Placement of multiple feed-forward microphones in an active noise reduction (ANR) system

Abstract

The technology described in this document may be embodied in an active noise reduction (ANR) headset earpiece, the ANR headset earpiece comprising: a first microphone, the first microphone disposed on the ANR headset earpiece, such that the first microphone is configured to capture a first input signal representing noise passing through a first noise path through the ANR headset earpiece; and a second microphone, the second microphone disposed on the ANR headset earpiece, such that the second microphone is configured to capture a second input signal representing noise passing through a second noise path through the ANR headset earpiece. The positions of the first microphone and the second microphone on the ANR headset earpiece are configured to achieve a first target coherence level at multiple frequencies, the first target coherence level at a particular frequency representing that the output signal may be jointly suppressed using a fraction of the first input signal and the second input signal.

Description

Technical Field

[0001] The present disclosure relates generally to active noise reduction (ANR) devices, and more particularly to ANR devices having multiple feed-forward microphones. Background Art

[0002] Acoustic devices such as headphones may include active noise reduction (ANR) capabilities that block at least a portion of ambient noise from reaching the user's ears. A single feed-forward microphone is advantageous in many acoustic devices because it is low cost and easy to implement. The performance of these devices can be estimated based on the level of coherence between the noise signals at the location of the microphone outside the device and the virtual microphone inside the device (e.g., the user's ear). However, the coherence of these devices may be reduced when there are noise signals from multiple noise sources that cannot be captured by a single feed-forward microphone. Summary of the invention

[0003] In general, in one aspect, the present document features a method comprising: receiving a first input signal captured by at least a first feed-forward microphone associated with an active noise reduction (ANR) device; and receiving a second input signal captured by at least a second feed-forward microphone associated with the ANR device. The method also includes: processing the first input signal using a first filter disposed in a first ANR signal flow path to generate a first output signal for an acoustic transducer of the ANR device; and processing the second input signal using a second filter disposed in a second ANR signal flow path to generate a second output signal for the acoustic transducer. The method includes: generating an output signal for the acoustic transducer based on combining the first output signal and the second output signal. The second filter is different from the first filter.

[0004] On the other hand, the document features an active noise reduction (ANR) device, the ANR device comprising: a first feedforward microphone, the first feedforward microphone configured to capture a first input signal; and a second feedforward microphone, the second feedforward microphone configured to capture a second input signal. The ANR device also includes: an acoustic transducer, the acoustic transducer configured to generate output audio. The ANR device includes: a first filter, the first filter is disposed in a first ANR signal flow path of the ANR device. The first filter is configured to: process the first input signal to generate a first output signal for the acoustic transducer of the ANR device. The ANR device includes: a second filter, the second filter is disposed in a second ANR signal flow path of the ANR device. The second filter is configured to: process the second input signal to generate a second output signal for the acoustic transducer. The second filter is different from the first filter. The acoustic transducer is driven by an output signal, the output signal being a combination of the first output signal and the second output signal.

[0005] In another aspect, the 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. These operations include: receiving a first input signal captured by at least a first feed-forward microphone associated with an active noise reduction (ANR) device; receiving a second input signal captured by at least a second feed-forward microphone associated with the ANR device; processing the first input signal using a first filter disposed in a first ANR signal flow path to generate a first output signal for an acoustic transducer of the ANR device; processing the second input signal using a second filter disposed in a second ANR signal flow path to generate a second output signal for the acoustic transducer, wherein the second filter is different from the first filter; and generating an output signal for the acoustic transducer based on combining the first output signal with the second output signal.

[0006] Specific implementations of the above aspects may include one or more of the following features.

[0007] The first ANR signal flow path and the second ANR signal flow path may be arranged in a feed-forward signal flow path of the ANR device.At least one of the first input signal or the second input signal may be captured using a plurality of microphones.

[0008] The above method may also include: receiving a third input signal captured by a third microphone associated with the ANR device; and using a third filter of the ANR device to process the third input signal to generate a third signal for the acoustic transducer. The output signal for the acoustic transducer can be generated based on combining the first output signal, the second output signal and the third signal. The third filter may be different from the first filter and the second filter. In some cases, the third microphone is a feedforward microphone of the ANR device, and the third filter is disposed in the feedforward signal flow path of the ANR device. In some other cases, the third input signal is a feedback signal, and the third microphone is a feedback microphone of the ANR device. In these other cases, the third filter is disposed in a feedback signal flow path, and the feedback signal flow path drives the output transducer to generate an anti-noise signal to reduce the impact of noise in the third input signal captured by the feedback microphone.

[0009] In another aspect, the document features an active noise reduction (ANR) headset earpiece, the ANR headset earpiece comprising: a first microphone, the first microphone disposed on the ANR headset earpiece, such that the first microphone is configured to capture a first input signal representing noise passing through a first noise path through the ANR headset earpiece; and a second microphone, the second microphone disposed on the ANR headset earpiece, such that the second microphone is configured to capture a second input signal representing noise passing through a second noise path through the ANR headset earpiece. The positions of the first microphone and the second microphone on the ANR headset earpiece are configured to achieve a first target coherence level at multiple frequencies, the first target coherence level at a particular frequency representing a fraction of the output signal that can be suppressed using the first input signal and the second input signal together.

