Real-time detection of feedforward instability

Abstract

The present invention provides an audio device and method for detecting instability in an associated feedforward audio processing system. A microphone provides a feedforward signal for processing by a feedforward filter. The processed signal can provide noise reduction and / or sound enhancement associated with an ambient environment. The processed signal contributes to a driver signal provided to an acoustic transducer (e.g., a driver) to generate an acoustic signal for a user. A processor is configured to detect an indication of instability in one or more signals and adjust a phase response of a feedforward signal path in response to detecting the indication of instability.

Description

Background Art

[0001] Audio earphones, headphones, headphone systems, and other personal audio devices are used in a variety of environments for purposes such as entertainment, communications, and professional applications. Many systems incorporate active noise reduction (ANR) features, also known as active noise cancellation (ANC), in which one or more microphones detect sound, such as external sound captured by a feedforward microphone or internal sound captured by a feedback microphone. In some examples, the signal from the feedforward microphone can be processed to provide an anti-noise signal that is fed to an acoustic transducer (e.g., speaker, driver) to cancel the noise, and can also be processed to enhance the sound, for example, to improve the user's awareness of his / her surroundings, to improve hearing in general, or to improve sounds that might otherwise be difficult for the user to hear. The feedforward microphone can sometimes pick up acoustic signals generated by the driver, thereby forming a closed-loop system that can sometimes become unstable.

[0002] Similarly, various audio systems that provide an amplified signal from a microphone to a loudspeaker (such as public address systems and studio recording or performance venue audio systems) may exhibit instabilities when the microphone picks up an acoustic signal produced by the loudspeaker. Although this may often be referred to as "feedback," especially the characteristic "howling" from this situation, this is a problem of feedforward instability caused by an unintended or undesired feedback loop (e.g., a signal fed back from a loudspeaker or driver to a microphone).

[0003] Therefore, in various situations, it is desirable to detect when a feedforward instability condition exists. Summary of the invention

[0004] Various aspects and examples relate to audio systems and methods for detecting instabilities in a feedforward signal path. The systems and methods operate to detect possible instabilities (e.g., by detecting tonal features), and when detected, adjust the phase response of the feedforward signal path (e.g., from a feedforward microphone to a driver signal), e.g., to change the instability. If the instability detection (e.g., tonal features) responds to the adjusted phase response, this may indicate or confirm that a feedforward instability exists.

[0005] According to one aspect, an audio device is provided, comprising: a microphone for providing a first signal; a processor comprising a filter, the processor being configured to receive the first signal and provide a second signal, the second signal being based at least in part on processing the first signal using the filter; and an acoustic transducer for converting a third signal into an acoustic signal based at least in part on the second signal, wherein the processor is further configured to detect an instability indication of any one of the first signal, the second signal, or the third signal, and to adjust a phase response of the filter in response to detecting the instability indication.

[0006] In some examples, the processor is further configured to confirm instability by monitoring changes in the instability indication caused by adjusting the phase response of the filter. In some examples, the processor also adjusts one or more parameters involved in providing the second signal in response to confirming the instability to mitigate the effects of the instability.

[0007] According to various examples, the processor is configured to detect an indication of instability by detecting a tonal feature in any of the first signal, the second signal, or the third signal. The processor may also be configured to determine whether the tonal feature changes in response to adjusting the phase response of the filter, and to confirm instability when it is determined that the tonal feature changes in response to adjusting the phase response of the filter. In some examples, the change in the tonal feature is a change in the amplitude of the tonal feature or at least one of the rate of rise or rate of fall of the amplitude of the tonal feature. In various examples, the tonal feature includes a component within a predetermined frequency range. In some examples, the predetermined frequency range is substantially between 1 KHz and 6 KHz. In other examples, the predetermined frequency range may be substantially between 3 KHz and 6 KHz.

[0008] According to another aspect, a method for detecting feedforward instability in an audio device is provided. The method includes: monitoring a potential instability in a feedforward signal path; in response to detecting the potential instability in the feedforward signal path, adjusting a phase response of the feedforward signal path; monitoring a change in the potential instability, the change being caused by the adjusted phase response; and confirming that the feedforward instability exists based on the detected change in the potential instability.

[0009] In some examples, adjusting the phase response includes shifting an inflection point in the phase response.

