Feedforward Instability Detection in Wearable Audio Devices

Abstract

A system for detecting feedforward instability in a wearable audio device is provided. The audio device includes an electroacoustic transducer configured to generate sound for a user, a housing that holds the transducer, a feedforward microphone configured to detect sound outside the housing and output a microphone signal, and an opening in the housing through which sound pressure from the transducer can reach the microphone. The feedforward instability detector is configured to apply two filters to the microphone signal. A first filter passes more energy in a frequency band than a second filter to produce a filtered signal. The filtered signal is compared to the microphone signal outside the frequency band to produce a comparison signal indicative of feedforward instability in the frequency band.

Description

[Technical field]

[0001] The present disclosure relates to wearable audio devices. [Background technology]

[0002] Wearable audio devices such as earphones and hearing aids can generate parasitic vibrations in the feed-forward loop that can result in undesirable instabilities and squealing noises. Summary of the Invention

[0003] All embodiments and features mentioned below can be combined in any technically possible manner.

[0004] In one aspect, a system is provided for detecting feedforward instability in a wearable audio device that includes an electroacoustic transducer configured to generate sound for a user, a housing that holds the transducer, a feedforward microphone configured to detect sound outside the housing and output a microphone signal, and an opening in the housing through which sound pressure from the transducer can reach the microphone, the system including a feedforward instability detector configured to apply two filters to the microphone signal, a first filter passing more energy in a frequency band than the second filter to generate a filtered signal, and comparing the filtered signal to a microphone signal outside the frequency band to generate a comparison signal indicative of feedforward instability in the frequency band.

[0005] Some examples include one of the above and / or the following features, or any combination thereof. In one example, the wearable audio device includes an earphone configured to output sound directly to the user's ear canal. In one example, the feedforward microphone is used in an active noise reduction (ANR) system. In one example, the feedforward microphone is used in a transmission mode in which environmental sounds are reproduced by the transducer. In one example, the first filter includes a peak filter. In one example, the second filter includes a notch filter. In one example, the feedforward instability detector is configured to apply multiple sets of detection and rejection filters in different frequency bands.

[0006] Some examples include one of the above and / or the following features, or any combination thereof. In one example, the first filter and the second filter jointly detect parasitic vibrations within a predetermined frequency range. In one example, the frequency range is centered around 3,100 Hz. In one example, the detector is further configured to apply a threshold energy level to the first filtered energy. In one example, feedforward instability is indicated only if an energy level of the energy passed by the first filter is above the threshold.

[0007] Some examples include one of the above and / or the following features, or any combination thereof. In one example, feedforward instability is indicated when an energy level of the energy passed through the first filter is greater than an energy level of the energy passed through the second filter. In some examples, feedforward instability is indicated when an energy level of the energy passed through the first filter remains greater than an energy level of the energy passed through the second filter for at least a threshold amount of time. In one example, feedforward instability is indicated when an energy level of the energy passed through the first filter is greater than an energy level of the energy passed through the second filter for at least a threshold amount of time, and a microphone signal outside the frequency band is greater than a signal level threshold.

[0008] Some examples include one of the above and / or the following features, or any combination thereof. In one example, the system further includes an instability reducer configured to adjust a gain applied to the microphone signal. In some examples, the gain is reduced for a predetermined amount of time. In one example, after a predetermined amount of time, the gain is increased back to its original value. In one example, the increase in gain occurs gradually over a predetermined period of time. In one example, the gain is adjusted in a frequency dependent manner.

[0009] In another aspect, a computer program product having a non-transitory computer readable medium including computer program logic encoded thereon is provided that, when executed on a wearable audio device including an electroacoustic transducer configured to generate sound for a user, a housing holding the transducer, a feedforward microphone configured to detect sound outside the housing and output a microphone signal, and an opening in the housing through which sound pressure from the transducer can reach the microphone, causes the wearable audio device to apply two filters to the microphone signal, a first filter passing more energy in a frequency band than the second filter to produce a filtered signal, and compare the filtered signal to the microphone signal outside the frequency band to produce a comparison signal indicative of feedforward instability in the frequency band.

