Wearable active noise cancellation (ANR) device with low-frequency feedback loop modulation

Abstract

Various aspects include a wearable audio device with active noise reduction (ANR), wherein the ANR device includes: a feedback microphone; an electroacoustic transducer; and a feedback compensator configured to output a noise reduction signal to the electroacoustic transducer in response to a feedback signal from the feedback microphone, wherein the feedback compensator includes a tunable filter that modulates a loop gain in response to detecting an adverse low-frequency event in the noise reduction signal output from the tunable filter, wherein the tunable filter is configured to maintain a substantially similar loop gain shape near a low-frequency crossover when the low-frequency crossover varies during loop gain modulation.

Description

Technical Field

[0001] The present disclosure generally relates to techniques for controlling overload conditions in active noise reduction (ANR) devices. Background Art

[0002] Headphones and other physical configurations of personal ANR devices that are worn around a user's ears in order to isolate the user's ears from unwanted ambient sounds have become commonplace. ANR devices counteract unwanted ambient noise by actively generating an anti-noise signal. These ANR devices are contrasted with passive noise reduction (PNR) headphones, which simply physically isolate the user's ears from ambient noise. Of particular interest to users are ANR audio devices, such as headphones, earphones and / or other head-mounted audio devices, which also incorporate audio listening functionality, thereby enabling the user to listen to electronically provided audio (e.g., recorded audio or playback of audio received from another device) without the interference of unwanted ambient noise. However, conventional ANR audio devices may not be able to adequately manage noise under certain conditions (e.g., under overload conditions). Summary of the Invention

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

[0004] Disclosed are systems and methods describing an ANR device having a feedback compensator that employs a tunable filter to address overload conditions caused by adverse low-frequency events.

[0005] In some aspects, a wearable audio device with ANR is provided. The device includes: a feedback microphone; an electroacoustic transducer; and a feedback compensator configured to output a noise reduction signal to the electroacoustic transducer in response to a feedback signal from the feedback microphone. The feedback compensator includes a tunable filter that modulates a loop gain in response to detecting an adverse low-frequency event in the noise reduction signal output from the tunable filter, wherein the tunable filter is configured to maintain a substantially similar loop gain shape near a low-frequency crossover when the low-frequency crossover varies during loop gain modulation.

[0006] In certain aspects, a feedback compensator for an ANR device is provided, and the feedback compensator is configured to output a noise reduction signal to an electroacoustic transducer in response to a feedback signal from a feedback microphone. The feedback compensator includes a tunable filter that modulates a loop gain in response to detecting an adverse low-frequency event in the noise reduction signal output from the tunable filter. The tunable filter is configured to maintain a substantially similar loop gain shape near a low-frequency crossover when the low-frequency crossover varies during loop gain modulation.

[0007] Implementations may include one or any combination of the following features.

[0008] In some cases, the feedback compensator includes a logic processor configured to calculate a frequency multiplier value in response to detecting an adverse low frequency event in the noise-reduced signal output from the tunable filter.

[0009] In certain aspects, the frequency multiplier value is calculated according to a method comprising: comparing the noise-reduced signal to a threshold value indicative of an adverse low-frequency event; and responsive to the noise-reduced signal exceeding the threshold value, calculating a current frequency multiplier value.

[0010] In some cases, the method further includes comparing the current multiplier value to a previous multiplier value to determine whether the adverse low-frequency event is increasing or dissipating.

[0011] In some implementations, in response to the current frequency multiplier value being greater than the previous frequency multiplier value, the current frequency multiplier value is output to the tunable filter.

[0012] In some implementations, in response to the current multiplier value being less than the previous multiplier value, an adjusted multiplier value is output to the tunable filter based on a decay function implemented by the logic processor.

[0013] In some cases, an estimator based on predicting an adverse low-frequency event outputs an adjusted frequency multiplier value to the tunable filter.

[0014] In some cases, the feedback compensator further includes a fixed filter configured to filter the feedback microphone signal and output the filtered signal to the tunable filter.

[0015] In various implementations, the substantially similar loop gain shape near the low-frequency crossover includes substantially similar magnitude and phase in shape.

[0016] In some cases, the tunable filter is configured to vary the low frequency crossover by a factor determined by an input multiplier value.