[0010] On the other hand, the present document features a method comprising: providing a first microphone on an active noise reduction (ANR) headphone earpiece, such that the first microphone is configured to capture a first input signal representing noise passing through a first noise path through the ANR headphone earpiece; providing a second microphone on the ANR headphone earpiece, such that the second microphone is configured to capture a second input signal representing noise passing through a second noise path through the ANR headphone earpiece; and configuring positions of the first microphone and the second microphone on the ANR headphone earpiece so that a first target coherence level is achieved at multiple frequencies, the first target coherence level at a particular frequency representing a fraction of the output signal that can be jointly suppressed using the first input signal and the second input signal.

[0011] Specific implementations of the above two aspects may include one or more of the following features. The ANR headset earpiece may include: a third microphone, the third microphone is arranged on the ANR headset earpiece, so that the third microphone is configured to capture a third input signal representing noise passing through a third noise path through the ANR headset earpiece. The positions of the first microphone, the second microphone and the third microphone on the ANR headset cup are configured so that a second target coherence level is achieved at multiple frequencies, and the second target coherence level at a specific frequency indicates that the output signal can jointly use the first input signal, the second input signal and the third input signal to suppress the fraction.

[0012] The first microphone and the second microphone can be feed-forward microphones. The first noise path can include an acoustic path through the pad of the headset receiver. The second noise path can include an acoustic path through a port of the headset receiver. In some specific implementations, the headset receiver can have two independent ports, including a mass port and a resistive port. In these specific implementations, the second noise path can include an acoustic path through a mass block port or a resistive port. In some other specific implementations, the headset receiver can have a port that can act as a mass port at some frequencies and as a resistive port at some other frequencies. The third noise path can include an acoustic path formed by leakage between the pad of the headset receiver and the head of the user of the ANR headset receiver.

[0013] The ANR headset earpiece may also include: an acoustic transducer configured to generate output audio; a first filter configured to process the first input signal to generate a first output signal for the acoustic transducer; and a second filter configured to process the second input signal to generate a second output signal for the acoustic transducer. The acoustic transducer may be driven by a combined signal that is a combination of the first output signal and the second output signal. In some implementations, the combined signal may include components combined at various portions of the electronics within the ANR headset.

[0014] Various embodiments described herein may provide one or more of the following advantages. By placing multiple feedforward microphones at different strategic locations on the ANR device earpiece (e.g., placed close to the noise path of the ANR device earpiece and / or close to the pad of the ANR device earpiece), the technology described herein may improve the coherence of the ANR device, which in turn may result in performance superior to existing ANR devices. In addition, multiple feedforward microphones may be spread around the periphery of the earpiece, thereby enabling the ANR device to capture noise signals from different directions at an early stage. This in turn may allow the corresponding anti-noise signal to be generated faster than a device that relies on feedback-based noise reduction process adjustment. The use of multiple feedforward microphones may potentially improve the performance of the ANR device in a variety of different environments, particularly in those environments where noise may come from different directions. For example, an ANR device with multiple microphones may provide significant advantages when used in an airplane, a crowded cafeteria, or a moving vehicle where noise comes from different noise sources.

[0015] Two or more features described in this disclosure, including those described in the Summary of the Invention, may be combined to form embodiments not specifically described herein. The details of one or more specific implementations are discussed in the accompanying drawings and the following description. Other features, objects, and advantages will be apparent in the specification, drawings, and claims. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 An example of an in-ear active noise cancelling (ANR) headphone is shown.

[0017] Figure 2 An exemplary circumaural ANR headset having an earpiece with three feed-forward microphones is illustrated.

[0018] Figure 3 An exemplary circumaural ANR headset having an earpiece with two feed-forward microphones is illustrated.

[0019] Figure 4 is a block diagram of an ANR device with multiple feed-forward microphones, each of which has its own controller.

[0020] Figure 5 is a flow chart of an exemplary process for generating an output signal for an acoustic transducer in an ANR device having multiple feed-forward microphones, each with its own controller.

[0021] Figure 6 is a flow chart of an exemplary process for configuring the positions of multiple microphones on an ANR headset earpiece so that a target coherence level is achieved. DETAILED DESCRIPTION

[0022] This document describes techniques for implementing multiple feed-forward microphones in active noise reduction (ANR) devices to improve the performance of the ANR devices. ANR devices, such as ANR headphones, are used to provide a potentially immersive listening experience by reducing the effects of ambient noise and sound. Many ANR devices use a single feed-forward microphone for noise reduction due to its low cost and simple implementation. However, the performance of these devices may be limited when noise comes from different directions. The performance of an ANR device can be estimated based on a coherence level, which represents the fraction of power in the output signal at each frequency that can be eliminated / suppressed using the input from the feed-forward microphone. The coherence of these devices may be reduced when noise signals from multiple noise sources are not adequately captured by a single feed-forward microphone. As used in this document, a feed-forward microphone refers to a microphone disposed at an outward-facing portion of the ANR headset (e.g., at Figure 2 The microphone on the outside of the ear cup 202 is mainly used to capture ambient sound. Figure 22 shows an example of a feed-forward microphone, for example, feed-forward microphones 204, 206, and 208 disposed on the outside of an ear cup 202. A feedback microphone refers to a microphone disposed adjacent to the acoustic transducer of an ANR headset (e.g., inside an ear cup), and its primary purpose is to capture noise in the same sound field as the ear (which is different from the sound field of the environment in which the feed-forward microphone is located).

