Real-time detection of feedback instability

Abstract

The playback audio signal is combined with a feedback signal from a feedback microphone to provide a first combined signal. The first combined signal is filtered using a feedback filter to provide a driver command signal. The driver command signal is provided to an acoustic transducer for conversion to acoustic energy. The first combined signal is compared to the feedback signal, and feedback instability is detected based on the comparison.

Description

[Technical Field]

[0001] Various audio devices incorporate active noise reduction (ANR) functionality, also known as active noise control or cancellation (ANC), in which one or more microphones detect sounds, such as external sounds captured by a feedforward microphone or internal sounds captured by a feedback microphone. Signals from the feedforward and / or feedback microphones are processed to provide anti-noise signals to be fed to an acoustic transducer (e.g., speaker, driver) to cancel noise that would otherwise be heard by a user. The feedback microphone picks up acoustic signals generated by the driver, thereby forming a closed-loop system that may become unstable from time to time or under certain conditions. Various audio systems that may provide feedback noise reduction include, for example, headphones, earphones, headsets, and other portable or personal audio devices, as well as automotive systems for reducing or eliminating engine and / or road noise, office or ambient sound systems, etc. Therefore, in various situations, it is desirable to detect when a condition of feedback instability exists. Summary of the Invention

[0002] All examples and features mentioned below can be combined in any technically possible manner.

[0003] In one aspect, the playback audio signal is combined with a feedback signal from a feedback microphone to provide a first combined signal. The first combined signal is filtered using a feedback filter to provide a driver command signal. The driver command signal is provided to an acoustic transducer for conversion to acoustic energy. The first combined signal is compared to the feedback signal, and feedback instability is detected based on the comparison.

[0004] Implementations may include one or any combination of the following features.

[0005] In some implementations, combining the reproduced audio signal with the feedback signal includes filtering the reproduced audio signal with an equalization filter to provide a filtered reproduced signal, and combining the filtered reproduced signal with the feedback signal to provide a first combined signal.

[0006] In some implementations, combining the playback audio signal with the feedback signal includes (i) filtering the feedforward signal from the feedforward microphone with an aware mode filter to provide an aware mode signal; and (ii) combining the aware mode signal, the filtered playback signal, and the feedback signal to provide a first combined signal.

[0007] In some cases, combining the playback signal with the feedback signal includes (i) filtering the feedforward signal with a feedforward filter to provide a feedforward noise cancellation signal; and (ii) combining the feedforward noise cancellation signal, the aware mode signal, and the filtered playback signal with the feedback signal to provide a first combined signal.

[0008] In some cases, combining the playback signal with the feedback signal includes (i) combining the feedforward noise cancellation signal, the aware mode signal, and the filtered playback signal to provide a second combined signal; and (ii) combining the second combined signal with the feedback signal to provide the first combined signal.

[0009] In some examples, in response to detecting the feedback instability, the driver command signal is filtered using a first notch filter to provide a filtered driver command signal, and the filtered driver command signal is provided to an acoustic transducer for conversion to acoustic energy.

[0010] In some examples, in response to detecting the feedback instability, the reproduced audio signal is filtered with a second notch filter.

[0011] In some implementations, the steps of combining the reproduced audio signal with a feedback signal and filtering the first combined signal using a feedback filter are performed on a first processing component, and the steps of comparing the first combined signal with the feedback signal and detecting feedback instability are performed on a second processing component.

[0012] In another aspect, a playback audio signal is filtered using an equalization filter to provide a filtered playback signal. A feedforward signal from a feedforward microphone is filtered using an awareness mode filter to provide an awareness mode signal. The awareness mode signal and the filtered playback signal are combined to provide a first combined signal. The feedforward signal is filtered using a feedforward filter to provide a feedforward noise cancellation signal. The feedforward noise cancellation signal and the first combined signal are combined to provide a second combined signal. The second combined signal is combined with a feedback signal from a feedback microphone to provide a third combined signal. The third combined signal is filtered using a feedback filter to provide a driver command signal. The driver command signal is provided to an acoustic transducer for conversion to acoustic energy. The third combined signal is compared to the feedback signal, and feedback instability is detected based on the comparison.

[0013] Implementations may include one or any combination of the above and / or below features.