[0017] Two or more features described in this disclosure, including those described in this Summary, can be combined to form implementations not specifically described herein.

[0018] The details of one or more implementations are discussed in the accompanying drawings and the description below. Other features, objects, and advantages will be apparent from the description, drawings, and claims. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1An ANR device according to various specific implementations is shown.

[0020] Figure 2 A block diagram of an ANR device having a feedback compensator including a tunable filter according to various implementations is shown.

[0021] Figure 3 Graphs illustrating different feedback loop gains for a tunable filter according to various implementations are shown.

[0022] Figure 4 Graphs illustrating loop gain sensitivity for different filter settings for a tunable filter according to various implementations are shown.

[0023] Figure 5 Shown for implementation Figure 3 Design of tunable filter with loop gain.

[0024] It should be noted that the drawings of various embodiments are not necessarily drawn to scale. The drawings are intended only to illustrate typical aspects of the present disclosure and therefore should not be considered to limit the scope of the embodiments. In the drawings, similar numbers represent similar elements between the drawings. DETAILED DESCRIPTION

[0025] The present disclosure is based, at least in part, on the recognition that a feedback compensator can be introduced into a wearable active noise reduction (ANR) audio device to provide improved performance. For example, an ANR audio device can include a feedback compensator configured to address adverse low-frequency events.

[0026] Embodiments of the present disclosure relate to an active noise reduction (ANR) device with a feedback compensator that is configured to address overload conditions caused by adverse low-frequency events. In some embodiments, the ANR device can include a configurable digital signal processor (DSP) that can be used to implement various signal flow topologies and filter configurations. Examples of such DSPs are described in U.S. Patents 8,073,150 and 8,073,151, which are incorporated herein by reference in their entirety. Figure 1 An exemplary in-ear ANR device 100 is shown, which includes a feedforward microphone 102, a feedback microphone 104, an output transducer 106 (which may also be referred to as an electroacoustic transducer or an acoustic transducer), and a noise reduction circuit (not shown) coupled to the two microphones and the output transducer to provide an anti-noise signal to the output transducer based on signals detected at the two microphones. Figure 1 (not shown) provides an additional audio signal, such as a music signal or a communication signal, for playback on the output transducer 106 independently of the noise reduction signal. U.S. Patent No. 9,082,388 (also incorporated herein by reference in its entirety) describes a method similar to Figure 1 A specific implementation of the in-ear ANR device is shown.

[0027] Despite Figure 1 Although shown as an in-ear device, features of the ANR device 100 can be incorporated into any type of wearable personal acoustic device, including headphones, earphones, in-ear headphones, over-ear headphones or circumaural headphones, earpieces, and hearing aids. A typical headphone or earphone may include an earbud or earmuff for each ear. The earbuds or earmuffs may be physically tied to each other, such as by a cord, a head-mounted bridge, or a headband or a behind-the-head retention structure. In some implementations, the earbuds or earmuffs of a headset may be connected to each other via a wireless link.

[0028] Figure 2 An exemplary block diagram of an ANR device 200 is shown that includes a feedback compensator 110 to reduce the effects of noise signals picked up by one or more feedback microphones 124. In this case, a feedback noise reduction path 130 drives an output transducer 126 to generate an anti-noise signal. The exemplary signal flow topology also includes other audio signals 122, such as a feedforward noise reduction signal, a music signal, or a communication signal, for playback on the output transducer 126.

[0029] Under nominal operating conditions, the acoustic noise energy that a typical ANR device attempts to reduce is small enough to keep the system hardware within normal operating capacity. However, in some cases, discrete acoustic signals or low-frequency pressure disturbances (e.g., loud pops, explosions, door slams, etc.), referred to herein as "unwelcome low-frequency events," picked up by the feedback microphone can cause the noise reduction circuit to exceed the capacity of the electronics or output transducer in its attempt to reduce the generated noise, thereby producing auditory artifacts that may be objectionable to some users. In other cases, unwelcome low-frequency events are generated internally, such as when a user walks with heavy footsteps or chews crunchy food, the user's ear canal walls may vibrate and generate a large amount of pressure through the inserted earplug. These conditions, referred to herein as overload conditions, can be manifested by, for example, clipping of the amplifier, reaching or exceeding the hard excursion limits of the acoustic driver or transducer, or causing sufficient changes in the acoustic response to cause oscillations and / or excursion levels that result in driver nonlinearity and distorted audio.

