One-dimensional array microphone with improved directivity

Abstract

An embodiment includes an array microphone including multiple microphone sets arranged in a linear pattern relative to a first axis and configured to cover multiple frequency bands, each microphone set comprising a first microphone arranged along the first axis and a second microphone arranged along a second axis orthogonal to the first microphone, wherein the distance between adjacent microphones along the first axis is selected from a first group of integer multiples of a first value, and within each element, the distance between the first and second microphones along the second axis is selected from a second group of integer multiples of a second value.

Description

[Technical field]

[0001] (Related Applications) This application claims priority to U.S. Provisional Application No. 62 / 891,088, filed August 23, 2019, the contents of which are incorporated herein in their entirety.

[0002] (Technical field) This application relates generally to array microphones, and more particularly to linear array microphones configured to provide improved frequency-dependent directionality. [Background technology]

[0003] Conferencing environments, such as conference rooms, boardrooms, video conferencing applications, etc., can include the use of one or more microphones to capture sound from various audio sources operating within the environment. Such audio sources can include, for example, human speakers in the room. The captured sound can be disseminated via loudspeakers to a local audience in the environment and / or to others remote from the environment (e.g., via telecasts and / or webcasts, telephony, etc.).

[0004] The types of microphones used and their placement in a particular conference environment can depend on the location of the audio source, physical space requirements, aesthetics, room layout, and / or other considerations. For example, in some environments, microphones may be placed on a table or podium near the audio source. In other environments, microphones may be mounted overhead, for example, to capture sound from throughout the room. In still other environments, microphones may be mounted on a wall facing the audio source, such as near a conference table.

[0005] As such, microphones are available in a variety of sizes, form factors, mounting options, and wiring options to suit the demands of a given application. Furthermore, different microphones can be designed to produce different polar response patterns, including, for example, omnidirectional, cardioid, subcardioid, supercardioid, hypercardioid, and bidirectional. The polar pattern selected for a particular microphone (or microphone cartridge contained therein) can depend, for example, on where the audio source is located, the desire to eliminate unwanted noise, and / or other considerations.

[0006] Conventional microphones (e.g., dynamic, crystal, condenser / capacitor (external bias and electret), boundary, button, etc.) typically have fixed polar patterns and few manually selectable settings. To capture sound in a conference environment, multiple conventional microphones, or microphone cartridges, are used at once to capture multiple audio sources in the environment (e.g., human speakers sitting on different sides of a table). However, conventional microphones also tend to capture unwanted audio such as room noise, echo, and other undesirable audio elements. The capture of these unwanted noises is exacerbated by the use of many microphones. Additionally, the use of multiple cartridges can also produce various independent polar patterns, but the audio signal processing and circuitry required to achieve the different polar patterns can be complex and time consuming. Additionally, conventional microphones may not produce the desired polar patterns uniformly and may not capture sound ideally due to irregularities in frequency response, as well as interference and reflections within and between cartridges.

[0007] Array microphones have several advantages over traditional microphones. Array microphones are composed of multiple microphone elements aligned in a particular pattern or geometry (e.g., linear, circular, etc.) to operate as one microphone device. Array microphones can have different configurations and frequency characteristics depending on the placement of the microphones relative to each other and the direction of arrival of the sound waves. For example, a linear array microphone is composed of microphone elements placed relatively close to each other along a single axis. One advantage of array microphones is that they can provide a steerable coverage or pick-up pattern, which allows the microphones in an array to focus on a desired audio source and eliminate unwanted sounds such as room noise. The ability to steer the audio pick-up pattern also allows for looser microphone placement accuracy, which makes array microphones more tolerable. Additionally, array microphones offer the ability to pick up multiple audio sources with a single array or unit due to the ability to steer the pick-up pattern. Nonetheless, existing arrays constructed from conventional microphones suffer from certain drawbacks, including a relatively large form factor compared to conventional microphones and a fixed overall size that often limits placement options in the environment.

[0008] Microelectromechanical system (MEMS) microphones, or microphones that have MEMS elements as their core transducers, are becoming increasingly popular due to their small package size (e.g., allowing for an overall low profile device) and high performance characteristics (e.g., high signal-to-noise ratio ("SNR"), low power consumption, good sensitivity, etc.). In addition, MEMS microphones are generally easy to assemble and available at lower costs than, for example, electret or condenser microphone cartridges found in many existing boundary microphones. However, due to the physical constraints of MEMS microphone packaging, the polar patterns of conventional MEMS microphones are inherently omnidirectional, meaning that the microphone is equally sensitive to sounds coming from all directions, regardless of the microphone's orientation. This can be less than ideal, especially in conference environments.