[0010] In various examples, monitoring for potential instability includes monitoring a tonal characteristic. In some examples, monitoring for changes in potential instability includes monitoring a change in the amplitude of the tonal characteristic or at least one of a rate of increase or a rate of decrease of the amplitude of the tonal characteristic. The tonal characteristic may include a component within a predetermined frequency range, and in some examples, the predetermined frequency range is substantially between 1 KHz and 6 KHz. In other examples, the predetermined frequency range may be substantially between 3 KHz and 6 KHz.

[0011] Certain examples include adjusting one or more parameters of the feedforward signal path in response to confirming that the feedforward instability exists.

[0012] According to another aspect, a headphone system is provided, the headphone system comprising: an earpiece having a feedforward microphone configured to detect an external acoustic signal and provide a feedforward signal; a feedforward processor for processing the feedforward signal to provide a feedforward driver component signal; an acoustic transducer generating an acoustic signal based on a driver signal, the driver signal being at least partially based on the feedforward driver component signal; an instability detector configured to monitor a signal indicating an unstable closed loop between the acoustic transducer and the feedforward microphone; and a phase adjuster configured to adjust the phase of a transfer function associated with the feedforward processor in response to detecting the signal indicating an unstable closed loop between the acoustic transducer and the feedforward microphone.

[0013] In some examples, the feedforward processor is configured to apply a transfer function to the feedforward signal.

[0014] According to various examples, the instability detector is configured to monitor a tonal feature indicating an unstable closed loop between the acoustic transducer and the feedforward microphone. In some examples, the instability detector may be further configured to monitor a change in the tonal feature in response to an adjusted phase of a transfer function, and confirm the unstable closed loop based on determining that the tonal feature changes in response to the adjusted phase. In some examples, the change in the tonal feature is a change in at least one of an amplitude of the tonal feature or a rate of increase or decrease of the amplitude of the tonal feature.

[0015] In certain examples, the feedforward processor is further configured to, in response to identifying the unstable closed loop, adjust a parameter of the feedforward process to mitigate the unstable closed loop.

[0016] Other aspects, examples and advantages of these exemplary aspects and examples are still discussed in detail below. The examples disclosed herein may be combined with other examples in any manner consistent with at least one principle disclosed herein, and references to "examples", "some examples", "alternative examples", "various examples", "an example", etc. are not necessarily mutually exclusive and are intended to indicate that the specific features, structures or characteristics described may be included in at least one example. The appearance of such terms herein may not all refer to the same example. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Various aspects of at least one example are discussed below with reference to the accompanying drawings, which are not intended to be drawn to scale. The accompanying drawings are included to provide illustration and further understanding of the various aspects and examples, and are incorporated into and constitute a part of this specification, but are not intended to be used as a definition of limitations of the present invention. In the accompanying drawings, the same or nearly the same components shown in various figures may be represented by the same or similar numbers. For clarity, not every component is labeled in every figure. In the accompanying drawings:

[0018] Figure 1 is a perspective view of an exemplary headphone form factor;

[0019] Figure 2 is a perspective view of another exemplary headphone form factor;

[0020] Figure 3 is a schematic block diagram of an exemplary audio process that may be incorporated into various audio systems;

[0021] Figure 4 is a schematic diagram of an exemplary audio system incorporating a feedforward component and a feedback component;

[0022] Figure 5 is a schematic diagram of an exemplary system for instability detection and confirmation; and

[0023] Figure 6 Schematic diagram of an exemplary filter response for phase adjustment. DETAILED DESCRIPTION

[0024] Aspects of the present disclosure relate to audio systems (such as sound enhancement and / or noise cancellation earphones or headphones) that include feedforward signal processing, and methods for detecting instability in feedforward systems. A noise cancellation system is used to reduce acoustic noise components heard by a user (e.g., a wearer of a headphone). A noise cancellation system may include feedforward and / or feedback characteristics. A feedforward component detects noise outside the headphone (e.g., via an external microphone) and is used to provide an anti-noise signal to offset the external noise expected to be transmitted to the user's ears. A feedback component detects acoustic signals reaching the user's ears (e.g., via an internal microphone) and processes the detected signals to offset any signal components that are not intended to be part of the user's acoustic experience. The examples disclosed herein may be coupled to other systems or configured to be connected to other systems by wired or wireless means, or may be independent of any other system or device.

