CN113196382A

CN113196382A - Robust adaptive noise cancellation system and method

Info

Publication number: CN113196382A
Application number: CN201980083949.3A
Authority: CN
Inventors: 阿里·阿波德拉扎德·米拉尼; 歌温迪·肯南; 特勒伊斯蒂·索尔蒙森; 哈利·哈里哈兰; 马克·米勒
Original assignee: Google LLC
Current assignee: Google LLC
Priority date: 2018-12-19
Filing date: 2019-12-19
Publication date: 2021-07-30
Also published as: EP3899926A4; JP2023116465A; KR20210092845A; JP7167273B2; EP3899926A1; WO2020132347A1; JP2022029451A; JP2022514895A; JP7282842B2; JP2022048107A; JP7254935B2

Abstract

The 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 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 adaptation 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 adaptation module during the detected transient noise event.

Description

Robust adaptive noise cancellation system and method

Ali Abdollahzadeh Milani、Govind Kannan、Trausti Thormundsson、Hari Hariharan、Mark Miller

Cross Reference to Related Applications

The present application claims U.S. provisional application No. 62/782,299 entitled "ROBUST ADAPTIVE NOISE CANCELING SYSTEMS AND METHODS" filed on 19/12/2019; U.S. provisional application No. 62/782,305 entitled "NOISE AMPLIFICATION CONTROL IN ADAPTIVE NOISE CANCELLING SYSTEMS (NOISE AMPLIFICATION CONTROL in adaptive NOISE cancellation system)" filed on 19/12/2019; and U.S. provisional application No. 62/782,312 entitled "EXTENDED band ADAPTIVE NOISE cancellation system and method" filed on 2019, 12, 19, each of which is incorporated herein by reference in its entirety.

Technical Field

The present application relates generally to noise cancellation systems and methods, and more particularly, for example, to adaptive noise cancellation systems and methods for use in (e.g., over-the-ear, and in-ear) headsets, ear buds, hearing aids, and other personal listening devices.

Background

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 magnitude but opposite in phase to the sensed noise. The noise and anti-noise signals acoustically cancel each other, allowing the user to hear only the desired audio signal. To achieve this effect, a low-latency programmable filter path from the reference microphone to the speaker outputting the anti-noise signal may be implemented. In operation, conventional anti-noise filtering systems do not completely remove all noise, leaving residual noise and/or generating audible artifacts (audible artifacts) that may distract the user. Accordingly, there is a continuing need for improved adaptive noise cancellation systems and methods for headsets, earphones, and other personal listening devices.

Disclosure of Invention

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.

In one or more embodiments, an 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 adaptation 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 adaptation module during the detected transient noise event.

In some embodiments, the adaptation module includes an adaptive gain control block operable to update the variable gain component. The input of the adaptive gain control block may be adjusted using a programmable filter to prevent low frequency transients and/or high frequency disturbing factors 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 region and an eardrum reference point; and/or a high pass filter that filters out low frequencies that are determined to be in a range that is inaudible to a user of the noise cancellation system. The adaptive module may be tuned using an error signal sensed in a noise cancellation region to cancel noise at the eardrum reference point.

In one or more embodiments, a method comprises: receiving a reference signal from a first sensor, the reference signal being representative of external noise; processing the reference signal through a noise cancellation path comprising 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 zone; and adaptively adjusting the noise cancellation filter to cancel the external noise at an eardrum reference point in response to the reference signal, the error signal, and an adaptive gain control process.

The method may further include using a programmable filter to adjust an input of the adaptive gain control process to prevent low frequency transients and/or high frequency disturbing factors in the external noise. The adjusting may further include: low-pass filtering high frequencies determined to be in a range that (i) creates constructive interference between a cancellation region and an eardrum reference point and (ii) differs in noise cancellation performance between the cancellation region and the eardrum reference point; and/or high pass filtering out low frequencies that are determined to be in a range that is inaudible to the user. The method may further include tuning a noise cancellation path using the error signal sensed in the noise cancellation zone to cancel noise at the eardrum reference point.

