Gain adjustment in ANR systems with multiple feed-forward microphones

Abstract

The invention relates to gain adjustment in ANR systems with multiple feed-forward microphones. Techniques described in this document may be embodied in a method that includes receiving a first input signal representing audio captured by a first sensor disposed in a signal path of an active noise reduction (ANR) device; and receiving a second input signal representing audio captured by a second sensor disposed in the signal path of the ANR device. The method further includes processing, by at least one compensator, the first input signal and the second input signal to generate a drive signal for an acoustic transducer of the ANR device. The gain applied to the signal path is at least reduced by 3 dB relative to an ANR signal path with a single sensor.

Description

[0001] This application is a divisional application of the Chinese patent application with the international filing date of May 28, 2020, national application number 202080049207.1, and invention title "Gain adjustment in an ANR system with multiple feedforward microphones". Technical Field

[0002] The present disclosure generally relates to active noise reduction (ANR) devices having multiple feedforward microphones. Background Art

[0003] An acoustic device such as a headset may include active noise reduction (ANR) capabilities that block and constructively cancel at least a portion of ambient noise from reaching a user's ear. Accordingly, the ANR device creates an acoustic isolation effect, thereby isolating the user from the environment at least in part. Summary of the Invention

[0004] Generally, in one aspect, the present document features a method that includes: receiving a first input signal that represents audio captured by a first sensor disposed in a signal path of an active noise reduction (ANR) device; and receiving a second input signal that represents audio captured by a second sensor disposed in the signal path of the ANR device. The method further includes processing the first input signal and the second input signal by at least one compensator to generate a drive signal for a sound transducer of the ANR device. A gain applied to the signal path is reduced by at least 3 dB relative to an ANR signal path having a single sensor.

[0005] In another aspect, the present document features an active noise reduction (ANR) device that includes a first sensor disposed in a signal path of the device and configured to generate a first audio input signal. The ANR device further includes: a second sensor disposed in the signal path of the ANR device and configured to generate a second audio input signal; and at least one compensator configured to receive and process the first audio input signal and the second audio input signal to generate a drive signal for a sound transducer of the ANR device. A gain of the signal path is reduced by at least 3 dB relative to an ANR signal path having a single sensor.

[0006] In another aspect, the present document features one or more machine-readable storage devices having computer-readable instructions encoded thereon for causing one or more processing devices to perform various operations. The operations include: receiving a first input signal representing audio captured by a first sensor disposed in a signal path of an active noise reduction (ANR) device; and receiving a second input signal representing audio captured by a second sensor disposed in the signal path of the ANR device. The operations further include processing the first input signal and the second input signal to generate a drive signal for a sound transducer of the ANR device. The gain of the signal path is reduced by at least 3 dB relative to an ANR signal path having a single sensor.

[0007] Specific implementations of the above aspect may include one or more of the following features.

[0008] Processing the first input signal and the second input signal to generate a drive signal may include: combining the first input signal and the second input signal to generate a combined input signal, applying a gain to the combined input signal using an amplifier, and filtering the output of the amplifier by the at least one compensator to generate a drive signal for the acoustic transducer. The amplifier may be arranged as part of the at least one compensator. Processing the first input signal and the second input signal to generate a drive signal may include: applying a first gain to the first input signal using a first amplifier to generate a first amplified input signal, and filtering the first amplified input signal by a first compensator to generate a first processed signal for the acoustic transducer of the ANR device. The processing further includes: applying a second gain to the second input signal using a second amplifier to generate a second amplified input signal, and filtering the second input signal by a second compensator to generate a second processed signal for the acoustic transducer of the ANR device. The processing further includes combining the first processed signal and the second processed signal to generate the drive signal for the acoustic transducer. The first compensator may apply one or more filters to the first amplified input signal, and the second compensator may apply one or more filters to the second amplified input signal. The one or more filters applied to the second amplified signal may be different from the one or more filters applied to the first amplified signal. Processing the first input signal and the second input signal to generate a drive signal may include: processing the first input signal by a first compensator to generate a first processed signal for the acoustic transducer of the ANR device, processing the second input signal by a second compensator to generate a second processed signal for the acoustic transducer of the ANR device, and combining the first processed signal and the second processed signal to generate a drive signal for the acoustic transducer. The first compensator may apply a first gain and use one or more filters to generate the first processed signal. The second compensator may apply a second gain and use one or more filters to generate the second processed signal. Processing the first input signal and the second input signal to generate a drive signal may include: applying a first gain to the first input signal using a first amplifier, applying a second gain to the second input signal using a second amplifier, combining the first input signal and the second input signal to generate a combined input signal, and filtering the combined input signal by the at least one compensator to generate a drive signal for the acoustic transducer. The first amplifier and the second amplifier may be part of the at least one compensator.

[0009] Two or more features described in this disclosure, including those described in the Summary of the Invention section, may be combined to form embodiments not specifically described herein. Details of one or more specific embodiments are discussed in the drawings and the following description. Other features, objects, and advantages will be apparent from the specification, drawings, and claims. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1 Shows an example of an active noise reduction (ANR) system deployed in headphones.

[0011] Figure 2 Is a block diagram of an exemplary configuration of the ANR system.

[0012] Figure 3 Is a block diagram of a feedforward compensator that has an ANR signal flow path arranged in parallel with a direct signal flow path.

[0013] Figure 4 Is a block diagram of an ANR system having multiple feedforward sensors.

[0014] Figure 5 Is a block diagram of an ANR system having multiple feedforward sensors with independently controllable gains.

[0015] Figure 6 Is a block diagram of an ANR system having multiple feedforward sensors with independently controllable gains and independent compensators.