[0009] One existing solution for obtaining directionality using MEMS microphones involves arranging multiple microphones in an array configuration and applying appropriate beamforming techniques (e.g., signal processing) to generate a desired directional response, or beam pattern that is more sensitive to sounds coming from one or more specific directions than to sounds coming from other directions. For example, a broadside linear array includes a series of MEMS microphones arranged perpendicular to the preferred direction of arrival of the sound. A delay-and-sum beamformer can be used to combine the signals from the various microphone elements to achieve the desired pickup pattern. In some broadside arrays, the microphone elements can be nested around a central point and spaced a certain distance from each other to cover various frequencies.

[0010] Linear or one-dimensional array microphones constructed with MEMS microphones can provide high performance, for example, in a small, thin form factor and with less complexity and cost than conventional array microphones. Furthermore, due to the omnidirectional nature of MEMS microphones, such linear arrays typically have an arbitrary directivity along the axis of the array. However, such linear arrays also have equal sensitivity in all other dimensions and a symmetric lobe or sound pickup pattern about the axis of the array, resulting in unwanted noise pickup.

[0011] Thus, there is a need for an array microphone that addresses these concerns, and more particularly, for a thin, low-profile, high-performance array microphone that provides full, natural-sounding voice pickup suitable for conferencing applications, with improved frequency-dependent directionality, especially at audio frequencies where intelligibility is important, and with the ability to reject unwanted sounds and reflections in a given environment. Summary of the Invention

[0012] The present invention seeks to solve these and other problems by, among other things, providing an array microphone and microphone system that is designed to: (1) provide a one-dimensional form factor with added directionality for most, if not all, frequencies in a dimension that is traditionally equally sensitive in all directions; (2) achieve additional directionality by arranging a row of first microphones along a first axis and, for each first microphone, arranging one or more additional microphones along a second axis orthogonal to the first microphone to form a multiple microphone set, and by configuring each microphone set to cover one or more of the desired octaves for the one-dimensional array microphone; (3) provide an audio output that utilizes a beamforming pattern selected based on the direction of arrival of sound waves captured by the microphones in the array, the selected beamforming pattern providing increased back rejection and steering control; and (4) have high performance characteristics suitable for conferencing environments, including consistent directionality in different frequency ranges, high signal-to-noise ratio (SNR) and wideband audio coverage.

[0013] For example, one embodiment includes an array microphone comprising multiple microphone sets arranged in a linear pattern relative to a first axis and configured to cover multiple frequency bands, each microphone set comprising a first microphone arranged along the first axis and a second microphone arranged along a second axis orthogonal to the first microphone, where the distance between adjacent microphones along the first axis is selected from a first group of integer multiples of a first value, and within each microphone set, the distance between the first and second microphones along the second axis is selected from a second group of integer multiples of a second value.

[0014] Another exemplary embodiment provides a method executed by one or more processors for generating output signals for an array microphone including a plurality of microphones and configured to cover a plurality of frequency bands, the method including receiving audio signals from a plurality of microphones arranged in a microphone set configured to form a linear pattern along a first axis and extend orthogonally from the first axis, determining a direction of arrival of the received audio signals, selecting one of a plurality of beamforming patterns based on the direction of arrival, combining the received audio signals according to the selected beamforming pattern to generate a directional output for each microphone set, and aggregating the outputs to generate an overall array output.

[0015] Another exemplary embodiment provides a microphone system comprising: an array microphone including a plurality of microphones configured to cover a plurality of frequency bands and arranged in microphone sets configured to form a linear pattern along a first axis and extend orthogonally from the first axis, a memory configured to store program code for processing audio signals captured by the plurality of microphones and generating an output signal based thereon, and at least one processor in communication with the memory and the array microphone and configured to execute the program code in response to receiving the audio signals from the array microphone, The program code is configured to receive the audio signals from the plurality of microphones, determine a direction of arrival of the received audio signals, select one of a plurality of beamforming patterns based on the direction of arrival, combine the received audio signals according to the selected beamforming pattern to generate a directional output for each microphone set, and aggregate the outputs to generate an overall array output.

[0016] Yet another exemplary embodiment provides a microphone system comprising: an array microphone configured to cover multiple frequency bands, the array microphone including a plurality of microphones arranged in a linear pattern along a first axis of the array microphone and extending orthogonally from the first axis; and at least one beamformer configured to receive audio signals captured by the plurality of microphones and generate an array output based thereon having a directional polar pattern selected based on a direction of arrival of the audio signals, the directional polar pattern further configured to reject audio sources from one or more other directions.

[0017] These and other embodiments, as well as various modifications and aspects, will become apparent and will be more fully understood from the following detailed description and the accompanying drawings that set forth illustrative embodiments that illustrate various ways in which the principles of the invention can be utilized. [Brief description of the drawings]

[0018] [Figure 1] FIG. 2 is a top view of an exemplary one-dimensional array microphone according to one or more embodiments.

