Robust adaptive noise cancellation system and method

Abstract

An adaptive noise cancellation system and method includes a reference sensor operable to sense ambient noise and generate a corresponding reference signal, an error sensor operable to sense noise in a noise cancellation area and generate a corresponding error signal, a noise cancellation filter operable to receive the reference signal and generate an anti-noise signal to cancel the ambient noise in the cancellation area, an adaptive module operable to receive the reference signal and the error signal and adaptively adjust the anti-noise signal, and a transient activity detection module operable to receive the reference signal, detect a transient noise event, and selectively disable the adaptive module during the detected transient noise event.

Description

[0001] Ali Abdollahzadeh Milani, Govind Kannan, Trausti Thormundsson, HariHariharan, Mark Miller

[0002] CROSS-REFERENCE TO RELATED APPLICATIONS

[0003] This application claims priority to and the benefit of U.S. Provisional Application No. 62 / 782,299, filed on December 19, 2019, entitled “ROBUST ADAPTIVE NOISECANCELING SYSTEMS AND METHODS”; U.S. Provisional Application No. 62 / 782,305, filed on December 19, 2019, entitled “NOISE AMPLIFICATION CONTROL IN ADAPTIVE NOISE CANCELLING SYSTEMS”; and U.S. Provisional Application No. 62 / 782,312, filed on December 19, 2019, entitled “EXTENDED BANDWIDTHADAPTIVE NOISE CANCELLING SYSTEM AND METHODS”, each of which is incorporated herein by reference in its entirety. Technical Field

[0004] The present application relates generally to noise cancellation systems and methods, and more particularly to adaptive noise cancellation systems and methods for use in (e.g., circumaural, supra-aural, and in-ear) headphones, earbuds, hearing aids, and other personal listening devices, for example. Background Art

[0005] Adaptive noise cancellation (ANC) systems typically operate by sensing noise via a reference microphone and generating a corresponding anti-noise signal that is approximately equal in amplitude but opposite in phase to the sensed noise. The noise and anti-noise signal acoustically cancel each other, allowing the user to hear only the desired audio signal. In order to achieve this effect, a low-latency programmable filter path from the reference microphone to the speaker that outputs the anti-noise signal can be implemented. In operation, traditional anti-noise filtering systems cannot completely eliminate all noise, leaving residual noise and / or generating audible artifacts that may distract the user's attention. Therefore, there continues to be a need for improved adaptive noise cancellation systems and methods for headphones, earbuds, and other personal listening devices. Summary of the invention

[0006] Systems and methods for providing adaptive noise cancellation in an audio listening device are disclosed. In various embodiments, the adaptive noise cancellation systems and methods include improved transient active noise detection.

[0007] In one or more embodiments, the adaptive noise cancellation system includes: a reference sensor, which is capable of operating to sense ambient noise and generate a corresponding reference signal, an error sensor, which is capable of operating to sense noise in a noise cancellation area and generate a corresponding error signal, a noise cancellation filter, which is capable of operating to receive the reference signal and generate an anti-noise signal to cancel the ambient noise in the cancellation area, an adaptive module, which is capable of operating to receive the reference signal and the error signal and adaptively adjust the anti-noise signal, and a transient activity detection module, which is capable of operating to receive the reference signal, detect transient noise events, and selectively disable the adaptive module during the detected transient noise event.

[0008] In some embodiments, the adaptive module includes an adaptive gain control block that is operable to update a variable gain component. The input to the adaptive gain control block can be adjusted using a programmable filter to prevent low-frequency transients and / or high-frequency disturbances in the ambient noise. The programmable filter may include: a low-pass filter that filters out high frequencies determined to be within a range that creates constructive interference between the cancellation area and the eardrum reference point; and / or a high-pass filter that filters out low frequencies determined to be within a range that cannot be heard by a user of the noise cancellation system. The adaptive module can be tuned using an error signal sensed in the noise cancellation area to cancel the noise at the eardrum reference point.

[0009] In one or more embodiments, a method includes: receiving a reference signal from a first sensor, the reference signal representing external noise; processing the reference signal through a noise cancellation path including a noise cancellation filter and a variable gain component to generate an anti-noise signal; receiving an error signal from a second sensor, the error signal representing noise in a noise cancellation area; and adaptively adjusting the noise cancellation filter in response to the reference signal, the error signal and an adaptive gain control process to cancel the external noise at an ear drum reference point.

[0010] The method may also include using a programmable filter to adjust the input of the adaptive gain control process to prevent low-frequency transients and / or high-frequency disturbance factors in the external noise. The adjustment may also include: low-pass filtering out high frequencies determined to be in a range that (i) creates constructive interference between the cancellation area and the eardrum reference point and (ii) is different in noise cancellation performance between the cancellation area and the eardrum reference point; and / or high-pass filtering out low frequencies determined to be in a range that the user cannot hear. The method may also include using an error signal sensed in the noise cancellation area to tune the noise cancellation path to cancel the noise at the eardrum reference point.

[0011] The scope of the present invention is defined by the claims, which are incorporated into this section by reference. By considering the following detailed description of one or more embodiments, those skilled in the art will more fully understand the embodiments of the present invention and realize their additional advantages. Reference will be made to the accompanying drawings which will first be briefly described. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Aspects of the present disclosure and their advantages may be better understood with reference to the following drawings and the detailed description that follows. It should be understood that the same reference numerals are used to identify the same elements shown in one or more figures, where the purpose of the illustration is to illustrate the embodiments of the present disclosure and not to limit the present disclosure. The components in the drawings are not necessarily drawn to scale, but emphasis is placed on clearly illustrating the principles of the present disclosure.