[0030] The problem of overload conditions can be particularly severe in small-form-factor ANR devices (such as in-ear headphones). For example, to compensate for adverse low-frequency events (e.g., the sound of a bus going over a pothole, a door slamming, or an airplane taking off), a conventional feedback compensator operating under nominal conditions can generate a signal that requires the acoustic transducer to exceed the corresponding physical excursion limit. Due to acoustic leakage, the excursion or driver displacement required to produce a given pressure typically increases as the frequency decreases. For example, a particular acoustic transducer may require a displacement of 1 mm to generate an anti-noise signal for 100 Hz noise, a displacement of 2 mm to generate an anti-noise signal for 50 Hz noise, and so on. Many acoustic transducers, especially small transducers used in small-form-factor ANR devices, are physically unable to produce such large displacements. In such cases, the high displacement requirements of the compensator can cause the transducer to generate sounds that cause auditory artifacts, which can lead to an unpleasant user experience. Auditory artifacts can include oscillations, potentially unpleasant transient sounds (e.g., "thumps," "breaks," "pops," or "clicks"), or crackling / buzzing sounds.

[0031] Figure 2 The feedback compensator 110 shown solves the above-mentioned problem by providing a tunable filter 114 that modulates the loop gain in response to an undesirable low-frequency event detected in the noise reduction signal 130 output from the tunable filter 114. In this exemplary embodiment, the fixed filter 112 first receives a signal from the feedback microphone 124 and then passes the filtered signal to the tunable filter 114. The fixed filter 112 may, for example, include a typical filter for providing feedback-based ANR and providing a nominal loop gain. The loop gain adjusted by the tunable filter 114 in response to the feedback signal typically comprises the feedback filter response (as implemented by the tunable filter 114) multiplied by the factory transfer function, i.e., the transfer function from the transducer 126 voltage to the microphone 124 voltage.

[0032] In some embodiments, the tunable filter 114 is configured to modulate the loop gain in a manner that increases and decreases at the low-frequency crossover while maintaining a similar loop gain shape near the crossover. In this way, the tunable filter 114 is able to change its filter response based on the feedback signal so that as the low-frequency crossover moves, the feedback loop gain maintains a substantially similar magnitude and phase in shape near the low-frequency crossover. Maintaining a substantially similar loop gain shape ensures that the desired trade-off between stability margin and ANR performance is always maintained, while ensuring that the device 200 does not attempt to react to low-frequency noise (typically subsonic) that is too loud for the device to handle.

[0033] In addition, in some embodiments, a logic processor 116 is employed to determine when the feedback compensator 110 needs to modulate, how much to modulate, and when to return to nominal conditions. In one approach, when an adverse event is detected, the logic processor 116 utilizes a fast attack strategy to cause the tunable filter 114 to immediately reduce low frequency ANR performance (to address the adverse effects as quickly as possible), followed by a slow decay in which the lower frequency performance gradually recovers (to minimize transient artifacts and unnecessary back-and-forth modulation due to repeated or continuous overload events). In some cases, an estimator 120 is provided to determine whether additional adverse events are encountered while modulating the tunable filter 114 so as not to move back to nominal operation until the problematic event no longer occurs. Although not shown, in some approaches, the estimator 120 may also process signals from feedback and feedforward microphones or other inputs, such as output from a machine learning model on a remote accessory device (such as a phone).

[0034] In the exemplary embodiment shown, the threshold processor 118 compares the noise reduction signal 130 to a threshold value indicating an adverse low-frequency event. In various specific implementations, if the threshold processor 118 detects that the threshold value is not exceeded, the low-frequency ANR performance is maintained at a nominal level to provide the desired ANR processing. In response to the threshold processor 118 detecting that the noise reduction signal 130 exceeds the threshold, a multiplier value (FMV) 134 is determined based on the amount by which the threshold value is exceeded (e.g., a continuous range of values ​​from 1 to 6, where 1 represents the nominal condition). For example, if the threshold value is only slightly exceeded, a multiplier value FMV=2 is assigned. If the threshold value is exceeded by a large amount, a multiplier value FMV=6 is assigned. The multiplier value 134 is then sent to the logic processor 116, which, after a delay 132, sends the adjusted multiplier value 136 to the tunable filter 114 to potentially modulate the loop gain. In some embodiments, logic processor 116 adjusts multiplier value 134 based on: (1) delayed (ie, previous) multiplier value 138 ; and (2) estimator output 140 .