[0023] The technology described herein allows the implementation of an ANR device with multiple feed-forward microphones arranged on the outside of the earpiece of the ANR device. By placing multiple feed-forward microphones at different strategic locations on the ANR device earpiece (e.g., placed as a noise path close to the ANR device earpiece and / or a pad close to the ANR device earpiece), the technology described herein can improve the coherence of the ANR device, which in turn can lead to performance superior to existing ANR devices. In addition, multiple feed-forward microphones can be spread around the periphery of the earpiece, so that the ANR device can capture noise signals from different directions at an early stage. This in turn can allow the corresponding anti-noise signal to be generated faster than the device that relies on the noise reduction process to be adjusted based on feedback. The use of multiple feed-forward microphones can potentially improve the performance of the ANR device in various different environments, particularly in those environments where noise can come from different directions. For example, an ANR device with multiple microphones can provide significant advantages in a mobile vehicle, in which the noise comes from different noise sources, such as an engine, an external vehicle, and a windshield wiper.

[0024] An active noise reduction (ANR) device may include a configurable digital signal processor (DSP) that can be used to implement various signal flow topologies and filter configurations. Examples of such DSPs are described in U.S. Patents 8,073,150 and 8,073,151, which are incorporated herein by reference in their entirety. U.S. Patent 9,082,388 (also incorporated herein by reference in its entirety) describes a DSP that can be used to implement various signal flow topologies and filter configurations. Figure 1 The acoustic implementation of an in-ear active noise reduction (ANR) headphone is shown. The headphone 100 includes a feedforward microphone 102, a feedback microphone 104, an output transducer 106 (which may also be referred to as an electroacoustic transducer or an acoustic transducer), and a noise reduction circuit (not shown) coupled to the two microphones and the output transducer to provide an anti-noise signal to the output transducer based on signals detected at the two microphones. The additional input ( Figure 1 ) provides an additional audio signal, such as music or a communication signal, to be played back on the output transducer 106 independently of the noise reduction signal.

[0025] The term "headphones", used interchangeably with the term "headphones" herein, includes various types of personal acoustic devices, such as in-ear, circumaural, or circumaural headphones, earphones, and hearing aids. Headphones or earphones may include earplugs or earmuffs for each ear. The earplugs or earmuffs may be physically tied to each other, such as by a cord, a head-mounted bridge, or a headband or a back-of-head holding structure. In some implementations, the earplugs or earmuffs of a headset may be connected to each other via a wireless link.

[0026] For an ANR device with a single feedforward microphone configured to capture a single input signal, the performance of the ANR device can be estimated by the coherence between (i) the input signal at the location of the feedforward microphone (placed on the outside of the device) and (ii) the output signal measured at the user's ear. Specifically, the coherence between two signals is a frequency domain quantity that quantifies the extent to which the two signals are linearly correlated with each other. The coherence is a number between 0 and 1 at each frequency. Assume that the input signal at time step t is x(t) and the output signal at time step t is y(t), where x(t) to y(t) are time domain quantities, then the coherence from x(t) to y(t) is the same as the coherence from y(t) to x(t). The coherence between x(t) and y(t) can be expressed as This reflects it as a power quantity. The coherence can be calculated using the following formula:

[0027]

[0028] In the above formula, S XX (ω) is the power spectrum of x(t), which is the expected value of the squared magnitude of the Fourier transform of x, as shown below:

[0029] S XX (ω)=E[X(ω)X(ω) * ]=E[|X(ω)| 2 ], (2)

[0030] Where ω is the frequency, and S XX (ω) is a frequency domain quantity.

[0031] Similarly, S YY (ω) is the power spectrum of y(t) and can be calculated as follows:

[0032] S YY (ω)=E[Y(ω)Y(ω) * ]=E[|Y(ω)| 2 ] (3)

[0033] S YX (ω) is the cross power spectrum between x(t) and y(t):

[0034] S YX (ω)=E[Y(ω)X(ω) * ] (4)

[0035] From a mathematical point of view, coherence is the fraction of power in the output signal y(t) that can be linearly explained by the input signal x(t). From an ANR point of view, coherence represents the fraction of power in the output signal at each frequency that can be cancelled using the input signal.

[0036] In the presence of noise signals from multiple noise sources that are not adequately captured by a single feed-forward microphone, the coherence of a single feed-forward microphone ANR device may be reduced. The techniques described herein may provide improved coherence (compared to a single feed-forward microphone device) by allowing the use of multiple feed-forward microphones in an ANR device (also referred to as an ANR earphone or headset). The performance of such a device may be further improved via strategic placement of the feed-forward microphone at a location adjacent to the noise path of the ANR earphone (the path through which ambient noise may reach the user's ear).