[0013] Figure 1 An adaptive noise cancelling headset is illustrated in accordance with one or more embodiments of the present disclosure.

[0014] Figure 2 An adaptive noise cancellation system in accordance with one or more embodiments of the present disclosure is illustrated.

[0015] Figure 3 An adaptive noise cancellation system including a noise amplification control subsystem according to one or more embodiments of the present disclosure is illustrated.

[0016] FIG. 4A to FIG. 4B An adaptive noise cancellation system including an adaptive gain control subsystem according to one or more embodiments of the present disclosure is illustrated.

[0017] Figure 5 A transient activity detector for an adaptive noise cancellation system according to one or more embodiments of the present disclosure is illustrated. DETAILED DESCRIPTION

[0018] According to various embodiments, improved adaptive noise cancellation (ANC) systems and methods are disclosed. An ANC system for headphones or other personal listening devices may include: a noise sensing reference microphone for sensing ambient noise; an error microphone for sensing an acoustic mixture of noise and anti-noise generated by an ANC device; and a signal processing subsystem that generates anti-noise to cancel ambient noise. The signal processing subsystem can be configured to continuously adjust the anti-noise signal to achieve consistent cancellation performance across users, ambient noise conditions, and device units. In various embodiments, the adaptive systems and methods disclosed herein improve the cancellation of ambient noise and reduce perceptible adaptive artifacts.

[0019] The present disclosure addresses many challenges associated with general adaptive noise cancellation systems, including unwanted noise amplification (e.g., due to constructive interference between ambient noise and anti-noise signals), noise cancellation performance during transient noise events, and reduction of audible artifacts produced during adaptation. The systems and methods disclosed herein provide a robust, practical ANC solution that generalizes well to a variety of listening devices and form factors.

[0020] In various embodiments, systems and methods are disclosed for reducing noise amplification that occurs when there is constructive interference between noise and anti-noise within a certain frequency range. An adaptive method is disclosed that includes defining a composite error signal that is incorporated into a noisy shaping filter and deriving a new weight update rule for controlling the adaptation. The solution disclosed herein is adaptive, computationally inexpensive, and can be implemented as an improvement over conventional adaptive frameworks.

[0021] In various embodiments, the systems and methods disclosed herein reduce adaptive artifacts that may be perceived by a listener. For example, low sound pressure level (SPL) artifacts may be present due to the proximity of the anti-noise source to the listener's eardrum. It is also recognized that some artifacts are caused by broadband fluctuations in the amplitude and phase response of the anti-noise path. The improved adaptive systems and methods disclosed herein include an adaptive gain element in the anti-noise signal path to generate a robust error correction signal.

[0022] In various embodiments, the systems and methods disclosed herein provide improved robustness to transient noise events. Many intermittent and unexpected noise events (e.g., head / jaw movement relative to a noise moving microphone, closing a door, turbulence during air travel, etc.) produce low-frequency transients that can potentially corrupt the adaptive loop, leaving unwanted residual noise or generating noise artifacts. In various embodiments, a transient activity detector (TAD) tracks transient behavior and controls adaptation during transient activity.

[0023] Example embodiments of the adaptive noise cancellation system of the present disclosure will now be described with reference to the accompanying drawings. Figure 1 , the adaptive noise cancellation system 100 includes an audio device (such as headphones 110) and audio processing circuits (such as a digital signal processor (DSP) 120, a digital-to-analog converter (DAC) 130, an amplifier 132, a reference microphone 140, a speaker 150, an error microphone 162, and other components).

[0024] In operation, the listener can hear external noise d(n) through the housing and components of the earphone 110. To cancel the noise d(n), the reference microphone 140 senses the external noise, thereby generating a reference signal x(n), which is fed to the DSP 120 through an analog-to-digital converter (ADC) 142. The DSP 120 generates an anti-noise signal y(n), which is fed to the speaker 150 through the DAC 130 and the amplifier 132 to generate anti-noise in the noise cancellation area 160. When the anti-noise is equal in amplitude and opposite in phase to the noise d(n) in the noise cancellation area 160, the noise d(n) will be cancelled in the noise cancellation area 160. The resulting mixture of noise and anti-noise is captured by the error microphone 162, which generates an error signal e(n) to measure the effectiveness of the noise cancellation. The error signal e(n) is fed to the DSP 120 via the ADC 164, which adjusts the amplitude and phase of the anti-noise signal y(n) to minimize the error signal e(n) within the cancellation region (e.g., drives the error signal e(n) to zero). In some embodiments, the speaker 150 may also generate desired audio (e.g., music), which is received by the error microphone 162 and removed from the error signal e(n) during processing. It will be appreciated that Figure 1 The embodiment is one example of an adaptive noise cancellation system, and the systems and methods disclosed herein may be implemented with other adaptive noise cancellation implementations including a reference microphone and an error microphone.

[0025] Figure 2 A robust, configurable adaptive noise cancellation system 200 is shown that achieves improved noise cancellation performance with substantially no audio artifacts. The system 200 is configured to detect noise at an external microphone (e.g., Figure 1The ambient noise is sensed at an external microphone 140 of the listening device, which generates an external noise signal x(n). The ambient noise also passes through a noise path P(z), which includes the housing and components of the listening device, where the ambient noise is received as d(n) at an error microphone (e.g., error microphone 162). The adaptive filter 202 receives the external noise signal x(n) and estimates the noise path P(z) to generate an anti-noise signal y(n) for canceling the noise signal d(n). The anti-noise signal y(n) is gain adjusted by the adaptive gain control 204 and further modified by the system 206 to account for the secondary path S(z) between the adaptive filter 202 and the error microphone.