[0014] According to another aspect, a feedback signal from a feedback microphone is filtered using a feedback noise cancellation filter to provide a feedback noise cancellation signal, the feedback noise cancellation signal being related to the feedback signal by a first transfer function. A playback audio signal is combined with the feedback noise cancellation signal to provide a driver command signal. The driver command signal is provided to an acoustic transducer for conversion to acoustic energy. The driver command signal is filtered using a first inverse filter to provide a reference signal, the first inverse filter being configured to have a second transfer function that is the inverse of the first transfer function. The feedback noise cancellation signal is filtered using a second inverse filter to provide an estimate of the feedback signal, the second inverse filter being configured to have a third transfer function that is the inverse of the first transfer function. The reference signal is compared to the estimate of the feedback signal to detect feedback instability based on the comparison.

[0015] Implementations may include one or any combination of the above and / or below features.

[0016] In some implementations, combining the reproduced audio signal with the feedback noise cancellation signal includes filtering the reproduced audio signal with an equalization filter to provide a filtered reproduced signal, and combining the filtered reproduced signal with the feedback noise cancellation signal to provide the driver command signal.

[0017] In some implementations, combining the playback audio signal with the feedback noise cancellation signal includes (i) filtering a feedforward signal from a feedforward microphone with an aware mode filter to provide an aware mode signal; and (ii) combining the aware mode signal, the filtered playback signal, and the feedback noise cancellation signal to provide a driver command signal.

[0018] In some examples, combining the playback signal with the feedback noise cancellation signal includes filtering the feedforward signal with a feedforward filter to provide the feedforward noise cancellation signal, and combining the feedforward noise cancellation signal, the aware mode signal, and the filtered playback signal with the feedback noise cancellation signal to provide the driver command signal.

[0019] In some examples, combining the playback signal with the feedback noise cancellation signal includes (i) combining the feedforward noise cancellation signal, the aware mode signal, and the filtered playback signal to provide a first combined signal; and (ii) combining the first combined signal with the feedback noise cancellation signal to provide the driver command signal.

[0020] In some implementations, in response to detecting the feedback instability, the feedback noise cancellation signal is filtered with a first notch filter to provide a filtered feedback noise cancellation signal.

[0021] In some implementations, in response to detecting the feedback instability, the reproduced audio signal is filtered with a second notch filter.

[0022] In some cases, the steps of filtering the feedback signal and combining the reproduced audio signal with the feedback noise cancellation signal are performed on a first processing component, and the steps of filtering the driver command signal with a first inverse filter, filtering the feedback noise cancellation signal with a second inverse filter, and comparing the reference signal with the estimate of the feedback signal are performed on a second processing component.

[0023] In yet another aspect, the playback audio signal is filtered using an equalization filter to provide a filtered playback signal. The feedforward signal from the feedforward microphone is filtered using an aware mode filter to provide an aware mode signal. The aware mode signal and the filtered playback signal are combined to provide a first combined signal. The feedforward signal is filtered using the feedforward filter to provide a feedforward noise cancellation signal. The feedforward noise cancellation signal and the first combined signal are combined to provide a second combined signal. The feedback signal from the feedback microphone is filtered using a feedback noise cancellation filter to provide a feedback noise cancellation signal. The feedback noise cancellation signal is related to the feedback signal by a first transfer function. The second combined signal is combined with the feedback noise cancellation signal to provide a driver command signal. The driver command signal is provided to an acoustic transducer for conversion to acoustic energy. The driver command signal is filtered using a first inverse filter to provide a reference signal. The first inverse filter is configured to have a second transfer function that is the inverse of the first transfer function. The feedback noise cancellation signal is filtered using a second inverse filter to provide an estimate of the feedback signal. The second inverse filter is configured to have a third transfer function that is the inverse of the first transfer function. The reference signal is compared to the estimate of the feedback signal to detect feedback instability based on the comparison.

[0024] Implementations may include one of the above features or any combination thereof.