The scope of the invention is defined by the claims, which are incorporated into this section by reference. Embodiments of the present invention will be more fully understood and additional advantages achieved by those skilled in the art upon consideration of the following detailed description of one or more embodiments. Reference will be made to the accompanying drawings, which will first be described briefly.

Drawings

Aspects of the present disclosure and advantages thereof may be better understood with reference to the following drawings and detailed description. It should be understood that like reference numerals are used to identify like elements illustrated in one or more of the figures, and the illustrations are for the purpose of describing embodiments of the disclosure and are not intended to limit the disclosure. The components in the drawings are not necessarily to scale, emphasis instead being placed upon clearly illustrating the principles of the present disclosure.

Fig. 1 illustrates an adaptive noise cancelling headset in accordance with one or more embodiments of the present disclosure.

Fig. 2 illustrates an adaptive noise cancellation system in accordance with one or more embodiments of the present disclosure.

Fig. 3 illustrates an adaptive noise cancellation system including a noise amplification control subsystem in accordance with one or more embodiments of the present disclosure.

Fig. 4A-4B illustrate an adaptive noise cancellation system including an adaptive gain control subsystem in accordance with one or more embodiments of the present disclosure.

Fig. 5 illustrates a transient activity detector for an adaptive noise cancellation system in accordance with one or more embodiments of the present disclosure.

Detailed Description

In accordance with various embodiments, improved Adaptive Noise Cancellation (ANC) systems and methods are disclosed. An ANC system for a headset or other personal listening device may include: a noise sensing reference microphone for sensing ambient noise; an error microphone for sensing an acoustic mix of noise and anti-noise generated by the ANC device; and a signal processing subsystem that generates anti-noise to cancel ambient noise. The signal processing subsystem may 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.

The present disclosure addresses many challenges associated with a generic adaptive noise cancellation system, 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 scales well to a variety of listening devices and form factors.

In various embodiments, systems and methods are disclosed for reducing noise amplification that occurs when there is constructive interference between noise and anti-noise in a range of frequencies. An adaptation method is disclosed that includes defining a composite error signal that incorporates a noise-shaping filter, and deriving new weight update rules for controlling the adaptation. The solution disclosed herein is adaptive, computationally inexpensive, and can be implemented as an improvement over conventional adaptation frameworks.

In various embodiments, the systems and methods disclosed herein reduce adaptive artifacts that may be perceived by a listener. For example, there may be low Sound Pressure Level (SPL) artifacts 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.

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 of the microphone relative to the noise, closing of the door, turbulence during air travel, etc.) create low frequency transients that can potentially disrupt the adaptation loop, leave unwanted residual noise or create noise artifacts. In various embodiments, a Transient Activity Detector (TAD) tracks transient behavior and controls adaptation during transient activity.

Example embodiments of the adaptive noise cancellation system of the present disclosure will now be described with reference to the accompanying drawings. Referring to fig. 1, an adaptive noise cancellation system 100 includes an audio device, such as a headset 110, and audio processing circuitry, 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.

In operation, a listener can hear the external noise d (n) through the housing and components of the earpiece 110. To cancel the noise d (n), the reference microphone 140 senses external noise, producing a reference signal x (n) that is fed to the DSP120 through an analog-to-digital converter (ADC) 142. The DSP120 generates an anti-noise signal y (n) that is fed through the DAC 130 and amplifier 132 to the speaker 150 to generate anti-noise in the noise cancellation region 160. When the anti-noise is equal in magnitude and opposite in phase to the noise d (n) in the noise cancellation region 160, the noise d (n) will be cancelled in the noise cancellation region 160. The resulting mix of noise and anti-noise is captured by an error microphone 162, which error microphone 162 generates an error signal e (n) to measure the effectiveness of noise cancellation. The error signal e (n) is fed to the DSP120 through the ADC 164, and the DSP120 adjusts the amplitude and phase of the anti-noise signal y (n) to minimize the error signal e (n) (e.g., drive the error signal e (n) to zero) within the cancellation region 162. In some embodiments, the speaker 150 may also generate desired audio (e.g., music) that is received by the error microphone 162 and removed from the error signal e (n) during processing. It will be appreciated that the embodiment of fig. 1 is one example of an adaptive noise cancellation system, and that the systems and methods disclosed herein may be implemented with other adaptive noise cancellation implementations, including a reference microphone and an error microphone.