[0035] In one approach, the logic processor 116 compares the current multiplier value 134 to the previous multiplier value 138 to determine whether the adverse low-frequency event is increasing or dissipating. If the adverse low-frequency event is increasing (i.e., the current value 134 is greater than the previous value 138), the current multiplier value 134 can be output to the tunable filter 114 without being modified to a fast attack to immediately resolve the event. Alternatively, if the current multiplier value 134 is less than the previous multiplier value 138, the current multiplier value 134 is adjusted and output to the tunable filter 114 based on: (1) the attenuation function 128 implemented by the logic processor 116; and (2) the estimator output 140.

[0036] Decay function 128 may, for example, comprise a time-based function that gradually reduces the initial fast-attack multiplier value over a period of time until it reaches a nominal state. For example, decay function 128 may specify a continuous range of values ​​for tunable filter 114. If estimator 120 determines that additional adverse events are occurring, estimator output 140 may further alter the behavior of decay function 128. For example, if the user of device 200 is running, each step may generate an adverse low-frequency event. Under these conditions, estimator 120 may cause logic processor 116 to maintain a moderate multiplier value rather than repeatedly generating higher fast-attack values ​​or lower decay values.

[0037] In the illustrative example, the FMV may first reach a high value, such as 5. After a short period of time (e.g., a quarter of a second), the FMV will then decay over a certain length of time to, for example, 3. The FMV will then remain at this level for a period of time (e.g., two seconds) before gradually decaying back to 1. If the estimator 120 detects another adverse event, the two-second period will be reset. Therefore, if adverse events continue to occur for less than two seconds, the FMV will remain at 3 until they stop occurring.

[0038] In the exemplary method, the estimator 120 passes the current driver signal 130 through another modulation filter. This modulation filter, unlike the tunable filter 114, uses an estimated value that transforms the current driver signal 130 to what it would be if the tunable filter 114 were not applied, essentially undoing what the tunable filter 114 did (although not in reverse because the estimator 120 is outside the loop).

[0039] In various embodiments, the tunable filter 114 is implemented to maintain a substantially similar loop gain shape when the low frequency crossover is increased or decreased during modulation. Figure 3 , which depicts magnitude and phase plots 300 associated with four different loop gains (e.g., resulting from different input multiplier values), shown as FMV=1, FMV=2, FMV=4, and FMV=8, where FMV=1 corresponds to the initial or nominal signal, FMV=2 corresponds to one octave above the initial signal, FMV=4 corresponds to two octaves above the initial signal, and FMV=8 corresponds to three octaves above the initial signal. As seen in the magnitude plots at the top, each loop gain plot has a substantially similar shape (i.e., slope) at the low-frequency crossover (i.e., the approximate point where the magnitude crosses zero), as indicated by arrow 310. Similarly, as seen in the phase plots at the bottom, each loop gain has a substantially similar phase offset relative to 180 degrees at the low-frequency crossover, as indicated by arrow 320.

[0040] Figure 4 An additional graph is shown for the magnitude and phase of the modulated sensitivity. It can be seen that the sensitivity of the tunable filter 114 also remains consistent for various multiplier values. The sensitivity is mathematically equal to

[0041]

[0042] , which depends on whether the loop gain is defined to include the negative sign of the feedback loop (in the case of Figure 3 (For , the loop gain includes a negative sign, so the first expression applies.) Sensitivity represents the active noise reduction at the feedback microphone 124 (which is slightly different from the situation in the ear at high frequencies), meaning lower is better. Furthermore, the amount of peaks above zero observed near the crossover is a direct measure of the stability margin. The lower the margin, the higher the peaks and the higher the amplification. The phase of the sensitivity check system should be stable.

[0043] Figure 5 Shown for implementation Figure 3 An exemplary tunable filter design with a loop gain of . It can be seen that Figure 3 The nominal loop gain shown (FMV=1) is achieved by the fixed filter 112 alone.