[0016] Figure 7 Is a flowchart of an exemplary process for generating a drive signal in an ANR system having multiple sensors arranged in a signal path.

[0017] Figure 8 Is a block diagram of an example of a computing device. Detailed Description

[0018] This document describes techniques for using multiple feedforward microphones in an active noise reduction (ANR) system to improve ANR performance, noise performance, and the likelihood of reducing instability conditions. When, for example, an ANR system is deployed in noise-canceling headphones, certain instability conditions can cause the headphones to produce acoustic artifacts (e.g., loud noises) that are uncomfortable for the user. By providing multiple feedforward microphones in the ANR system, the techniques described herein enable the gain through each feedforward signal path to be reduced relative to the case of using a single feedforward microphone. Since the gain through the individual signal paths is lower, there is more headroom in the system, resulting in fewer opportunities for clipping and more margin to handle instabilities that may arise, for example, due to the coupling between one of the feedforward microphones and the transducer. Additionally, the individual gains of the multiple feedforward microphones can be assigned based on their likelihood of coupling, such that the total target gain is not affected compared to the single microphone case. For example, if one of the microphones is located in a position where the microphone is prone to coupling to the driver (and by extension, is susceptible to instability), a lower gain can be applied to that microphone to reduce the likelihood of coupling. However, the gain of the other microphone can be adjusted accordingly so that the target total gain of the feedforward microphones is not reduced. In one example, the overall target gain can be distributed between two feedforward paths such that the first microphone, which is more prone to coupling, has a gain of 0.25, while the second microphone, which is less prone to coupling, has a gain of 0.75. Thus, while the gain of the individual signal paths is reduced compared to the overall gain (e.g., to enable the ANR system to tolerate non-ideal microphone positions, such as microphone positions closer to the earcup perimeter or near ports where there may be greater coupling between the microphone and the transducer), the total feedforward gain is not affected due to the weighted distribution of the gains between the multiple feedforward paths. In some embodiments, the weighting can also be done on a per-frequency basis such that the gain distribution between two or more feedforward paths is different for different frequencies (or frequency ranges).

[0019] Active noise reduction (ANR) systems can be deployed in various acoustic devices to cancel or reduce unwanted or unpleasant noise. For example, ANR headphones can provide a potentially immersive listening experience by reducing the effects of ambient noise and sounds. As used herein, the term headphones includes various types of such personal acoustic devices, such as in-ear, around-ear, or over-ear headphones, earbuds, and hearing aids. ANR systems can also be used in automotive or other transportation systems (e.g., for cars, trucks, buses, airplanes, boats, or other vehicles) to cancel or attenuate unwanted noise generated, for example, by mechanical vibrations or engine harmonics.

[0020] In some cases, an ANR system may include an electroacoustic or electromechanical system that may be configured to cancel at least some of an undesired noise (commonly referred to as primary noise) based on the superposition principle. For example, the ANR system may identify the amplitude and phase of the primary noise and generate another signal (commonly referred to as an anti-noise signal) of approximately the same amplitude and opposite phase. The anti-noise signal may then be combined with the primary noise such that both are substantially canceled at a desired location. As used herein, the term substantially canceled may include reducing the “canceling” of the noise to a specified level or within an acceptable tolerance and does not require complete cancellation of all noise. The ANR system may be used to attenuate a wide range of noise signals, including, for example, broadband noise and / or low-frequency noise, which may not be easily attenuated using passive noise control systems.

[0021] Figure 1 An example of an ANR system 100 deployed in headphones 102 is shown. The headphones 102 include earcups 104 on each side that are adapted to fit over, around, or above a user's ear. The earcups 104 may include a layer 106 of soft material (e.g., soft foam) for comfortably fitting over the user's ear. The ANR system 100 may include or otherwise be coupled to a feedforward sensor 108, a feedback sensor 110, and a sound transducer 112. The feedforward sensor 108 may be a microphone or another acoustic sensor and may be disposed on or near the outside of the earcup 104 to detect ambient noise. The feedback sensor 110 may be a microphone or another acoustic sensor and may be deployed near the user's ear canal and / or the transducer 112. The transducer 112 may be a sound transducer that emits an audio signal from an audio source device (not shown) to which the headphones 102 are connected and / or other signals from the ANR system 100. While Figure 1 An example of deploying the ANR system in over-ear headphones is shown, but the ANR system may also be deployed in other form factors, including in-ear headphones, ear-hook headphones, or off-ear personal acoustic devices (e.g., devices designed not to contact the wearer's ear but that may be worn on the wearer's head or body near the wearer's ear).

[0022] The ANR system 100 can be configured to process signals detected by the feedforward sensor 108 and / or the feedback sensor 110 to generate an anti-noise signal provided to the transducer 112. The ANR system 100 can be of various types. In some specific embodiments, the ANR system 100 is based on feedforward noise cancellation, where the primary noise is sensed by the feedforward sensor 108 before the noise reaches a secondary source such as the transducer 112. In some specific embodiments, the ANR system 100 can be based on feedback noise cancellation, where the ANR system 100 cancels the primary noise based on the residual noise detected by the feedback sensor 110 and without the benefit of the feedforward sensor 108. In some specific embodiments, both feedforward noise cancellation and feedback noise cancellation are used. The ANR system 100 can be configured to control noise in various frequency bands. In some specific embodiments, the ANR system 100 can be configured to control broadband noise such as white noise. In some specific embodiments, the ANR system 100 can be configured to control narrowband noise such as harmonic noise from a vehicle engine.