Fig. 2 illustrates a robust, configurable adaptive noise cancellation system 200, the adaptive noise cancellation system 200 achieving improved noise cancellation performance substantially free of audio artifacts. The system 200 senses ambient noise at an external microphone (e.g., microphone 140 of fig. 1) that generates an external noise signal x (n). Ambient noise also passes through a noise path p (z) that includes the housing and components of the listening device, where the ambient noise is received at an error microphone (e.g., error microphone 162) as d (n). The adaptive filter 202 receives the external noise signal x (n) and estimates the noise path p (z) to produce 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 (to account for) the secondary path s (z) between the adaptive filter 202 and the error microphone.

The system 200 also includes an adaptation block 220, the adaptation block 220 including 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, the transient activity detector 226 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 further described herein with reference to fig. 3-5.

Referring to fig. 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 cancellation of the noise. The anti-noise signal is generated using a filter adapted to estimate the amplitude and phase offset for each frequency to align the anti-noise with the noise. Depending on the time 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 narrow-band amplification of the ambient noise (e.g., a "hissing" sound). In many ANC product designs, reducing or eliminating the "hissing" sound without sacrificing depth and bandwidth of the elimination is a challenge. In conventional low power embedded systems (e.g., consumer headphones), the reduction in hiss can be extremely difficult to compute and control and tune.

The NAC subsystem 300 of fig. 3 provides a method for controlling hiss and related voice artifacts that adaptively controls noise amplification in the hiss region while effectively achieving cancellation in the non-hiss region. NAC block 320 is configured to define a composite error signal incorporating noise-shaping filter c (z) (e.g., noise-shaping block 308 and noise-shaping block 310), and to derive new weight update rules for adaptive filter 302. In some embodiments, a Least Mean Square (LMS) architecture may be used, including a composite error signal incorporating a noise shaping filter for deriving new weight update rules.

In operation, NAC block 320 updates adaptive filter 302w (z) based on a filtered version of error signal e (n) and reference signal x (n). In the illustrated embodiment, NAC block 320 receives data from a filter

Signal x of₁(n) and the signal x from filter 308C (z)₂(n) of (a). The cost function minimizes the mean square error: minimization

In various embodiments, the anti-noise signal is filtered using a noise-shaping filter c (z), such as noise-shaping filter 308 and noise-shaping filter 310, which may be configured to enhance the signal in the hissing region. In some casesIn an embodiment, in a test environment prior to distribution, the hissing region of a particular earpiece may be detected, and the noise-shaping filter c (z) may be tuned. In some embodiments, the hiss level may be detected during operation, and the noise-shaping filter c (z) may be adaptively tuned during operation. For example, the hiss level may be determined by comparing the error signal e (n) to a noise signal to determine areas of constructive interference.

The cost function being adapted to

Minimizing, wherein E { } is the desired operator, γ is a constant that controls aggressiveness, and E₁(n) is the noise-shaped anti-noise signal y' (n). In some embodiments, NAC320 derives weight update rules based on a gradient approach. Embodiments of the method may 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 as to minimize noise amplification by defining a cost function optimization and deriving an adaptive algorithm that can achieve this optimization.

Referring to fig. 4A and 4B, an embodiment of an adaptive gain (ADG) subsystem 400 is disclosed. In various embodiments, adaptive gain control block 420 continuously updates gain element 404 to adjust for changes in the various coupling paths. Using a programmable filter B_G(z) (e.g., programmable filter 408 and programmable filter 410) to adjust the input of the ADG, programmable filter B_G(z) is designed to prevent low frequency transients and high frequency disturbing factors 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 (e.g., inaudible from a speaker)<20Hz)。

It will be appreciated that the physical geometry of the headset and wearing variations between different persons may affect the noise cancellation performance. For example, the shape of the outer ear and the length of the ear canal may alter the acoustic transfer function of interest in ANC applications. In some embodiments, an ANC system (e.g., the system of fig. 1) in a headset or other personal listening device 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 25mm from the error microphone) drops significantly for higher frequencies (lower wavelengths), resulting in a loss of cancellation bandwidth as perceived by the user of the noise cancellation system. The embodiments of fig. 4A-4B address these and other problems by maximizing the cancellation bandwidth at the eardrum during the tuning phase and formulating an adaptive approach that uses an error microphone to adapt to user-specific characteristics during operation.