[0044] Return to Figure 2 In various implementations, the tunable filter 114 is implemented in any manner such that the low-frequency crossover can be increased and decreased while maintaining a similar loop gain shape near the crossover. In one exemplary embodiment, a lookup table is used to select a set of filter coefficients based on the input multiplier value 136. Thus, the tunable filter 114 is modulated each time a new multiplier value 136 is received to maintain a similar shape at the low-frequency crossover. In such an embodiment, the tunable filter 114 can be implemented using a set of biquad filters (also known as second-order block (SOS) filters) that can be dynamically updated to change the loop gain and meet the crossover requirements. In one approach, the filter coefficients are pre-calculated for a set of stepped FMVs (e.g., 10). When the FMV fed into the tunable filter 114 changes, the closest value of the 10 at any given time is selected, and the corresponding filter coefficients from the lookup table are loaded into the tunable filter. In another variation, when the FMV falls between two values ​​in the lookup table, interpolation coefficients are calculated to obtain a smoother filter. In another variation, the coefficients are dynamically calculated based on the FMV pairs and then loaded into the filter, eliminating the need for a lookup table but requiring more computing resources.

[0045] In another embodiment, the tunable filter 114 is implemented using a set of "fixed" biquad filters, each of which is associated with one or more multiplier values. In this case, when the multiplier value 136 is changed, the coefficients do not change, but rather different actual filters are selectively used.

[0046] It should be understood that one or more functions in the ANR device 200 may be implemented as hardware and / or software, and the various components may include communication paths connecting the components by any conventional means (e.g., hard-wired and / or wireless connections). For example, one or more non-volatile devices (e.g., centralized or distributed devices such as flash memory devices) may store and / or execute programs, algorithms and / or parameters for one or more systems in the ANR device 200. In addition, the functions or portions thereof described herein, and various modifications thereof (hereinafter referred to as "functions") may be implemented at least in part via a computer program product, such as a computer program tangibly embodied in an information carrier, such as one or more non-transitory machine-readable media, for executing, or controlling the operation of, one or more data processing devices, such as a programmable processor, a computer, multiple computers and / or programmable logic components.

[0047] A computer program can be written in any form of programming language, including compiled or interpreted languages, and it can be deployed in any form, including as a stand-alone program or as a module, component, subroutine, or other unit suitable for use in a computing environment. A computer program can be deployed on one computer or executed on multiple computers distributed at one site or multiple sites and interconnected by a network.

[0048] The actions associated with implementing all or part of the functions may be performed by one or more programmable processors executing one or more computer programs to perform the functions. All or part of the functions may be implemented as special-purpose logic circuits, such as FPGAs (field programmable gate arrays) and / or ASICs (application-specific integrated circuits). Processors suitable for executing computer programs include, for example, both general-purpose microprocessors and special-purpose microprocessors, as well as any one or more processors of any type of digital computer. Generally speaking, a processor may receive instructions and data from a read-only memory or a random access memory or both. The components of a computer include a processor for executing instructions and one or more memory devices for storing instructions and data.

[0049] Additionally, actions associated with implementing all or part of the functionality described herein may be performed by one or more networked computing devices. Networked computing devices may be connected via a network, for example, one or more wired and / or wireless networks such as a local area network (LAN), a wide area network (WAN), a personal area network (PAN), an internet-connected device and / or a network and / or cloud-based computing (e.g., a cloud-based server).

[0050] In various specific implementations, electronic components described as being "coupled" may be linked via conventional hardwires and / or wireless means so that these electronic components can transmit data to each other. Additionally, subcomponents within a given component may be considered to be linked via conventional pathways, which may not necessarily be shown.

[0051] For purposes of illustration, components generally labeled in the drawings are considered to be substantially equivalent components, and redundant discussion of those components has been omitted for clarity. The numerical ranges and values ​​described according to various embodiments are merely examples of such ranges and values ​​and are not intended to limit those embodiments. In some cases, the term "about" is used to modify a value, and in these cases, may refer to a value + / - a margin of error (such as measurement error), which may be in the range of up to 1% to 5%.

[0052] A number of implementations have been described. However, it will be appreciated that additional modifications may be made without departing from the scope of the inventive concepts described herein, and therefore, other implementations are within the scope of the following claims.

