing frequency <NUM>. This may result in the (pre-)selecting of frequencies <NUM>-<NUM>, <NUM>-<NUM>, <NUM>-<NUM>, which are shown by solid lines, and may result in the not selecting of frequencies <NUM>-<NUM>, <NUM>-<NUM>, <NUM>-<NUM>, and <NUM>-<NUM>, which are shown by dashed lines. This operation can result in the (pre-)selecting of different frequencies for each ear <NUM>, including, for example, zero-crossing frequencies <NUM> having a highest amplitude. The autocorrelation <NUM> applied by the evaluator <NUM> for evaluating performance of each one of the selected frequencies <NUM> with respect to audioplethysmography <NUM> is further described with respect to <FIG>.

<FIG> illustrates a graph <NUM> that depicts example autocorrelations <NUM>-<NUM> and <NUM>-<NUM>. The autocorrelations <NUM>-<NUM> and <NUM>-<NUM> can be associated with different ones of the frequencies <NUM> shown in <FIG>. As can be seen from the corresponding plots of <NUM>-<NUM> and <NUM>-<NUM>, the calculated autocorrelations <NUM>-<NUM> and <NUM>-<NUM> may indicate that with a (pre-)selected frequency a physiological metric, such as a heart rate of the user <NUM>, may not be determined. Accordingly, the evaluator <NUM>, will (finally) select frequencies <NUM> that generate an autocorrelation <NUM> with a peak-to-average ratio that is greater than a predetermined threshold in order to determine the frequencies <NUM> to be used for the audioplethysmography <NUM>. In this context, the autocorrelation <NUM>-<NUM> can have a sufficiently high peak-to-average ratio, which causes its associated frequency <NUM> to be selected. The autocorrelation <NUM>-<NUM>, however, has a peak-to-average ratio that is too low and causes its associated frequency <NUM> to not be selected.

<FIG> depict example methods <NUM>, <NUM>, and <NUM> for implementing aspects of audioplethysmography <NUM>. Methods <NUM>, <NUM>, and <NUM> are shown as sets of operations (or acts) performed but not necessarily limited to the order or combinations in which the operations are shown herein. Further, any of one or more of the operations may be repeated, combined, reorganized, or linked to provide a wide array of additional and/or alternate methods. In portions of the following discussion, reference may be made to the environment <NUM> of <FIG>, and entities detailed in <FIG> and <FIG>, reference to which is made for example only. The techniques are not limited to performance by one entity or multiple entities operating on one device.

At <NUM> in <FIG>, an acoustic transmit signal is transmitted. The acoustic transmit signal propagates within at least a portion of an ear canal of a user. For example, at least one speaker <NUM> transmits the acoustic transmit signal <NUM>. The at least one speaker <NUM> can represent the speaker of the hearable <NUM>-<NUM>, the speaker of the hearable <NUM>-<NUM>, or both. The acoustic transmit signal <NUM> propagates within at least a portion of the ear canal <NUM> of the user <NUM>, as described with respect to <FIG> or <FIG>.

At <NUM>, an acoustic receive signal is received. The acoustic receive signal represents a version of the acoustic transmit signal with one or more waveform characteristics modified due to the propagation within the ear canal. For example, at least one microphone <NUM> receives the acoustic receive signal <NUM>, as described with respect to <FIG> or <FIG>. The at least one microphone <NUM> can represent the microphone <NUM> of the hearable <NUM>-<NUM>, the microphone of the hearable <NUM>-<NUM>, or both. The acoustic receive signal <NUM> represents a version of the acoustic transmit signal <NUM> with one or more waveform characteristics modified due to the propagation within the ear canal <NUM>. The waveform characteristics can also be modified, at least in part, by the user's biometrics, by the user's facial behavior, or by the environment around the ear canal <NUM>. Example waveform characteristics include amplitude, phase, and/or frequency. In some implementations, a feedback microphone <NUM> of an active-noise-cancellation circuit <NUM> can receive the acoustic receive signal <NUM>.

At <NUM>, at least one physiological metric of the user is determined based on the one or more modified waveform characteristics of the acoustic receive signal. For example, the hearable <NUM> determines at least one physiological metric of the user <NUM> in accordance with biometric monitoring <NUM>. Example physiological metrics include a heart rate, a respiration rate, blood pressure, body temperature, and a carbon dioxide level.