[0023] In some specific embodiments, the ANR system 100 can include a configurable digital signal processor (DSP) and other circuitry to implement various signal flow topologies and filter configurations. Examples of such DSPs are described in U.S. Patents 8,073,150 and 8,073,151, which are incorporated herein by reference in their entirety. Various signal flow topologies can be implemented in the ANR system 100 to achieve functions such as audio equalization, feedback noise cancellation, and feedforward noise cancellation. For example, as Figure 2 shown, the signal flow topology of the ANR system 100 can include a feedforward signal flow path 114 that drives the transducer 112 (using, for example, the feedforward compensator 116) to generate an anti-noise signal to reduce the effect of the noise signal picked up by the feedforward sensor 108. Also, for example, the signal flow topology can include a feedback signal flow path 118 that drives the transducer 112 (using, for example, the feedback compensator 120) to generate an anti-noise signal to reduce the effect of the noise signal picked up by the feedback sensor 110. The signal flow topology can also include an audio path 122 that includes circuitry (e.g., the equalizer 124) for processing an input audio signal 126 such as music or a communication signal for playback on the transducer 112.

[0024] In some specific implementations, the earphone 102 may include a feature that can be referred to as a "transparent mode" or "hear-through mode". In this mode, the feedforward sensor 108 or other detection devices can be used to detect external sounds that the user may want to hear, and the ANR system 100 can be configured to transmit such sounds reproduced by the transducer 112. In some cases, the sensor for the transparent feature can be a sensor separate from the feedforward sensor 108, such as a microphone. In some specific implementations, signals captured by multiple sensors (e.g., using a beamforming process) can be used to, for example, focus on the user's voice or another source of ambient sound. In some specific implementations, the earphone 102 can allow multimode operation including a hear-through mode, in which the ANR function can be turned off or at least reduced within at least a certain frequency range (e.g., the voice frequency band) to allow a relatively wideband of ambient sound to reach the user. In some specific implementations, the ANR system 100 can also be used to shape the frequency response of the signal passing through the earphone. For example, the feedforward compensator 116 and / or the feedback compensator 120 can be used to change the acoustic experience of the ear canal blocked by the earbud into an acoustic experience in which ambient sounds (e.g., the user's own voice) sound more natural to the user.

[0025] In some specific implementations, the ANR system 100 can allow the user to control the amount of ambient noise passing through the device and at the same time maintain the ANR function, as described in, for example, U.S. Patent No. 10,096,313, the entire patent application of which is incorporated herein by reference. For example, in order to allow an intermediate target insertion gain between 0 and 1 and enable the user to control the amount of ambient noise passing through the device, the feedforward compensator 116 can include an ANR filter 302 and a direct-through filter 304 arranged in parallel, where the gain of the direct-through filter can be adjusted by a coefficient C, as Figure 3 shown. The adjustable gain C can be implemented using a variable gain amplifier (VGA) provided in the direct-through signal flow path of the feedforward compensator 116.

[0026] In specific implementations where the earphone 102 includes a hear-through mode, some conditions can lead to the onset of an unstable situation. For example, if the output of the transducer 112 is fed back to the feedforward sensor 108 and the ANR system 100 transmits the signal back to the transducer 112, a rapidly deteriorating unstable situation may occur, resulting in poor sounds emitted from the transducer 112. This situation can be demonstrated, for example, by forming a cup with the hand over the earphone to facilitate the feedback path between the transducer 112 and the feedforward sensor 108. Such a feedback path can be established during earphone use, for example, if the user puts on a hat (e.g., a hood or a winter hat) above the earphone 102.

[0027] In some specific implementations, even when the headset 102 does not include a transparent hearing mode, unstable conditions may occur. For example, the unstable conditions may occur due to changes in the transfer function of the secondary path of the ANR system 100 (e.g., the acoustic path between the feedback sensor 110 and the transducer 112). For example, if the acoustic path between the transducer 112 and the feedback sensor 110 changes in size or shape, such conditions may occur. This condition can be demonstrated, for example, by blocking the opening through which sound emanates from the headset 102 (e.g., using a finger or palm). In the case of a headset with a nozzle having an acoustic channel that acoustically couples the front cavity of the acoustic transducer to the user's ear canal, this condition can be referred to as a blocked nozzle condition. In practice, this condition may occur, for example, during the insertion / removal of the headset into / from the ear. This effect can be particularly observable in smaller headsets (e.g., in-ear headphones) or in-ear hearing aids, where the secondary path can change if the headset or hearing aid moves during wear. For example, moving an in-ear headset or hearing aid can cause a change in the air volume in the corresponding secondary path, resulting in the ANR system becoming unstable. In some cases, pressure fluctuations in the ambient air can also cause the ANR system to become unstable. For example, when the door or window of a vehicle (e.g., a bus door) is closed, the accompanying pressure change may cause the ANR system to become unstable. Another example of a pressure fluctuation that can cause an unstable condition is a significant change in the ambient pressure of the air relative to the normal atmospheric pressure at sea level.

[0028] Unless unstable conditions are quickly detected and resolved, they can cause the transducer 112 to produce acoustic artifacts (e.g., loud audible noise) that may be uncomfortable to the wearer. The techniques described herein use multiple feedforward sensors such as microphones to improve ANR performance and reduce the likelihood of unstable conditions. In some embodiments, when multiple feedforward sensors are used in the ANR system 100, the gain through each feedforward path can be lower compared to when a single feedforward sensor is used. Thus, the compensators, filters, and other circuitry in any individual signal path can have a lower total gain than when a single feedforward sensor is used. Additionally, since the gain of any individual signal path is lower compared to using a single sensor, there is more headroom in the system, resulting in fewer opportunities for clipping and providing more margin to prevent instabilities that may be caused, for example, by coupling between the feedforward sensor and the transducer. As used herein, the term headroom refers to the difference between the signal processing capabilities of an electrical component and the maximum level of the signal in a signal path such as a feedforward signal path. The reduced gain applied to any individual signal path can also enable the ANR system to better tolerate non-ideal sensor positions, such as sensor positions closer to the perimeter of the earcup 104 where the likelihood of coupling between the sensor and the transducer may be higher compared to sensors located at a greater distance from the perimeter of the earcup 104.