[0025] Further aspects, embodiments, and advantages of these exemplary aspects and embodiments are discussed in detail below. The examples disclosed herein can be combined with other examples in any manner consistent with at least one of the principles disclosed herein, and further, references to "an example," "some examples," "an alternate example," "various examples," "one example," etc. are not necessarily mutually exclusive and are intended to indicate that a particular feature, structure, or characteristic described may be included in at least one embodiment. Appearances of such terms herein do not necessarily all refer to the same embodiment. [Brief explanation of the drawings]

[0026] 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. These 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 as a limiting boundary of the invention. In the drawings, identical or nearly identical components shown in various figures may be labeled with the same or similar numerals. For clarity, not all components may be labeled in every figure. In the drawings, [Figure 1] FIG. 1 is a perspective view of an exemplary headset form factor. [Figure 2] FIG. 1 is a schematic block diagram of an exemplary audio processing system that may be incorporated into various audio systems. [Figure 3] 1 is a schematic diagram of a prior art system for instability detection; [Figure 4] 1 is a schematic diagram of an exemplary system for instability detection according to the present disclosure. [Figure 5] FIG. 1 is a schematic diagram of another exemplary system for instability detection according to the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0027] Aspects of the present disclosure are directed to noise-canceling headphones, headsets, or other audio systems and methods for detecting instabilities in the noise-canceling system. The noise-canceling system operates to reduce acoustic noise components heard by a user of the audio system. The noise-canceling system may include feedforward and / or feedback characteristics. The feedforward component detects noise outside the headset (e.g., via an external microphone) and acts to provide an anti-noise signal that counters the external noise that is likely to be transmitted through the user's ear. The feedback component detects acoustic signals reaching the user's ear (e.g., via an internal microphone) and processes the detected signal to address any signal components that should not be part of the user's acoustic experience. The embodiments disclosed herein may be coupled to or located in connection with other systems via wired or wireless means, or may be independent of any other systems or devices.

[0028] The systems and methods disclosed herein may, in some examples, include or operate in headsets, headphones, hearing aids, or other personal audio devices, as well as acoustic noise reduction systems that may be applied in home, office, or automotive environments. Throughout this disclosure, the terms "headset," "headphones," "earphones," and "headphone set" are used interchangeably, and no distinction is meant to be made by using one term over another unless the context clearly indicates otherwise. Furthermore, aspects and examples according to aspects and examples disclosed herein are applicable to various form factors, such as in-ear transducers or earphones and on-ear or over-ear headphones.

[0029] The disclosed examples may be combined with other examples in any manner consistent with at least one of the principles disclosed herein, and further, references to "an example," "some examples," "an alternate example," "various examples," "one example," etc. are not necessarily mutually exclusive and are intended to indicate that a particular feature, structure, or characteristic being described may be included in at least one example. Appearances of such terms herein do not necessarily all refer to the same example.

[0030] It will be understood that the example methods and devices discussed herein are not limited in application to the details of construction and the arrangement of components set forth in the following description or illustrated in the accompanying drawings. The methods and devices of the present invention can be implemented in other embodiments and can be practiced or carried out in various ways. Specific examples are provided herein for purposes of illustration only and are not intended to be limiting. Additionally, the phraseology and terminology used herein are for descriptive purposes only and should not be considered limiting. The use of words such as "including," "comprising," "having," "containing," and "involving," as well as variations thereof, herein are meant to encompass the items listed below and equivalents thereof, as well as other items. References to "or" may be construed as inclusive, such that all terms preceded by "or" refer to either one, more than one, or all of the listed terms. References to front, back, left, right, up, down, above, below, and across are for convenience of description and are not intended to limit the present systems and methods, or components thereof, to any one positional or spatial orientation.

[0031] For various components described herein, the designation "a" or "b" in a reference number may be used to indicate a "right" or "left" version of one or more components. If no such designation is included, the description is equally applicable to either the right or left, regardless of right or left, which is generally the case for the various embodiments described herein. Furthermore, the aspects and examples described herein are equally applicable to mono or single-sided personal audio devices, and do not necessarily require both right and left sides.