For the purposes of this disclosure, the error microphone position is referred to as ERP (error reference point) and the eardrum position is referred to as DRP (eardrum reference point). For ANC systems 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-pass version of the error microphone signal. The correction signal may then be used to adapt the gain in the anti-noise signal path.

To maximize cancellation, the ideal placement of the error microphone would be at the eardrum, but this location is impractical for many consumer devices. Thus, ERP is used to provide an actual signal that roughly indicates cancellation performance at DRP. The adaptive algorithm attempts to minimize the ERP signal, which results in (i) a reduction in the cancellation of high frequency signals at the DRP, and (ii) a higher likelihood of hissing artifacts due to constructive interference of high frequencies at the DRP. In the conventional method, an adaptive algorithm using a transfer function from ERP to DRP is employed. These methods have a number of drawbacks, including transfer function estimation inaccuracy at high frequencies, low estimation accuracy that may affect wideband cancellation performance and result in transient hiss levels, high computational cost, and difficulty tuning and calibrating for all use conditions, making deployment impractical for many devices. The embodiment of fig. 4A-4B provides a computationally inexpensive method that overcomes many of the disadvantages of conventional systems, is easy to tune, for example by measuring certain transfer functions during system design, and is self-calibrating.

Fig. 4A shows a calibration and tuning arrangement for an adaptive gain subsystem. In this arrangement, 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 with a second error microphone at the DRP. P_E2D(z)，S_E2D(z) modeling the ERP to DRP transfer function in the acoustic path shown. The system may then be optimized using min-averaging block 422 to perform ANC tuning to derive an optimal value W based on error signal e (n)_DRP(z). Tuning in this manner helps achieve an extended cancellation bandwidth and better performance in the high frequency band. Secondly, as shown in fig. 4B, the adaptive algorithm is arranged to continuously update the gain element 404, G, which enables the proposed method to adjust for changes in the various coupling paths. In some embodiments, the signal is low pass filtered and gain adjusted for good low frequency cancellation. Thirdly, using a programmable filter B_G(z) to adjust the input to the adaptive algorithm, the programmable filter B_G(z) is programmed such that the ERP signal can mimic cancellation performance at the DRP. In addition, B_G(z) can be programmed to optimize performance during low frequency transients and high frequency disturbing factors in the environment.

It will be appreciated that the embodiment of fig. 4A-B is an example implementation, and that the method disclosed therein may be modified for adaptive versions of feedback, feedforward and hybrid ANC solutions. In some embodiments, purposely constrained filter elements may be adapted instead of adaptive gain elements. The calculated gain may have additional non-linear processing to further increase robustness.

Referring to fig. 5, an embodiment of a Transient Activity Detector (TAD)500 is shown. In operation, the TAD 500 detects changes in the acoustic environment and temporarily halts the update process when sudden/intermittent noise activity is detected. As a result, unwanted adaptation artifacts (e.g., artifacts that may result from fast adaptation) in the anti-noise signal are minimized. Examples of transient events may include talking of the headset wearer, sounding a car horn, head movements, and other similar sound events. A separate set of TAD calculations may be performed on input from each microphone in the ANC system (e.g., a total of 4 microphones in the headset, including the left error microphone, the left outer microphone, the right error microphone, the right outer microphone). Each of the four microphones may be independently enabled or disabled.

Fig. 5 illustrates an embodiment of a transient activity detection process for a microphone. The detect state machine 514 is used to assert and de-assert the "detect" output. In various embodiments, the detection output will be 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 falls below the scaled average noise amplitude C, the release delay counter will cause the detection output to last a programmable period of time before being de-asserted.

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 followed by a low pass filter 506 to generate a smoothed instantaneous amplitude a. In one embodiment, output a comprises the average amplitude of the audio sample 502 over a certain time period and represents the instantaneous noise value. The value a is provided to the detection state machine 514 and to the low pass filter 508 with saturation, the low pass filter 508 having an output B representing the average value of the a value over the second time period (i.e., the average noise amplitude). The programmable scaling factor defines a threshold (e.g., 5 times the average noise amplitude) for detecting transients and is multiplied by the average noise amplitude at component 516 to produce a second input C to the detection state machine 514.