[0029] Figure 4 FIG. 4 is a block diagram of an ANR system 400 having a plurality of feedforward sensors 402a, 402b, …, 402N disposed along a feedforward path 114. Each of the feedforward sensors 402a, 402b, 402N can be an analog microphone, a digital microphone, or another acoustic sensor and can be disposed on or near the exterior of the earcup 104 to detect ambient noise. In some embodiments, each of the feedforward sensors 402a, 402b, …, 402N can be positioned to detect ambient noise incident from a particular direction and / or to detect certain types or frequencies of ambient noise, such as the user's voice. The number of feedforward sensors included in the ANR system 400 can be as few as two sensors. Generally, there is no upper limit to the number of feedforward sensors that can be included in the ANR system 400. In some embodiments, practical considerations such as space and cost can create an upper limit to the number of sensors included in the system. In some embodiments, technical limitations of other circuitry (such as compensators or transducers) in the feedforward path 114 can create an upper limit to the number of sensors included in the system. Although the ANR system 400 is described in the context of being deployed within the headset 102, the techniques described herein are equally applicable to ANR systems deployed in other contexts, such as automotive or other transportation systems.

[0030] The ambient noise signals generated by each of the feedforward sensors 402a, 402b, …, 402N in the ANR system 400 can be combined using a combinational circuit 404 such as a summing circuit. It should be understood that the combinational circuit 404 can perform summation in the digital or analog domain, and the position of the combinational circuit 404 can vary along the feedforward signal path 114. Although not shown, it should also be understood that the feedforward signal path 114 can include additional circuits such as amplifiers and analog-to-digital converters. The gain of the combined signal can be adjusted by a variable gain amplifier (VGA) 406 or other amplification circuits provided in the feedforward path 114 by a gain factor G ff The gain factor G ff can be a reduced gain factor relative to the gain factor applied in an ANR system having a single feedforward sensor, as described in detail below. The feedforward compensator 116 can process the combined ambient noise signal to generate, for example, an anti-noise signal. In some embodiments, the feedforward compensator 116 can include an ANR signal flow path arranged in parallel with the direct signal flow path to provide at least a portion of the ambient noise to the user, as described in reference Figure 3 In some embodiments, the VGA 406 can be included within the feedforward compensator 116. The signal generated by the feedforward compensator 116 can be combined with other signals in the ANR system 400 (such as signals from the feedback path 118 and / or the audio path 122), and the resulting signal can be provided to the transducer 112.

[0031] In some embodiments, the gain factor G ff can be selected by the ANR system 400 based on the number of feedforward sensors 402a, 402b, …, 402N present in the system. For example, if the ANR system 400 includes two feedforward sensors, the gain factor G ff can be reduced by up to 50% relative to an ANR system having a single feedforward sensor and can be approximately 6 decibels (dB) in one example. In other cases, if the ANR system 400 includes three feedforward sensors, the gain factor G ff can be reduced by up to 67% relative to an ANR system having a single feedforward sensor and can be approximately 9 dB to 10 dB in one example. In other cases, if the ANR system 400 includes four feedforward sensors, the gain factor G ff can be reduced by up to 75% relative to an ANR system having a single feedforward sensor and can be approximately 12 dB in one example.

[0032] In some cases, the ANR system 400 can adjust the gain factor G based on the intended application of the system, the requirements of other parts of the system, or other practical considerations ffFor example, if the ANR system 400 includes two feedforward sensors, the gain factor G ff can be reduced by up to 50% relative to an ANR system having a single feedforward sensor, as described above. However, the ANR system 400 can reduce the gain by some amount less than 50% relative to an ANR system having a single feedforward sensor to account for, e.g., the signal level requirements of the feedforward compensator 116.

[0033] The lower overall gain reduces the likelihood that coupling between, e.g., the transducer 112 and one or more of the feedforward sensors 402a, 402b, …, 402N will result in instability. This in turn allows for non-ideal placement of one or more of the feedforward sensors 402a, 402b, …, 402N (e.g., near locations that may cause acoustic leakage that could couple to the driver, such as near the earcup perimeter or near an acoustic port). Additionally, combining the ambient noise signals detected by multiple feedforward sensors can produce a combined ambient noise signal that has a higher signal-to-noise ratio than the ambient noise signal from a single sensor. For example, when the random noise generated by each feedforward path is uncorrelated with each other feedforward path, the total combined noise can be reduced by a certain amount (e.g., 3 dB) per pair of combinations while obtaining a higher total signal amount (e.g., 6 dB) per pair of combinations. This improves the performance of the ANR system 400 by, e.g., reducing the background noise and providing a more reliable signal for processing to generate the anti-noise signal.

