Classifications

• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; ELECTRIC HEARING AIDS; PUBLIC ADDRESS SYSTEMS
  • H04R1/00—Details of transducers, loudspeakers or microphones
  • H04R1/10—Earpieces; Attachments therefor ; Earphones; Monophonic headphones
  • H04R1/1091—Details not provided for in groups H04R1/1008 - H04R1/1083
• • G—PHYSICS
  • G06—COMPUTING OR CALCULATING; COUNTING
  • G06F—ELECTRIC DIGITAL DATA PROCESSING
  • G06F16/00—Information retrieval; Database structures therefor; File system structures therefor
  • G06F16/60—Information retrieval; Database structures therefor; File system structures therefor of audio data
  • G06F16/63—Querying
  • G06F16/635—Filtering based on additional data, e.g. user or group profiles
  • G06F16/636—Filtering based on additional data, e.g. user or group profiles by using biological or physiological data
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; ELECTRIC HEARING AIDS; PUBLIC ADDRESS SYSTEMS
  • H04R1/00—Details of transducers, loudspeakers or microphones
  • H04R1/10—Earpieces; Attachments therefor ; Earphones; Monophonic headphones
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; ELECTRIC HEARING AIDS; PUBLIC ADDRESS SYSTEMS
  • H04R1/00—Details of transducers, loudspeakers or microphones
  • H04R1/10—Earpieces; Attachments therefor ; Earphones; Monophonic headphones
  • H04R1/1041—Mechanical or electronic switches, or control elements
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; ELECTRIC HEARING AIDS; PUBLIC ADDRESS SYSTEMS
  • H04R27/00—Public address systems
  • H04R27/02—Amplifying systems for the deaf
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; ELECTRIC HEARING AIDS; PUBLIC ADDRESS SYSTEMS
  • H04R29/00—Monitoring arrangements; Testing arrangements
  • H04R29/001—Monitoring arrangements; Testing arrangements for loudspeakers

Definitions

• the present invention relates generally to the provision of an auditory stimulus by one or more loudspeakers, such as consumer headphones or earphones, and in particular to the personalization of the auditory stimulus produced by such loudspeakers in order to adjust for the unique characteristics of a user's hearing.
• loudspeakers such as consumer headphones or earphones
• Audio headphones are generally designed to transduce an electronic input signal to an acoustic wave across a frequency range with the expectation that all users hear in the same way.
• Standard audio headphones are unable to take into account differences in conductive and sensorineural hearing in users. Hearing loss is experienced by many people, especially with aging, and even people with "normal hearing” have varying sensitivity to different frequencies of sound. The clinical definition of "normal” hearing is wide (i.e., thresholds between -10 to +25dB across frequency).
• headphones on a user's head include a sensor and a speaker. While the speaker plays an audio signal to the user, the sensor records the user's response to the audio signal.
• the sensor can be a microphone, a brainwave sensor, an EEG sensor, etc.
• the user's response can be the audio response inside the user's ear, the brainwave response associated with the user, the electrical skin response associated with the user, etc. Based on the measured response, and based on the knowledge of how people perceive sound, the audio signal is modified to compensate for the difference between the user's hearing and ideal hearing and/or desired hearing, therefore increasing the user's enjoyment of sound.
• FIG. J depicts a set of headphones including a dry electrode or capacitive sensors, speakers, and a signal processing module, according to one embodiment.
• FIG. 2 is a schematic diagram depicting the electrical components of the signal processing module located within each of the housings of the headphones, according to one embodiment.
• FIG. 3 depicts an alternative arrangement to that shown in FIG. 1, according to one embodiment.
• FIG. 4A is a schematic diagram of the electrical components of the digital signal processing module of the earbud arrangement shown in FIG. 3, according to one embodiment.
• FIG. 4B shows a schematic of a probe for measurement of distortion-product otoacoustic emissions (DP-OAE), according to one embodiment.
• FIG. 4C shows a frequency response of each speaker in FIG. 4B, according to one embodiment.
• FIG. 4D is a flowchart of the digital signal processing algorithm for measuring the hearing transfer function and/or the hearing profile associated with the user, using the probe in FIG. 4B, according to one embodiment.
• FIG. 5 is a flowchart depicting the signal processing operation performed by the signal processing modules depicted in FIGS. 2 and 4, according to one embodiment, [0017]
• FIG. 6 depicts the frequency response in the time domain of a representative normal ear compared to an ear with mild hearing loss.
• FIG. 7 shows the RMS amplitude of an auditory evoked potential response in the frequency domain of a normal ear and an ear with mild hearing loss.