[0026] The system 200 also includes an adaptation block 220 that includes a noise amplification control (NAC) block 222 and an adaptive gain control block (ADG) 224. In various embodiments, the NAC 222 is operable to minimize frequency-dependent constructive interference, and the ADG 224 is operable to minimize broadband fluctuations in the anti-noise path. The system 200 also includes a transient activity detector (TAD) 226 that is operable to control the system 200 in response to sudden noise fluctuations and impulsive environmental events. The filters 208, 210, 212, 228, 230, 232 provide additional filtering, as described herein with reference to Figures 3 to 5 Further described.

[0027] refer to Figure 3 , an embodiment of a noise amplification control (NAC) subsystem 300 will now be described. The goal of many adaptive noise cancellation systems is to estimate the noise at the eardrum of the listener. This is typically achieved by using noise measurements from a reference microphone and an error microphone, which are located at a small distance from the eardrum. The estimated noise is then inverted into an anti-noise signal that destructively interferes with the actual noise, resulting in the cancellation of the noise. The anti-noise signal is generated using a filter that is adapted to estimate the amplitude and phase offset of each frequency to align the anti-noise with the noise. Depending on the delay and physical transfer function in question, destructive interference may be maintained in certain bandwidths, while constructive interference may be experienced beyond these bandwidths. The listener may perceive this constructive interference as a narrowband amplification of ambient noise (e.g., a "hissing" sound). In many ANC product designs, it is a challenge to reduce or eliminate the "hissing" sound without sacrificing the depth and bandwidth of the cancellation. In traditional low-power embedded systems (e.g., consumer headphones), the reduction of hissing may be extremely difficult to calculate and difficult to control and tune.

[0028] Figure 3The NAC subsystem 300 provides a method for controlling hiss and related sound artifacts that adaptively controls noise amplification in hiss regions while effectively achieving cancellation in non-hiss regions. The NAC block 320 is configured to define a composite error signal incorporated with a noise shaping filter C(z) (e.g., the noise shaping block 308 and the noise shaping block 310) and derive a new weight update rule for the adaptive filter 302. In some embodiments, a least mean square (LMS) framework may be used, including a composite error signal incorporated with a noise shaping filter for deriving a new weight update rule.

[0029] In operation, the NAC block 320 updates the adaptive filter 302W(z) based on the error signal e(n) and a filtered version of the reference signal x(n). In the illustrated embodiment, the NAC block 320 receives the error signal from the filter 312 The cost function minimizes the mean square error: In various embodiments, the anti-noise signal is filtered using a noise shaping filter C(z), such as the noise shaping filter 308 and the noise shaping filter 310, which can be configured to enhance the signal in the hiss region. In some embodiments, in a test environment prior to distribution, the hiss region of a particular headphone can be detected and the noise shaping filter C(z) can be tuned. In some embodiments, the hiss level can be detected during operation and the noise shaping filter C(z) can be adaptively tuned during operation. For example, the hiss level can be determined by comparing the error signal e(n) to the noise signal to determine the region of constructive interference.

[0030] The cost function is suitable for Minimize, where E{.} is the expectation operator, γ is a constant controlling the aggressiveness, and e1(n) is the noise shaped anti-noise signal y'(n). In some embodiments, the NAC 320 derives the weight update rule based on a gradient method. Embodiments of the method can be applied to filtered least mean square methods, adaptive feedback, adaptive hybrid methods, and other noise cancellation methods. In various embodiments, the adaptation is controlled in such a way that the noise amplification is minimized by defining a cost function optimization and deriving an adaptive algorithm that can achieve the optimization.

[0031] refer to Figure 4A and Figure 4B , discloses an embodiment of an adaptive gain (ADG) subsystem 400. In various embodiments, an adaptive gain control block 420 continuously updates a gain element 404 to adjust for changes in various coupling paths. Using a programmable filter B G(z) (e.g., programmable filter 408 and programmable filter 410) to adjust the input of ADG. G (z) is designed to prevent low-frequency transients and high-frequency disturbances in the environment. In some embodiments, filter B G (z) may include a low pass filter and / or a band pass filter that further filters out very low frequencies (eg, <20 Hz that cannot be heard from a speaker).

[0032] It will be appreciated that the physical geometry of the earphones and fit variations between different people can affect noise cancellation performance. For example, the shape of the outer ear and the length of the ear canal can change the acoustic transfer function of interest in ANC applications. In some embodiments, an ANC system in a headphone or other personal listening device (e.g., Figure 1 A system (of the type described herein) uses a noise sensing reference microphone, an error microphone, and a DSP subsystem that generates appropriate anti-noise to cancel the noise field as measured by the error microphone. This results in a cancellation region where the degree of cancellation is maximized at the error microphone location and degrades inversely with wavelength. As a result, the cancellation performance at the ear drum (which is approximately 25 mm from the error microphone) drops significantly for higher frequencies (lower wavelengths), resulting in a loss of cancellation bandwidth as perceived by a user of the noise cancellation system. FIG. 4A to FIG. 4B Embodiments of the invention address these and other problems by maximizing the cancellation bandwidth at the ear drum during the tuning phase and developing an adaptive method that uses an error microphone to adapt to user-specific characteristics during operation.

[0033] For the purposes of this disclosure, the error microphone position is referred to as the ERP (Error Reference Point), and the ear drum position is referred to as the DRP (Ear Drum Reference Point). For an ANC system tuned at the DRP, the error microphone is a good indicator of low frequency cancellation at the DRP, so a robust error correction signal can be derived from a low-passed version of the error microphone signal. This correction signal can then be used to adapt the gain in the anti-noise signal path.