[0034] Figure 5 FIG. shows a block diagram of an ANR system 500 having a plurality of feedforward sensors 402a, 402b, …, 402N disposed along the feedforward signal path 114. As Figure 5 shown, each of the feedforward sensors 402a, 402b, …, 402N can be coupled to a corresponding VGA 502a, 502b, …, 502N. Each VGA in the VGA 502a, 502b, …, 502N can be configured to apply a respective gain factor G ff1 、G ff2 、…、G ffN to the ambient noise signal generated by the corresponding feedforward sensor. For example, VGA 502a can be coupled to feedforward sensor 402a and can apply the gain factor G ff1, and so on. This in turn allows the gain of different feedforward microphones to be adjusted individually, such that a microphone that is more easily coupled to the driver has a lower gain compared to another microphone that is less easily coupled. Additionally, the total target gain can be allocated across different microphones such that the total feedforward gain is at the target level. For example, the overall target gain can be allocated between two feedforward microphones such that the first microphone, which is more easily coupled, has a gain of 0.25, while the second microphone, which is less easily coupled, has a gain of 0.75.

[0035] Signals output by each of the VGAs 502a, 502b, …, 502N can be combined using a combining circuit 404 (e.g., a circuit including one or more adders). It should be understood that the combining circuit 404 can perform summation in the digital or analog domain, and the location of the combining circuit 404 can vary along the feedforward signal path 114. Although not shown, it should also be understood that the feedforward signal path 114 can include additional circuitry, such as amplifiers and analog-to-digital converters. The feedforward compensator 116 can process the combined signal to generate, for example, an anti-noise signal. In some embodiments, the feedforward compensator 116 can include an ANR signal flow path arranged in parallel with the direct signal flow path to provide at least a portion of the ambient noise to the user, as described in reference Figure 3 The signal generated by the feedforward compensator 116 can be combined with other signals in the ANR system 500 (such as signals from the feedback path 118 and / or the audio path 122), and the resulting signal can be provided to the transducer 112. Although Figure 5 the VGAs 502 and the combining circuit 404 are shown as separate entities from the feedforward compensator 116, in some embodiments, the VGAs 502 and the combining circuit 404 can be included as part of the feedforward compensator 116.

[0036] The individual gain applied by each of the VGAs 502a, 502b, …, 502N can be reduced relative to the gain applied in an ANR system having a single feedforward sensor. This in turn reduces the likelihood of unstable conditions in the system and improves ANR performance. The amount of gain reduction can be determined by the ANR system 500 based on, for example, the number of feedforward sensors present in the system (as described in reference Figure 4 and / or other factors as described herein. Additionally, by providing each of the feedforward sensors 402a, 402b, …, 402N with a separate VGA 502a, 502b, …, 502N, the ANR system 500 can individually adjust the gain applied to the ambient noise signals generated by the respective feedforward sensors (e.g., by setting G ff1 G ff2 … G ffNAdjusted). In this case, the ANR system 500 can apply control to the individual ambient noise signals before they are combined and processed by the feedforward compensator 116, without affecting the target overall gain of the feedforward path.

[0037] Reference Figure 6 , in some specific embodiments, the ANR system 600 can include individual compensators 602a, 602b,..., 602N for each of the feedforward sensors 402a, 402b,..., 402N in the feedforward sensors. As Figure 6 shown, each compensator 602a, 602b,..., 602N can be coupled to the corresponding feedforward sensors 402a, 402b,..., 402N through VGAs 502a, 502b,..., 502N. In some specific embodiments, the individual compensators for each feedforward sensor 402 allow for individual frequency-dependent filtering and / or gain allocation for different feedforward paths. For example, if a particular microphone is located near the perimeter or port that may be coupled to a high-frequency driver, a digital filter can be set in the corresponding compensator K ff to reduce the likelihood of such coupling. Such digital filters can be configured to filter out a portion of the spectrum of the signal captured by the particular microphone to reduce the likelihood of coupling. In some cases, if the sensors / microphones 402 are far apart from each other on the earcup or earpiece, the signals captured by the microphones may be uncorrelated with each other. In this case, different frequencies can be weighted differently by applying individual K ff to each microphone.

[0038] In some specific embodiments, each compensator 602a, 602b,..., 602N can include the corresponding VGAs 502a, 502b,..., 502N. Each compensator 602a, 602b,..., 602N can include one or more filters, controllers, or other circuits to process the signals generated by the corresponding feedforward sensors to generate, for example, anti-noise signals. In some specific embodiments, each compensator 602a, 602b,..., 602N can include an ANR signal flow path arranged in parallel with the direct signal flow path to provide at least a portion of the ambient noise to the user, as referenced Figure 3As described above, the signals output by each of the compensators 602a, 602b, …, 602N can be combined using the combining circuit 404. It should be understood that the combining circuit 404 can perform summation in the digital or analog domain, and the location of the combining circuit 404 can vary along the feedforward signal path 114. Although not shown, it should also be understood that the feedforward signal path 114 can include additional circuitry, such as amplifiers and analog-to-digital converters. The resulting signal can be combined with other signals in the ANR system 600, such as signals from the feedback path 118 and / or the audio path 122, and the resulting signal can be provided to the transducer 112.

[0039] Figure 7 FIG. is a flow chart of an exemplary process for generating a drive signal in an ANR system having a plurality of acoustic sensors disposed in a signal path. At least a portion of process 700 can be implemented using one or more processing devices, such as the DSPs described in U.S. Patent Nos. 8,073,150 and 8,073,151, which are hereby incorporated by reference in their entirety. Operations of process 700 include receiving a first input signal that represents audio captured by a first sensor disposed in the signal path of the ANR device (702). Operations of process 700 also include receiving a second input signal that represents audio captured by a second sensor disposed in the signal path of the ANR device (704). In some embodiments, each of the first sensor and the second sensor includes a microphone, such as a feedforward microphone of the ANR device. In some embodiments, the ANR device can be an earloop headphone, such as the headphone described in Figure 1 reference. In some embodiments, the ANR device can include, for example, in-ear headphones, earhook headphones, open-back headphones, hearing aids, or other personal acoustic devices. In some embodiments, the audio captured by the first sensor and / or the second sensor can be ambient noise associated with the ANR device. In some embodiments, the signal path can be the feedforward signal path of the ANR device. In some embodiments, the gain of the signal path can be reduced relative to the ANR signal path having only the first input signal, as described in Figures 4 to 6 reference.