• FIG. 8A shows Fourier analysis of the low-pass filtered outputted sound signal and EEG (frequency following response), according to one embodiment.
• FIG. 8B is a flowchart of a technique to determine a low frequency portion of the hearing transfer function, according to one embodiment.
• FIG. 9 A shows information about the high frequency hearing which is obtained by analyzing the EEG signal after acoustic transients, according to one embodiment.
• FIG. 9B is a flowchart of a technique to determine a high frequency portion of the hearing transfer function, according to one embodiment.
• FIG. 10 depicts an example of distortion product OAE fine structure, according to one embodiment.
• FIG. 1 depicts an embodiment of this invention where the OAE probe also functions as a set of headphones for consumer audio use.
• Ideal hearing is the average level of perception across the audible frequency spectrum of young, ontologically normal ears when a constant amplitude across the audible frequency spectrum is provided as the audio stimulus.
• “Desired Hearing” is the desired level of perception across the audible frequency spectrum when a constant amplitude across the audible frequency spectrum is provided as the audio stimulus.
• the desired hearing profile can be arbitrarily set and may or may not be set as ideal hearing profile.
• Normal hearing is a range around the ideal hearing. Many people are considered to have “normal hearing,” meaning that their hearing sensitivity is within 15- 20 dB of ideal hearing across frequencies, [0029] "Hearing transfer function" correlates a given input frequency and a corresponding input amplitude associated with an input audio signal, to a perceived amplitude of the given input frequency.
• Hearing profile comprises a set of measurements of a person's hearing based on which that person's hearing transfer function can be estimated.
• “Channels of audio” are separate audio signals coming from one source or separate sources. Multiple channels of audio could be combined and played through the same speaker or they could be played from separate speakers.
• Statistical information representing data regarding human hearing profiles is a collection of statistics regarding the hearing profiles of many people. Statistical information comprises one or more of: the average of human hearing profiles at one or more frequencies, the standard deviation of human hearing profiles at one or more frequencies, hearing profiles or hearing transfer functions of individual listeners, and correlations between types of objective or subjective hearing data.
• Reference in this specification to "one embodiment” or “an embodiment” means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the disclosure.
• the appearances of the phrase “in one embodiment” in various places in the specification do not necessarily all refer to the same embodiment, nor are separate or alternative embodiments mutually exclusive of other embodiments.
• various features are described that may be exhibited by some embodiments and not by others.
• various requirements are described that may be requirements for some embodiments but not others.
• the words “comprise,” “comprising,” and the like are to be construed in an inclusive sense as opposed to an exclusive or exhaustive sense; that is to say, in the sense of "including, but not limited to.”
• the terms “connected,” “coupled,” or any variant thereof means any connection or coupling, either direct or indirect, between two or more elements.
• the coupling or connection between the elements can be physical, logical, or a combination thereof.
• two devices may be coupled directly, or via one or more intermediary channels or devices.
• devices may be coupled in such a way that information can be passed therebetween, while not sharing any physical connection with one another.
• module refers broadly to locally executed software, software executed in the cloud, hardware, or firmware components (or any combination thereof). Modules are typically functional components that can generate useful data or other output using specified input(s). A module may or may not be self-contained. An application program (also called an "application”) may include one or more modules, or a module may include one or more applications.
• FIG. 1 depicts a set of headphones including a dry electrode or capacitive sensors, speakers and an electronics module including a signal processing module, according to one embodiment.
• a set of headphones 10 includes the speakers 12 and 14 located within cups 16 and 18 in order to position the speakers 12 and 14 close to both of a user's ears.
• the two cups 16 and 18 are coupled to an adjustable head support member 20.
• housings 22 and 24 housing electrical/electronic modules and interface units, the function of which is described below.
• FIG. 2 is a schematic diagram depicting the electrical components located within each of the housings 22 and 24 of the headphones 10, according to one embodiment.
• the electronics module 40 includes a signal processing module 42, wired or wireless connections 60 and 62 (such as an audio input jack or Bluetooth module), and an external microphone 32, 34 for noise cancellation.
• the signal processing module 42 further includes anal og-to-di gital and/or digital-to-analog converters 48 to 54 for interfacing with external digital or analog devices, together with a power source 56 providing power to the signal processing module 42.
• Interconnected to the signal processing module 42 are an interface for external microphones 32 and 34, a wired or wireless connection 60 for receiving digital or audio analog signal inputs, as well as a wired or wireless connection 62 for digital data transfer, for example, to change stored settings maintained in the memory 46 of the signal processing module 42 to control operation of the processor 44 or to output audiometric data for display on a smartphone.