[0032] FIG. 1 illustrates a headset 100. The headset 100 includes a right earpiece 102a and a left earpiece 102b interconnected by a support structure 104 (e.g., a headband) worn by a user. In some examples, the two earpieces 102 may be independent of each other and not interconnected by a support structure. In some cases, the two earpieces 102 may be in the form of in-ear headphones (e.g., earphones). Each earpiece 102 may include one or more microphones, such as a feedforward microphone 106 and / or a feedback microphone 108. The feedforward microphone 106, when properly worn, can be configured to detect acoustic signals outside the earpiece 102, e.g., to detect acoustic signals in the surrounding environment before they reach the user's ears. The feedback microphone 108, when properly worn, can be configured to detect acoustic signals within an acoustic volume formed with the user's ears, e.g., to detect acoustic signals reaching the user's ears. Each earpiece also includes a driver 110a, 110b (collectively 110), which is an acoustic transducer for converting, for example, an electrical signal into an acoustic signal that the user can hear. In various examples, one or more drivers may be included in an earpiece, and in some cases, the earpiece may include only a feedforward microphone or only a feedback microphone.

[0033] Although reference numerals 106 and 108 are used to refer to one or more microphones, the visual elements shown in the figures may, in some instances, represent acoustic ports through which acoustic signals enter and ultimately reach such microphones, which may be internal and physically invisible from the outside. In embodiments, one or more of the microphones 106, 108 may be immediately adjacent to the interior of the acoustic port or may be removed a distance from the acoustic port, and may include an acoustic waveguide between the acoustic port and the associated microphone.

[0034] 2 illustrates an example of a processing unit 200 that may be physically housed somewhere on or within headset 100. Processing unit 200 may include a processor 202, an audio interface 204, and a battery 206. As shown, processor 202 comprises multiple processors, including a high-speed digital signal processor (high-speed DSP) 208 and a general-purpose digital signal processor (general-purpose DSP) 210. In various examples, processing unit 200 may be coupled to one or more feedforward microphones 106, drivers 110, and / or feedback microphones 108. In various examples, interface 204 may be a wired or wireless interface for receiving audio signals, such as playback audio signals or program content signals, and may include additional interface functionality, such as a user interface for receiving user input and / or configuration options. In various examples, battery 206 may be replaceable and / or rechargeable. In various examples, processing unit 200 may be powered through means other than or in addition to battery 206, such as by a wired power source. In some examples, the system may be designed for noise reduction only and may not include an interface 204 for receiving a playback signal.

[0035] FIG. 3 illustrates a system and method for processing a microphone signal to reduce noise reaching a user's ear. FIG. 3 is a simplified schematic diagram for clarifying the characteristics of a noise reduction system. Various examples of complete systems may include amplifiers, analog-to-digital conversion (ADC), digital-to-analog conversion (DAC), equalization, subband separation and synthesis, and other signal processing. In some examples, a playback signal 302, p(t), may be received to be rendered as an acoustic signal by a driver 110. The feedforward microphone 106 may be coupled to a feedforward transfer function K nc to generate a feedforward anti-noise signal 308. The feedback microphone 108 may provide a feedforward signal 304 that is processed by a feedforward filter 306 having a feedback transfer function K fb to generate a feedback anti-noise signal 314. In some examples, any of the regenerated signal 302, the feedforward anti-noise signal 308, and / or the feedback anti-noise signal 314 may be combined to generate a driver signal 316 (also known as a “driver command signal” or “command signal”) that is provided to the driver 110. In some examples, the regenerated signal may be equalized via an equalization filter 313 to provide an equalized regenerated signal 315 that is combined with the feedforward anti-noise signal 308 and the feedback anti-noise signal 314 to generate the driver signal 316. In various examples, any of the regenerated signal 302, the feedforward anti-noise signal 308, and / or the feedback anti-noise signal 314 may be omitted, and / or the components necessary to support any of these signals may not be included in a particular implementation of the system.

[0036] In some implementations, headphones 100 can include a feature that may be referred to as an "aware mode." In some cases, this feature may also be referred to as a "hear-through" mode, a "talk-through" mode, or a "pass-through" mode. In such a mode, feed-forward microphone 106 or other detection means can be used to detect external sounds that a user may want to hear, and the ANR system can be configured to pass such sounds to be reproduced by driver 110. In some cases, the sensor used for the aware mode feature can be a sensor, such as a microphone, separate from feed-forward microphone 106.