[0040] Operations of process 700 also include processing the first input signal and the second input signal by at least one compensator and / or variable gain amplifier to generate a drive signal for the acoustic transducer of the ANR device (706). In some embodiments, the at least one compensator can include a feedback compensator and / or a feedforward compensator, such as the compensator described in Figure 2As described. In some specific embodiments, the at least one compensator may include a compensator having an ANR signal flow path arranged in parallel with the direct signal flow path to provide at least a portion of the ambient noise to the user, as referenced Figure 3 As described. In some specific embodiments, the drive signal may be combined with one or more additional signals (e.g., signals generated in the audio path of the ANR device) before being provided to the acoustic transducer. Thus, the audio output of the acoustic transducer may represent noise-canceling audio that is an audio combination representing the environment adjusted according to the user's preference.

[0041] In some specific embodiments, the processing in step 706 includes combining the first input signal and the second input signal to generate a combined input signal, applying a gain to the combined input signal using an amplifier, and processing the output of the amplifier using at least one compensator to generate a drive signal for the acoustic transducer, as referenced Figure 4 As described. In some specific embodiments, the processing includes applying a first gain to the first input signal using a first amplifier, applying a second gain to the second signal using a second amplifier, combining the first input signal and the second input signal to generate a combined input signal, and processing the combined input signal using at least one compensator to generate a drive signal for the acoustic transducer, as referenced Figure 5 As described. In some specific embodiments, the processing includes processing the first input signal using a first variable gain amplifier and a compensator to generate a first processed signal for the acoustic transducer of the ANR device, processing the second input signal using a second variable gain amplifier and a compensator to generate a second processed signal for the acoustic transducer of the ANR device, and combining the first processed signal and the second processed signal to generate a drive signal for the acoustic transducer, as referenced Figure 6 As described. In each case, it should be understood that the variable gain amplifier may be included within the corresponding compensator associated with the corresponding feedforward signal path.

[0042] Although Figures 4 to 6 shows a specific exemplary arrangement of components for implementing the techniques described herein, other components and / or arrangements of components may be used without departing from the scope of the present disclosure. In some specific embodiments, the arrangement of components along the feedforward path may include an analog microphone, an amplifier, an analog-to-digital converter (ADC), a digital adder (in the case of multiple microphones), a VGA, and a feedforward compensator (in this order). This arrangement is similar to Figure 4The arrangement of the components shown in FIG. where an amplifier and an ADC are added between each microphone 402 and the combining circuit 404 (which includes a digital adder in this example). In some specific embodiments, the arrangement of the components along the feedforward path may include an analog microphone, an analog adder (in the case of multiple microphones), an ADC, a VGA, and a feedforward compensator. This arrangement is also similar to Figure 4 The arrangement of the components shown in FIG., where the combining circuit 404 includes an analog adder and an ADC disposed between the combining circuit 404 and the VGA 406. The arrangement of the components can be selected based on the target performance parameters. For example, in applications where limiting quantization noise is important, the latter arrangement can be selected because it introduces only a single noise source (the ADC) before the gain stage. However, this may come at the cost of dynamic range issues (since the signals from all microphones pass through a single ADC), which may in turn result in clipping of the signals captured by some microphones. On the other hand, if avoiding clipping is more important at the cost of potentially more quantization noise, the former arrangement (where the amplifier and ADC are disposed between each microphone 402 and the combining circuit 404) can be used.

[0043] Figure 8 FIG. is a block diagram of an exemplary computer system 800 that can be used to perform the above operations. For example, at least a portion of the computer system 800 can be used to implement any of the systems 400, 500, and 600 described above with reference to Figure 4 , Figure 5 and Figure 6 respectively. The system 800 includes a processor 810, a memory 820, a storage device 830, and an input / output device 840. Each of the components 810, 820, 830, and 840 can be interconnected, for example, using a system bus 850. The processor 810 is capable of processing instructions for execution within the system 800. In one specific embodiment, the processor 810 is a single-threaded processor. In another specific embodiment, the processor 810 is a multi-threaded processor. The processor 810 is capable of processing instructions stored in the memory 820 or on the storage device 830.

[0044] The memory 820 stores information within the system 800. In one specific embodiment, the memory 820 is a computer-readable medium. In one specific embodiment, the memory 820 is a volatile storage unit. In another specific embodiment, the memory 820 is a non-volatile storage unit.

[0045] The storage device 830 can provide a mass storage device for the system 800. In one specific implementation, the storage device 830 is a computer-readable medium. In various different specific implementations, the storage device 830 can include, for example, a hard disk device, an optical disc device, a storage device shared over a network by multiple computing devices (e.g., a cloud storage device), or some other large-capacity storage device.

[0046] The input / output device 840 provides input / output operations for the system 800. In one specific implementation, the input / output device 840 can include one or more network interface devices (e.g., Ethernet cards), serial communication devices (e.g., RS-232 ports), and / or wireless interface devices (e.g., 802.11 cards). In another specific implementation, the input / output device can include a drive device that is configured to receive input data and send output data to other input / output devices such as a keyboard, a printer, and the display device 860, as well as the audio transducer / speaker 870.