[0034] To maximize cancellation, the ideal placement of the error microphone would be at the eardrum, but this location is unrealistic for many consumer devices. Therefore, the ERP is used to provide an actual signal that roughly indicates the cancellation performance at the DRP. The adaptive algorithm attempts to minimize the ERP signal, which results in (i) reduced cancellation of high-frequency signals at the DRP, and (ii) a higher likelihood of hissing sound artifacts due to constructive interference of high frequencies at the DRP. In traditional methods, an adaptive algorithm using a transfer function from the ERP to the DRP is employed. These methods have many disadvantages, including that the transfer function estimate is inaccurate at high frequencies, low estimation accuracy may affect broadband cancellation performance and cause transient hiss levels, high computational cost, and difficulty in tuning and calibrating for all usage conditions, making deployment impractical for many devices. FIG. 4A to FIG. 4B Embodiments of provide a computationally inexpensive approach that overcomes many of the shortcomings of conventional systems, is easily tuned, for example by measuring certain transfer functions during system design, and is self-calibrating.

[0035] Figure 4A A calibration and tuning arrangement for the adaptive gain subsystem is shown. In this arrangement, the ANC filter 402 is optimized to cancel noise at the DRP during the initial tuning phase. In one embodiment, the device is placed on a head and torso simulator that has a second error microphone at the DRP. E2D (z), S E2D (z) Modeling the ERP to DRP transfer function in the acoustic path shown. The system can then be optimized using a least mean square block 422 to perform ANC tuning to derive the optimal value W based on the error signal e′(n). DRP (z). Tuning in this way helps achieve extended cancellation bandwidth and better performance in the high frequency band. Figure 4B As shown, the adaptive algorithm is configured to continuously update the gain element 404, G, which enables the proposed method to adjust to changes in various coupling paths. In some embodiments, the signal is low-pass filtered and gain adjusted for good low frequency elimination. Third, a programmable filter B is used. G (z) to adjust the input to the adaptive algorithm, the programmable filter B G (z) is programmed so that the ERP signal can mimic the cancellation performance at the DRP. G (z) can be programmed to optimize performance during low frequency transients and high frequency disturbances in the environment.

[0036] will understand, Figure 4AThe embodiments to FIG. B are example implementations, and the methods disclosed therein can be modified for adaptive versions of feedback, feedforward, and hybrid ANC solutions. In some embodiments, instead of adaptive gain elements, purposefully constrained filter elements can be adaptively applied. The calculated gain can have additional nonlinear processing to further increase robustness.

[0037] refer to Figure 5 , an embodiment of a transient activity detector (TAD) 500 is shown. In operation, the TAD 500 detects changes in the sound environment and temporarily stops the update process when sudden / intermittent noise activity is detected. As a result, unwanted adaptation artifacts in the anti-noise signal (e.g., artifacts that may be caused by rapid adaptation) are minimized. Examples of transient events may include conversations by the headphone wearer, honking car horns, head movements, and other similar sound events. A separate set of TAD calculations can be performed on the inputs from each microphone in the ANC system (e.g., a total of 4 microphones in the headphones, including a left error microphone, a left external microphone, a right error microphone, and a right external microphone). Each of the four microphones can be independently enabled or disabled.

[0038] Figure 5 An embodiment of a transient activity detection process for a microphone is shown. The detection state machine 514 is used to assert and de-assert a "detection" output. In various embodiments, the detection output is asserted when the smoothed instantaneous amplitude (output A from LPF 506) is greater than the scaled average noise amplitude (C in this disclosure). After the smoothed instantaneous amplitude A drops below the scaled average noise amplitude C, a release delay counter will cause the detection output to last for a programmable period of time before being de-asserted.

[0039] In the illustrated embodiment, an audio sample 502 from a microphone (e.g., a reference microphone or an error microphone) is received and fed through an absolute value block 504 and then through a low pass filter 506 to generate a smoothed instantaneous amplitude A. In one embodiment, output A includes the average amplitude of the audio sample 502 over a period of time and represents the instantaneous noise value. The value A is provided to a detection state machine 514 and is provided to a saturated low pass filter 508, which has an output B representing the average value of the A value over a second period of time (i.e., the average noise amplitude). A programmable scaling factor defines a threshold for detecting a transient (e.g., 5 times the average noise amplitude) and is multiplied by the average noise amplitude at component 516 to produce a second input C to the detection state machine 514.

[0040] In one embodiment, if the smoothed instantaneous noise amplitude A is greater than the scaled average noise amplitude C, the detection state machine 514 can be operated to indicate adaptive processing (e.g., Figure 2 In various embodiments, the adaptation will be frozen until the instantaneous noise amplitude A is lower than the scaled average noise amplitude C. Figure 2 , when adaptation is stopped, the filter 202 and the adaptive gain control 204 will continue to use the most recent weight and gain values ​​to modify the noise input x(n). In some embodiments, the programmable release delay counter can be operated to maintain the detection output for a programmable time period before being de-asserted. In addition, the attack and release component 512 can be operated to control how quickly the low pass filter 508 rises and falls in response to the instantaneous noise amplitude A. The programmable attack time constant defines the time it takes for the average noise amplitude B to rise when the instantaneous noise is greater than the average noise amplitude B. The programmable release time constant defines the time it takes for the average noise amplitude B to fall when the instantaneous noise amplitude A is lower than the average noise amplitude B.

[0041] Example Embodiments

[0042] Various embodiments of the present disclosure will now be described. In one or more embodiments, a robust adaptive noise cancellation system includes: a reference sensor operable to sense ambient noise and generate a corresponding reference signal; an error sensor operable to sense noise in a noise cancellation region and generate a corresponding error signal; a noise cancellation filter operable to receive the reference signal and generate an anti-noise signal to cancel the ambient noise in the cancellation region; an adaptive module operable to receive the reference signal and the error signal and adaptively adjust the anti-noise signal; and a transient activity detection module operable to receive the reference signal, detect a transient noise event, and selectively disable the adaptive module during the detected transient noise event.