At <NUM> in <FIG>, an acoustic transmit signal is transmitted. The acoustic transmit signal propagates within at least a portion of an ear canal of a user. For example, at least one speaker <NUM> transmits the acoustic transmit signal <NUM>. The at least one speaker <NUM> can represent the speaker of the hearable <NUM>-<NUM>, the speaker of the hearable <NUM>-<NUM>, or both. The acoustic transmit signal <NUM> propagates within at least a portion of the ear canal <NUM> of the user <NUM>, as described with respect to <FIG> and<FIG>.

At <NUM>, an acoustic receive signal is received. The acoustic receive signal represents a version of the acoustic transmit signal with one or more waveform characteristics modified due to the propagation within the ear canal. For example, at least one microphone <NUM> receives the acoustic receive signal <NUM>, as described with respect to <FIG> or <FIG>. The at least one microphone <NUM> can represent the microphone <NUM> of the hearable <NUM>-<NUM>, the microphone <NUM> of the hearable <NUM>-<NUM>, or both. The acoustic receive signal <NUM> represents a version of the acoustic transmit signal <NUM> with one or more waveform characteristics modified due to the propagation within the ear canal <NUM>. As the user <NUM> breathes, the gas composition within the ear canal <NUM> changes, as shown in <FIG>. In particular, the carbon dioxide concentration changes, which impacts the speed of sound within the ear canal <NUM>. Example waveform characteristics can include amplitude, phase, and/or frequency. In some implementations, a feedback microphone <NUM> of an active-noise-cancellation circuit <NUM> can receive the acoustic receive signal <NUM>.

At <NUM>, a respiration rate of the user is determined by analyzing the one or more waveform characteristics of the acoustic receive signal. For example, the hearable <NUM> determines the respiration rate based on the one or more waveform characteristics of the acoustic receive signal <NUM> using the audioplethysmography measurement module <NUM> and the respiration rate detector <NUM>, as described with respect to <FIG>.

Optionally at <NUM>, the respiration rate is communicated to a smart device to enable the smart device to display the respiration rate to the user. For example, the hearable <NUM> communicates the respiration rate to the smart device <NUM> to enable the smart device <NUM> to communicate (e.g., display) the respiration rate to the user <NUM>.

At <NUM> in <FIG>, a calibration process is performed that identifies at least one acoustic frequency suitable for audioplethysmography using at least one speaker and at least one microphone. For example, the hearable <NUM> uses at least one speaker <NUM>, at least one microphone <NUM> and the audioplethysmography calibration module <NUM> to perform a calibration process that identifies at least one acoustic frequency that is suitable for audioplethysmography <NUM>, as described with respect to <FIG>.

At <NUM>, audioplethysmography is performed using the at least one acoustic frequency at an ear of a user. For example, the hearable <NUM> performs audioplethysmography <NUM> using the selected frequency <NUM>. In particular, the hearable <NUM> uses the at least one acoustic frequency (e.g., transmits an acoustic transmit signal <NUM> using the selected frequency <NUM>) to perform audioplethysmography at an ear <NUM> (e.g., at one or more ears <NUM>) of a user <NUM>. The hearable <NUM> analyzes a received acoustic receive signal <NUM> using the audioplethysmography measurement module <NUM>.

In some situations, the methods <NUM>, <NUM>, and/or <NUM> are performed using one hearable <NUM> for single-ear audioplethysmography <NUM>, as described with respect to <FIG>. In other situations, the methods <NUM>, <NUM>, and/or <NUM> are performed using two hearables <NUM> for two-ear audioplethysmography <NUM>, as described with respect to <FIG>.

<FIG> illustrates various components of an example computing system <NUM> that can be implemented as any type of client, server, and/or computing device as described with reference to the previous <FIG> and <FIG> to implement aspects of audioplethysmography calibration.

The computing system <NUM> includes communication devices <NUM> that enable wired and/or wireless communication of device data <NUM> (e.g., received data, data that is being received, data scheduled for broadcast, or data packets of the data). The communication devices <NUM> or the computing system <NUM> can include one or more hearables <NUM>. The device data <NUM> or other device content can include configuration settings of the device, media content stored on the device, and/or information associated with a user of the device. Media content stored on the computing system <NUM> can include any type of audio, video, and/or image data. The computing system <NUM> includes one or more data inputs <NUM> via which any type of data, media content, and/or inputs can be received, such as human utterances, user-selectable inputs (explicit or implicit), messages, music, television media content, recorded video content, and any other type of audio, video, and/or image data received from any content and/or data source.