[0037] For example, during the use of headphones, acoustic leakage between the user's skin and the headphone cushion in contact with the skin forms a typical noise path. Therefore, one or more of the multiple feed-forward microphones may be placed near the outer periphery of the earphone receiver (e.g., near the outer periphery of the ear cup of the circum-aural headphone) and close to the cushion of the receiver. As another example, the port of the ANR headset (e.g., a resistive port or a mass port as described in, for example, U.S. Patent 9,762,990, which is incorporated herein by reference) may also form a noise path in the headset. Therefore, one or more of the multiple feed-forward microphones may be arranged to be close to one or more of such ports of the ANR headset. As described in U.S. Patent 9,762,990, the ANR headset may have a front cavity and a rear cavity separated by a driver, wherein the mass port tube is connected to the rear cavity to present a reactive acoustic impedance to the rear cavity, in parallel with the resistive port. In some specific implementations, it may be beneficial to place at least one of the multiple feed-forward microphones close to the resistive port or the mass port of the ANR headset to improve coherence. In some implementations, the corresponding microphone can be placed adjacent to both the resistive port and the mass port of the ANR device. Figure 2 An ear cup 202 of an ANR device is shown. The ear cup 202 includes three microphones 204, 206, and 208. Microphone 206 may be placed adjacent to a mass port (not shown) of the ANR device, and microphone 208 may be placed adjacent to a resistive port 212 of the ANR device.

[0038] In some implementations, the positions of the multiple microphones can be distributed around the earpiece so that the multiple microphones can capture noise signals from different directions. When two microphones are used for feed-forward active noise reduction, the two microphones can be placed, for example, at substantially diametrically opposite positions on the earpiece. For example, Figure 3 An ANR headset ear cup 302 is shown that includes two microphones 304 and 306. Microphone 306 is positioned toward the front of ear cup 302, and microphone 304 is positioned toward the back of ear cup 302 relative to the position of microphone 306.

[0039] The relative positions of the multiple feedforward microphones are configured such that a target coherence level is achieved.When multiple feedforward microphones are used, the coherence (also called "multi-coherence" to distinguish it from the coherence in the case of a single feedforward microphone) is calculated as follows.

[0040] If x1(t),x2(t),…,x n (t) represents multiple input signals captured by multiple feed-forward microphones, then the multi-coherence of the ANR headset can be calculated as follows:

[0041]

[0042] The bold symbols represent vectors or matrices (due to multiple input signals), and (.) H Represents the Hermitian (complex conjugate transpose) of a matrix or vector. Multicoherence is a single number between 0 and 1 at each frequency ω.

[0043] S YX (ω) is the cross power spectrum vector between the input signal and the output signal:

[0044]

[0045] where each element is defined using the following formula 4. In addition, instead of the power spectrum of the input signal, the cross-power spectrum matrix of all input signals is calculated as follows:

[0046]

[0047] The multi-coherence represents the fraction of the output signal (at the user's ear) that can be eliminated using all the input signals together. The relative positions of the multiple feed-forward microphones on the ANR earphone are configured so as to achieve a target multi-coherence level. For example, the target multi-coherence level can be 0.91, 0.94, 0.95, or any value between 0.9 and 0.9999.

[0048] Figure 2An exemplary circumaural ANR headset 200 having an earpiece with three microphones is illustrated. The earpiece is the right ear cup 202 of the headset 200 as viewed from the outside. The ear cup 202 has three microphones 204, 206, and 208, which are feed-forward microphones located near the outer periphery of the ear cup housing (or ear cup cover). Figure 2 Three feedforward microphones 204, 206, and 208 are shown, but in some implementations, the headset may have only two microphones as feedforward microphones. In some other implementations, the headset may have two feedforward microphones and one feedback microphone. In some other implementations, the headset may have more than three feedforward microphones and optionally one feedback microphone.

[0049] Generally speaking, when three microphones are used, the positions of the three microphones are spread around the outer periphery of the ear cup 202 to capture noise input signals from different directions. A first microphone of the three microphones is disposed on the ear cup 202 such that the first microphone is configured to capture a first input signal representing noise passing through a first noise path through the ANR headset ear cup 202. A second microphone is disposed on the ANR headset ear cup 202 such that the second microphone is configured to capture a second input signal representing noise passing through a second noise path through the ANR headset ear cup 202. A third microphone is disposed on the ANR headset ear cup 202 such that the third microphone is configured to capture a third input signal representing noise passing through a third noise path through the ANR headset ear cup 202. Each of the first noise path, the second noise path, and the third noise path can be selected from the following group of noise paths: (i) an acoustic path through the cushion 210 of the ear cup 202; (ii) an acoustic path through the port of the headphone ear cup 202; and (iii) an acoustic path formed by leakage between the cushion of the headphone ear cup 202 and the head of the user of the ANR headset 200.

[0050] exist Figure 2 In the example of FIG. 1 , the positions of the microphones 204, 206, and 208 are evenly distributed around the outer periphery of the ear cup 202. The microphones 204 and 206 are placed close to the cushion 210 of the ear cup 202 to capture the input signal representing the noise passing through the cushion 210. The bottom microphone 208 is placed close to the resistive port 212 to capture the input signal representing the noise passing through the resistive port 212 of the ear cup 202.