[0010] Some examples include one of the above and / or the following features, or any combination thereof: In one example, the wearable audio device comprises an earphone configured to output sound directly to the user's ear canal. [Brief description of the drawings]

[0011] [Figure 1] FIG. 1 is a perspective view of a wearable audio device. [Diagram 2] FIG. 2 is a partial cross-sectional view of a wearable audio device. [Diagram 3] FIG. 1 is a block diagram of an embodiment of a wearable audio device. [Figure 4A] 1A and 1B respectively show a filter applied to the feedforward microphone signal of a wearable audio device. [Figure 4B] 1A and 1B respectively show a filter applied to the feedforward microphone signal of a wearable audio device. [Figure 4C]1A and 1B respectively show a filter applied to the feedforward microphone signal of a wearable audio device. [Figure 4D] 1A and 1B respectively show a filter applied to the feedforward microphone signal of a wearable audio device. [Diagram 5] 1 is a flowchart of the operation of a feedforward instability detection and mitigation method for an earphone. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] The present disclosure relates to wearable audio devices. Some non-limiting examples of the present disclosure describe a type of wearable audio device known as an earphone. An earphone generally includes an electroacoustic transducer for generating sound and is configured to deliver sound directly to the ear canal of a user. An earphone can be wireless or wired. In a non-limiting example described herein, the earphone includes one or more feedforward (external) microphones that sense external sounds outside the housing. The feedforward microphones can be used for functions such as active noise reduction (ANR) and transparency mode operation, where external sounds are reproduced for the user by the electroacoustic transducer. Other aspects of the earphone not included in the present disclosure are not shown or described.

[0013] Some embodiments of the present disclosure also describe a type of wearable audio device known as an open-type audio device. An open-type audio device has one or more electroacoustic transducers (i.e., audio drivers) located away from the ear canal opening. In some embodiments, the open-type audio device also includes one or more microphones, which may be used to pick up the user's voice, for ANR, and / or for operation in a transparent mode. Open-type audio devices are further described in U.S. Patent No. 10,397,681, the entire disclosure of which is incorporated herein by reference for all purposes.

[0014] Open audio devices include, but are not limited to, off-ear headphones, i.e., devices having one or more electroacoustic transducers that are coupled to the head or ear (typically by a support structure) but do not occlude the ear canal opening. In some examples, the open audio device is an off-ear headphone with audio glasses, but this is not a limitation of the present disclosure, since in open audio devices, the device is configured to deliver sound to one or both ears of the wearer, typically without ear cups or ear buds. Wearable audio systems contemplated herein may include a variety of devices, including over-ear hooks, such as wireless headsets, hearing aids, glasses, protective helmets, and other open ear audio devices.

[0015] Headphones generally refer to devices worn around, on, or in the ear and radiate acoustic energy directly or indirectly into the ear canal. Headphones are sometimes referred to as earbuds, earphones, headsets, mini-ears, or sports headphones and can be wired or wireless. Headphones include drivers that convert audio signals into acoustic energy. The drivers may or may not be housed in earcups or housings configured to sit on the head or on the ear, or to be inserted directly into the ear canal of a user. A headphone may be a single standalone unit, one for each ear, or one of a pair of headphones (each including at least one acoustic driver). One of the headphones may be mechanically connected to the other of the headphones, for example, by a headband and / or by leads that carry audio signals to the acoustic drivers in the headphones. The headphones may include components that wirelessly receive audio signals. The headphones may include components of an ANR system, which may include an internal microphone in the headphone housing and an external microphone that picks up sounds outside the housing. The headphones may also include other features, such as an additional microphone for an ANR system, or one or more microphones used to pick up the user's voice.

[0016] One or more of the devices, systems, and methods described herein may be used in various implementations and combinations in a wide variety of wearable audio devices or systems, including wearable audio devices of various form factors. One such form factor is an earphone. Unless otherwise specified, a wearable audio device or system may include various other types of wearable audio devices, such as headphones that include one or more acoustic transducers for receiving and / or generating sound, with or without contacting the user's ear, as well as acoustic devices worn on the head, shoulders, or body (e.g., audio glasses or other head-mounted audio devices).

[0017] Although a specific implementation of a wearable audio device primarily serving the purpose of acoustically outputting audio has been presented in some detail, it should be noted that the presentation of such a specific implementation is intended to facilitate understanding through the provision of an example and should not be construed as limiting either the scope of the disclosure or the scope covered by the claims.