[0025] In some examples, the systems and methods disclosed herein may include, or operate in, an aviation headset, a telephone headset, a media headset, an online gaming headset, a hearing aid headset, a hearing aid, or any combination of these or others. Throughout this disclosure, the terms "headphones," "earphones," "earplugs," and "headphone sets" are used interchangeably, and unless the context clearly indicates otherwise, the use of one term in place of another is not intended to make a distinction. In addition, various form factors are applicable according to the various aspects and examples disclosed herein, such as in-ear transducers or earplugs and post-ear or over-ear headphones. Therefore, as used herein, the terms "headphones," "earphones," and "headphone sets" contemplate any suitable form factor.

[0026] The examples disclosed herein may be combined with other examples in any manner consistent with at least one principle disclosed herein, and references to "examples," "some examples," "alternative examples," "various examples," "an example," etc. are not necessarily mutually exclusive and are intended to indicate that the particular features, structures, or characteristics described may be included in at least one example. The appearances of such terms herein do not necessarily all refer to the same example.

[0027] It should be understood that the examples of the methods and devices discussed herein are not limited to the construction details and component arrangements listed in the following description or shown in the accompanying drawings. These methods and devices can be implemented in other examples and can be operated or executed in various ways. The examples of specific implementations provided herein are for illustrative purposes only and are not intended to be limiting. In addition, the words and terms used herein are for descriptive purposes and should not be considered as limiting. The use of "including", "comprising", "having", "containing", "involving" and their variants herein is intended to cover the items listed thereafter and their equivalents and additional items. References to "or" can be understood to be inclusive, so that any term described using "or" can indicate any of a single, more than one and all of the terms. Any reference to the front and back, left and right, top and bottom, upper and lower, and vertical and horizontal is for ease of description, not for limiting the present system and method or their components to any one position or spatial orientation.

[0028] For various components described herein, the designation of "a" or "b" in the reference numerals may be used to indicate a "right" or "left" version of one or more components. When such a designation is not included, the description does not consider left or right sides, and applies equally to either left or right side, which is generally the case for the various examples described herein. Additionally, the various aspects and examples described herein apply equally to monaural or unilateral personal acoustic devices, and do not necessarily require both left and right sides.

[0029] Figure 1 and Figure 2 Two exemplary headsets 100A, 100B are shown. Each headset 100 includes a right earpiece 110a and a left earpiece 110b that are mutually coupled by a supporting structure 106 (e.g., headband, neckband, etc.) worn by a user. In some examples, the two earpieces 110 can be independent of each other, rather than mutually coupled by a supporting structure. Each earpiece 110 may include one or more microphones, such as a feedforward microphone 120 and / or a feedback microphone 140. The feedforward microphone 120 may be configured to sense an acoustic signal outside the earpiece when the earpiece 110 is correctly worn, for example, being configured to detect the acoustic signal in the surrounding environment before it reaches the user's ear. The feedback microphone 140 may be configured to sense an acoustic signal inside the acoustic volume formed by the user's ear when the earpiece 110 is correctly worn, for example, being configured to detect the acoustic signal that reaches the user's ear. Each earpiece also includes a driver 130, which is a sound transducer for converting, for example, an electrical signal into an audible acoustic signal for the user. In various examples, one or more drivers may be included in the earpiece, and in some cases the earpiece may include only feedforward microphones or only feedback microphones.

[0030] Although reference numerals 120 and 140 are used to refer to one or more microphones, in some examples, such visual elements shown in the figures may represent acoustic holes from which acoustic signals enter to ultimately reach such microphones that may be located internally and not physically visible from the outside. In examples, one or more of microphones 120, 140 may be immediately adjacent to the interior of an acoustic port or may be moved a distance from the acoustic port and may include an acoustic waveguide between the acoustic port and the associated microphone.

[0031] Figure 3 , an example of a processing unit 310 is shown, which can be physically accommodated at a certain position on or within the headset 100. The processing unit 310 may include a processor 312, an audio interface 314, and a battery 316. In various examples, the processing unit 310 may be coupled to one or more feedforward microphones 120, a driver 130, and / or a feedback microphone 140. In various examples, the interface 314 may be a wired or wireless interface for receiving an audio signal (such as a playback audio signal or a program content signal), and may include additional interface functions, such as a user interface for receiving user input and / or configuration options. In various examples, the battery 316 may be replaceable and / or rechargeable. In various examples, the processing unit 310 may be powered by a device other than the battery 316 or in addition to the battery 316, such as by a wired power supply, etc. In some examples, the system may not include an interface 314 for receiving a playback signal.