[0051] In some implementations, the ear cup 202 may have more than two feedforward microphones and optionally one feedback microphone, rather than having three microphones (two feedforward microphones and one feedback microphone, or three feedforward microphones). For example, the ear cup 202 may have three, four, or five feedforward microphones and one feedback microphone.

[0052] Figure 3 An exemplary circumaural ANR headset 300 having an earpiece with two feedforward microphones is illustrated. The earpiece is the right ear cup 302 of the headset 300 viewed from the outside. The ear cup 302 has two feedforward microphones 304 and 306. Generally speaking, when two feedforward microphones are used, the positions of the two microphones are set at positions approximately diametrically opposite on the ear cup 302. In some specific implementations, this can maximize the ability of the microphone to capture input signals originating from different noise sources. One of the microphones is set on the ear cup 302 so that the microphone is configured to capture a first input signal representing noise passing through a first noise path through the ANR headset ear cup. The second microphone is set on the ANR headset ear cup 302 so that the second microphone is configured to capture a second input signal representing noise passing through a second noise path through the ANR headset ear cup 302. The first noise path and the second noise path can be selected from the following group of noise paths: (i) an acoustic path through the cushion 310 of the ear cup 302; (ii) an acoustic path through the port of the headphone ear cup 302; and (iii) an acoustic path formed by leakage between the cushion of the headphone ear cup 302 and the head of the user of the ANR headset 300.

[0053] exist Figure 3In the example of , microphones 304 and 306 are located at approximately diametrically opposed locations on the perimeter of the ear cup. Microphone 306 is positioned toward the front of ear cup 302, and microphone 304 is positioned toward the back of ear cup 302 relative to the position of microphone 306. During use, microphone 304 is adjacent to where the user's hair may come from between cushion 310 and the user's skin, which in turn may cause noise leakage between the surrounding environment and the ear. Therefore, microphone 304 can capture input signals representing noise that has passed through the acoustic path formed by the leakage between cushion 310 and the user's head. In some implementations, it may be desirable to place microphones 304 and 306 as close to cushion 310 as possible to capture leakage through. However, if the ANR headset 300 is operated in ANR mode and hear-through mode (also known as "perception mode", in which the noise reduction function is turned off for a period of time and a portion of the ambient sound is allowed to pass to the user's ears), the microphones 304 and 306 can be set away from the periphery of the pad 310 to reduce the possibility of coupling between the microphones 304 and 306 and the driver (or acoustic transducer) of the ANR headset 300. In the hear-through mode, the microphone captures the ambient sound, and the captured sound is played back through the driver with a gain of 1 or greater. Placing the microphone close to the pad 310 brings the microphone close to the driver, thereby increasing the possibility of the microphone picking up the output of the driver. Since such coupling can adversely affect the stability of the hear-through mode, it may not be ideal to place the microphone close to the periphery of the pad 310 when the microphone is also used in the hear-through mode.

[0054] Figure 4 is a block diagram of an exemplary ANR device with multiple feedforward microphones. Generally speaking, in an ANR device, each feedforward microphone has its own filter (also called a controller), where the signals generated by each filter are combined to generate a combined signal to be fed to the acoustic transducer (or driver). Various signal flow topologies can be implemented in an ANR device to implement functions such as audio equalization, feedback noise cancellation, and feedforward noise cancellation. For example, as in Figure 4 As shown in the exemplary block diagram of the ANR device 400 in , the signal flow topology may include two or more feedforward signal flow paths (e.g., signal flow paths 414, 418, and 422) and optionally a feedback signal flow path 432 and / or an audio path 426.

[0055] Specifically, the ANR device 400 includes a first feedforward microphone 402, which is configured to capture a first input signal FF1 representing a noise passing through a first noise path through the ANR device 400. The ANR device 400 includes a first filter 416 disposed in an ANR signal flow path. The filter 416 is configured to process the first input signal to generate a first output signal. The ANR signal flow path may be disposed in a feedforward signal flow path 414 of the ANR device 400. The feedforward signal flow path 414 is disposed between the feedforward microphone 402 and the acoustic transducer 406 of the ANR device.

[0056] The ANR device 400 also includes a second feedforward microphone 404, which is configured to capture a second input signal FF2 representing the noise passing through the second noise path through the ANR device 400. The ANR device 400 includes a second filter 420 arranged in the ANR signal flow path. The filter 420 is configured to process the first input signal to generate a first output signal. The ANR signal flow path can be arranged in the feedforward signal flow path 418 of the ANR device 400. The feedforward signal flow path 418 is arranged between the feedforward microphone 404 and the acoustic transducer 406.

[0057] The ANR device 400 may optionally include other feedforward microphones, such as a feedforward microphone 408. Microphone 408 is configured to capture a third input signal FF3 representing the noise passing through the third noise path of the ANR device 400. The ANR device 400 includes a third filter 424, which is arranged in the ANR signal flow path and is configured to process the third input signal to generate a third output signal. The ANR signal flow path may be arranged in a feedforward signal flow path 422, which is arranged between the feedforward microphone 408 and the acoustic transducer 406.

[0058] In some implementations, the two feed-forward microphones of the ANR device 400 can use the same filter to process input signals captured by the two feed-forward microphones.