[0018] In some examples, a wearable audio device includes an electroacoustic transducer configured to generate sound for a user, a housing that holds the transducer, a feedforward microphone configured to detect sound outside the housing and output a microphone signal, and an opening in the housing that emits sound pressure from the transducer that can reach the microphone. The processor system is programmed to implement a feedforward instability detector function that is configured to apply two filters to the feedforward microphone signal, a first filter passing more energy in a frequency band than a second filter. The filtered signal is compared to the microphone signal outside that frequency band to generate an indication of feedforward instability in that frequency band.

[0019] FIG. 1 is a perspective view of a wireless in-ear earphone 10. An earphone is a non-limiting example of a wearable audio device. Earphone 10 includes a body or housing 12 that houses the active components of the earphone. A portion 14 is coupled to body 12 and is flexible so that it can be inserted into the entrance of the ear canal. Sound is delivered through opening 15. A retention loop 16 is configured and arranged to be positioned within the outer ear, e.g., within the antihelix, to help retain the earphone within the ear. Earphones are known in the art (e.g., as disclosed in U.S. Pat. No. 9,854,345, the disclosure of which is incorporated herein by reference in its entirety for all purposes), and therefore specific details of earphones will not be described further herein.

[0020] FIG. 2 is a partial cross-sectional view of only certain elements of earphone 20 that are useful for better understanding the present disclosure. Earphone 20 comprises a housing 21 that encloses an electro-acoustic transducer (audio driver) 30. Housing 21 includes a front housing portion 50 and rear housing portions 60 and 62. Transducer 30 has a diaphragm 32 that is driven to create sound pressure in front cavity 52. ​​Sound is also generated in rear cavity 53. Sound pressure is directed outward from front housing portion 50 through sound outlet 54. An internal microphone 80 is located inside housing 21. An exemplary microphone 80 is within sound outlet 54 as shown in FIG. 2. An external microphone 81 is configured to sense sounds outside of housing 21. An exemplary external microphone 81 is located inside the housing and is acoustically coupled to the external environment via a housing opening 82 that allows environmental sounds to reach microphone 81. The exemplary internal microphone 80 is used as a feedback microphone for active noise reduction, and the external microphone 81 is used as a feedforward microphone for active noise reduction and / or for transparent mode operation, in which environmental sounds are played back to the user so that the user can hear others speaking so that they are more aware of the external environment. An earphone, such as that shown by the earphone 10 of FIG. 1, typically includes a flexible tip (not shown) that engages with the neck 51 of the housing portion 50 to help direct sound into the ear canal. The earphone housing 21 further includes a rear enclosure made from rear housing portions 60 and 62, and a grille 64. It should be noted that the details of the earphone 20 are exemplary embodiments of earphones and are not intended to limit the scope of the present disclosure, as the present feedforward instability detection can be used in various types and designs of in-ear and other earphones, as well as other wearable audio devices.

[0021] The transducer 30 further comprises a magnetic structure 34. The magnetic structure 34 includes a transducer magnet 38 and magnetic material that functions to contain and guide the magnetic field from the magnet 38 so that it appropriately interacts with the coil 33 to drive the diaphragm 32, as is well known in the art of electro-acoustic transducers. The magnetic material includes a cup 36 and a front plate 35, both of which are preferably made from a material having a relatively high magnetic susceptibility, also as is known in the art. A transducer printed circuit board (PCB) 40 carries the electrical and electronic components (not shown) involved in driving the transducer. Pads 41 and 42 are locations where wires (not shown) can be coupled to the PCB 40.

[0022] The earphone 20 also includes a processor 74. In some examples, the processor 74 is configured to process the output of the microphones 80 and 81. As will be apparent to one skilled in the art, it will be appreciated that the processor is typically involved in other processing necessary for the earphone function, such as processing digital sound files played by the earphone. In one example, the processor is configured to detect feedforward instability. The processor may also be configured to mitigate the instability. In one example, feedforward instability may be caused when a feedforward microphone (used to sense environmental sounds outside the earphone) picks up sound from the earphone's audio driver, resulting in parasitic vibrations. This may occur when sound pressure exiting the housing through a resistive port 84 in the rear cavity 53 is sensed by the microphone 81. Direct coupling through other ports or even leakage in the acoustic cavity may result in feedforward instability. The resulting feedforward instability may cause vibrations or squealing sounds. The squealing sounds may occur even when the earphone is in the proper position in the user's ear. The squeaking noise can also occur when the earbuds are placed in their case and are not powered off. This can occur when there is improper communication between the earbuds and the case, for example when the case's battery is depleted.