[0043] In a robust adaptive noise cancellation system, the transient noise event may include speech by an operator of the adaptive noise cancellation system, and the transient activity detection module may include a state machine operable to detect the transient noise event and transmit a state command to the adaptive module. The adaptive module is operable to receive the state command and enable and / or disable the adaptation according to the state command.

[0044] In some embodiments of the robust adaptive noise cancellation system, if the smoothed instantaneous amplitude of the received signal is greater than the scaled average noise amplitude of the received signal, the transient noise event is detected, and after the end of the transient noise event is detected, a delay is applied before enabling adaptation. The end of the transient noise event can be detected when the smoothed instantaneous amplitude drops below the scaled average noise amplitude. The scaled average noise amplitude can be derived by applying a programmable scaling factor to the average noise amplitude.

[0045] In some embodiments of the robust adaptive noise cancellation system, the noise cancellation filter is further operable to generate an anti-noise signal based on the stored filter coefficients, and the adaptive module is further operable to modify the stored filter coefficients. The adaptive noise cancellation system also includes a speaker operable to receive the anti-noise signal and generate anti-noise to cancel the noise in the cancellation area. The adaptive module also includes a noise amplification control subsystem and / or an adaptive gain control subsystem.

[0046] In one or more embodiments, a robust active noise cancellation method includes: receiving a reference signal from a first sensor, the reference signal representing external noise; processing the reference signal through a noise cancellation filter to generate an anti-noise signal; outputting the anti-noise signal to a speaker; receiving an error signal from a second sensor, the error signal representing noise in a noise cancellation area; adaptively adjusting the noise cancellation filter in response to the reference signal, the error signal, and a transient noise detection state; and detecting a transient noise event and selectively setting the transient noise detection state to enable and disable adaptive adjustment of the noise cancellation accordingly.

[0047] In some embodiments of the active noise cancellation method, setting the transient noise detection state includes transmitting a state command, wherein the adaptively adjusting the noise cancellation filter also includes receiving the state command and enabling and disabling the adaptation accordingly according to the state command. Detecting the transient noise event may include comparing the smoothed instantaneous amplitude of the received signal with the scaled average noise amplitude of the received signal. In some embodiments, after detecting the end of the transient noise event, a delay is applied before enabling adaptation.

[0048] In some embodiments, the transient noise event is detected when the smoothed instantaneous amplitude falls below the scaled average noise amplitude. The scaled average noise amplitude can be derived by applying a programmable scaling factor to the average noise amplitude. The adaptively adjusting the noise cancellation filter can include a noise amplification control process and / or an adaptive gain control process.

[0049] In one or more embodiments, an adaptive noise cancellation system with noise amplification control includes: a reference sensor operable to sense ambient noise and generate a corresponding reference signal; an error sensor operable to sense noise in a noise cancellation region and generate a corresponding error signal; a noise cancellation filter operable to receive the reference signal and generate an anti-noise signal to cancel the ambient noise in the cancellation region; and an adaptive module operable to receive the reference signal and the error signal and adaptively adjust the anti-noise signal. The adaptive module includes a noise amplification control module operable to adaptively control noise amplification in at least one hiss region of the anti-noise signal while achieving cancellation in a non-hiss region of the anti-noise signal.

[0050] In some embodiments of an adaptive noise cancellation system with noise amplification control, the hiss region of the anti-noise signal includes a frequency bandwidth in which constructive interference between the ambient noise and the anti-noise signal is detected. The noise amplification control module is operable to define a composite error signal, the composite error signal is incorporated into a noise shaping filter, and to derive a new weight update rule for the noise cancellation filter, and / or to derive a new weight update rule using a least mean square algorithm. The noise shaping filter can be adaptively tuned during operation, and / or the weight update rule is derived using a gradient.

[0051] In some embodiments of an adaptive noise cancellation system having noise amplification control, the noise amplification control adapts the cost function to Minimize, where E{.} is an expectation operator, γ is a constant controlling aggressiveness, and e1(n) is the noise shaped anti-noise signal y'(n). A transient activity detection module may be provided to receive the reference signal, detect transient noise events and selectively disable the adaptive module during the detected transient noise event. The noise cancellation filter may also be operable to generate the anti-noise signal based on stored filter coefficients; and wherein the adaptive module is further operable to modify the stored filter coefficients. The system may also include a speaker operable to receive the anti-noise signal and generate anti-noise to cancel the noise in the cancellation area.

[0052] In one or more embodiments, a method for adaptive noise cancellation with noise amplification control includes: receiving a reference signal from a first sensor, the reference signal representing external noise; processing the reference signal through a noise cancellation filter to generate an anti-noise signal; outputting the anti-noise signal to a speaker; receiving an error signal from an error sensor, the error signal representing noise in a noise cancellation region; and adaptively adjusting the noise cancellation filter in response to the reference signal, the error signal, and a noise amplification control process. The noise amplification control process includes adaptively controlling noise amplification in at least one hiss region of the anti-noise signal while achieving cancellation in a non-hiss region of the anti-noise signal.

[0053] In some embodiments of the method of adaptive noise cancellation with noise amplification control, the hiss region of the anti-noise signal includes the following frequency bandwidth in which constructive interference between the ambient noise and the anti-noise signal is detected. The noise amplification control process may also include: defining a composite error signal, the composite error signal is incorporated into a noise shaping filter, and deriving a new weight update rule for the noise cancellation filter; using a least mean square algorithm to derive a new weight update rule; adaptively tuning the noise shaping filter during operation; and / or adapting a cost function to Minimize, where E{.} is the expectation operator, γ is a constant controlling the aggressiveness, and e1(n) is the noise-shaped anti-noise signal y'(n). The weight update rule can be derived using the gradient.

