Audioplethysmography calibration
Techniques and apparatuses are described that perform 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. The hearable can utilize audioplethysmography to monitor a user's biometrics, recognize facial behaviors, and/or sense an environment using acoustic signals. The techniques for audioplethysmography calibration enable the hearable to dynamically select frequencies that improve the performance of audioplethysmography. With audioplethysmography calibration, the hearable may utilize different frequencies for different ears and these frequencies may change over time.
1 . A method comprising:
performing a calibration process that identifies, from a set of multiple frequencies, at least one acoustic frequency suitable for audioplethysmography using at least one speaker and at least one microphone, the performing of the calibration process comprising:
transmitting a first acoustic transmit signal having the set of multiple frequencies, the first acoustic transmit signal propagating within at least a portion of an ear canal of a user;
receiving a first acoustic receive signal, the first acoustic receive signal representing a version of the first acoustic transmit signal that has one or more waveform characteristics modified based on the propagation within the ear canal; and
selecting the at least one acoustic frequency from the set of multiple frequencies based on the one or more waveform characteristics; and
performing, using the at least one acoustic frequency selected by the calibration process, the audioplethysmography at an ear of the user.
2 . The method of claim 1 , further comprising:
detecting whether an ear canal of the user is at least partially sealed by a device comprising the at least one speaker and/or the at least one microphone; and
responsive to the detecting, initiating the performing of the calibration process.
3 . The method of claim 1 , wherein:
the performing of the calibration process comprises performing a first calibration process at a first ear using a first speaker of the at least one speaker and a first microphone of the at least one microphone;
the using the at least one acoustic frequency comprises using the at least one acoustic frequency for performing the audioplethysmography at the first ear; and
the method further comprises:
performing, at a second ear of the user, a second calibration process that identifies at least one second acoustic frequency suitable for the audioplethysmography using a second speaker of the at least one speaker and a second microphone of the at least one microphone; and
using the at least one second acoustic frequency for performing the audioplethysmography at the second ear.
4 . The method of claim 1 , further comprising:
transmitting audible content during at least a portion of time that the calibration process is performed or during at least a portion of time that the audioplethysmography is performed.
5 . The method of claim 1 , wherein the at least one frequency comprises two or more frequencies from the set of multiple frequencies.
6 . The method of claim 1 , wherein the selecting the at least one acoustic frequency comprises:
demodulating the first acoustic receive signal by mixing a digital version of the first acoustic receive signal with a digital version of the first acoustic transmit signal to generate a first mixed signal;
passing the first mixed signal through a low-pass filter to generate a first filtered signal;
determining a second derivative of the first filtered signal;
identifying zero-crossing frequencies associated with the second derivative of the first filtered signal; and
selecting the at least one acoustic frequency from the zero-crossing frequencies.
7 . The method of claim 1 , wherein the transmitting of the first acoustic transmit signal comprises transmitting the first acoustic transmit signal having a bandwidth of at least four kilohertz.
8 . The method of claim 1 , wherein the first acoustic transmit signal comprises at least one of the following:
an ultrasound signal having frequencies between approximately twenty kilohertz and two megahertz; or
an audible signal having frequencies between approximately twenty hertz and twenty kilohertz.
9 . The method of claim 1 , wherein the performing of the audioplethysmography comprises:
transmitting a second acoustic transmit signal having the at least one acoustic frequency, the second acoustic transmit signal propagating within at least a portion of an ear canal of the user;
receiving a second acoustic receive signal, the second acoustic receive signal representing a version of the second acoustic transmit signal that has one or more waveform characteristics modified based on the propagation within the ear canal; and
determining at least one physiological metric of the user based on the one or more modified waveform characteristics of the second acoustic receive signal.
10 . The method of claim 9 , wherein the determining of the at least one physiological metric of the user comprises:
demodulating the second acoustic receive signal by mixing a digital version of the second acoustic receive signal with a digital version of the second acoustic transmit signal to generate a second mixed signal;
passing the second mixed signal through a low-pass filter to generate a second filtered signal;
generating an autocorrelation of the second filtered signal; and
determining a period of the autocorrelation of the second filtered signal to determine the at least one physiological metric.
11 . The method of claim 9 , wherein the at least one physiological metric comprises at least one of the following:
a heart rate of the user; or
a respiration rate of the user.
12 . A device comprising:
at least one speaker;
at least one microphone; and
at least one processor, the device configured to:
perform, using the at least one speaker, the at least one microphone, and the at least one processor, a calibration process that identifies, from a set of multiple frequencies, at least one acoustic frequency suitable for audioplethysmography, the device is further configured to perform the following as part of the calibration process:
transmit, using the at least one speaker, a first acoustic transmit signal having the set of multiple frequencies, the first acoustic transmit signal propagating within at least a portion of an ear canal of a user;
receive, using the at least one microphone, a first acoustic receive signal, the first acoustic receive signal representing a version of the first acoustic transmit signal that has one or more waveform characteristics modified based on the propagation within the ear canal; and
select, using the at least one processor, the at least one acoustic frequency from the set of multiple frequencies based on the one or more waveform characteristics; and
perform, using the at least one speaker and the at least one microphone, the audioplethysmography at an ear of the user using the at least one acoustic frequency selected by the calibration process.
13 . The device of claim 12 , further comprising:
an active-noise-cancellation circuit comprising the at least one microphone.
14 . The device of claim 13 , wherein the at least one speaker and the at least one microphone are configured to be positioned proximate to one ear of a user.
15 . The device of claim 12 , wherein:
the at least one speaker is configured to be positioned proximate to a first ear of a user; and
the at least one microphone is configured to be positioned proximate to a second ear.
16 . The device of claim 12 , wherein at least one of the at least one speaker or the least one microphone is part of at least one transducer of the device.
17 . The device of claim 12 , wherein the device is configured to at least partially seal one or more ears of a user.
18 . The device of claim 12 , wherein the device comprises:
at least one earbud; or
headphones.
19 . The device of claim 12 , wherein the at least one frequency comprises two or more frequencies from the set of multiple frequencies.
20 . The device of claim 12 , wherein the device is further configured to:
demodulate the first acoustic receive signal by mixing a digital version of the first acoustic receive signal with a digital version of the first acoustic transmit signal to generate a first mixed signal;
pass the first mixed signal through a low-pass filter to generate a first filtered signal;
determine, using the at least one processor, a second derivative of the first filtered signal;
identify, using the at least one processor, zero-crossing frequencies associated with the second derivative of the first filtered signal; and
select, using the at least one processor, the at least one acoustic frequency from the zero-crossing frequencies.