[0032] Figure 4 Systems and methods are shown for processing microphone signals to provide sound to a user's ears, whether for noise reduction or sound enhancement. Figure 4 A simplified schematic diagram is given that highlights the features of such an audio system. Various examples of a complete system may include amplifiers, analog-to-digital conversion (ADC), digital-to-analog conversion (DAC), equalization, sub-band separation and synthesis, and other signal processing. In some examples, a playback signal 410, p(t) may be received to be presented as an acoustic signal by a driver 130. A feedforward microphone 120 may provide a feedforward signal 122 that is generated by a feedforward transfer function 126, K ff The feedforward processor 124 processes the feedback signal 128 to generate a feedforward driver component signal 128, which may be an anti-noise signal or an enhanced sound signal, or a combination of the two. The feedback microphone 140 may provide a feedback signal 142, which is a feedback transfer function 146, K fbThe feedback processor 144 processes the playback signal 410 to generate the feedback anti-noise signal 148. In various examples, any of the playback signal 410, the feedforward driver component signal 128, and / or the feedback anti-noise signal 148 may be combined, for example, by the combiner 420 to generate the driver signal 132, d(t) to be provided to the driver 130. In various examples, any of the playback signal 410, the feedforward driver component signal 128, and / or the feedback anti-noise signal 148 may be omitted, and / or the components required to support any of these signals may not be included in a particular implementation of the system.

[0033] Various examples described herein include a feed-forward audio system, such as a feed-forward microphone 120 and a feed-forward processor 124, for example, to provide a feed-forward driver component signal 128 to be included in a driver signal 132. The feed-forward microphone 120 can be configured to detect external sounds before they reach an acoustic volume including the user's ear. However, the feed-forward microphone 120 can also detect an acoustic signal 136 generated by the driver 130, so that there is a closed loop. For example, the feed-forward microphone 120 can pick up an acoustic signal 136 when the headset 100 is played at a high volume, when the headset 100 is not worn (e.g., away from the head, reducing the physical isolation between the driver 130 and the feed-forward microphone 120), or when the feed-forward signal 122 is purposefully processed to enhance or improve external sounds rather than reduce external sounds (e.g., amplify to be heard through the earpiece), or under various other conditions.

[0034] Thus, in various examples and / or at various times, the feedforward signal path may include a feedback loop (e.g., a closed feedforward loop) that, for example, passes from the driver signal 132 through the driver 130 to produce an acoustic signal 136 that may reach and be picked up by the feedforward microphone 120 and, through the feedforward transfer function 126, K ff The acoustic signal 136 is processed to be included back into the driver signal 132. Thus, at least some components of the feedforward signal 122 may be formed from the acoustic signal 136. In other words, the feedforward signal 122 may include components that are related to the driver signal 132. If the closed loop exhibits instability, this may result in a gradual increase in the amplitude of at least one frequency component of the driver signal 132. This may be perceived by the user as an audible artifact, such as a tone or a howling sound, and may reach a limit at the maximum amplitude that the driver 130 is capable of producing, which may be extremely loud. Thus, when this condition exists, the feedforward system may be described as unstable.

[0035] Figure 4The electrical and physical system shown exhibits a transfer function 134, G, which characterizes the transfer of the driver signal 132 to the feedforward signal 122. In other words, the response of the feedforward signal 122 to the driver signal 132 is characterized by the transfer function 134, G. Thus, the system of the feedforward noise reduction loop is characterized by the combined transfer function GK ff If for one or more frequencies, GK ff =1, the feedforward noise reduction system may be unstable. In various examples, the transfer function 134, G is typically small (e.g., G<<1), but (as described above) various situations may cause the transfer function 134, G to be larger than the typical value, and under various situations or user configurations, the feedforward transfer function 126, K ff can be larger than typical values ​​(e.g., K ff >>1) (such as when headphones are used to amplify some external sound), any of the above can produce instabilities at one or more frequencies.