[0019] [Diagram 2] 2 is a schematic diagram of the microphone array of FIG. 1 illustrating exemplary microphone pair selection according to a first beamforming pattern, according to an embodiment.

[0020] [Diagram 3] 2 is a schematic diagram of the microphone array of FIG. 1 illustrating exemplary microphone pair selection according to a second beamforming pattern, according to an embodiment.

[0021] [Figure 4] 2 is a schematic diagram of the microphone array of FIG. 1 illustrating exemplary microphone pair selection according to a third beamforming pattern, according to an embodiment.

[0022] [Diagram 5]FIG. 2 is a block diagram of a microphone system including the one-dimensional array microphone of FIG. 1, according to an embodiment.

[0023] [Figure 6] FIG. 6 is a block diagram of a sum-difference beamformer included in the microphone system of FIG. 5, according to an embodiment.

[0024] [Figure 7] FIG. 6 is a block diagram of an aggregate beamformer included in the microphone system of FIG. 5, according to an embodiment.

[0025] [Figure 8] FIG. 6 is a block diagram of a linear delay-and-sum beamformer included in the microphone system of FIG. 5, according to an embodiment.

[0026] [Figure 9] 1 is a flowchart illustrating an example method for generating a beamforming output signal for a one-dimensional array microphone in accordance with one or more embodiments.

[0027] [Figure 10A] FIG. 2 is a side view of the array microphone of FIG. 1 positioned on a table in a conference environment in accordance with one or more embodiments. [Figure 10B] 2 is a top view of the array microphone of FIG. 1 positioned on a table in a conference environment in accordance with one or more embodiments.

[0028] [Figure 11A] 10B is a polar plot illustrating the selective polarity response of the array microphone shown in FIG. 10A perpendicular to the table in accordance with one or more embodiments.

[0029] [Figure 11B] 10C is a polar plot illustrating the selective polar response of the array microphone shown in FIG. 10B in the plane of the table in accordance with one or more embodiments.

[0030] [Figure 12] 2 is a polar plot illustrating the selective polar response of the array microphone of FIG. 1 in accordance with one or more embodiments.

[0031] [Figure 13] FIG. 2 is a front view of the array microphone of FIG. 1 mounted on a vertical wall in a conference environment, according to an embodiment.

[0032] [Figure 14] 14 is a directional response plot of the array microphone shown in FIG. 13 according to an embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0033] In the following description, one or more specific embodiments of the present invention according to the principles of the present invention are described, illustrated, and illustrated. This description is not provided to limit the present invention to the embodiments described herein, but to explain and teach the principles of the present invention so that those skilled in the art can understand these principles and, based on that understanding, apply them to the implementation of not only the embodiments described herein, but also other embodiments that may be conceived in accordance with these principles. The scope of the present invention is intended to cover all such embodiments that may fall within the scope of the appended claims, either literally or under the doctrine of equivalents.

[0034] It should be noted that in the present specification and drawings, the same or substantially similar elements may be labeled with the same reference numerals. However, these elements may be labeled with different numerals, for example, when such labeling facilitates a clearer description. Furthermore, the drawings described herein are not necessarily drawn to scale, and in some cases, proportions may be exaggerated to more clearly depict certain features. Such representations and implementation of the drawings do not necessarily imply the essential purpose at the base thereof. As stated above, the present specification is to be taken as a whole and interpreted in accordance with the principles of the present invention as taught herein and understood by those skilled in the art.

[0035] Systems and methods are provided herein for a high-performance array microphone with a one-dimensional form factor configured to provide good directionality and high signal-to-noise ratio (SNR) at various frequencies, including high frequencies in the audible range. In particular, the array microphone comprises a first plurality of microphones arranged along a first axis to achieve coverage of a desired frequency band or octave, and a second plurality of microphones arranged orthogonal to the first axis, the microphones arranged to achieve a directional polar pattern for the covered octave. An exemplary embodiment includes arranging the microphones in multiple sets, each set including a first microphone positioned on the first axis and one or more additional microphones positioned on a second axis perpendicular to the first axis and arranged orthogonal to the first microphone. In an embodiment, the microphones of each set can be combined to generate a narrow beam pattern perpendicular to the array microphone or a narrow cardioid polar pattern oriented within the dimensions of the microphone set, depending on the particular application or environment. In either case, the lobes of the array microphone can be aimed at the desired sound source, thus better rejecting unwanted sound sources and reflections in the environment. In a preferred embodiment, the microphones are MEMS transducers or other omnidirectional microphones.