In one embodiment, the detection state machine 514 can operate to instruct the adaptation process (e.g., adaptation block 220 of fig. 2) to stop if the smoothed instantaneous noise amplitude a is greater than the scaled average noise amplitude C. In various embodiments, the adaptation will freeze until the instantaneous noise amplitude a is below the scaled average noise amplitude C. Referring to fig. 2, when the adaptation is stopped, the filter 202 and the adaptive gain control 204 will continue to use the most recent weights and gain values to modify the noise input x (n). In some embodiments, the programmable release delay counter is operable to maintain the detection output for a programmable period of time before being de-asserted. In addition, an attack and release component 512(attack and release component 512) can operate to control how quickly the low pass filter 508 rises and falls in response to the instantaneous noise amplitude a. A programmable attack time constant (programmable attack time constant) defines the time it takes for the average noise amplitude 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.

Example embodiments

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 adaptation module operable to receive the reference signal and the error signal and to 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 adaptation module during the detected transient noise event.

In a robust adaptive noise cancellation system, the transient noise event may comprise speaking by an operator of the adaptive noise cancellation system, and the transient activity detection module may comprise a state machine operable to detect the transient noise event and transmit a state command to the adaptation module. The adaptation module is operable to receive the status command and enable and/or disable the adaptation in accordance with the status command.

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

In some embodiments of the robust adaptive noise cancellation system, the noise cancellation filter is further operable to generate the anti-noise signal according to the stored filter coefficients, and the adaptation 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 the anti-noise to cancel noise in the cancellation region. The adaptive module further includes a noise amplification control subsystem and/or an adaptive gain control subsystem.

In one or more embodiments, a robust active noise cancellation method includes: receiving a reference signal from a first sensor, the reference signal being representative of external noise; processing the reference signal by 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 zone; 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 adaptively adjust the noise cancellation accordingly enabled and disabled.

In some embodiments of the active noise cancellation method, setting the transient noise detection state comprises transmitting a status command, wherein said adaptively adjusting the noise cancellation filter further comprises receiving the status command and enabling and disabling the adaptation accordingly in accordance with the status command. Detecting the transient noise event may include comparing the smoothed instantaneous amplitude of the received signal to a 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.

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 may be derived by applying a programmable scaling factor to the average noise amplitude. The adaptively adjusting the noise cancellation filter may include a noise amplification control process and/or an adaptive gain control process.

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 adaptation module operable to receive the reference signal and the error signal and to 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 hissing region of the anti-noise signal while enabling cancellation in a non-hissing region of the anti-noise signal.

In some embodiments of the adaptive noise cancellation system with noise amplification control, 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. The noise amplification control module is operable to define a composite error signal incorporating a noise shaping filter and to derive new weight update rules for the noise cancellation filter and/or to derive new weight update rules using a least mean square algorithm. The noise shaping filter may be adaptively tuned during operation and/or the weight update rule is derived using a gradient.

In some embodiments of an adaptive noise cancellation system having noise amplification control that adapts a cost function to a noise level

Minimizing, wherein E { } is the desired operator, γ is a constant that controls 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 a transient noise event, and selectively disable the adaptation module during the detected transient noise event. The noise cancellation filter may also be operable to generate the anti-noise signal in accordance with the stored filter coefficients; and wherein the adaptation 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 a cancellation region.

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 being representative of external noise; processing the reference signal by 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 fizzing region of the anti-noise signal while enabling cancellation in a non-fizzing region of the anti-noise signal.

In some embodiments of the method of adaptive noise cancellation with noise amplification control, the hissing region of the anti-noise signal comprises a frequency bandwidth in which constructive interference between the ambient noise and the anti-noise signal is detected. The noise amplification control process may further include: defining a composite error signal incorporating a noise shaping filter and deriving new weight update rules for the noise cancellation filter; deriving a new weight update rule using a least mean square algorithm; adaptively tuning the noise shaping filter during operation; and/or adapting a cost function to

Minimizing, wherein E { } is the desired operator, γ is a constant that controls aggressiveness, and E₁(n) is the noise-shaped anti-noise signal y' (n). The weight update rule may be derived using a gradient.