[0047] Although Figure 8 an exemplary processing system has been described, the specific implementations of the subject matter and functional operations described in this specification can be implemented in other types of digital electronic circuits, in computer software, firmware, or hardware (including the structures disclosed in this specification and their structural equivalents), or in a combination of one or more of them.

[0048] This specification uses the term "configured" in connection with systems and computer program components. For a system of one or more computers, being configured to perform a particular operation or action means that software, firmware, hardware, or a combination of them has been installed on the system that, in operation, causes the system to perform these operations or actions. For one or more computer programs, being "configured to" perform a particular operation or action means that the one or more programs include instructions that, when executed by a data processing apparatus, cause the apparatus to perform the operation or action.

[0049] The implementations of the subject matter and the functional operations described in this specification can be realized in digital electronic circuitry, in tangibly embodied computer software or firmware, in computer hardware, including the structures disclosed in this specification and their structural equivalents, or in a combination of one or more of them. The implementations of the subject matter described in this specification can be realized as one or more computer programs, i.e., one or more modules of computer program instructions encoded on a tangible non-transitory storage medium for execution by, or to control the operation of, a data processing apparatus. The computer storage medium can be a machine-readable storage device, a machine-readable storage substrate, a random or serial access memory device, or a combination of one or more of them. Alternatively or in addition, the program instructions can be encoded on an artificially generated propagated signal, which (such as a machine-generated electrical, optical, or electromagnetic signal) is generated to encode information for transmission to a suitable receiving device for execution by the data processing apparatus.

[0050] The term “data processing apparatus” refers to data processing hardware and encompasses all types of devices, equipment, and machines for processing data, including, for example, programmable processors, computers, or multiple processors or computers. The apparatus can also be or further include special-purpose logic circuitry, such as an FPGA (Field Programmable Gate Array) or an ASIC (Application Specific Integrated Circuit). In addition to the hardware, the apparatus can optionally include code that creates an execution environment for the computer program, such as code that constitutes processor firmware, a protocol stack, a database management system, an operating system, or a combination of one or more of them.

[0051] A computer program can also be referred to as or described as a program, software, a software application, an application, a module, a software module, a script, or code, written in any form of programming language, including compiled or interpreted languages, or declarative or procedural languages, and a computer program can be deployed in any form, including as a stand-alone program or as a module, component, subroutine, or other unit suitable for use in a computing environment. A program can, but need not, correspond to a file in a file system. A program can be stored in a part of a file that holds other programs or data, such as one or more scripts stored in a markup language document, stored in a single file dedicated to the program being considered, or stored in multiple coordinated files, such as files that store one or more modules, subroutines, or portions of code. A computer program can be deployed to execute on one computer or on multiple computers distributed at one site or multiple sites and interconnected by a data communication network.

[0052] The processes and logical flows described in this specification can be performed by one or more programmable computers executing one or more computer programs to perform functions by operating on input data and generating output. The processes and logical flows can also be performed by, or by a combination of, special purpose logic circuitry, such as an FPGA or ASIC, or special purpose logic circuitry and one or more programmed computers.

[0053] To provide for interaction with a user, embodiments of the subject matter described in this specification can be implemented on a computer having a display device (e.g., a light emitting diode (LED) or liquid crystal display (LCD) monitor) for displaying information to the user and a keyboard and a pointing device (e.g., a mouse or a trackball) by which the user can provide input to the computer. Other types of devices can also be used to provide for interaction with the user; for example, the feedback provided to the user can be any form of sensory feedback, such as visual feedback, auditory feedback, or tactile feedback; and any form of input can be received from the user, including acoustic, speech, or tactile input. Additionally, a computer can interact with the user by sending and receiving documents to and from the device used by the user; for example, by sending a web page to a web browser in response to a request received from the web browser on the user device. Additionally, a computer can interact with the user by sending a text message or other form of message to a personal device (e.g., a smartphone running a messaging application) and receiving a returned response message from the user.

[0054] Embodiments of the subject matter described in this specification can be implemented in a computing system that includes a back-end component (e.g., as a data server), or that includes a middleware component (e.g., an application server), or that includes a front-end component (e.g., a client computer having a graphical user interface, a web browser, or an application through which a user can interact with a particular implementation of the subject matter described in this specification), or any combination of one or more of such back-end, middleware, or front-end components. The components of the system can be interconnected by any form or medium of digital data communication (e.g., a communication network). Examples of communication networks include a local area network (LAN) and a wide area network (WAN), such as the Internet.

[0055] A computing system may include a client and a server. The client and the server are typically remote from each other and typically interact via a communication network. The relationship between the client and the server is generated by computer programs that run on respective computers and have a client-server relationship with each other. In some embodiments, the server transmits data (e.g., an HTML page) to a user device, e.g., to display the data to a user interacting with the device and to receive user input from the user, where the user acts as the client. Data generated at the user device, e.g., the result of a user interaction, may be received at the server from the device.

[0056] Other examples and applications not specifically described herein are also within the scope of the following claims. Elements of the different specific implementations described herein may be combined to form other examples not specifically recited above. Some elements may be removed from the structures described herein without adversely affecting their operation. Additionally, various separate elements may be combined into one or more separate elements to perform the functions described herein.

Claims

1. A method, the method comprising: Receiving an input signal generated by one of a plurality of sensors of an active noise reduction (ANR) device; Determining a gain for the input signal based on: The number of the plurality of sensors of the ANR device, and A relationship between the likelihood of each of the plurality of sensors being coupled to a sound transducer of the ANR device, the likelihood of coupling being determined based on a known position of each of the plurality of sensors relative to an acoustic leakage point of the ANR device; And Applying the gain to the input signal to generate a drive signal for the sound transducer of the ANR device.