• the wired connection can be a phone jack, while the wireless connection can be a Bluetooth module.
• the external microphones 32 and 34 are used by the signal processing module 42 to record ambient noise for use in noise cancellation operations. However, in other embodiments the signal processing module 42 may exclude results if ambient noise recorded by the microphones is too high.
• the dry electrode or capacitive sensors 26, 28, and 30 are interconnected via the anal og-to-di gital converter 54.
• the loudspeakers 12 and 14 are interconnected to the signal processing module 42 by means of a digital-to-analog converter 52 and amplifier.
• an internal microphone 64 is provided for calibration of the operations of the headphones 10.
• the signal processing module 42 is also adapted to receive audiometric data 66 via the wired or wireless connection 62.
• the audiometric data 66 characterizes the audible threshold or equal loudness curve of the user across a frequency range.
• that audiometric data 66 may be provided by an external source; for example, the results of an audiogram testing process may be provided by an audiologist.
• the audiometric data 66 can be input via a wired or a wireless connection 62 into the signal processing module 42.
• user controls such as a button 68, may be provided on the headset 10 to enable the user to generate input signals to the processor 44 in response to the user's perception of auditor ⁇ ' stimuli provided by the loudspeakers 12 and 14.
• FIG. 3 depicts an alternative arrangement to that shown in FIG. 1, according to one embodiment.
• An earbud 70 arrangement adapted to be located within the ear canal of one of a user's ears includes two speakers 84 and 86, an internal microphone 82, and an optional external microphone.
• the earbud 70 is connected to an electronics module 72 similar to that located in the housings 22 and 24 of the headset 10 depicted in FIG. 1.
• FIG. 4A is a schematic diagram of the electrical and electronic components of the earbud 70 arrangement shown in FIG. 3, according to one embodiment.
• the electronics module 72 includes a signal processing module 74, wired or wireless connections 76 and 78 (such as an audio input jack or wireless module), and an optional external microphone 80 for noise cancellation.
• the internal microphone 82 for calibration and for measurement of otoacoustic emissions (OAEs) is co-located with the earbud 70, as are the loudspeakers 84 and 86 that form part of the earbud 70. In this arrangement, two speakers per ear are included to allow measurement of distortion-product otoacoustic emissions.
• OAEs otoacoustic emissions
• DP-OAEs Distortion-product otoacoustic emissions
• DP-OAEs Distortion-product otoacoustic emissions
• the processing unit 74 includes a processor 88 for executing operations of the processing unit, a memory 90 for storing programming instructions and data used by the processor 88 during program execution, a power source 92, such as a batten,', for providing power to the various electronic components in the processing unit 74, as well as analog-to- digital or digitai-to-anaiog converters 94, 96, and 98 in order to enable the processing unit 74 to interface with the various devices such as external microphone 80, internal microphone 82, and speakers 84 and 86.
• the processing unit 74 is adapted to receive audiometric data 100 via wired or wireless connection 78 from an external source, such as an audiogram test result provided by an audiologist.
• FIG. 4B shows a schematic of a probe for measurement of distortion-product otoacoustic emissions, according to one embodiment.
• DP-OAE probe 1 includes two balanced armature speakers, a woofer 2 and a tweeter 3, and a microphone 9.
• the microphone 9 is connected to a preamplifier 4 and analog-to-digital converter 5.
• the speakers 2 and 3 are connected to a dual-channel headphone amplifier 6, which is connected to a dual- channel digital-to-analog converter 7.
• Converters 5 and 7 are connected to a digital signal processor 8, which provides equalization to control the stimuli loudness in test mode, playback equalization (if desired) and a digital crossover to the two receivers.
• An embodiment of this invention includes one probe for each ear.
• FIG. 4C shows a frequency response of each speaker in FIG. 4B, according to one embodiment.
• Both woofer 2 and tweeter 3 are capable of generating stimuli of sufficient loudness over the standard audiological testing frequency and loudness range, which is approximately 250 Hz to 8000 Hz up to 80 dB sound pressure level (SPL).
• SPL sound pressure level
• FIG. 4D is a flowchart of the digital signal processing algorithm for measuring the hearing transfer function and/or the hearing profile associated with the user, using the probe in FIG. 4B, according to one embodiment.
• the digital signal processor 8 receives an audio input which may be the test audio signal and/or the audio playback signal comprising audio content such as music, speech, environment sounds, animal sounds, etc.