[0023] In some examples, the processor is programmed to apply one or more filters to the signal received from the external microphone to detect feedforward instability. In one example, the processor implements a detection filter and a rejection filter that operate in a predetermined frequency band. The detection filter selectively detects energy within a frequency band. The rejection filter selectively detects energy outside this same band. The processor can compare the detected in-frequency band energy to energy outside the same frequency band to help reject broadband sounds or impulse events while still detecting feedforward instability in that frequency band. In some examples, the processor applies a threshold to the detection filter to help ensure that quiet tone signals originating from outside the device are not detected as instability. In some examples, the processor applies a timer to the detected signal so that in-band sounds of short duration are not detected as instability.

[0024] The detection filter and / or the rejection filter can take any desired shape across the frequency band. In one example, the detection filter is a peak filter and the rejection filter is a notch filter. The peak and notch filters can be configured to be centered around a desired frequency. In one non-limiting example, the center frequency is about 3,000 Hz. In another example, the notch filter can be biased outside the frequency band of interest to help reject false positives. An upwardly biased notch results in energy outside the band of interest being weighted more heavily towards the target region. An impulse event can have equal energy across a wide range of frequencies. If that energy is centered in the target band, it can be detected as a false positive. Biasing the rejection band upward helps to mitigate this. In another example, the intersection of the two filters (which can be achieved at about -3 dB) helps to define their combined effect. In another example, the filter is a notch filter and a filter with a flat frequency response across the band of interest.

[0025] In another example, the processor is configured to apply multiple sets of detection and rejection filters across different frequency bands or regions of interest. This configuration can provide greater flexibility in applying more targeted vibration mitigation (e.g., narrowband reduction of gain). The advantage of considering a more narrowly defined detection region and correspondingly narrowing the bandwidth of the gain reduction mitigation is that false positive detections are less likely and less noticeable, respectively.

[0026] FIG. 3 is a block diagram of an aspect of a wearable audio device 100. The exemplary device 100 is an earphone, although the disclosure is not limited thereto. The wearable audio device 100 includes a processor 102 that receives audio data from an external source via a wireless transceiver 104. The processor 102 also receives the output of a feedback microphone(s) 108 and a feedforward microphone(s) 110. The processor 102 outputs the audio data that is converted to an analog signal that is provided to an audio driver 106. The exemplary device 100 includes a memory having instructions that, when executed by the processor, implement the filters and other processing described herein configured to detect feedforward instabilities. In some examples, the detected instabilities are also mitigated via the processor. In some examples, the device 100 is configured to store a computer program product using a non-transitory computer-readable medium, the medium including computer program logic encoded thereon that, when executed on the wearable audio device (e.g., by the processor), causes the device to filter and otherwise process signals as described herein. It should be noted that the details of wearable audio device 100 are exemplary aspects of an earphone and are not intended to limit the scope of the present disclosure, as the present feedforward instability detection techniques can be used in in-ear and other earphones of various types and designs, as well as other wearable audio devices. It should also be noted that aspects of wearable audio device 100 that are not involved in feedforward instability detection and mitigation are not shown in FIG. 3 for simplicity.

[0027] FIG. 4A shows an exemplary filter set 120 applied to the signal of a feedforward microphone of a wearable audio device. In this example, the filter set 120 includes a notch (rejection) filter 122 and a peak (detection) filter 124 centered at about 3100 Hz in a narrow band of about 100 Hz defined by their width at -3 dB. FIG. 4B shows a different set of detection and rejection filters, where the detection filter 128 is a gain-only filter and the rejection filter 127 is a notch filter. FIG. 4C shows a filter set 130 with a bimodal detection filter 136 and rejection filter 132. Bimodal filters are useful in systems with two modes, where the system can vibrate as a function of the acoustic volume and the acoustic path. The detection filter 136 includes peaks 137 and 138 at both of these frequencies, while the rejection filter 132 has notches 133 and 134 at these same frequencies, similar to the reverse of the above. Further adapting this bimodal example to multiple detect / reject filters, each frequency range in which the system may oscillate may have its own dedicated filter, with the purpose of applying different mitigation techniques depending on the frequency range in which instability is detected. Figure 4D shows an exemplary two-frequency range filter set 140, with a first detect / reject filter set 142 having a peak filter 144 and a notch filter 143 centered on a first frequency, and a second detect / reject filter set 146 having a peak filter 148 and a notch filter 147 centered on a second, higher frequency. As shown, in some examples, multiple sets of detect and reject filters may be used across different frequency bands.