In some embodiments of the method of adaptive noise cancellation with noise amplification control, the method further comprises detecting a transient noise event and selectively setting a transient noise detection state to enable and disable the adaptively adjusting the noise cancellation filter accordingly, and/or generating the anti-noise signal according to the stored filter coefficients.

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 comprising 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 eardrum reference point; and an adaptation module operable to receive the reference signal and the error signal and to adaptively adjust weights of the noise cancellation filter and/or the variable gain component. The adaptation module may include an adaptive gain control block operable to update the variable gain component.

In some embodiments of an extended bandwidth adaptive noise cancellation system, the input to the adaptive gain control block is adjusted using a programmable filter operable to prevent low frequency transients and/or high frequency disturbing factors in the ambient noise, and/or the programmable filter comprises a low pass filter that filters out high frequencies that are determined to be within a range that creates constructive interference between the cancellation region and the eardrum reference point. The programmable filter may include a high pass filter that filters out low frequencies that are determined to be in a range that is inaudible to a user of the noise cancellation system.

In some embodiments of an extended bandwidth adaptive noise cancellation system, the error signal sensed in the noise cancellation region is used to tune the adaptation module to cancel 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 hissing region of the anti-noise signal while enabling cancellation in a non-hissing region of the anti-noise signal. The hissing 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.

In some embodiments, the extended bandwidth adaptive noise cancellation system further comprises 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. The noise cancellation filter may also be operable to generate the anti-noise signal in accordance with the stored filter coefficients; and wherein the adaptation module is further operable to modify the stored filter coefficients. The extended bandwidth adaptive noise cancellation system may also include a speaker operable to receive the anti-noise signal and generate anti-noise to cancel the noise in a cancellation region.

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 being representative of external noise; processing the reference signal through a noise cancellation path comprising 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 zone; and adaptively adjusting the noise cancellation filter to cancel the external noise at an eardrum reference point in response to the reference signal, the error signal, and an adaptive gain control process.

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 disturbing factors in the external noise, wherein the adjusting further comprises low pass filtering high frequencies determined to be in a range that creates constructive interference between the cancellation region and the eardrum reference point, and/or wherein the adjusting further comprises high pass filtering low frequencies determined to be in a range that is inaudible to a user.

In one or more embodiments, the method of operating an extended bandwidth adaptive noise cancellation system further includes tuning the noise cancellation path using the error signal sensed in the noise cancellation region to cancel noise at the eardrum reference point, and/or adaptively controlling noise amplification in at least one hissing region of the anti-noise signal while achieving cancellation in a non-hissing region of the anti-noise signal by a noise amplification control process. The hissing 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.

In one or more embodiments, the method of operating an extended bandwidth adaptive noise cancellation system further includes 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 further include generating the anti-noise signal according to 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 a cancellation region.

The foregoing disclosure is not intended to limit the disclosure to the precise forms or particular fields of use disclosed. Accordingly, various alternative embodiments and/or modifications to the present disclosure are possible in light of the present disclosure, whether explicitly described or implied herein. Having thus described embodiments of the present disclosure, persons of ordinary skill in the art will recognize that changes may be made in form and detail without departing from the scope of the disclosure. Accordingly, 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 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 adaptation module operable to receive the reference signal and the error signal and to 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 adaptation module during the detected transient noise event.

2. The adaptive noise canceling system of claim 1 wherein the transient noise event comprises speaking into an operator of the adaptive noise canceling system.

3. The adaptive noise cancellation system of claim 1, wherein the transient activity detection module includes a state machine operable to detect the transient noise event and transmit a state command to the adaptation module; and wherein the adaptation module is operable to receive the status command and to enable and/or disable the adaptation in dependence on the status command.

4. The adaptive noise cancellation system of claim 3, wherein the transient noise event is detected if the smoothed instantaneous amplitude of the received signal is greater than the scaled average noise amplitude of the received signal.