• the audio signals can be input via an analog or digital, wired or wireless audio interface 76 (shown in FIG. 4A), or can be stored in memory 90 (in FIG. 4A), and/or memory 46 (in FIG. 2).
• the processor 8 determines whether the mode is in a testing or playback mode.
• step 15 if the mode is testing mode, the processor 8 applies a first and a second filter to the audio input, corresponding to the woofer 2 (in FIG. 4B) and the tweeter 3 (in FIG. 4B), respectively.
• the first and the second filter are no- operation filters or filters that provide a flat frequency response from the speakers allowing calibrated test stimuli to be played to the speakers 2 and 3.
• step 17 if the mode is playback mode, the processor 8 applies a third and a fourth filter to the audio input, corresponding to the woofer 2 and the tweeter 3, respectively.
• the third and the fourth filters include low-pass and high-pass filters respectively, creating a digital crossover.
• the processor 8 sends the audio signal to the digital-to-analog converter 7 (in FIG. 4B).
• FIG. 5 is a flowchart depicting the signal processing operation performed by the signal processing modules depicted in FIGS. 2 and 4, according to one embodiment.
• Each memory 46 and/or 90 in step 1 10, stores a copy of the hearing transfer function for each of the user's ears.
• the memory 46 and/or 90 can be a remote database storing various needed information.
• each processor 8, 44 or 88 receives an audio signal corresponding to a sound that is desired to be reproduced by the loudspeakers of either the headset 10 or the earbud 1, 70.
• an input audio signal is received at step 118 by the external microphone 32, 34, and/or 80, and at step 120, the processor 8, 44, and/or 88 performs a noise cancellation function in order to minimize the impact of ambient noise on the audio signal input in step 116.
• the processor 8, 44, and/or 88 uses the stored hearing transfer function, the stored estimate of the accuracy and completeness of the hearing transfer function, and optionally the user preference for a degree of correction to be applied to the hearing transfer function, to make frequency-specific adjustments for amplitude and phase to automatically compensate for a user's hearing transfer function.
• the correction need not attempt to completely correct the sound. For example, only a partial correction may be applied if the accuracy or completeness of the hearing transfer function is low, as is described below, or according to a preference of the user.
• the processor 8, 44, or 88 may also be configured to limit a sound output signal that may be perceived to be dangerously loud by a user.
• the processor 8, 44, and/or 88 modifies the input audio signal so that the user perceives the input audio signal, as if the user had ideal hearing and/or desired hearing.
• the processor 8, 44, and/or 88 can modify the amplitude, the phase, the latency, etc., of the input audio signal. Since the response of a human ear to varying amplitudes at a given frequency is not linear, the processor 8, 44, and/or 88 can determine how to modify the input audio signal in several ways.
• the desired hearing can be set by the user. For example, the user can specify to amplify a specified frequency range, such as low frequencies, mid frequencies, or high frequencies. In another example, the user can specify to attenuate a specified frequency range, such as low frequencies, mid frequencies, or high frequencies. The amplification and the attenuation can happen independently, or at the same time.
• the processor 8, 44, and/or 88 receives a plurality of hearing profiles associated with a plurality of people.
• the plurality of hearing profiles can be received via a wired or wireless connection 62 (in FIG. 2), and/or 78 (in FIG. A), or can be stored in memory 46 (in FIG. 2), and/or 90 (in FIG. 4A).
• a hearing profile in the plurality of hearing profiles comprises a hearing transfer function associated with a person, and a perceived amplitude of the input frequency as the input amplitude associated with the input frequency varies.
• the processor 8, 44, and/or 88 finds one or more similar hearing profiles that closely match the hearing transfer function associated with the user. Based on the similar hearing profiles, the processor 8, 44, and/or 88 determines by how much to vary the input audio signal so that the user perceives the input audio signal, as if the user had ideal hearing and/or desired hearing.
• the hearing transfer function associated with a user specifies that an input audio signal comprising 1000 Hz at 70 dB, is perceived by the user as having 25 dB, while an input audio signal comprising 2000 Hz at 70 dB, is perceived by the user is having 50 dB.
• the processor 8, 44, and/or 88 determines a set of similar hearing profiles from the plurality of hearing profiles, where a similar hearing profile is associated with a person who perceives 1000 Hz to be roughly 25 dB (i.e. 20 dB to 30 dB) softer than 2000 Hz.
• the hearing profiles contain information regarding what modified amplitude the 1000 Hz signal needs to be so that the person perceives the amplitude of an input signal of 1000 Hz at 70 dB to be the same as the amplitude of an input signal of 2000 Hz at 70 dB.