[0054] In some embodiments of the method of adaptive noise cancellation with noise amplification control, the method further comprises detecting transient noise events and selectively setting a transient noise detection state to correspondingly enable and disable the adaptive adjustment of the noise cancellation filter, and / or generate the anti-noise signal according to the stored filter coefficients.

[0055] In one or more embodiments, an extended bandwidth adaptive noise cancellation system includes: a reference sensor operable to sense ambient noise and generate a corresponding reference signal; an error sensor operable to sense noise in a noise cancellation region and generate a corresponding error signal; a noise cancellation path, the noise cancellation path including a noise cancellation filter and a variable gain component, the noise cancellation path operable to receive the reference signal and generate an anti-noise signal to cancel the ambient noise at an ear drum reference point; and an adaptive module operable to receive the reference signal and the error signal and adaptively adjust the weights of the noise cancellation filter and / or the variable gain component. The adaptive module may include an adaptive gain control block operable to update the variable gain component.

[0056] In some embodiments of the extended bandwidth adaptive noise cancellation system, the input to the adaptive gain control block is conditioned using a programmable filter operable to prevent low frequency transients and / or high frequency disturbances in the ambient noise, and / or the programmable filter includes a low pass filter that filters out high frequencies determined to be within a range that creates constructive interference between the cancellation zone and the ear drum reference point. The programmable filter may include a high pass filter that filters out low frequencies determined to be within a range that cannot be heard by a user of the noise cancellation system.

[0057] In some embodiments of the extended bandwidth adaptive noise cancellation system, the error signal sensed in the noise cancellation region is used to tune the adaptive module to cancel the noise at the eardrum reference point. The adaptive module may also include a noise amplification control module operable to adaptively control noise amplification in at least one hiss region of the anti-noise signal while achieving cancellation in a non-hiss region of the anti-noise signal. The hiss region of the anti-noise signal may include a frequency bandwidth in which constructive interference between the ambient noise and the anti-noise signal is detected.

[0058] In some embodiments, the extended bandwidth adaptive noise cancellation system further comprises a transient activity detection module operable to receive the reference signal, detect transient noise events, and selectively disable the adaptive module during the detected transient noise event. The noise cancellation filter may also be operable to generate the anti-noise signal based on the stored filter coefficients; and wherein the adaptive module is further operable to modify the stored filter coefficients. The extended bandwidth adaptive noise cancellation system may further comprise a speaker operable to receive the anti-noise signal and generate anti-noise to cancel the noise in the cancellation area.

[0059] In one or more embodiments, a method of operating an extended bandwidth adaptive noise cancellation system includes: receiving a reference signal from a first sensor, the reference signal representing external noise; processing the reference signal through a noise cancellation path including a noise cancellation filter and a variable gain component to generate an anti-noise signal; receiving an error signal from a second sensor, the error signal representing noise in a noise cancellation area; and adaptively adjusting the noise cancellation filter in response to the reference signal, the error signal and an adaptive gain control process to cancel the external noise at an ear drum reference point.

[0060] In some embodiments, the method of operating an extended bandwidth adaptive noise cancellation system further comprises using a programmable filter to adjust an input to the adaptive gain control process to prevent low frequency transients and / or high frequency disturbance factors in the external noise, wherein the adjustment further comprises low pass filtering out high frequencies determined to be within a range that creates constructive interference between the cancellation region and the eardrum reference point, and / or wherein the adjustment further comprises high pass filtering out low frequencies determined to be within a range that is inaudible to a user.

[0061] In one or more embodiments, the method of operating an extended bandwidth adaptive noise cancellation system further comprises using the error signal sensed in the noise cancellation region to tune the noise cancellation path to cancel the noise at the eardrum reference point, and / or adaptively controlling noise amplification in at least one hiss region of the anti-noise signal through a noise amplification control process while achieving cancellation in a non-hiss region of the anti-noise signal. The hiss region of the anti-noise signal may include a frequency bandwidth in which constructive interference between the external noise and the anti-noise signal is detected.

[0062] In one or more embodiments, the method of operating an extended bandwidth adaptive noise cancellation system further comprises receiving the reference signal through a transient activity detection process, detecting a transient noise event, and selectively disabling adaptively adjusting the noise cancellation filter during the detected transient noise event. The method may also include generating the anti-noise signal based on the stored filter coefficients; and adaptively modifying the stored filter coefficients during operation, and / or outputting the anti-noise signal to a speaker to generate anti-noise to cancel the noise in the cancellation area.

[0063] The above disclosure is not intended to limit the disclosure to the precise form disclosed or to the specific field of use. Therefore, in view of the disclosure, various alternative embodiments and / or modifications to the disclosure are possible, whether explicitly described or implied herein. Having thus described the embodiments of the disclosure, one of ordinary skill in the art will recognize that changes can be made in form and detail without departing from the scope of the disclosure. Therefore, the disclosure is limited only by the claims.

Claims

1. An adaptive noise cancellation system, comprising: a reference sensor operable to sense ambient noise and generate a corresponding reference signal; an error sensor operable to sense noise in the noise cancellation region and generate a corresponding error signal; a noise cancellation filter operable to receive the reference signal and generate an anti-noise signal to cancel the ambient noise in the cancellation zone; an adaptive module operable to receive the reference signal and the error signal and adaptively adjust the anti-noise signal; as well as A transient activity detection module is operable to receive the reference signal, detect a transient noise event, and selectively disable the adaptive module during the detected transient noise event, wherein the transient noise event is detected if a smoothed instantaneous amplitude of the received signal is greater than a scaled average noise amplitude of the received signal.