[0037] In some implementations, the ANR system can allow a user to control the amount of ambient noise passing through the device while maintaining ANR functionality, as described in U.S. Patent No. 10,096,313, which is incorporated herein by reference in its entirety. For example, an adjustable gain can be implemented, such as by selecting a set of coefficients for the aware mode filter 318, to allow a user to control the amount of ambient noise passing through the device. Alternatively or additionally, the adjustable gain can be implemented using a variable gain amplifier (not shown) placed in series with the aware mode filter 318. In some cases, the adjustable gain can be implemented using a combination of a variable gain amplifier (not shown) and an adjustment to the aware mode filter 318, each placed in the aware mode signal path.

[0038] 3, the feedforward microphone signal 304 is filtered with an aware mode filter 318 to provide an aware mode signal 320, which is combined with the equalized playback signal 315, the feedforward anti-noise signal 308, and the feedback anti-noise signal 314 to provide the driver signal 316. As shown in FIG. 3, the aware mode signal 320 may first be combined with the equalized playback signal 315 to provide a first combined signal 322. The first combined signal 322 may then be combined with the feedforward anti-noise signal 308 to provide a second combined signal 324, which may then be combined with the feedback anti-noise signal 308 to provide the driver signal 316.

[0039] The electrical and physical system shown in FIG. 3 is a plant transfer function G that characterizes the transfer from the driver signal 316 to the feedback signal 310. sd In other words, the response of the feedback signal 310 to the driver signal 316 is expressed as a function of the plant transfer function G sd Therefore, the feedback noise reduction loop system is characterized by the combined (loop) transfer function G sd K fb It is characterized by:

[0040] At one or more frequencies, the loop transfer function G sd K fb When is equal to 1, G sd K fb =1, the loop system may diverge, gradually increasing the amplitude of at least one frequency component of the driver signal 316. This may be perceived by the user as an audible artifact such as a tone or squeal, or may reach a limit at the maximum amplitude that the driver 110 can produce, which may be very loud. Therefore, when such a condition exists, the feedback noise reduction system may be described as unstable.

[0041] To detect impending squeal / instability, the prior art system of Figure 3 compares the feedback microphone input to a filtered version of the driver command signal 316. In that regard, the driver command signal 316 is filtered using a feedback filter transfer function K fb The transfer function K is the inverse of fb -1 The inverse filtered signal 328 is compared to the feedback microphone signal 310 to detect instability.

[0042] The comparison operation is offloaded to the general-purpose DSP 210. First, the signals are each filtered through a respective high-pass filter 330a, 330b. Next, the sum and difference are calculated for these high-pass filtered signals. The sum and difference signals are then squared (332a, 332b) and smoothed (334a, 334b). Finally, the smoothed sum of squares (SSS) and the smoothed difference of squares (SSD) are compared. In one particular example, instability is detected when the following two conditions are met: SSS>-15dB, and SSS / SSD>9dB for 2 ms

[0043] If instability is detected, the notch filter 336 is activated, which reduces the controller gain in the sensitive frequency region, resulting in a stable overall system even if the nozzle is blocked. When the system is stable, the feedback notch filter 336 acts as a simple pass-through filter. The system also includes a second notch filter 338.

[0044] Because the aware mode signal 320 and equalized audio signal 315 are injected after the feedback filter 312, the feedback filter 312 is actually trying to reject the playback signal 315 and the aware mode content (input audio). The equalization filter 313 is designed to account for the fact that the controller is naturally trying to reject its input. Simply put, the equalization filter 313 essentially increases the gain until it sounds correct. However, when the feedback filter 312 is effectively changed by activating the feedback notch filter 336, the input audio path needs to be modified to account for that change, which is the function of the second notch filter 338.

[0045] This existing system has two undesirable aspects. First, the inverse feedback filter 326 must be the same size as the feedback filter 312, with the same number of biquads. Unfortunately, there is a limited number of instructions that can fit into the high-speed processor 208, and it may be preferable to use these instructions for other things. Second, once instability is detected and a notch filter 336 is added to the controller, the transfer function K of the feedback filter is reduced. fb is effectively changed. As a result, the filtered driver signal 328 is fb -1 is no longer a valid detection signal, and when the notch filter 336 is added, fb The transfer function K of the inverse feedback filter 326 is not updated to match changes to fb -1 can also be updated when a notch filter 336 is added, but that requires using up more instructions.