• the processor 8, 44 and/or 88 averages the modified amplitudes associated with the similar hearing profiles, to obtain the modified amplitude associated with the user.
• the hearing transfer function associated with a user specifies that an audio signal comprising 1000 Hz at 70 dB, is perceived by the user as having 45 dB
• the processor 8, 44, and/or 88 determines a set of hearing profiles, in which a person perceives 1000 Hz to be roughly 25 dB softer than the input amplitude.
• the hearing profiles contain information regarding what modified amplitude the 1000 Hz signal needs to be so that the person perceives an input audio signal of 1000 Hz at 70 dB to be 70 dB
• the processor 8, 44 and/or 88 averages the modified amplitudes associated with the hearing profiles, to obtain the modified amplitude associated with the user.
• the processor 8, 44, and/or 88 modifies the input signal accordingly.
• the processor 8, 44, and/or 88 does not receive the plurality of hearing profiles associated with the plurality of people. Instead, the processor measures a hearing profile associated with the user, by playing an input audio signal comprising varying amplitudes at a single frequency.
• the input audio signal can be a generated test audio signal, and/or a content audio signal comprising music, speech, environment sounds, animal sounds, etc.
• the input audio signal can include the content audio signal with an embedded test audio signal .
• the hearing transfer function associated with a user specifies that an audio signal compri sing 1000 Hz at 70 dB, is perceived by the user as having 60 dB while a 1500 Hz at 70 dB, is perceived by the user is having 50 dB.
• the hearing profile associated with the user specifies that, in order for the user to perceive 1000 Hz and 1500 Hz at equal loudnesses there must be a relative increase in the 1500 Hz loudness of 10 dB.
• the processor 8, 44, and/or 88, in step 122 modifies the input signal accordingly.
• the processor 8, 44, and/or 88 receives statistical information representing data regarding human hearing profiles.
• the statistical information can be received via a wired or wireless connection 62 (in FIG. 2), and/or 78 (in FIG. 4A), or can be stored in memory 46 (in FIG. 2), and/or 90 (in FIG. 4A),
• statistical information representing data regarding human hearing profiles could include the average and standard deviation of human hearing profiles at one or more frequencies. It may also include correlations between types of objective or subjective hearing data.
• the processor 8, 44, and/or 88 determines one or more similar hearing profiles that closely match the hearing transfer function associated with the user.
• the processor constructs a plurality of hearing profiles that are similar to the hearing transfer function associated with the user. Based on the similar hearing profiles, the processor 8, 44, and/or 88 determines by how much to vary the input audio signal so that the user perceives the input audio signal, as if the user had ideal hearing and/or desired hearing.
• the processor 8, 44, and/or 88 continues to refine the hearing transfer function associated with a user, as the user continues to listen to audio.
• the modified audio signal from the processor 8, 44, or 88 is then output at step 124 to the loudspeakers 12 and 14 or 84 and 86 to produce an auditor ⁇ ' stimulus to one or both of the user's ears.
• the hearing transfer function stored in the memory 46 or 90 may be generated in a number of ways, namely by subjective measurement, by otoacoustic emissions (OAE), auditor ⁇ - evoked potentials (AEP), or other objective tests such as the middle ear reflex.
• OAE otoacoustic emissions
• AEP auditor ⁇ - evoked potentials
• Other objective tests such as the middle ear reflex.
• Audiometric measurements performed by an audiologist or via a computer program or the like can be provided to the signal processing modules 42 and 74 from an external source.
• the button 68 or other user controls on the headphones 10 can be used by a user to directly acquire auditory threshold data by having the user press the button in response to sound signals.
• an auditory stimulus can be played to the user at increasing or decreasing amplitudes at different frequencies across the audible frequency range.
• a convenient psychophysical test is a pure tone audiometry with which the user interacts in order to determine their audible threshold of hearing.
• a test can be conducted at the same loudness but at different frequencies, namely an "Equal Loudness Contours" test.
• OAE Otoacoustic emissions
• Otoacoustic emissions can be measured within the user's ear canal and then used to determine thresholds at multiple frequencies or relative amplitudes of the otoacoustic emissions at multiple frequencies to one or more suprathreshold sound levels in order to develop the frequency dependent hearing transfer function of the user's ear(s).
• Stimulus frequency OAE, swept-tone OAE, transient evoked OAE, DP-OAE, or pulsed DP-OAE can be used for this purpose.