[0036] FIG. 1 illustrates an exemplary array microphone 100 for detecting sounds from one or more audio sources at various frequencies, according to an embodiment. The array microphone 100 can be utilized in a conference environment, such as, for example, a conference room, boardroom, or other meeting room where the audio sources can include one or more human speakers. There may be other undesirable sounds in the environment, such as noise from ventilation systems, other people, audio / visual equipment, electronic devices, etc. In a typical situation, the audio sources may be seated in chairs at a table, although other configurations and arrangements of audio sources are contemplated and possible, including, for example, audio sources moving around the room. The array microphone 100 can be positioned on a table, podium, tabletop, ceiling, or other horizontal surface, as well as on a wall or other vertical surface in the conference environment, to detect and capture sounds from audio sources, such as voices spoken by human speakers.

[0037] The array microphone 100 includes multiple microphones 102 (also referred to herein as "transducers" and "cartridges") that can form multiple pickup patterns to optimally or consistently detect and capture sounds from an audio source. The polar patterns that can be formed by the array microphone 100 can depend on the arrangement of the microphones 102 in the array 100 as well as the type of beamformer used to process the audio signals generated by the microphones 102. For example, a sum-difference beamformer can be used to form cardioid, subcardioid, supercardioid, hypercardioid, bidirectional, and / or toroidal polar patterns directed toward the desired audio source. Additional polar patterns can be created by combining the original polar patterns and steering the combined pattern to any angle, for example, along the plane of a table on which the array microphone 100 rests. Other beamforming techniques can be utilized to combine the microphone outputs so that the overall array microphone 100 achieves a desired frequency response, including, for example, lower noise characteristics, higher microphone sensitivity, and coverage of discrete frequency bands, as described in more detail herein. Although Figure 1 shows a particular number of microphones, other quantities of microphones 102 (e.g., more or less) are possible and contemplated.

[0038] In a preferred embodiment, each of the microphones 102 may be a MEMS (microelectromechanical system) transducer with a unique omnidirectional polar pattern. In other embodiments, the microphones 102 may have other polar patterns, may be any other type of omnidirectional microphone, and / or may be a condenser microphone, a dynamic microphone, a piezoelectric microphone, etc. In still other embodiments, the arrangement and / or processing techniques described herein may be applied to other types of arrays composed of omnidirectional transducers or sensors where directionality is desired (e.g., sonar arrays, radio frequency applications, seismic devices, etc.).

[0039] Each of the microphones 102 can detect sound and convert the sound into an audio signal. In some cases, the audio signal can be a digital audio output (e.g., a MEMS transducer). In other types of microphones, the audio signal can be an analog audio output, and components of the array microphone 100, such as an analog-to-digital converter, a processor, and / or other components, can process the analog audio signal and ultimately generate one or more digital audio output signals. The digital audio output signals can conform to the Dante standard for transmitting audio over Ethernet, in some embodiments, or can conform to another standard. In certain embodiments, one or more pickup patterns can be formed from the audio signals of the microphones 102 by a processor of the array microphone 100, and the processor can generate a digital audio output signal corresponding to each of the pickup patterns. In other embodiments, the microphones 102 can output analog audio signals, and other components and devices external to the array microphone 100 (e.g., processors, mixers, recorders, amplifiers, etc.) can process the analog audio signals.

[0040] As shown in FIG. 1, the microphones 102 include a first plurality of microphones 104 arranged linearly along the length of the array microphone 100 and perpendicular to the preferred or expected direction of arrival of incident sound waves. The first plurality of microphones 104 (also referred to herein as "first microphones") are arranged along a common axis of the array microphone 100, such as a first axis 105. The first microphones 104 can be arranged in a linear array pattern configured to cover multiple frequency bands using one or more beamformers or other audio processing techniques. In particular, the linear pattern can be configured to operate in different octaves (e.g., 600-1200 Hertz (Hz), 1200-2400 Hertz, 2400-4800 Hertz, etc.) within the covered multiple frequency bands such that the overall beam pattern of the array microphone 100 remains essentially constant from octave to octave. For example, a linear pattern can be implemented using a subband-based scaled aperture (SSA) approach that uses a different array aperture for each octave, such that progressively lower frequency octaves are served by progressively wider linear arrays. To increase spatial resolution, the linear array aperture can be doubled when going from a higher octave to the next lower octave.

[0041] For example, with additional reference to FIG. 2, the first microphone 104 may include a first group of microphones 106 spaced apart from one another by a first distance D1 to form a first subarray configured to cover a first or Nth frequency octave. The first microphone 104 also includes a second group of microphones 108 configured to form a second subarray for covering a second or next lower frequency octave (e.g., the (N-1)th octave) by spacing the microphones 108 a second distance D1 that is twice the first distance D1. Similarly, a third group 110 of the first microphones 104 may be configured to form a third subarray for covering a third even lower octave (e.g., the (N-2)th octave) by spacing the microphones 110 a third distance D1 that is twice the second distance or four times the first distance. In other words, the distance or spacing between the first microphones 104 can be halved for each octave of frequency or can be increased by a factor of two for each subsequent octave, so that the microphones 106 for covering the highest or Nth octave are closest to each other or form the smallest aperture size, and the microphones 110 for covering the lowest octave (e.g., the (N-2)th octave) and below are farthest apart or form the largest aperture size.