2. The adaptive noise cancellation system according to claim 1, wherein: The transient noise event includes speech by an operator of the adaptive noise cancellation system.

3. The adaptive noise cancellation system according to claim 1, wherein: The transient activity detection module includes a state machine operable to detect the transient noise event and communicate a state command to the adaptation module; And wherein the adaptation module is operable to receive the status command and enable and / or disable the adaptation according to the status command.

4. The adaptive noise cancellation system of claim 1, wherein: After detecting the end of the transient noise event, a delay is applied before enabling adaptation.

5. The adaptive noise cancellation system of claim 4, wherein: The end of the transient noise event is detected when the smoothed instantaneous amplitude drops below the scaled average noise amplitude.

6. The adaptive noise cancellation system of claim 5, wherein: The scaled average noise amplitude is derived by applying a programmable scaling factor to the average noise amplitude.

7. The adaptive noise cancellation system of claim 1, wherein: The noise cancellation filter is further operable to generate the anti-noise signal in accordance with stored filter coefficients; and wherein the adaptation module is further operable to modify the stored filter coefficients.

8. The adaptive noise cancellation system of claim 1, further comprising a speaker operable to receive the anti-noise signal and generate anti-noise to cancel the noise in the noise cancellation zone.

9. The adaptive noise cancellation system of claim 1, wherein: The adaptive module also includes a noise amplification control subsystem.

10. The adaptive noise cancellation system of claim 1, wherein: The adaptive module also includes an adaptive gain control subsystem.

11. A method for active noise cancellation, comprising: receiving a reference signal from a first sensor, the reference signal representing external noise; processing the reference signal through a noise cancellation filter to generate an anti-noise signal; outputting the anti-noise signal to a speaker; receiving an error signal from a second sensor, the error signal being representative of noise in the noise cancellation region; adaptively adjusting the noise cancellation filter in response to the reference signal, the error signal, and a transient noise detection state; as well as Detecting a transient noise event and selectively setting the transient noise detection state to correspondingly enable and disable the operation of adaptively adjusting the noise cancellation, detecting the transient noise event includes comparing a smoothed instantaneous amplitude of the received signal with a scaled average noise amplitude of the received signal.

12. The method according to claim 11, wherein: The transient noise event includes speech by a user.

13. The method according to claim 11, wherein: Selectively setting the transient noise detection state includes transmitting a state command; and wherein adaptively adjusting the noise cancellation filter further includes receiving the state command and enabling and disabling the adaptation accordingly based on the state command.

14. The method according to claim 11, wherein: After detecting the end of the transient noise event, a delay is applied before enabling adaptation.

15. The method according to claim 14, wherein: The transient noise event is detected when the smoothed instantaneous amplitude drops below the scaled average noise amplitude.

16. The method according to claim 15, wherein: The scaled average noise amplitude is derived by applying a programmable scaling factor to the average noise amplitude.

17. The method according to claim 11, wherein: Adaptively adjusting the noise cancellation filter includes a noise amplification control process.

18. The method according to claim 11, wherein: Adaptively adjusting the noise cancellation filter includes an adaptive gain control process.

19. An adaptive noise cancellation system comprising: a reference sensor operable to sense ambient noise and generate a corresponding reference signal; an error sensor operable to sense noise in the noise cancellation region and generate a corresponding error signal; a noise cancellation filter operable to receive the reference signal and generate an anti-noise signal to cancel the ambient noise in the cancellation zone; as well as an adaptive module operable to receive the reference signal and the error signal and adaptively adjust the anti-noise signal; wherein the adaptive module comprises a noise amplification control module operable to adaptively control noise amplification in at least one hiss region of the anti-noise signal while achieving noise cancellation in a non-hiss region of the anti-noise signal, The hissing region of the anti-noise signal includes a frequency bandwidth in which constructive interference between the ambient noise and the anti-noise signal is detected.

20. The adaptive noise cancellation system of claim 19, wherein: The noise amplification control module is operable to define a noise shaping filter and to derive a new weight update rule for the noise cancellation filter.

21. The adaptive noise cancellation system of claim 20, wherein: The noise amplification control module is operable to derive new weight update rules using a least mean square algorithm.

22. The adaptive noise cancellation system of claim 20, wherein: The noise shaping filter is adaptively tuned during operation.

23. The adaptive noise cancellation system of claim 20, wherein: The gradients are used to derive the weight update rule.

24. The adaptive noise cancellation system of claim 19, wherein: The noise amplification control adapts the cost function to Minimize, where E{.} is the expectation operator, e(n) is the error signal, γ is a constant controlling the aggressiveness, and e1(n) is the noise-shaped anti-noise signal.

25. The adaptive noise cancellation system of claim 19, wherein: Also included is a transient activity detection module operable to receive the reference signal, detect a transient noise event, and selectively disable the adaptation module during the detected transient noise event.

26. The adaptive noise cancellation system of claim 19, wherein: The noise cancellation filter is further operable to generate the anti-noise signal in accordance with stored filter coefficients; and wherein the adaptation module is further operable to modify the stored filter coefficients.

27. The adaptive noise cancellation system of claim 19, further comprising a speaker operable to receive the anti-noise signal and generate anti-noise to cancel the noise in the noise cancellation zone.