• the amplitude, latency, hearing threshold, and/or phase of the measured OAEs can be compared to response ranges from normal-hearing and hearing-impaired listeners to develop the frequency dependent hearing transfer function for each ear of the user.
• one stimulus frequency/loudness combination yields a response amplitude.
• the measurement of multiple frequencies in this manner yields a plot of response amplitude versus frequency, which is stored in the memory 46 or 90 of the signal processing modules 42 or 74, or can be stored in a remote database.
• Many OAE techniques rely upon the measurement of one frequency per stimulus; however, the swept tone OAE measures all frequencies in the range of the sweep.
• the hearing transfer function remains the same regardless of the measuring method used, that is, the hearing transfer function comprises a plot of the signal amplitude versus frequency of the OAE evoked in the user's ear upon application of an input audio signal.
• the hearing transfer function can also comprise the input amplitude associated with the input frequency.
• the processor 8, 44, and/or 88 captures data points for an input audio signal comprising a number of frequencies, for example, 500, 1000, 2000 and 4000 Hz, which are typically the same frequencies used in the equalizer that acts upon the output sound signal to the loudspeakers 12 and 14, 84 and 86, 2 and 3.
• the processor measures the response to an input audio signal at reducing levels, for example, at 70 dB, 60 dB, 50 dB, 40 dB, etc., until there is no longer a measurable response.
• the processor 8, 44, and/or 88 records the data point at that time.
• the input audio signal can include a test audio signal, and/or a content audio signal comprising music, speech, environment sounds, animal sounds, etc.
• the input audio signal can include the content audio signal with an embedded test audio signal,
• In-situ calibration of the speakers to the user's ear canal can be performed by the processor 8, 44, and/or 88 prior to making an OAE measurement.
• in-situ refers to measurements made at times when the speakers and microphone are situated for use inside the ear canal. Where the acoustic characteristic of the speakers are known, the acoustic impedance of the ear can be calculated from this data and utilized for deriving corrections.
• in-situ calibration can be done by playing a test audio signal, such as a chirp, or the content signal, covering the frequency range of the speakers, recording the frequency response with the microphone, and adjusting output by changing the equalizer settings to make a flat frequency response of the desired loudness.
• a test audio signal such as a chirp, or the content signal
• this calibration can be done in real time to any playback sound (e.g., music, or any audio comprising content) by constantly comparing the predicted output of the speakers in the frequency domain given the electric input to the speaker to the microphone and altering the equalizer gains until they match.
• the in-situ calibration accounts for variations in different users' external portion of the ear and variations in the placement of earbuds. If no audiometric data is yet available, then the in-situ calibration alone can be used for adjusting the sound. [0079] Any variation with an internal microphone can use that microphone for in-situ calibration of the speakers performed every time the user places the headphones on.
• AEPs involve the measurement of nanovolt range signals from the dry electrode or capacitive sensors 26, 28, and 30 depicted in FIG. 1. [0081] In order to boost the signal-to-noise ratio of the AEPs, multiple repetitions of auditory stimuli are generally required to be applied.
• AEPs are measured using wet electrodes after preparing the skin by gentle abrasion. This is impractical for use in consumer audio headphones, which is why dry electrodes and/or capacitive sensors are used in this case.
• multiple repetitions of stimuli are generally required, which means that the hearing transfer function estimation generally takes a longer period of time or, alternatively, is less accurate than in the case when wet electrodes are used.
• Any AEP can be measured, such as auditory brainstem response, mid latency response, cortical response, acoustic change complex, auditory steady state response, complex auditory brainstem response, electrocochleography, cochlear microphonic, or cochlear neurophonic AEPs.
• the frequency dependent hearing transfer function for each ear is determined by the processor 8, 44, and/or 88 by using frequency-specific stimuli, such as tones or band- limited chirps, or audio content signal, such as music or speech, which are used as the auditor ⁇ ' stimuli applied to the user's ear, and thereafter determining either frequency-specific thresholds or using one or more suprathreshold sound levels and determining relative amplitudes and/or latencies of the AEP responses.
• frequency-specific stimuli such as tones or band- limited chirps
• audio content signal such as music or speech
• Comparisons of amplitude, latency, hearing threshold and/or phase can be made to response ranges from normal-hearing and hearing-impaired listeners to develop an hearing transfer function for each ear.
• the response ranges of normal-hearing and hearing-impaired listeners can be maintained in the memory 46 or 90 for use by the processor 8, 44, and/or 88 in such an operation.