[0042] In an embodiment, the minimum distance value D1 can be selected based on the desired linear array aperture size of the array microphone 100 and the total number of first microphones 104 used to form the linear array pattern, as well as the frequency bands to be spatially sampled in the array microphone 100. Other design considerations can determine the D1 value, including, for example, the desired location of frequency nulls, the desired amount of electrical delay, and criteria for avoiding spatial aliasing. In one exemplary embodiment, the D1 distance is approximately 8 millimeters (mm).

[0043] In a preferred embodiment, a harmonic nesting technique is used to select the distance between adjacent first microphones 104 such that the linear patterns formed by the subarrays 106, 108, and 110 are harmonically nested. As will be appreciated, arranging the first microphones 104 in a harmonically nested subarray (or nested) manner can be more efficient and economical since one or more of the microphones 104 can be reused as part of multiple subarrays, thus reducing the total number of microphones 104 required to cover the octave of interest for the array microphone 100. For example, the second and third subarrays 108 and 110 are arranged at various multiples of two (e.g., 2 and 4, respectively) of the distance D1 between the microphones 104 in the first subarray 106, such that the first subarray 106 can be nested within the second and third subarrays 108 and 110, and the second subarray 108 can be nested within the third subarray 110. As a result, some of the first microphones 104 can be reused in multiple nests. In particular, as shown in FIG. 2, at least three of the microphones 104 in the first nest 106 also form part of the second nest 108, and at least three of the microphones 104 from the second nest 108 also form part of the third nest 110.

[0044] As depicted in FIG. 1, the plurality of microphones 102 further includes a second plurality of microphones 112 (also referred to herein as "second microphones" or "additional microphones") arranged orthogonally to the first microphones 104 for additional directivity at various frequencies or octaves of interest. In particular, each second microphone 112 is added to the array 100 so as to overlap with one of the first microphones 104 in terms of its arrangement relative to the first axis 105, but is arranged on another axis that is orthogonal to the corresponding first microphone 104 and perpendicular to the first axis 105, such as the second axis 107 or another axis parallel thereto (also referred to herein as an "orthogonal axis"). As shown in FIG. 1, the first axis 105 passes through or intersects with the second axis 107 at a center point (or midpoint) of the first axis 105.

[0045] In some embodiments, the first axis 105 coincides with the x-axis of the array microphone 100, and the second axis 107 coincides with the y-axis of the array microphone 100, such that the array microphone 100 lies in an xy plane, as shown in FIG. 1. For example, when the array microphone 100 is placed on a table or other horizontal surface, the microphones 102 can be arranged planarly in a first plane parallel to the table or to the top surface of the table. In other embodiments, the second axis 107 can be another one of the orthogonal axes of the array microphone 100, such as the Z-axis, depending on the orientation of the microphone 100. For example, when the array microphone 100 is placed on a wall or other vertical surface, the microphones 102 can be arranged planarly in a second plane parallel to the wall or to the front surface of the wall, as shown in FIG. 13. In still other embodiments, the array microphone can be suspended in free space. In such cases, the orientation can be any of the previous orientations depending on the desired acoustic effect and the configuration of the room.

[0046] In an embodiment, each overlapping second microphone 112 and first microphone 104 thereby jointly form a microphone set or pair configured to operate in the frequency octave covered by the overlapping microphone 104. For example, in each microphone set, the spacing or distance between the first microphone 104 and the corresponding second microphone 112 along an orthogonal axis can be selected based on the frequency octave covered by that set. Furthermore, the first and second microphones 104 and 112 of each microphone set can be processed or treated as a single microphone "element" or unit of the array microphone 100 by acoustically combining the microphones 104 and 112 to create a new pickup pattern for that microphone set (e.g., using appropriate beamforming techniques). In some embodiments, various microphone sets can be further grouped as sub-arrays to generate one or more combined outputs for the array microphone 100. As an example, all of the microphone sets configured to cover a first octave (e.g., N) can be combined or aggregated to generate a subarray for operation in that octave (e.g., using appropriate beamforming techniques). Each of the various subarrays can be further aggregated, e.g., to create an overall output of the array microphone 100 having an essentially constant beamwidth.