5. The adaptive noise cancellation system of claim 4, wherein a delay is applied before adaptation is enabled after detecting the end of the transient noise event.

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

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

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

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

10. The adaptive noise cancellation system of claim 1, wherein the adaptation module further comprises a noise amplification control subsystem.

11. The adaptive noise cancellation system of claim 1, wherein the adaptation module further comprises an adaptive gain control subsystem.

12. A method for active noise cancellation, comprising:

receiving a reference signal from a first sensor, the reference signal being representative of external noise;

processing the reference signal by 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 zone;

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 adaptively adjusting the noise cancellation operation accordingly.

13. The method of claim 12, wherein the transient noise event comprises speaking by a user.

14. The method of claim 12, wherein selectively setting the transient noise detection state comprises: transmitting a status command; and wherein said adaptively adjusting said noise cancellation filter further comprises: the status command is received and the adaptation is enabled and disabled accordingly in accordance with the status command.

15. The method of claim 14, wherein detecting the transient noise event comprises: comparing the smoothed instantaneous amplitude of the received signal to a scaled average noise amplitude of the received signal.

16. The method of claim 15, wherein after detecting the end of the transient noise event, applying a delay before enabling adaptation.

17. The method of claim 16, wherein the transient noise event is detected when the smoothed instantaneous amplitude falls below the scaled average noise amplitude.

18. The method of claim 17, wherein the scaled average noise amplitude is derived by applying a programmable scaling factor to the average noise amplitude.

19. The method of claim 12, wherein adaptively adjusting the noise cancellation filter comprises a noise amplification control process.

20. The method of claim 12, wherein adaptively adjusting the noise cancellation filter comprises an adaptive gain control process.

21. An adaptive noise cancellation system comprising:

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 adaptation module operable to receive the reference signal and the error signal and to 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 hissing region of the anti-noise signal while enabling cancellation in a non-hissing region of the anti-noise signal.

22. The adaptive noise canceling system of claim 21, wherein the hissing region of the anti-noise signal comprises a frequency bandwidth where constructive interference between the ambient noise and the anti-noise signal is detected.

23. The adaptive noise cancellation system of claim 21, wherein the noise amplification control module is operable to define a composite error signal incorporating a noise shaping filter and to derive new weight update rules for the noise cancellation filter.

24. The adaptive noise cancellation system of claim 23, wherein the noise amplification control module is operable to derive the new weight update rule using a least mean square algorithm.

25. The adaptive noise cancellation system of claim 23, wherein the noise shaping filter is adaptively tuned during operation.

26. The adaptive noise cancellation system of claim 23, wherein the weight update rule is derived using a gradient.

27. An adaptive noise cancellation system according to claim 21, wherein the noise amplification control adapts a cost function to be used in the noise cancellation system

Minimizing, wherein E { } is the desired operator, γ is a constant that controls aggressiveness, and E₁(n) is the noise-shaped anti-noise signal y' (n).

28. The adaptive noise cancellation system of claim 21, further comprising 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.

29. An adaptive noise cancellation system according to claim 21, wherein the noise cancellation filter is further operable to generate the anti-noise signal in accordance with the stored filter coefficients; and wherein the adaptation module is further operable to modify the stored filter coefficients.

30. The adaptive noise canceling system of claim 21, further comprising a speaker operable to receive the anti-noise signal and generate anti-noise to cancel the noise in a cancellation zone.

31. A method, comprising:

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;

wherein the noise amplification control process comprises adaptively controlling noise amplification in at least one hissing region of the anti-noise signal while enabling cancellation in a non-hissing region of the anti-noise signal.

32. The method of claim 31, wherein the hissing region of the anti-noise signal includes a frequency bandwidth where constructive interference between the ambient noise and the anti-noise signal is detected.

33. The method of claim 31, wherein the noise amplification control process further comprises defining a composite error signal incorporating a noise shaping filter and deriving new weight update rules for the noise cancellation filter.

34. The method of claim 33, wherein the noise amplification control procedure further comprises using a least mean square algorithm to derive new weight update rules.

35. The method of claim 33, wherein the noise amplification control procedure further comprises adaptively tuning the noise shaping filter during operation.