Claims

1. A wearable audio device with active noise reduction (ANR), comprising: Feedback microphone; electroacoustic transducers; as well as a feedback compensator configured to output a noise reduction signal to the electroacoustic transducer in response to a feedback signal from the feedback microphone, wherein the feedback compensator includes a tunable filter that modulates a loop gain in response to detecting an undesirable low-frequency event in the noise reduction signal output from the tunable filter, and wherein the tunable filter is configured to maintain a similar loop gain shape near a low-frequency crossover when the low-frequency crossover varies during loop gain modulation; wherein the feedback compensator further comprises a logic processor configured to calculate a frequency multiplier value in response to detecting an adverse low frequency event in the noise-reduced signal output from the tunable filter; wherein the frequency multiplier value is calculated according to a method comprising the following operations: comparing the noise-reduced signal to a threshold value indicative of an adverse low-frequency event; as well as In response to the noise reduction signal exceeding the threshold, calculating a current frequency multiplier value; The method further comprises: The current frequency multiplier value is compared to a previous frequency multiplier value to determine whether the adverse low frequency event is increasing or dissipating. 2 . The wearable audio device of claim 1 , wherein in response to the current frequency multiplier value being greater than the previous frequency multiplier value, the current frequency multiplier value is output to the tunable filter.

3. The wearable audio device of claim 1 , wherein in response to the current multiplier value being less than the previous multiplier value, an adjusted multiplier value is output to the tunable filter based on a decay function implemented by the logic processor.

4. The wearable audio device of claim 1 , wherein in response to the current multiplier value being less than the previous multiplier value, an estimator based on predicting an adverse low-frequency event outputs an adjusted multiplier value to the tunable filter. 5 . The wearable audio device of claim 1 , wherein the feedback compensator further comprises a fixed filter configured to filter the feedback signal and output the filtered signal to the tunable filter. 6 . The wearable audio device of claim 1 , wherein the similar loop gain shape near the low-frequency crossover comprises a similar magnitude and phase in shape.

7. The wearable audio device of claim 1 , wherein the tunable filter is configured to vary the low frequency crossover by a factor determined by an input multiplier value.

8. A feedback compensator for an active noise reduction (ANR) device, the feedback compensator configured to output a noise reduction signal to an electroacoustic transducer in response to a feedback signal from a feedback microphone, wherein the feedback compensator comprises: a tunable filter that modulates a loop gain in response to detecting an adverse low-frequency event in the noise-reduced signal output from the tunable filter, wherein the tunable filter is configured to maintain a similar loop gain shape near a low-frequency crossover as the low-frequency crossover varies during loop gain modulation; a logic processor configured to calculate a frequency multiplier value in response to detecting an adverse low frequency event in the noise-reduced signal output from the tunable filter; wherein the frequency multiplier value is calculated according to a method comprising the following operations: comparing the noise-reduced signal to a threshold value indicative of an adverse low-frequency event; as well as In response to the noise reduction signal exceeding the threshold, calculating a current frequency multiplier value; The method further comprises: The current frequency multiplier value is compared to a previous frequency multiplier value to determine whether the adverse low frequency event is increasing or dissipating.

9. The feedback compensator of claim 8, wherein in response to the current frequency multiplier value being greater than the previous frequency multiplier value, the current frequency multiplier value is output to the tunable filter.

10. The feedback compensator of claim 8, wherein in response to the current multiplier value being less than the previous multiplier value, an adjusted multiplier value is output to the tunable filter based on a decay function implemented by the logic processor.

11. The feedback compensator of claim 8, wherein in response to the current multiplier value being less than the previous multiplier value, an estimator based on predicting future adverse low-frequency events outputs an adjusted multiplier value to the tunable filter. 12 . The feedback compensator of claim 8 , wherein the feedback compensator further comprises a fixed filter configured to filter the feedback signal and output the filtered signal to the tunable filter.

13. The feedback compensator of claim 8, wherein the similar loop gain shape near the low frequency crossover comprises similar magnitude and phase in shape.

14. The feedback compensator of claim 8, wherein the tunable filter is configured to vary the low frequency crossover by a factor determined by an input multiplier value.

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