[0047] 2 shows a plurality of microphone sets 114, 116, and 118 formed from the first and second microphones 104 and 112 of the array microphone 100 according to an embodiment. The first group of the microphone sets 114 includes a first microphone 104 from a first nest 106 for covering a first or Nth octave and a second microphone 112 added to overlap the first nest 106. In the microphone set 114, each second microphone 112 is located at a first distance D2 from the corresponding first microphone 104. The second group of the microphone sets 116 includes a first microphone 104 from a second nest 108 for covering a second or (N-1)th octave and a second microphone 112 added to overlap the second nest 108. In the microphone set 116, each second microphone 112 is positioned at a second distance, D2, from the corresponding first microphone 104. The array microphone 100 may further include a third microphone set 118 group including the first microphones 104 from a third nest 110 for covering a third or (N-2)th octave and a second microphone 112 added to overlap the third nest 110. In the microphone set 118, each second microphone 112 is positioned at a third distance, D2, from the corresponding first microphone 104.

[0048] Thus, the distance between the microphones 104 and 112 of a given microphone set, as well as the distance between adjacent first microphones 104 along the first axis 105, is halved for each octave of frequency or increased by a factor of two (i.e., a factor of two) for each octave down. In an embodiment, the distance D2 between the microphones 104, 112 of the first plurality of microphone sets 114 can be equal to a half wavelength of a desired frequency from the octave covered by the set 114 (i.e., the Nth octave) to create a null at the desired frequency. The distance D2 can also be selected to optimize cardioid formation when the microphones 104 and 112 of a given microphone set are combined to produce a combined output, as described below. In one exemplary embodiment, the distance D2 is about 16 mm.

[0049] As shown in FIG. 2, several microphone sets can include the same first microphone 104 and can therefore be arranged on the same orthogonal axis. This arrangement is due, at least in part, to the harmonic nesting of the first microphones 104 along the first axis 105 and the coverage of multiple octaves by some of the first microphones 104. More specifically, each first microphone 104 configured to cover several frequency octaves can be duplicated by an equal number of second microphones 112 arranged at an appropriate (e.g., frequency-dependent) distance along the same orthogonal axis, thus creating a co-located microphone set. In other words, the total number of second microphones 112 that can be arranged on the same orthogonal axis depends on the number of octaves covered by the first microphones 104 of the set. As an example, in FIG. 1, the first microphone 104a is included in all three of the nests 106, 108, 110 and is therefore used to cover all three octaves (e.g., N, N-1, N-2). Thus, in FIG. 2, the first microphone 104a is paired with three different second microphones 112a, 112b, 112c to provide coverage for each of the three octaves. Conversely, in FIG. 1, the first microphone 104b is included in only one nest 110 and is therefore used to cover one octave (e.g., N-1). As a result, in FIG. 2, the first microphone 104b is paired with only one second microphone 112d.

[0050] In an embodiment, to maintain the linear array pattern created by the first microphone 104 along the first axis 105, the multiple microphone sets formed by the microphones 102 are arranged orthogonally to the first axis 105. More specifically, the first microphone 104 can constitute the primary, or top, layer of the array microphone 100, and the additional or second microphones 112 can be arranged in the array 100 to form multiple secondary, or lower layers that are arranged orthogonally or spatially behind the primary layer. This layered arrangement of the microphones 102 allows the array microphone 100 to have a thin and narrow form factor similar to a one-dimensional or linear array microphone. For example, the overall length and width of the front surface 120 of the array microphone 100 can be determined primarily by the dimensions of the primary layer, or more specifically, the aperture size and other physical characteristics of each first microphone 104, as well as the total amount of space between adjacent microphones 104 in the primary layer (e.g., D1 or an integer multiple thereof). In some cases, the front surface 120 may coincide with or form the overall aperture of the array microphone 100.

[0051] The total depth of the array microphone 100, or the distance between the front 120 and rear 122 of the array 100 (e.g., along the y-axis), can be determined by the number of secondary layers included in the array microphone 100 and the spacing between each layer. The exact number of secondary layers included in the array 100 can depend on the total number of octaves covered by the array microphone 100, which can determine the distance between each layer, as described herein. In some cases, the number of secondary layers, i.e., the number of octaves covered, can be determined by physical limitations on the device housing for the array microphone 100 (e.g., the maximum depth of the housing). In the illustrated embodiment, other secondary layers are nested in the space between the first layer and the last layer, so that the total depth of the array microphone 100 can be determined by the distance between the primary layer and the last secondary layer (e.g., four times the distance D2). In some embodiments, a harmonic nesting technique is used to select the distance between the primary layer and each secondary layer. Although the illustrated embodiment shows three secondary layers configured to provide added directivity for three different octaves (e.g., N, N-1, and N-2), other embodiments can include more layers to cover more octaves, thus increasing the depth of the array 100, or fewer layers to cover fewer octaves, thus decreasing the array depth.