[0028] FIG. 5 is a flow chart of an exemplary operation of a method 150 for detecting and mitigating feedforward instability in an earphone. In one example, all steps are performed by a processor. Thus, the operation can be modified as necessary simply by programming the processor appropriately. The input signal is the output of the feedforward microphone. In an optional first step 152, a bandpass filter is applied. In one example, the bandpass reduces energy below about 500 Hz and above about 6 kHz. The bandpass reduces the processing that needs to be applied to the signal in the subsequent steps. In step 154, a detection filter and a rejection filter are applied, squared, and low-pass smoothing is applied. In one example, the filters are realized in the time domain, and each sample is smoothed and squared. The detection filter is configured to detect signals in a detection band of at least a predetermined energy. The rejection filter (nominally a notch filter) is configured to detect energy outside the detection band. The purpose of the rejection filter is to pass less energy in the band or bands in which the signal associated with the detection filter is being searched. The key to achieving these objectives is the relative difference from filter to filter. Step 154 ​​is configured to compare the filtered signal with a signal outside the detection band to generate a comparison signal indicative of feedforward instability within the detection band. In step 156, a threshold is applied to the energy in the peak filter. The threshold is a parameter that can be adjusted to balance maximizing detection and minimizing false positives. It is a scalar value. In one respect, this threshold helps ensure that quiet tone signals are not detected as parasitic vibrations. The result of steps 154 and 156 is that instability is detected only if the peak filtered, square smoothed signal is above the threshold and the peak filtered signal is larger than the notch filtered, square smoothed signal.Another optional step 158 applies a timer to a logical condition on the filtered signal (e.g., the squared smoothed detection filter signal being greater than the squared smoothed rejection filter signal). This helps to avoid detecting transient sounds. The result of steps 154-158 is that instability is detected only if the peak filtered squared smoothed signal is above a threshold and the peak filtered signal is greater than the notch filtered squared smoothed signal for at least a minimum duration.

[0029] In optional step 160, if an event (i.e., an undesired parasitic vibration) is detected, the vibration is mitigated. One goal is to quickly eliminate the vibration without reducing or eliminating the desired sound, even if the mitigation algorithm is triggered during a false positive event (e.g., an external sound). In an example of step 160, the mitigation involves adjusting the gain applied to the signal from the feedforward microphone before the signal is provided to the driver. In one extreme example, the entire feedforward gain applied to the feedforward microphone is reduced. However, this may be audible to the user. Typically (but not necessarily), the gain is reduced in a more controlled manner to reduce and eliminate the vibration. In some examples, the gain is reduced for a predetermined amount of time and then increased back to its original value. The increase may be done over a predetermined amount of time, but gradually over that time. In some examples, the gain adjustment is made frequency dependent. In one example, the gain is gradually reduced by about 20 dB over a period of about 0.5 seconds. In one example, the gain is then gradually restored to its original value over about 0.5 seconds. This recovery can be done in several steps to reduce the chances of a user detecting an anomaly.

[0030] When a process is depicted or suggested in a block diagram, the steps may be performed by one element or by multiple elements. The steps may be performed collectively or at different times. The elements performing the activities may be physically the same or in close proximity to each other, or may be physically separate. An element may perform more activities than one block. The audio signal may be coded or uncoded and may be transmitted in either digital or analog form. Conventional audio signal processing equipment and operations may be omitted from the drawings.