[0046] FIG. 4 shows an implementation that can help address these shortcomings. In this new configuration, various components of the driver signal, including the feedforward noise cancellation signal, the awareness mode signal, and the equalized audio signal, are combined, and the combined signal 324 is injected upstream of the feedback filter 310 (summed with the feedback microphone signal 310) to provide the reference signal 402. This requires us to design a different filter because all of these signals must pass through the feedback filter 312, but it is a simple filter design. This simple modification allows us to move the tap for the reference signal upstream of the feedback filter 312, eliminating the need for the inverse filter 326 (FIG. 3). In other words, this is essentially the same as taking the signal at the output of the feedback filter 312 and passing it through the inverse filter 326, as done in conventional systems. Therefore, this modification essentially allows instability detection to be performed without the need for the inverse filter 326 (FIG. 3). This is the first advantage.

[0047] A second advantage is that because the detection is unaffected by the feedback filter 312, the detection should still be valid even if the feedback filter 312 is effectively changed via activation of the feedback notch filter 336. That is, because the reference signal 402 is tapped before passing through the feedback filter 312, changing the effective transfer function of the feedback filter 312 does not change the meaning of the signal 402. Thus, the reference signal 402 can still be usefully compared to the feedback microphone signal 310.

[0048] All processing for the comparison remains the same, only the reference signal 402 is different. Operations are rearranged in the high-speed DSP 208 so that equivalent signals can be obtained without the need to use an extra inverse feedback filter 326. Changes to the command injection point do not change anything that is being performed in the general-purpose DSP 210.

[0049] FIG. 5 shows another implementation. In this configuration, rather than moving the injection point of the other driver signal components, the feedback microphone signal 310 is tapped after being filtered by the feedback filter 312. That is, the feedback anti-noise signal 314 is tapped for comparison with the driver signal 316. As shown in FIG. 5, the feedback anti-noise signal 314 may be tapped downstream of the feedback notch filter 336, such that when the feedback notch filter 336 is activated, the notch-filtered feedback anti-noise signal 314' is tapped for comparison with the driver signal 316. The feedback anti-noise signal 314 and the driver signal 316 are spectrally shaped to look like the unfiltered feedback microphone signal, and respective inverse feedback filters 502a, 502b may be used, although it may still be desirable not to require these filters to be implemented on the high-speed DSP 208. The inverse feedback filters 502a, 502b may be approximations. They do not need to be closely matched to the feedback filter 312 because they are identical and are applied to both the feedback anti-noise signal 314 and the driver signal 316, respectively. fb is effectively changed via activation of feedback notch filter 336, the inverse feedback filter 326 (FIG. 3) no longer has its new effective transfer function K fb However, if both signals are captured after the feedback loop, they will be matched by the transfer function K fbRegardless of such changes to , they may or may not still be matched. In some cases, it may be desirable to shape the feedback anti-noise signal 314 and the driver signal 316 to look like the unfiltered feedback microphone signal 310. To achieve that, approximate inverse feedback filters 502 a, 502 b can be applied, which can be done on the slow processor 210 without utilizing valuable instructions on the fast processor 208.

[0050] All of the processing for the comparison remains essentially the same except for the addition of inverse feedback filters 502a, 502b in the processing path on the slower (general purpose) processor.

[0051] The above-described aspects and examples offer numerous potential benefits for personal audio devices that include feedback noise reduction. Stability criteria for feedback control may be defined by engineers during the controller design phase, with various considerations assuming a limited range of variation (of system characteristics) over the life of the system. For example, driver output and microphone sensitivity may change over time and contribute to the electroacoustic transfer function between the driver and feedback microphone. Additional variability may affect design criteria, such as production variation, individual-to-individual variation, variation in user handling, and environmental factors. Such variation may violate stability constraints, and designers must traditionally take a conservative approach to feedback system design to ensure that instability is avoided. Such instability may cause the noise reduction system to add undesired signal components rather than reduce them; therefore, traditional design practices may take a highly conservative approach to avoid instability, potentially at a severe cost to system performance.