2. The method according to claim 1, the method further comprising: Receiving a second input signal generated by another one of the plurality of sensors of the ANR device; Determining a second gain for the second input signal based on: The number of the plurality of sensors of the ANR device, and The relationship between the likelihood of each of the plurality of sensors being coupled to the sound transducer of the ANR device; And Applying the second gain to the second input signal to generate the drive signal for the sound transducer of the ANR device.

3. The method according to claim 2, wherein the value of the gain is different from the value of the second gain.

4. The method according to claim 2, wherein determining the gain and the second gain comprises: Allocating a target gain between the gain applied to the input signal and the second gain applied to the second input signal, at least partially based on the number of the plurality of sensors and the relationship between the likelihood of each of the plurality of sensors being coupled to the sound transducer of the ANR device.

5. The method according to claim 1, wherein the gain is selected at least partially based on one or more frequencies of the input signal.

6. The method according to claim 1, wherein each of the plurality of sensors includes a feedforward sensor disposed in a feedforward signal path of the ANR device.

7. The method according to claim 1, wherein each of the plurality of sensors includes a feedback sensor disposed in a feedback signal path of the ANR device.

8. The method according to claim 1, the method further comprising: Combining the input signal with a second input signal generated by another one of the plurality of sensors to generate a combined input signal; Applying a gain to the combined input signal using an amplifier; And Processing an output of the amplifier by at least one compensator to generate the drive signal for the sound transducer.

9. The method according to claim 1, the method further comprising: Applying the gain to the input signal using a first amplifier to generate a first amplified input signal; Processing the first amplified input signal by a first compensator to generate a first processed signal for the sound transducer of the ANR device; Apply a second gain to a second input signal generated by another one of the plurality of sensors using a second amplifier to generate a second amplified input signal; Process the second input signal by a second compensator to generate a second processed signal for the acoustic transducer of the ANR device; And Combine the first processed signal and the second processed signal to generate the drive signal for the acoustic transducer.

10. The method according to claim 9, wherein the first compensator applies one or more first filters to the first amplified input signal, and wherein the second compensator applies one or more second filters to the second amplified input signal, the one or more second filters being different from the one or more first filters.

11. The method according to claim 1, the method further comprising: Apply the gain to the input signal using a first amplifier; Apply a second gain to a second input signal generated by another one of the plurality of sensors using a second amplifier; Combine the input signal and the second input signal to generate a combined input signal; And Process the combined input signal by at least one compensator to generate the drive signal for the acoustic transducer.

12. An active noise reduction (ANR) device, the ANR device comprising: An acoustic transducer; A plurality of sensors; And A circuit configured to: Receive an input signal generated by one of the plurality of sensors; Determine a gain for the input signal based on: The number of the plurality of sensors of the ANR device, and A relationship between the likelihood of each of the plurality of sensors being coupled to the acoustic transducer, the likelihood of coupling being determined based on the known position of each of the plurality of sensors relative to an acoustic leakage point of the ANR device; And Apply the gain to the input signal to generate a drive signal for the acoustic transducer of the ANR device.

13. The apparatus according to claim 12, wherein determining the gain comprises: Allocate a portion of a target gain to the input signal at least partially based on the relationship between the number of the plurality of sensors and the likelihood of each of the plurality of sensors being coupled to the acoustic transducer.

14. The device according to claim 12, wherein each of the plurality of sensors includes a feedforward sensor disposed in a feedforward signal path of the ANR device.

15. The device according to claim 12, wherein each of the plurality of sensors includes a feedback sensor disposed in a feedback signal path of the ANR device.

16. The device according to claim 12, further comprising: A combination circuit configured to combine the input signal with a second audio input signal generated by another one of the plurality of sensors to generate a combined input signal; And An amplifier configured to apply a gain to the combined input signal, wherein the circuit is configured to process an output of the amplifier to generate the drive signal for the acoustic transducer.

17. The apparatus according to claim 12, further comprising: a first amplifier configured to apply the gain to the input signal to generate a first amplified input signal; a first compensator configured to process the first amplified input signal to generate a first processed signal; a second amplifier configured to apply a second gain to a second input signal generated by another one of the plurality of sensors to generate a second amplified input signal; a second compensator configured to process the second amplified input signal to generate a second processed signal; and a combining circuit configured to combine the first processed signal and the second processed signal to generate the drive signal for the acoustic transducer.

18. The apparatus according to claim 17, wherein the first compensator is configured to apply one or more first filters to the first amplified input signal, and wherein the second compensator is configured to apply one or more second filters to the second amplified input signal, the one or more second filters being different from the one or more first filters.

19. The apparatus according to claim 12, further comprising: a first amplifier configured to apply the gain to the input signal; a second amplifier configured to apply a second gain to a second input signal generated by another one of the plurality of sensors; and a combining circuit configured to combine the input signal and the second input signal to generate a combined input signal, wherein the circuit is configured to process the combined input signal to generate the drive signal for the acoustic transducer.

20. One or more machine-readable storage devices having computer-readable instructions encoded thereon for causing one or more processing devices to perform operations, the operations including: receiving an input signal generated by one of a plurality of sensors of an active noise reduction (ANR) device; determining a gain for the input signal based on: the number of the plurality of sensors of the ANR device, and a relationship between the likelihood of each of the plurality of sensors being coupled to an acoustic transducer of the ANR device, the likelihood of coupling being determined based on a known position of each of the plurality of sensors relative to an acoustic leakage point of the ANR device; and applying the gain to the input signal to generate a drive signal for the acoustic transducer of the ANR device.

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