• methods applied by the processor 8, 44, and/or 88 include the use of a peak picking algorithm, or a window root mean square (RMS) measure of the response compared to baseline RMS or a frequency-specific RMS of the signal above baseline noise.
• RMS window root mean square
• other methods are well described, such as in Valderrama, Joaquin T., et al. "Automatic quality assessment and peak identification of auditor ⁇ ' brainstem responses with fitted parametric peaks," Computer methods and programs in biomedicine 1 14.3 (2014): 262- 275,
• FIG. 6 depicts the frequency response in the time domain of a representative normal ear compared to an ear with mild hearing loss.
• FIG. 7 shows the RMS amplitude of an auditory evoked potential response in the frequency domain of a normal ear and an ear with mild hearing loss.
• the solid line depicts an hearing transfer function associated with the normal ear
• the dashed line depicts an hearing transfer function associated with the ear with a mild hearing loss.
• ASSR auditory steady state response
• cABR complex auditory brainstem response
• ® Transient features of sound such as sudden onsets at the start of speech, a musical note, or a drum beat, cause extra cABR-like waveforms in the EEG waveform.
• ® cABR analyses can also be adapted to estimate an ear's hearing transfer function in response to continuous sound, such as music.
• FIG. 8A shows Fourier analyses of the low-pass filtered outputted sound signal and EEG (frequenc following response), according to one embodiment.
• the low-pass filtered output signal and the EEG frequency following response provide the low frequency part of the hearing transfer function. Frequency domain averaging is required due to the low signal-to-noise ratio (SNR).
• SNR signal-to-noise ratio
• FIG. 8B is a flowchart of a technique to determine a low frequency portion of the hearing transfer function, according to one embodiment.
• the processor 8, 44, and/or 88 repeatedly performs Fourier transforms and/or fast Fourier transforms of the audio signal and the response, such as an EEG response.
• the audio signal comprises multiple frequency ranges, such as 125, 250, 500, and 1000 Hz.
• the processor 8, 44, and/or 88 determines loudness for each frequency range and the amplitude of the detected response, such as an EEG response.
• the processor 8, 44, and/or 88 continuously builds an average value of the multiple frequency range/1 oudness pairs. This technique is easier and more accurate than the high frequency version; but the body low-pass filters the response, so this technique works less well with increasing frequency.
• FIG. 9A shows information about the high frequency hearing which is obtained by analyzing the response, such as an EEG response signal after acoustic transients, according to one embodiment.
• Element 900 is the input audio signal.
• Element 910 is the signal obtained from a sensor, such as an EEG sensor.
• Elements 920 are the detected peaks in the input audio signal 900.
• FIG. 9B is a flowchart of a technique to determine a high frequency portion of the hearing transfer function, according to one embodiment.
• the processor 8, 44, and/or 88 identifies the transients in the output sound, for example, by detecting the sound volume moving from below a threshold to a certain level above that threshold over the course of a few milliseconds.
• the processor 8, 44, and/or 88 determines the stimulated part of the cochlea by performing a Fourier analysis to the first few milliseconds of the transient.
• a Fast Fourier Transform is performed on the first few milliseconds of transients to identify the excited part of the cochlea (hypotheticaily 1 kHz) in the loudness of the stimulus.
• the processor 8, 44, and/or 88 checks whether the baseline noise from the sensor is acceptable, for example, whether it is less than 10 ⁇ RMS, in the time immediately preceding the transient.
• the noise on the signal such as an EEG signal
• the processor 8, 44, and/or 88 continuously repeats the above steps when the user listens to music, to work out an average value for multiple frequency/loudness pairs.
• comparisons of both amplitude and phase can be compared to response ranges from normal-hearing and hearing-impaired listeners by the processor 8, 44, and/or 88 in order to develop the frequency-dependent hearing transfer function for each ear of the user.
• OAEs and ASSRs can give a response phase in addition to signal magnitude.
• one of these two techniques should be used.
• the processor 8, 44, and/or 88 may only be able to compare amplitude.
• the processor 8, 44, and/or 88 effectively implements a finite input response (FIR) filter fitted with magnitudes to minimize the effect of hearing loss and phase- shifts (for embodiments where phase information from the objective audiometric measures is available) to make the user's perception of the audio signal the same as the perception of an ideal-hearing person.
• FIR finite input response
• the frequency-dependent hearing transfer function for a user's ear is entirely composed of gains for each frequency band as discussed previously, for example, 500, 1000, 2000 and 4000 Hz.
• gains for example, 500, 1000, 2000 and 4000 Hz.