[0052] However, aspects and examples of feedback instability detection, as described herein, allow corrective action to be taken to eliminate instability when such conditions occur, enabling system designers to design systems that operate under conditions closer to the instability boundary, thus achieving improved performance over a wider feedback bandwidth. Aspects and examples herein enable reliable detection of if or when the instability boundary is crossed. For example, in in-ear noise-canceling headphones, user handling can commonly block the “nozzle” of the earphone (e.g., a finger momentarily covering the audio port), which can cause extreme physical changes in the electro-acoustic coupling between the driver and the feedback microphone. While conventional systems must be designed to avoid instability even with a blocked nozzle, instability detection according to aspects and examples described herein allows a feedback controller or processor to be designed without the “blocked nozzle” condition as a constraint. Thus, the systems and methods herein can more than double the bandwidth range in which noise reduction by a feedback processor can be effective.

[0053] In various examples, any of the functions of the systems and methods described herein may be implemented or performed by a digital signal processor (DSP), a microprocessor, a logic controller, logic circuitry, or the like, or any combination thereof, and may include analog circuitry and / or other components for any particular implementation. The functions and components disclosed herein may operate in the digital domain, and some examples include analog-to-digital (ADC) conversion of analog signals generated by a microphone, despite the absence of an ADC in the various figures. Such ADC functionality may be incorporated into or otherwise within the signal processor. Any suitable hardware and / or software, including firmware, etc., may be configured to perform or implement components of the aspects and embodiments disclosed herein, and various implementations of the aspects and embodiments may include components and / or functionality in addition to those disclosed.

[0054] Having described several aspects of at least one embodiment, it will be appreciated that various alterations, modifications, and improvements will readily occur to those skilled in the art. Such alterations, modifications, and improvements are intended to be part of this disclosure and be within the scope of the invention. Accordingly, the foregoing description and drawings are by way of example only, with the scope of the invention to be determined from proper construction of the appended claims and their equivalents.

[0055] Although multiple implementations have been described, it is nevertheless understood that additional modifications may be made without departing from the scope of the inventive concepts described herein, and, accordingly, other implementations are within the scope of the following claims.

Claims

1. 1. A method comprising: combining the playback audio signal with a feedback signal from a feedback microphone to provide a first combined signal; filtering the first composite signal with a feedback filter to provide a driver command signal, and providing the driver command signal to an acoustic transducer for conversion into acoustic energy; comparing the first composite signal to the feedback signal and detecting feedback instability based on the comparison.

2. 2. The method of claim 1 , wherein combining the reproduced audio signal with the feedback signal comprises filtering the reproduced audio signal with an equalization filter to provide a filtered reproduced signal, and combining the filtered reproduced signal with the feedback signal to provide the first combined signal.

3. 3. The method of claim 2, wherein combining the playback audio signal with the feedback signal further comprises filtering a feedforward signal from a feedforward microphone with an aware mode filter to provide an aware mode signal; and combining the aware mode signal, the filtered playback signal, and the feedback signal to provide the first combined signal.

4. 4. The method of claim 3, wherein combining the playback signal with the feedback signal further comprises: filtering the feedforward signal with a feedforward filter to provide a feedforward noise-canceling signal; and combining the feedforward noise-canceling signal, the aware mode signal, and the filtered playback signal with the feedback signal to provide the first combined signal.

5. 5. The method of claim 4, wherein combining the playback signal with the feedback signal further comprises combining the feedforward noise cancellation signal, the aware mode signal, and the filtered playback signal to provide a second combined signal, and combining the second combined signal with the feedback signal to provide the first combined signal.

6. 10. The method of claim 1, further comprising: in response to detecting the feedback instability, filtering the driver command signal with a first notch filter to provide a filtered driver command signal; and providing the filtered driver command signal to an acoustic transducer for conversion into acoustic energy.

7. 7. The method of claim 6, further comprising filtering the reproduced audio signal with a second notch filter in response to detecting the feedback instability.

8. 2. The method of claim 1, wherein combining the reproduced audio signal with the feedback signal and filtering the first combined signal with the feedback filter is performed on a first processing component, and comparing the first combined signal with the feedback signal and detecting feedback instability is performed on a second processing component.