[0059] In some other implementations, two feedforward microphones may use filters having common components and independent components. In some cases, this may be accomplished with two completely independent filters. In some other cases, to save computational power, the input signals captured by the two microphones may each be processed by a small single filter to generate a corresponding output signal. The output signals generated by the small single filters may be combined together and then processed by a larger common filter.

[0060] In some implementations, the signal flow topology implemented in the ANR device 400 may also include an audio path 426 that includes circuitry (e.g., an equalizer 428) for processing an input audio signal 410 (such as a music or communication signal) for playback on the acoustic transducer 406.

[0061] In some implementations, the signal flow topology can include a feedback signal flow path 432 that drives the acoustic transducer 406 (using, for example, the feedback filter 430 ) to generate an anti-noise signal to reduce the effects of the noise signal FB picked up by the feedback microphone 412 .

[0062] In some implementations, the feedforward signal flow paths 414, 418, and 422 may include an ANR signal flow path arranged in parallel with the listen-through path. An example of such a configuration is described in U.S. Patent No. 10,096,313 B1, published on October 9, 2018, the entire contents of which are incorporated herein by reference.

[0063] The acoustic transducer 406 is driven by a combined signal, which is generated based on combining the output signals generated by the feedforward filters (e.g., based on combining the first output signal, the second output signal, and optionally the third output signal generated by its corresponding filter). The acoustic transducer 406 is configured to generate output audio to the user's ear by using filters 416, 420, and 424 to generate anti-noise signals to reduce the impact of noise signals picked up by the feedforward microphones 402, 404, and 408. In some specific implementations, the output signal may be combined with one or more additional signals (e.g., a signal generated by the feedback filter 430 of the ANR device 400 and / or a signal generated in the audio path 426 of the ANR device 400, etc.) before being provided to the acoustic transducer 406. Therefore, the output audio representation of the acoustic transducer 406 is a noise-reduced audio of any audio combination representing an environment adjusted according to user preferences (e.g., by using a perception mode).

[0064] Figure 5 Flowchart of an exemplary process 500 for generating an output signal for an acoustic transducer in an ANR device having multiple feed-forward microphones, each of which has its own controller. At least a portion of process 500 may be implemented using one or more processing devices (such as the DSPs described in U.S. Pat. Nos. 8,073,150 and 8,073,151, which are incorporated herein by reference in their entirety).

[0065] The operation of process 500 includes receiving a first input signal captured by at least a first feed-forward microphone associated with an ANR device (502). In some implementations, the ANR device may be an in-ear headphone, such as a reference Figure 1In some embodiments, the ANR device may include, for example, a circumaural headset, a circumaural headset (e.g., see Figure 2 and Figure 3 The first feedforward microphone may be a part of a microphone array.

[0066] The operations of process 500 also include receiving a second input signal captured by at least a second feed-forward microphone associated with the ANR device (504). In some implementations, the second feed-forward microphone can be part of a microphone array.

[0067] In some implementations, multiple microphones are used to capture at least one of the first input signal or the second input signal.

[0068] The operation of process 500 includes: processing a first input signal using a first filter disposed in a first ANR signal flow path to generate a first output signal for an acoustic transducer of the ANR device (506). The first ANR signal flow path is disposed in a feedforward signal flow path of the ANR device. The feedforward signal flow path is disposed between a first feedforward microphone and the acoustic transducer of the ANR device. In some embodiments, the first filter may be substantially similar to the method described above with reference to Figure 4 The ANR filter 416 described above. In some implementations, the first output signal may include an anti-noise signal generated in response to noise detected by the first feedforward microphone, wherein the anti-noise signal is configured to eliminate or at least reduce the effects of the noise. In some implementations, the first filter may be a fixed coefficient filter.

[0069] The operation of process 500 also includes: processing the second input signal using a second filter disposed in a second ANR signal flow path to generate a second output signal for the acoustic transducer (508). The second filter is different from the first filter. The second ANR signal flow path is disposed in a feedforward signal flow path of the ANR device. The feedforward signal flow path is disposed between a second feedforward microphone of the ANR device and the acoustic transducer. In some embodiments, the second filter may be substantially similar to the above referenced Figure 4 The ANR filter 420 described above. In some implementations, the second output signal may include an anti-noise signal generated in response to noise detected by the second feedforward microphone, wherein the anti-noise signal is configured to eliminate or at least reduce the effects of the noise. In some implementations, the second filter may be a fixed coefficient filter. In some implementations, the coefficients of the second filter may be determined substantially independently of a set of coefficients of the first filter.

[0070] The operation of process 500 also includes: generating a combined signal for the acoustic transducer based on combining the first output signal and the second output signal (510). In some specific implementations, the combined signal can be further combined with one or more additional signals (e.g., a signal generated by a feedback filter of the ANR device, a signal generated in an audio path of the ANR device, etc.) before being provided to the acoustic transducer. Thus, the output audio of the acoustic transducer can represent the noise-reduced audio combined with the audio representing the environment adjusted according to the user's preferences.