28. A method for noise cancellation, comprising: receiving a reference signal from a first sensor, the reference signal representing external noise; processing the reference signal through a noise cancellation filter to generate an anti-noise signal; outputting the anti-noise signal to a speaker; receiving an error signal from an error sensor, the error signal being representative of noise in the noise cancellation region; as well as adaptively adjusting the noise cancellation filter in response to the reference signal, the error signal, and a noise amplification control process; The noise amplification control process includes adaptively controlling noise amplification in at least one hissing region of the anti-noise signal while achieving noise cancellation in a non-hissing region of the anti-noise signal, The hissing region of the anti-noise signal includes a frequency bandwidth in which constructive interference between the external noise and the anti-noise signal is detected.

29. The method according to claim 28, wherein: The noise amplification control process also includes defining a noise shaping filter and deriving a new weight update rule for the noise cancellation filter.

30. The method of claim 29, wherein: The noise amplification control process also includes using a least mean square algorithm to derive a new weight update rule.

31. The method of claim 29, wherein: The noise amplification control process also includes adaptively tuning the noise shaping filter during operation.

32. The method of claim 29, wherein: The gradients are used to derive the weight update rule.

33. The method of claim 28, wherein: The noise amplification control process also includes adapting the cost function to Minimize, where E{.} is the expectation operator, e(n) is the error signal, γ is a constant controlling the aggressiveness, and e1(n) is the noise-shaped anti-noise signal.

34. The method of claim 28, further comprising: A transient noise event is detected, and a transient noise detection state is selectively set to enable and disable the adaptively adjusting the noise cancellation filter accordingly.

35. The method of claim 28, further comprising: The anti-noise signal is generated according to the stored filter coefficients.

36. An adaptive noise cancellation system comprising: a reference sensor operable to sense ambient noise and generate a corresponding reference signal; an error sensor operable to sense noise in the noise cancellation region and generate a corresponding error signal; a noise cancellation path, the noise cancellation path comprising a noise cancellation filter and a variable gain component, the noise cancellation path being operable to receive the reference signal and generate an anti-noise signal to cancel the ambient noise at an ear drum reference point; an adaptive module operable to receive the reference signal and the error signal and adaptively adjust a weight of the noise cancellation filter and / or the variable gain component; wherein the adaptive module comprises an adaptive gain control block operable to update the variable gain component, and Wherein the adaptive module is tuned based on the error signal to optimize noise cancellation at the ear drum reference point.

37. The adaptive noise cancellation system of claim 36, wherein: The input to the adaptive gain control block is conditioned using a programmable filter operable to prevent low frequency transients and / or high frequency noise.

38. The adaptive noise cancellation system of claim 37, wherein: The programmable filter includes a low pass filter that filters out high frequencies determined to be within a range that creates constructive interference between the cancellation zone and the ear drum reference point.

39. The adaptive noise cancellation system of claim 37, wherein: The programmable filter includes a high pass filter that filters out low frequencies determined to be within a range that is inaudible to a user of the noise cancellation system.

40. The adaptive noise cancellation system of claim 36, wherein: The adaptation module further includes a noise amplification control module operable to adaptively control noise amplification in at least one hiss region of the anti-noise signal while enabling cancellation in non-hiss regions of the anti-noise signal.

41. The adaptive noise cancellation system of claim 40, wherein: The hiss region of the anti-noise signal is a frequency region where constructive interference between the ambient noise and the anti-noise signal is detected.

42. The adaptive noise cancellation system of claim 36, further comprising a transient activity detection module operable to receive the reference signal, detect a transient noise event, and selectively disable the adaptive module during the detected transient noise event.

43. The adaptive noise cancellation system of claim 36, wherein: The noise cancellation filter is further operable to generate the anti-noise signal in accordance with stored filter coefficients; and wherein the adaptation module is further operable to modify the stored filter coefficients.

44. The adaptive noise cancellation system of claim 36, further comprising a speaker operable to receive the anti-noise signal and generate anti-noise to cancel the noise in the noise cancellation zone.

45. A method for noise cancellation, comprising: receiving a reference signal from a first sensor, the reference signal representing external noise; processing the reference signal through a noise cancellation path including a noise cancellation filter and a variable gain component to generate an anti-noise signal; receiving an error signal from a second sensor, the error signal being representative of noise in the noise cancellation region; adaptively adjusting the noise cancellation filter to cancel the external noise at an ear drum reference point in response to the reference signal, the error signal, and an adaptive gain control process; as well as The noise cancellation path is tuned based on the error signal to optimize noise cancellation at the ear drum reference point.

46. ​​The method of claim 45, further comprising: A programmable filter is used to condition the input to the adaptive gain control process to prevent low frequency transients and / or high frequency noise.

47. The method of claim 46, wherein: The adjusting further includes low pass filtering out high frequencies determined to be within a range that creates constructive interference between the cancellation region and the ear drum reference point.

48. The method of claim 47, wherein: The adjusting further includes high-pass filtering out low frequencies that are determined to be in a range that is inaudible to the user.

49. The method of claim 45, further comprising a noise amplification control process, the noise amplification control process comprising adaptively controlling noise amplification in at least one hiss region of the anti-noise signal while achieving cancellation in non-hiss regions of the anti-noise signal.

50. The method of claim 49, wherein: The hissing region of the anti-noise signal is a frequency region in which constructive interference between the external noise and the anti-noise signal is detected.

51. The method of claim 45, further comprising a transient activity detection process, the transient activity detection process comprising: The reference signal is received, a transient noise event is detected, and adaptively adjusting the noise cancellation filter is selectively disabled during the detected transient noise event.

52. The method of claim 45, further comprising: generating the anti-noise signal according to the stored filter coefficients; and adaptively modifying the stored filter coefficients during operation.

53. The method of claim 45, further comprising: The anti-noise signal is output to a speaker to generate anti-noise to cancel the noise in the noise cancellation area.

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