The computing system <NUM> also includes communication interfaces <NUM>, which can be implemented as any one or more of a serial and/or parallel interface, a wireless interface, any type of network interface, a modem, and as any other type of communication interface. The communication interfaces <NUM> provide a connection and/or communication links between the computing system <NUM> and a communication network by which other electronic, computing, and communication devices communicate data with the computing system <NUM>.

The computing system <NUM> includes one or more processors <NUM> (e.g., any of microprocessors, controllers, and the like), which process various computer-executable instructions to control the operation of the computing system <NUM>. Alternatively or in addition, the computing system <NUM> can be implemented with any one or combination of hardware, firmware, or fixed logic circuitry that is implemented in connection with processing and control circuits which are generally identified at <NUM>. Although not shown, the computing system <NUM> can include a system bus or data transfer system that couples the various components within the device. A system bus can include any one or combination of different bus structures, such as a memory bus or memory controller, a peripheral bus, a universal serial bus, and/or a processor or local bus that utilizes any of a variety of bus architectures.

The computing system <NUM> also includes a computer-readable medium <NUM>, such as one or more memory devices that enable persistent and/or non-transitory data storage (i.e., in contrast to mere signal transmission), examples of which include random access memory (RAM), non-volatile memory (e.g., any one or more of a read-only memory (ROM), flash memory, EPROM, EEPROM, etc.), and a disk storage device. The disk storage device may be implemented as any type of magnetic or optical storage device, such as a hard disk drive, a recordable and/or rewriteable compact disc (CD), any type of a digital versatile disc (DVD), and the like. The computing system <NUM> can also include a mass storage medium device (storage medium) <NUM>.

The computer-readable medium <NUM> provides data storage mechanisms to store the device data <NUM>, as well as various device applications <NUM> and any other types of information and/or data related to operational aspects of the computing system <NUM>. For example, an operating system <NUM> can be maintained as a computer application with the computer-readable medium <NUM> and executed on the processors <NUM>. The device applications <NUM> may include a device manager, such as any form of a control application, software application, signal-processing and control module, code that is native to a particular device, a hardware abstraction layer for a particular device, and so on.

Claim 1:
A method comprising:
performing (<NUM>) a calibration process that identifies at least one acoustic frequency (<NUM>) suitable for audioplethysmography (<NUM>) using at least one speaker (<NUM>) and at least one microphone (<NUM>, <NUM>); and
using (<NUM>) the at least one acoustic frequency (<NUM>) for performing the audioplethysmography (<NUM>) at an ear (<NUM>) of a user (<NUM>), wherein the audioplethysmography (<NUM>) comprises:
transmitting (<NUM>), by the at least one speaker (<NUM>), an acoustic transmit signal (<NUM>, <NUM>-<NUM>, <NUM>-<NUM>) that propagates within at least a portion of an ear canal (<NUM>) of the user (<NUM>), the acoustic transmit signal including the at least one frequency;
receiving (<NUM>), by the at least one microphone (<NUM>, <NUM>), an acoustic receive signal (<NUM>, <NUM>-<NUM>, <NUM>-<NUM>), wherein the acoustic receive signal (<NUM>, <NUM>-<NUM>, <NUM>-<NUM>) represents a version of the acoustic transmit signal (<NUM>, <NUM>-<NUM>, <NUM>-<NUM>) with one or more waveform characteristics modified due to the propagation within the ear canal (<NUM>); and
determining (<NUM>) at least one physiological metric of the user (<NUM>) based on the one or more modified waveform characteristics of the acoustic receive signal (<NUM>, <NUM>-<NUM>, <NUM>-<NUM>),
wherein the performing (<NUM>) of the calibration process comprises:
transmitting a first acoustic transmit signal (<NUM>-<NUM>) having multiple frequencies, the first acoustic transmit signal (<NUM>-<NUM>) propagating within at least a portion of an ear canal (<NUM>) of the user (<NUM>);
receiving a first acoustic receive signal (<NUM>-<NUM>), the first acoustic receive signal (<NUM>-<NUM>) representing a version of the first acoustic transmit signal (<NUM>-<NUM>) that has one or more waveform characteristics modified based on the propagation within the ear canal (<NUM>); and
selecting the at least one acoustic frequency (<NUM>) from the multiple frequencies based on the one or more waveform characteristics.