[0036] In various examples, feedforward instability can be detected in various ways. In at least one example, the processing system can monitor any of the feedforward signal 122, the feedforward driver component signal 128, the driver signal 132, and / or other signals for tone characteristics. For example, instability can cause one or more tones to be raised (in amplitude, in signal energy) to an expected, average, or base level that exceeds the various components of any of the above signals, and the raised tones can be detected in various ways. In various examples, the tone characteristics can fall within the range of 1kHz to 8kHz, or within the range of 3kHz to 6kHz, or other ranges, and can depend on the size and scale of the system (e.g., over-ear headphones vs. in-ear headphones). Further details of the tone characteristics (such as raised tones) that detect instability are included in U.S. Patent 9,922,636, entitled "MITIGATION OF UNSTABLE CONDITIONS IN AN ACTIVE NOISE CONTROL SYSTEM", which is incorporated herein by reference in its entirety for all purposes. Various examples may use such instability detection or other instability detections, and may also use systems and methods according to the aspects and examples described herein to confirm that the instability detection is correct and not a false positive (e.g., detecting instability when it is not actually present).

[0037] Various aspects and examples described herein adjust the feedforward signal path, for example, by phase changes, which can confirm instability detection. For example, if the tonal characteristics of the instability remain unchanged despite the adjustment of the feedforward signal path, the tonal characteristics may be due to external sounds rather than instability. If the tonal characteristics respond to the adjusted feedforward signal path, the tonal characteristics may be due to instability, and this may be the basis for confirming the detection of instability. Therefore, in various examples, a system or method for detecting instability may use one or more of a variety of adjusted phase responses (according to those described herein) in the signal path, and may require the detection system or method to react to the adjusted phase response (e.g., move closer to or further away from stability due to the adjusted phase response) to confirm detection, thereby reducing false positives.

[0038] Figure 5 An exemplary system 500 is shown that includes a detector 510 for detecting signs of feedforward instability, which can be any of a variety of types of detection, such as detection of a tonal feature as described above. In some examples, if the detector 510 detects instability, a phase adjuster 520 can adjust the phase response of the feedforward signal path, thereby changing the driver component signal 128. In various examples, the phase adjuster 520 can be an all-pass filter (e.g., unity gain at all frequencies of interest) with a phase response that causes various frequencies of phase variation to emerge from the filter. In other examples, the phase adjuster 520 can be a delay block with a delay added, effectively phase shifting all frequencies. For example, the delay block can provide a delay of tens or hundreds of microseconds, such as 125 microseconds or 250 microseconds. For example, a 125 microsecond delay can result in a 45° phase shift at 1 kHz, a 90° phase shift at 2 kHz, and a 180° phase shift at 4 kHz, etc. In other examples, the phase adjuster 520 can be incorporated into the feedforward processor 124, for example, by adding the phase adjuster 520 before or after the feedforward transfer function 126 and / or by changing the feedforward transfer function 126 in response to the detector 510 indicating the detected instability. In various examples, the phase shift can be provided (e.g., by the phase adjuster 520) at any of a variety of locations in the feedforward signal path, such as after the combiner 420 (e.g., acting on the driver signal 132).

[0039] Adjusting the phase response of the feedforward signal path (e.g., by the phase adjuster 520) may change or alter the instability in the feedforward signal path, thereby changing the indication of the detected instability. Thus, the phase adjuster 520 may be advantageously used to confirm instability detection. For example, the detector 510 may monitor various signs (indicators) of instability (e.g., tonal characteristics), and when detected, the phase adjuster 520 may be activated to adjust the phase response of the feedforward signal path. If the sign of instability responds to the adjusted phase response, such as by the tonal characteristics increasing or decreasing (e.g., in amplitude or frequency), or the rate of change of the tonal characteristics increasing or decreasing, this may confirm that instability exists and is not a false alarm. In an exemplary case of a false alarm, an external sound may trigger the detector 510 to indicate potential instability, and this may be a false alarm, while adjusting the phase response of the feedforward signal path (e.g., by the phase adjuster 520) does not change the external sound source. Thus, the symptom (external sound) detected by detector 510 remains unchanged in response to the phase adjustment, so that detector 510 (or other processing) can determine that the detected symptom is a false positive indication of instability and that no actual instability exists.

[0040] Although Figure 5 The above description relates to phase adjustments made in the feedforward signal path to confirm detection of feedforward instability, but phase adjustments may also be placed in the feedback signal path in a similar manner to detect (or confirm) instability in the feedback noise reduction system.