• Two practical ways of setting the gains are firstly to simply set the gain according to the difference between detected audible threshold and the amplitude from the hearing transfer function of an ideal-hearing profile.
• the relative amplitudes of the AEP/OAE at multiple frequencies can be compared to one or more suprathreshold sound levels.
• the equalizer gains are adjusted accordingly by the processor 8, 44, and/or 88. It will be appreciated that different users may have different head sizes, more hair, thicker skin, etc., so it is the actual ratio between the values for the different frequencies rather than the absolute values that the processor 8, 44, and/or 88 compensates for, as depicted in FIGS. 6 and 7.
• a complete hearing transfer function of the user's ears can be made on request from the user.
• a complete hearing transfer function of the user's ears can be made the first time the user places the headphones on, or the first time the user listens to audio.
• a partial hearing transfer function can be measured each time the user places the headphones on, or each time the user listens to audio, which over time becomes a full hearing transfer function, once a full hearing transfer function is complete, further partial hearing transfer functions iteratively improve the stored function.
• ® Partial hearing transfer functions can be interleaved between songs or during any time when audio is being input into the device.
• the EEG recording is made continuously during any time audio is playing. Many hours of audio are required to acquire enough transient events to estimate the high frequency part of the hearing transfer function.
• Any external or internal microphone can also be used to decide if the ambient noise level is too high for accurate objective or psychophysical measurements and measurements not made during such times.
• a normalized hearing transfer function can be input into the processor 8, 44, and/or 88, for example, by wireless or wired connection to the Internet by synching to a smartphone app, for subsequent storage in the memory 46 and/or 90.
• This normalized hearing transfer function can then be used by the processor 8, 44, and/or 88 during the performance of the above-described functions.
• an hearing transfer function can also be derived by the processor 8, 44, and/or 88 from audiometric data using more complicated methods similar to those used in hearing aid fitting rules described in the following sources:
• FIG. 10 depicts an example of distortion-product OAE fine structure, according to one embodiment.
• the figure is adapted from Shaffer, Lauren A., et al. "Sources and mechanisms of DP-OAE generation: implications for the prediction of auditory sensitivity.” Ear and hearing 24.5 (2003): 367-379.
• Element 1000 is the cubic difference tone
• element 1010 is the noise for inside a user's ear. Assume primary tone fl is lower in frequency and primary tone f2 is higher in frequency.
• the cubic difference tone 1000 is generated from two separate sites within the cochlea, a primary and a secondary site, the signals from each constructively and destructively interfere with each other, making crests and troughs in the response.
• the pattern of the specific locations (in the frequency domain) of the crests and troughs is called fine structure and is unique to each ear.
• the cubic difference tone 1000 response from a user can be compared to a plurality of cubic difference tones stored in a database.
• the database can be integrated into the headphones 1, 10, 70, or it can be a remote database.
• the processor 8, 44, and/or 88 compares the measured cubic difference tone 1000 and the plurality of cubic difference tones stored in the database to identify the subject.
• the processor 8, 44, and/or 88 uses a match score such as a root mean square error to make the comparison. For example, the processor, 8, 44, and/or 88 selects the cubic difference tone with the best match score, such as the cubic difference tone with the lowest root mean square error. If the selected cubic difference tone match score satisfies a specified threshold, such as the root mean square error is below 25%, the match is found. If the selected cubic difference tone does not satisfy the threshold requirement, no identification/authentication is made. When a match is found, the processor retrieves a user ID associated with the matched cubic difference tone. [00109] According to one embodiment, biometric data associated with the user, such as the head with of the user, can be used to improve the accuracy of the identification.
• a user's perception of sound i.e., the hearing transfer function
• the hearing transfer function can be measured using any of the above-disclosed methods, such as the subjective method, AEP, EEG, etc.
• Each user hearing transfer function is unique.
• the user hearing transfer function is stored in the database, such as a database integrated into the headphones 1, 10, 70, or a remote database.
• the processor 8, 44, and/or 88 compares the measured hearing transfer function to the user hearing profiles in the database to identify the subject.
• the headphones can modify the sound according to the user hearing profile, can load and play a playlist associated with the identified user, etc.
• the user identification on its own, or with other methods, can be used for security purposes as well.
• FIG. 11 depicts an embodiment of this invention where the OAE probe also functions as a set of headphones for consumer audio use.
• the probe 1 from FIG. 4B is duplicated on the other ear and connected to a wired or wireless analog or digital audio interface 1 100,
• the microprocessor 1110 controls measurement of the biometnc profile and performs analysis. If no discrepancy is found, the audio information is routed to the speakers.

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