[0071] In some specific implementations, the operations of process 500 may include receiving a third input signal captured by a third microphone associated with the ANR device, and processing the third input signal using a third filter of the ANR device to generate a third signal for the acoustic transducer. In some cases, the third microphone may be a feedforward microphone of the ANR device, and the third filter is disposed in the feedforward signal flow path of the ANR device. In some other cases, the third microphone is a feedback microphone of the ANR device, and the third input signal is a feedback signal. In these other cases, the third filter is disposed in a feedback signal flow path that drives the acoustic transducer (by using the third filter) to generate an anti-noise signal to reduce the effects of noise in the third input signal captured by the feedback microphone.

[0072] In the above implementations where there is a third input signal captured by a third microphone, the combined signal for the acoustic transducer is generated based on combining the first output signal, the second output signal, and the third signal.

[0073] Figure 6 is a flow chart of an exemplary process for configuring the positions of multiple microphones on an ANR headset earpiece so that a target coherence level is achieved.

[0074] The operation of process 600 includes providing a first microphone on an active noise reduction (ANR) headset earpiece, such that the first microphone is configured to capture a first input signal (602) representing noise passing through a first noise path through the ANR headset earpiece. Providing the first microphone includes providing a first feed-forward microphone. The first noise path can be an acoustic path through a cushion of the ANR headset earpiece.

[0075] The operation of process 600 also includes: providing a second microphone on the ANR headset earpiece, so that the second microphone is configured to capture a second input signal (604) representing the noise passing through the second noise path through the ANR headset earpiece. Providing the second microphone includes providing a second feedforward microphone. The second noise path can be an acoustic path through a port of the ANR headset earpiece. The port can be a resistive port of the ANR headset earpiece or (ii) one of the mass ports of the ANR headset earpiece.

[0076] The operation of process 600 may optionally include providing a third microphone on the headset earpiece, such that the third microphone is configured to capture a third input signal (606) representing noise passing through a third noise path through the ANR headset earpiece. The third noise path may be an acoustic path formed by leakage between a cushion of the headset earpiece and a head of a user of the ANR headset earpiece.

[0077] The operation of process 600 includes: configuring the position of the microphone on the ANR headset cup so that the target coherence level of the ANR is achieved (608). When a first microphone and a second microphone are present, the positions of the first microphone and the second microphone on the ANR headset earpiece are configured so that a first target coherence level is achieved at multiple frequencies. The first target coherence level at a specific frequency indicates that the output signal can be suppressed by the first input signal and the second input signal together. When a first microphone, a second microphone, and a third microphone are present, the positions of the first microphone, the second microphone, and the third microphone are configured so that the positions of the first microphone, the second microphone, and the third microphone on the ANR headset cup are configured so that a second target coherence level is achieved at multiple frequencies. The second target coherence level at a specific frequency indicates that the output signal can be suppressed by the first, second, and third input signals together.

[0078] Coherence is a single number between 0 and 1 and can be calculated using Equation 5 as described above. The target coherence level can be a number between 0 and 1, for example, the target multi-coherence level can be 0.6, 0.7, 0.75, 0.82, or 0.95.

[0079] The functions or parts thereof described herein, as well as various modifications thereof (hereinafter referred to as "functions") may be implemented at least in part via a computer program product, such as a computer program tangibly embodied in an information carrier, such as one or more non-transitory machine-readable media or storage devices, for executing, or controlling the operation of one or more data processing apparatuses, such as a programmable processor, a computer, multiple computers and / or a programmable logic component.

[0080] A computer program can be written in any form of programming language, including compiled or interpreted languages, and it can be deployed in any form, including as a stand-alone program or as a module, component, subroutine or other unit suitable for use in a computing environment. A computer program can be deployed on one computer or executed on multiple computers distributed at one site or multiple sites and interconnected by a network.

[0081] The actions associated with implementing all or part of the functionality may be performed by one or more programmable processors executing one or more computer programs to perform the functionality of the calibration process. All or part of the functionality may be implemented as a special-purpose logic circuit, such as an FPGA and / or an ASIC (application-specific integrated circuit). In some specific implementations, at least a portion of the functionality may also be performed on a floating-point or fixed-point digital signal processor (DSP), such as the Super Harvard Architecture Single-Chip Microcontroller (SHARC) developed by Analog Devices Inc.

[0082] Processors suitable for executing computer programs include, for example, both general-purpose and special-purpose microprocessors, and any one or more processors of any type of digital computer. Generally speaking, a processor will receive instructions and data from a read-only memory or a random access memory, or both. The components of a computer include a processor for executing instructions and one or more memory devices for storing instructions and data.

[0083] Other embodiments and applications not specifically described herein are also within the scope of the following claims. The elements of the different embodiments described herein can be combined to form other embodiments not specifically set forth above. Some elements can be removed from the structure described herein without adversely affecting their operation. In addition, various independent elements can be combined into one or more separate elements to perform the functions described herein.