[0041] Figure 6 An exemplary response 600 (e.g., transfer function) of the phase adjuster 520 is shown. The magnitude response 610 is unity (gain = 1.0x, 0 dB), and the phase response 620 adjusts the frequency range by various phase shifts. In some examples, the phase adjuster 520 may be configured so that the phase response 620 only shifts the phase of a certain frequency range (such as a frequency range where the tonal characteristics of instability can be expected). The phase response 620 is only one example of a suitable phase response for the phase adjuster 520. In various examples, the phase adjuster 520 may shift the phase of a certain frequency range by a fixed amount (e.g., the phase response 620 may be a straight horizontal line of non-zero phase values), or may shift the timing of all frequencies by a fixed delay (e.g., the phase response 620 may be a straight inclined line with no curvature), or may change the phase response in various other ways. In some examples, the phase adjuster 520 may be implemented as a modification of the feedforward transfer function 126, which itself has a baseline phase response. Thus, the phase adjuster 520 may be implemented as a change in the baseline phase response of the feedforward transfer function 126. For example, the feedforward transfer function 126 may have a phase response similar to Figure 6The phase response shown is for illustrative purposes only, and phase adjustments may be applied by changing the phase response of the feedforward transfer function 126 (such as by shifting the inflection point) or other changes to the phase response of the feedforward transfer function 126. In some examples, the indication from the detector 510 may be applied as a command to the feedforward processor 124 to make such a shift or change to the phase response of the feedforward transfer function 126.

[0042] When the detector 510 indicates that a potential feedforward instability has been detected and confirmed by responding to the phase adjuster 520, various systems and methods according to various aspects and examples herein may take different actions in response to the instability, for example, to mitigate or eliminate the instability and / or the undesirable consequences of the instability. For example, the audio system according to the present invention may change or replace the feedforward transfer function 126, change the feedforward controller or feedforward processor 124, change to a less aggressive feedforward gain form or other processing, change various parameters of the feedforward system to be less aggressive, change the driver signal (e.g., attenuate the sound of the driver signal 132, reduce or limit the driver signal 132), provide an indicator to the user (e.g., an audible or visual message, indicator light, etc.), and / or other actions.

[0043] The above aspects and examples provide multiple potential benefits for personal audio devices including feedforward noise reduction. The stability criteria for feedforward control can be defined by engineers at the controller design stage, and various considerations assume that the range of variation (of system characteristics) is limited during the life of the system. For example, the driver output and microphone sensitivity may vary over time and contribute to the electroacoustic transfer function between the driver and the feedforward microphone. Further variability may affect the design criteria, such as production variations, head-to-head variations, changes in user handling, and environmental factors. Any such variation may result in a violation of stability limits, and designers must generally take a conservative approach to feedforward system design to ensure that instability is avoided. Such instabilities may cause the noise reduction system to add undesirable signal components rather than reduce them, so conventional design practices may adopt a highly conservative approach to avoid instabilities that may bring serious costs to system performance.

[0044] However, as described herein, aspects and examples of detecting feedforward instability allow corrective measures to be taken to eliminate instability when such conditions occur, thereby allowing system designers to design systems that operate closer to the instability boundary and, therefore, achieve improved performance over a wider feedforward bandwidth. The aspects and examples herein allow reliable detection of whether or when an instability boundary is crossed. Conventional systems need to be designed to avoid instability, but instability detection according to the aspects and examples described herein allows a feedforward controller or processor to be designed with loose constraints and improved performance. Therefore, the systems and methods herein can more than double the bandwidth range over which noise reduction by the feedforward processor may be effective.

[0045] It should be understood that any functionality of the systems and methods described herein may be implemented or performed in a digital signal processor (DSP), a microprocessor, a logic controller, a logic circuit, etc., or any combination of these components, and may include analog circuit components and / or other components relative to any particular implementation. The functions and components disclosed herein may operate in the digital domain, and certain examples include analog-to-digital (ADC) conversion of analog signals generated by a microphone, even though there is no illustration of the ADC in the various figures. Such ADC functionality may be incorporated into a signal processor or otherwise within a signal processor. Any suitable hardware and / or software (including firmware, etc.) may be configured to implement or realize the components of the various aspects and examples disclosed herein, and various embodiments of the various aspects and examples may include components and / or functions other than those disclosed.