36. The method of claim 33, wherein the weight update rule is derived using a gradient.

37. The method of claim 31, wherein the noise amplification control procedure further comprises adapting a cost function to fit the cost function to the noise signal

38. The method of claim 31, further comprising: detecting a transient noise event, and selectively setting a transient noise detection state to enable and disable the adaptively adjusting the noise cancellation filter accordingly.

39. The method of claim 31, further comprising: generating the anti-noise signal according to the stored filter coefficients.

40. An adaptive noise cancellation system comprising:

a noise cancellation path comprising 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 eardrum reference point;

an adaptation module operable to receive the reference signal and the error signal and to adaptively adjust weights of the noise cancellation filter and/or the variable gain component;

wherein the adaptation module comprises an adaptive gain control block operable to update the variable gain component.

41. The adaptive noise cancellation system of claim 40, wherein an input to the adaptive gain control block is adjusted using a programmable filter operable to prevent low frequency transients and/or high frequency disturbing factors in the ambient noise.

42. The adaptive noise canceling system of claim 41 wherein the programmable filter comprises a low pass filter that filters out high frequencies determined to be within a range that creates constructive interference between the canceling area and the eardrum reference point.

43. An adaptive noise canceling system according to claim 41 wherein said programmable filter comprises a high pass filter that filters out low frequencies that are determined to be within a range inaudible to a user of the noise canceling system.

44. The adaptive noise canceling system of claim 40 wherein the error signal sensed in the noise canceling region is used to tune the adaptive module to cancel noise at the eardrum reference point.

45. The adaptive noise cancellation of claim 40, wherein the adaptive module further comprises a noise amplification control module operable to adaptively control noise amplification in at least one hissing region of the anti-noise signal while enabling cancellation in a non-hissing region of the anti-noise signal.

46. The adaptive noise canceling system of claim 45, wherein the hissing region of the anti-noise signal comprises a frequency bandwidth in which constructive interference between the ambient noise and the anti-noise signal is detected.

47. The adaptive noise cancellation system of claim 40, further comprising 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.

48. An adaptive noise cancellation system according to claim 40, wherein the noise cancellation filter is further operable to generate the anti-noise signal in accordance with the stored filter coefficients; and wherein the adaptation module is further operable to modify the stored filter coefficients.

49. The adaptive noise canceling system of claim 40, further comprising a speaker operable to receive the anti-noise signal and generate anti-noise to cancel the noise in a cancellation zone.

50. A method, comprising:

processing the reference signal through a noise cancellation path comprising 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 zone; and

adaptively adjusting the noise cancellation filter to cancel the external noise at an eardrum reference point in response to the reference signal, the error signal, and an adaptive gain control process.

51. The method of claim 50, further comprising: a programmable filter is used to adjust the input to the adaptive gain control process to prevent low frequency transients and/or high frequency disturbing factors in the external noise.

52. The method of claim 51, wherein the adjusting further comprises: low pass filtering out high frequencies determined to be within a range that creates constructive interference between the cancellation zone and the eardrum reference point.

53. The method of claim 52, wherein the adjusting further comprises: high-pass filters out low frequencies, which are determined to be in a range inaudible to the user.

54. The method of claim 50, further comprising: tuning the noise cancellation path using the error signal sensed in the noise cancellation region to cancel noise at the eardrum reference point.

55. The method of claim 50, further comprising a noise amplification control process including adaptively controlling noise amplification in at least one hissing region of the anti-noise signal while enabling cancellation in non-hissing regions of the anti-noise signal.

56. The method of claim 55, wherein the hissing region of the anti-noise signal includes a frequency bandwidth where constructive interference between the external noise and the anti-noise signal is detected.

57. The method of claim 50, further comprising a transient activity detection process, the transient activity detection process comprising: receiving the reference signal, detecting a transient noise event, and selectively disabling adaptively adjusting the noise cancellation filter during the detected transient noise event.

58. The method of claim 50, further comprising: generating the anti-noise signal according to the stored filter coefficients; and adaptively modifying the stored filter coefficients during operation.

59. The method of claim 50, further comprising: outputting the anti-noise signal to a speaker to generate anti-noise to cancel the noise in a cancellation region.