[0052] The array microphone 100 may further include one or more supports 124 (e.g., a substrate, a printed circuit board (PCB), a frame, etc.) for supporting the microphones 102 within a housing of the array microphone 100. In an embodiment, each of the microphones 102 may be mechanically and / or electrically coupled to at least one of the supports 124. In some cases, each layer of the microphones 102 may be disposed on an individual support 124, and the various supports 124 may be stacked side-by-side (e.g., in the Y-axis direction) within the microphone housing. In the case of PCB supports 124, the microphones 102 may be MEMS transducers electrically coupled to one or more PCBs, and each PCB may be electrically coupled to one or more processors or other electronic devices for receiving and processing audio signals captured by the microphones 102. The supports 124 may have any suitable size or shape. In some cases, the supports 124 may have a size and shape to meet the constraints of an existing device housing and / or to achieve desired performance characteristics (e.g., a selected operating band, a high SNR, etc.). For example, the maximum width and / or length of the support 124 may be determined by the overall height and / or length of the device housing for the array 100.

[0053] In general, the array microphone 100 shown in Figs. 1 and 2 can be configured for broadside use, or preferably, to capture sounds arriving generally perpendicular to the front microphone 104 and ignore or separate sounds from other directions. According to an embodiment, the array microphone 100 can be configured to generate a sound beam (or main lobe) toward either the broadside direction to capture sounds arriving broadside at 0 degrees to the front microphone 104 or sounds arriving broadside at 180 degrees to the front microphone 104. That is, the array microphone 100 can be independent of the direction of arrival in the xy plane. When a sound source is located 180 degrees broadside, the roles of the microphones 102 may be reversed. For example, the primary layer, i.e., the first microphone 104, can function as the secondary layer, and one of the secondary layers of the additional microphones 112 (e.g., layer N in Fig. 1) can function as the primary layer. In this manner, the array microphone 100 can be configured to produce a directional polar pattern toward any broadside direction of arrival and isolate sounds coming from all other directions.

[0054] Furthermore, sound beams formed by individual microphone pairs (e.g., microphone sets 114, 116, 118) can be steered toward desired audio sources that are not broadside using appropriate beamforming techniques. For example, a linear delay-and-sum beamforming approach can be used to add an amount of delay to the audio signal of each microphone set, which determines the beam steering angle for that set. The amount of delay can depend, for example, on the frequency as well as the distance between the microphone set and the audio source. Through such frequency-dependent steering, a constant beamwidth can be achieved over a wide frequency range for the array microphone 100.

[0055] In an embodiment, the array microphone 100 can be independent of the direction of arrival in the xy plane for non-broadside or oblique conditions as well. For example, the array microphone 100 can capture sounds arriving at a first oblique angle relative to the front face 120 as well as sounds arriving at an equal but opposite angle relative to the rear face 122, i.e., an angle 180 degrees greater than the first oblique angle relative to the front face 120 of the array microphone. In such cases, the primary and secondary layers of the microphone can be reversed or swapped in the same manner as described herein for the broadside condition.

[0056] In an embodiment, due to the inherent geometry or layout of the microphones 102 in the array 100, the first microphone 104 and the second microphone 112 can be paired in multiple ways to create microphone sets to cover the same desired octave. In the array microphone 100, a particular pattern or arrangement of microphone pairs can be selected depending on the preferred direction of arrival of sound waves. In particular, when the direction of arrival of sound waves is perpendicular to the first microphone 104 or the front face 120 of the array microphone 100, the multiple microphone sets can be formed according to one or more beamforming patterns for broadside use of the array microphone 100. Alternatively, the multiple microphone sets can be formed according to one or more beamforming patterns for oblique angle use of the array microphone 100 when the direction of arrival of sound waves is at an angle to the front face 120 of the array microphone 100.

[0057] For example, Figure 2 shows a first broadside beamforming pattern 200 configured for a direction of arrival that is perpendicular to the front microphone 104 and 0 degrees to the front face 120 of the array microphone 100. In an embodiment, a second broadside beamforming pattern (not shown) can be used when the direction of arrival for the sound waves is perpendicular to the front microphone 104 but approaches at 180 degrees to the front face 120 of the array microphone 100. The second broadside beamforming pattern can be the same as the beamforming pattern 200 shown in Figure 2, except that the primary layer of microphone 104 swaps roles with one of the secondary layers of microphone 112, since the sound waves will reach the second microphone 112 before reaching the first microphone 104.