[0046] Having described several aspects of at least one example above, it should be understood that various changes, modifications and improvements will be readily apparent to those skilled in the art. Such changes, modifications and improvements are intended to be part of this disclosure and are intended to fall within the scope of the present invention. Therefore, the above description and drawings are exemplary only, and the scope of the present invention should be determined by the appropriate construction of the appended claims and their equivalents.

Claims

1. An audio device, comprising: a feedforward microphone, the feedforward microphone being used to provide a first signal; a processor including a filter, the processor configured to receive the first signal and provide a second signal, the second signal being an anti-noise signal in a feed-forward signal path, the second signal being based at least in part on processing the first signal using the filter; and an acoustic transducer for converting a third signal into an acoustic signal based at least in part on the second signal; wherein the processor is further configured to detect a feedforward instability indication of any of the first signal, the second signal, or the third signal, and adjust a phase response of the filter in response to detecting the feedforward instability indication; and Wherein the processor is further configured to confirm feedforward instability by monitoring a change in the feedforward instability indicator caused by adjusting the phase response of the filter. 2 . The audio device of claim 1 , wherein the processor is further configured to adjust one or more parameters involved in providing the second signal in response to identifying the instability to mitigate effects of the instability.

3. The audio device of claim 1, wherein the processor is configured to detect the instability indication by detecting a tonal feature in any of the first signal, the second signal, or the third signal.

4. An audio device according to claim 3, wherein the processor is further configured to determine whether the pitch characteristic changes in response to adjusting the phase response of the filter, and to confirm instability when it is determined that the pitch characteristic changes in response to adjusting the phase response of the filter.

5. The audio device of claim 4, wherein the change in the tone feature is a change in at least one of an amplitude of the tone feature or a rate of increase or a rate of decrease of the amplitude of the tone feature. The audio device of claim 3 , wherein the tonal characteristics include components within a predetermined frequency range.

7. The audio device of claim 6, wherein the predetermined frequency range is between 1 KHz and 6 KHz.

8. A method of detecting feedforward instability in an audio device, the method comprising: monitoring potential instabilities in feedforward signal paths including anti-noise signals; responsive to detecting a potential instability in the feedforward signal path, adjusting a phase response of the feedforward signal path; monitoring a change in the potential instability, the change resulting from the adjusted phase response; as well as The presence of feedforward instability is confirmed based on the detected change in the potential instability.

9. The method of claim 8, wherein adjusting the phase response comprises shifting a point of inflection in the phase response.

10. The method of claim 8, wherein monitoring for potential instability comprises monitoring tonal characteristics.

11. The method of claim 10, wherein monitoring the potential instability for changes comprises monitoring a change in an amplitude of the tonal feature or at least one of a rate of increase or rate of decrease of the amplitude of the tonal feature.

12. The method of claim 11, wherein the tonal characteristics include components within a predetermined frequency range. The method of claim 12 , wherein the predetermined frequency range is between 1 kHz and 6 kHz.

14. The method of claim 8, further comprising adjusting one or more parameters of the feedforward signal path in response to confirming the presence of the feedforward instability.

15. An earphone system, comprising: an earpiece having a feedforward microphone configured to detect an external acoustic signal and provide a feedforward signal; a feedforward processor for processing the feedforward signal to provide a feedforward driver component signal, wherein the feedforward driver component signal is a noise-resistant signal; an acoustic transducer that generates an acoustic signal based on a driver signal that is based at least in part on the feedforward driver component signal; an instability detector configured to monitor for a signal indicative of an unstable closed loop between the acoustic transducer and the feedforward microphone; and a phase adjuster configured to adjust a phase of a transfer function associated with the feedforward processor in response to detecting the signal indicative of an unstable closed loop between the acoustic transducer and the feedforward microphone; wherein the instability detector is configured to monitor for tonal characteristics indicative of an unstable closed loop between the acoustic transducer and the feedforward microphone; as well as Wherein the instability detector is further configured to monitor a change in the tonal characteristic in response to an adjusted phase of the transfer function, and to confirm the unstable closed loop based on determining that the tonal characteristic changes in response to the adjusted phase.

16. The headphone system of claim 15, wherein the feedforward processor is configured to apply the transfer function to the feedforward signal.

17. The headphone system of claim 15, wherein the change in the tonal characteristic is a change in at least one of an amplitude of the tonal characteristic or a rate of increase or decrease of the amplitude of the tonal characteristic.

Images