[0031] Examples of the systems and methods described herein include computer components and computer-implemented steps that will be apparent to one of ordinary skill in the art. For example, it should be understood by one of ordinary skill in the art that the computer-implemented steps can be stored as computer-executable instructions on a computer-readable medium, such as, for example, a floppy disk, a hard disk, an optical disk, a flash ROM, a non-volatile ROM, and a RAM. Furthermore, it should be understood by one of ordinary skill in the art that the computer-executable instructions can be executed on a variety of processors, such as, for example, a microprocessor, a digital signal processor, a gate array, and the like. For ease of description, not all steps or elements of the systems and methods are described herein as part of a computer system, but one of ordinary skill in the art will recognize that each step or element may have a corresponding computer system or software component. Thus, such computer systems and / or software components are enabled by describing their corresponding steps or elements (i.e., their functionality) and are within the scope of the present disclosure.

[0032] Although multiple implementations have been described, it is understood that additional modifications can be made without departing from the scope of the inventive concepts described herein, and therefore, other examples are within the scope of the following claims.

Claims

1. 1. A system for detecting feedforward instability in a wearable audio device comprising: an electroacoustic transducer configured to generate sound for a user; a housing for holding the transducer; a feedforward microphone configured to detect sound outside the housing and output a microphone signal; and an opening in the housing for emitting sound pressure from the transducer that can reach the microphone, the system comprising:

1. A feedforward instability detector comprising: applying two filters to the microphone signal, a first filter passing more energy in a frequency band than a second filter to produce a filtered signal; comparing the filtered signal with the microphone signal outside the frequency band to generate a comparison signal indicative of feedforward instability in the frequency band; The system wherein the second filter comprises a notch filter.

2. The system of claim 1 , wherein the wearable audio device comprises an earphone configured to output sound directly to the user's ear canal.

3. The system of claim 1 , wherein the feedforward microphone is used in an active noise reduction (ANR) system.

4. The system of claim 1 , wherein the feedforward microphone is used in a transparent mode in which ambient sounds are reproduced by the transducer.

5. The system of claim 1 , wherein the first filter comprises a peak filter.

6. The system of claim 1 , wherein the first filter and the second filter collectively detect parasitic vibrations within a predetermined frequency range.

7. The system of claim 6 , wherein the frequency range is centered around 3,100 Hz.

8. The system of claim 1 , wherein the detector is further configured to apply a threshold energy level to the energy that passes through the first filter.

9. The system of claim 8 , wherein feedforward instability is indicated only if an energy level of the energy passed by the first filter is above the threshold.

10. The system of claim 1 , wherein a feedforward instability is indicated when an energy level of the energy passed through the first filter is greater than an energy level of the energy passed through the second filter.

11. 11. The system of claim 10, wherein feedforward instability is indicated when an energy level of the energy passed through the first filter remains greater than an energy level of the energy passed through the second filter for at least a threshold amount of time.

12. 2. The system of claim 1, wherein feedforward instability is indicated when an energy level of the energy passed through the first filter is greater than an energy level of the energy passed through the second filter for at least a threshold amount of time and the microphone signal outside the frequency band is greater than a signal level threshold.

13. The system of claim 1 , further comprising an instability reducer configured to adjust a gain applied to the microphone signal.

14. The system of claim 13 , wherein the gain is reduced for a predetermined amount of time.

15. 15. The system of claim 14, wherein after the predetermined amount of time, the gain is increased back to its original value.

16. 16. The system of claim 15, wherein the increase in gain occurs gradually over a predetermined period of time.

17. The system of claim 13 , wherein the gain is adjusted depending on frequency.

18. The system of claim 1 , wherein the feedforward instability detector is configured to apply multiple sets of detection and rejection filters in different frequency bands.

19. A computer program product having a non-transitory computer readable medium including encoded computer program logic which, when executed on a wearable audio device comprising an electro-acoustic transducer configured to generate sound for a user, a housing to hold the transducer, a feedforward microphone configured to detect sound outside the housing and output a microphone signal, and an opening in the housing that releases sound pressure from the transducer that can reach the microphone, causes the wearable audio device to: applying two filters to the microphone signal, a first filter passing more energy in a frequency band than a second filter to produce a filtered signal; comparing the filtered signal with the microphone signal outside the frequency band to generate a comparison signal indicative of feedforward instability in the frequency band; The second filter comprises a notch filter.

20. 20. The computer program product of claim 19, wherein the wearable audio device comprises an earphone configured to output sound directly to the user's ear canal.

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