9. 1. A method comprising: filtering the reproduced audio signal with an equalization filter to provide a filtered reproduced signal; filtering a feedforward signal from a feedforward microphone with an aware mode filter to provide an aware mode signal; and combining the aware mode signal with the filtered playback signal to provide a first combined signal. filtering the feedforward signal with a feedforward filter to provide a feedforward noise-canceling signal; and combining the feedforward noise-canceling signal with the first combined signal to provide a second combined signal. combining the second composite signal with a feedback signal from a feedback microphone to provide a third composite signal; filtering the third composite signal with a feedback filter to provide a driver command signal, and providing the driver command signal to an acoustic transducer for conversion into acoustic energy; comparing the third composite signal to the feedback signal and detecting feedback instability based on the comparison.

10. 1. A method comprising: filtering a feedback signal from a feedback microphone with a feedback noise cancellation filter to provide a feedback noise cancellation signal, the feedback noise cancellation signal being related to the feedback signal by a first transfer function; combining a playback audio signal with the feedback noise cancellation signal to provide a driver command signal; providing the driver command signals to an acoustic transducer for conversion into acoustic energy; filtering the driver command signal with a first inverse filter configured to have a second transfer function that is an inverse of the first transfer function to provide a reference signal; filtering the feedback noise cancellation signal with a second inverse filter configured to have a third transfer function that is an inverse of the first transfer function to provide an estimate of the feedback signal; comparing the reference signal to the estimate of the feedback signal and detecting feedback instability based on the comparison.

11. 11. The method of claim 10, wherein combining the reproduced audio signal with the feedback noise cancellation signal comprises filtering the reproduced audio signal with an equalization filter to provide a filtered reproduced signal, and combining the filtered reproduced signal with the feedback noise cancellation signal to provide the driver command signal.

12. 12. The method of claim 11 , wherein combining the playback audio signal with the feedback noise cancellation signal further comprises filtering a feedforward signal from a feedforward microphone with an aware mode filter to provide an aware mode signal, and combining the aware mode signal, the filtered playback signal, and the feedback noise cancellation signal to provide the driver command signal.

13. 13. The method of claim 12, wherein combining the playback signal with the feedback noise cancellation signal further comprises filtering the feedforward signal with a feedforward filter to provide a feedforward noise cancellation signal, and combining the feedforward noise cancellation signal, the aware mode signal, and the filtered playback signal with the feedback noise cancellation signal to provide the driver command signal.

14. 14. The method of claim 13, wherein combining the playback signal with the feedback noise cancellation signal further comprises: combining the feedforward noise cancellation signal, the aware mode signal, and the filtered playback signal to provide a first combined signal; and combining the first combined signal with the feedback noise cancellation signal to provide the driver command signal.

15. 11. The method of claim 10, further comprising, in response to detecting the feedback instability, filtering the feedback noise cancellation signal with a first notch filter to provide a filtered feedback noise cancellation signal.

16. 16. The method of claim 15, further comprising filtering the reproduced audio signal with a second notch filter in response to detecting the feedback instability.

17. The steps of filtering the feedback signal and combining the reproduced audio signal with the feedback noise cancellation signal are performed on a first processing component, and include: filtering the driver command signal with the first inverse filter; filtering the feedback noise cancellation signal with the second inverse filter; and The method of claim 10 , wherein the step of comparing the reference signal to the estimate of the feedback signal is performed on a second processing component.

18. 1. A method comprising: filtering the reproduced audio signal with an equalization filter to provide a filtered reproduced signal; filtering a feedforward signal from a feedforward microphone with an aware mode filter to provide an aware mode signal; and combining the aware mode signal with the filtered playback signal to provide a first combined signal. filtering the feedforward signal with a feedforward filter to provide a feedforward noise-canceling signal; and combining the feedforward noise-canceling signal with the first combined signal to provide a second combined signal. filtering a feedback signal from a feedback microphone with a feedback noise cancellation filter to provide a feedback noise cancellation signal, the feedback noise cancellation signal being related to the feedback signal by a first transfer function; combining the second combined signal with the feedback noise cancellation signal to provide a driver command signal; providing the driver command signals to an acoustic transducer for conversion into acoustic energy; filtering the driver command signal with a first inverse filter configured to have a second transfer function that is an inverse of the first transfer function to provide a reference signal; filtering the feedback noise cancellation signal with a second inverse filter configured to have a third transfer function that is an inverse of the first transfer function to provide an estimate of the feedback signal; comparing the reference signal to the estimate of the feedback signal and detecting feedback instability based on the comparison.

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