Claims

1. An active noise reduction (ANR) headset earpiece, comprising: a first microphone disposed on the ANR headset earpiece such that the first microphone is configured to capture a first input signal representative of noise passing through a first noise path through the ANR headset earpiece; and a second microphone disposed on the ANR headset earpiece such that the second microphone is configured to capture a second input signal representative of noise passing through a second noise path through the ANR headset earpiece, wherein the positions of the first microphone and the second microphone on the ANR headset earpiece are configured so as to achieve a first target coherence level at a plurality of frequencies, the first target coherence level at a particular frequency representing a fraction of an output signal that can be suppressed by using the first input signal and the second input signal together; The coherence is a single number between 0 and 1 at each frequency ω and is calculated as Where S YX (ω) is the cross power spectrum vector between the input signal and the output signal, S XX (ω) is the cross power spectrum matrix of the input signal, S YY (ω) is the power spectrum of the output signal and (.) H Represents the Hermitian representation of a matrix or vector.

2. The ANR headset earpiece according to claim 1, further comprising: A third microphone is disposed on the ANR headset earpiece such that the third microphone is configured to capture a third input signal representative of noise passing through a third noise path through the ANR headset earpiece.

3. An ANR headset earpiece according to claim 2, wherein the positions of the first microphone, the second microphone and the third microphone on the ANR headset earpiece are configured to achieve a second target coherence level at multiple frequencies, and the second target coherence level at a specific frequency represents the fraction of the output signal that can be suppressed by using the first input signal, the second input signal and the third input signal together.

4. The ANR headset earpiece of claim 1, wherein the first microphone and the second microphone are feed-forward microphones.

5. The ANR headphone earpiece of claim 1, wherein the first noise path comprises an acoustic path through a cushion of the headphone earpiece.

6. The ANR headset earpiece of claim 1, wherein the second noise path comprises an acoustic path through a port of the headset earpiece.

7. The ANR headset earpiece of claim 6, wherein the port is a resistive port of the ANR headset earpiece.

8. The ANR headset earpiece of claim 6, wherein the port is a mass port of the ANR headset earpiece.

9. The ANR headphone earpiece of claim 2, wherein the third noise path comprises an acoustic path formed by leakage between a cushion of the headphone earpiece and a head of a user of the ANR headphone earpiece.

10. The ANR headset earpiece of claim 1, further comprising: an acoustic transducer configured to generate output audio; a first filter configured to process the first input signal to generate a first output signal for the acoustic transducer; a second filter configured to process the second input signal to generate a second output signal for the acoustic transducer; Wherein the acoustic transducer is driven by a combined signal, the combined signal being a combination of the first output signal and the second output signal.

11. A method for placing a plurality of microphones, comprising: providing a first microphone on an active noise reduction (ANR) headphone earpiece, such that the first microphone is configured to capture a first input signal representative of noise passing through a first noise path through the ANR headphone earpiece; providing a second microphone on the ANR headset earpiece, such that the second microphone is configured to capture a second input signal representative of noise passing through a second noise path through the ANR headset earpiece; as well as Configuring the positions of the first microphone and the second microphone on the ANR headset earpiece to achieve a first target coherence level at a plurality of frequencies, the first target coherence level at a particular frequency representing a fraction of an output signal that can be suppressed by using the first input signal and the second input signal together; The coherence is a single number between 0 and 1 at each frequency ω and is calculated as Where S YX (ω) is the cross power spectrum vector between the input signal and the output signal, S XX (ω) is the cross power spectrum matrix of the input signal, S YY (ω) is the power spectrum of the output signal and (.) H Represents the Hermitian representation of a matrix or vector.

12. The method according to claim 11, further comprising: A third microphone is provided on the headset earpiece such that the third microphone is configured to capture a third input signal representative of noise passing through a third noise path through the ANR headset earpiece.

13. The method according to claim 12, further comprising: The positions of the first microphone, the second microphone and the third microphone on the ANR headset earpiece are configured so as to achieve a second target coherence level at multiple frequencies, and the second target coherence level at a specific frequency represents the fraction of the output signal that can be suppressed by jointly using the first input signal, the second input signal and the third input signal. The method of claim 11 , wherein providing the first microphone comprises providing a first feed-forward microphone.

15. The method of claim 11, wherein providing the second microphone comprises providing a second feed-forward microphone.

16. The method of claim 11, wherein providing the first microphone on the ANR headset earpiece comprises: The first microphone is disposed on the ANR headphone earpiece such that the first microphone is configured to capture the first input signal representing noise of an acoustic path through a cushion of the ANR headphone earpiece.

17. The method of claim 11, wherein providing the second microphone on the ANR headset earpiece comprises: The second microphone is disposed on the ANR headset earpiece such that the second microphone is configured to capture the second input signal representing noise of an acoustic path through a port of the ANR headset earpiece.

18. The method of claim 17, wherein the port is one of (i) a resistive port of the ANR headset earpiece, or (ii) a mass port of the ANR headset earpiece.

19. The method of claim 12, wherein providing the third microphone on the ANR headset earpiece comprises: The third microphone is disposed on the ANR headphone earpiece so that the third microphone is configured to capture the third input signal representing noise passing through an acoustic path formed by leakage between a pad of the headphone earpiece and a head of a user of the ANR headphone earpiece.

20. The method of claim 12, further comprising: providing an acoustic transducer configured to generate output audio; processing the first input signal using a first filter to generate a first output signal for the acoustic transducer; processing the second input signal using a second filter to generate a second output signal for the acoustic transducer; Wherein the acoustic transducer is driven by a combined signal, the combined signal being a combination of the first output signal and the second output signal.

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