[0058] 3 illustrates a first oblique beamforming pattern 300 configured for a direction of arrival greater than 30 degrees (e.g., 45 degrees) relative to the first axis 105. The beamforming pattern 300 includes a first plurality of microphone sets 314 configured for a first or Nth octave coverage, similar to the first plurality of sets 114 of FIG. 2, a second plurality of microphone sets 316 configured for a second or (N-1)th octave coverage, similar to the second plurality of sets 116 of FIG. 2, and a third plurality of microphone sets 318 configured for a third or (N-2)th octave coverage, similar to the third plurality of sets 118 of FIG. 2. Each of the microphone sets in the pattern 300 includes the same first microphone 104 as the corresponding microphone set in the first beamforming pattern 200, but includes a different second microphone 112. In particular, for each set, a first microphone 104 is paired with a second microphone 112 that is located approximately 45 degrees (or diagonally to the right as shown in FIG. 3) from the first microphone 104 (as in FIG. 2), rather than with the second microphone 112 directly orthogonal to the corresponding first microphone 104. In an embodiment, when the arrival direction is reversed from that shown in FIG. 4 (i.e., incident on or directed towards the rear surface 122), the same microphone set is formed, but the second microphone 112 and the first microphone 104 are swapped in terms of functionality.

[0059] 4 illustrates a second diagonal beamforming pattern 400 configured for a direction of arrival that is offset from the direction of arrival shown in FIG. 3 by about 90 degrees relative to the first axis 105 or greater than 120 degrees (e.g., 135 degrees or −45 degrees, etc.). The beamforming pattern 400 includes a first plurality of microphone set 414 configured for a first or Nth octave coverage, similar to the first plurality of set 114 of FIG. 2, a second plurality of microphone set 416 configured for a second or (N−1)th octave coverage, similar to the second plurality of set 116 of FIG. 2, and a third plurality of microphone set 418 configured for a third or (N−2)th octave coverage, similar to the third plurality of set 118 of FIG. 2. Similar to pattern 300, each of the microphone sets of pattern 400 comprises the same first microphone 104 as the corresponding microphone set from the first beamforming pattern 200, but a different second microphone 112. In particular, for each set, the first microphone 104 is paired with a second microphone 112 located approximately -45 degrees (or diagonally left as shown in FIG. 4) from the first microphone 104, rather than with a second microphone 112 directly orthogonal to the corresponding first microphone 104 (as in FIG. 2). In an embodiment, if the arrival direction is reversed from that shown in FIG. 3 (i.e., incident on or directed towards the rear surface 122), the same microphone set can be formed, but the second microphone 112 and the first microphone 104 are swapped in terms of functionality.

[0060] According to an embodiment, the alternative or angled beamforming patterns 300 and 400 allow the array microphone 100 to cover oblique or tilted directions of arrival with minimal or less steering than would be required, for example, when using the broadside pattern 200. The oblique patterns 300 and 400 also reduce lobe deformation as the steering angle tends toward the endfire array (e.g., 0 degrees or 180 degrees relative to the first axis 105). Furthermore, the ability to select the appropriate beamforming pattern based on the direction of arrival improves the steering directivity of the array microphone 100 without resorting to computationally intensive signal processing as required in conventional array microphones. The oblique or 45 degree beamforming patterns 300 and 400 shown in Figures 3 and 4, respectively, take advantage of the particular geometry of the array microphone 100 with a symmetrical lattice-like pattern produced by the layered or orthogonal arrangement of microphones 102 and by the harmonic nesting configuration of the first microphones 104 relative to each other within the primary layer and of the additional layers relative to the primary layer. Other embodiments may include diagonal beamforming patterns configured for different direction of arrival angles, for example, depending on particular values ​​selected for the first distance D1 between the first microphones 104 and / or the second distance D2 between the primary layer and the first secondary layer.

[0061] In the illustrated embodiment, the first broadside pattern 200 places each of the microphones 102 in a microphone set or pair, while each of the diagonal patterns 300, 400 excludes one or more of the microphones 102 from the microphone pairing. Additionally, in each pattern 300, 400, the third group of microphone sets 318, 418 includes only six microphone pairs, while the third group of microphone sets 118 of pattern 200 includes seven microphone pairs. These differences between the patterns 200, 300, 400 can be attributed to the specific placement and number of microphones 102 in the array microphone 100. In some embodiments, the array microphone 100 can include additional microphones 102 placed in positions designed to increase the number of microphone sets in each of the third groups 318 and 418 from six to seven. For example, in such a case, the array microphone 100 may include an additional second microphone 112 in the third secondary layer and / or an additional first microphone 104 in the primary layer to create a seventh pair for one or both of the diagonal patterns 300 and 400.

[0062] FIG. 5 illustrates an exemplary microphone system 500, according to an embodiment. The microphone system 500 includes a plurality of microphones 502, similar to the microphone 102, a beamformer 504, and an output generating unit 506. Various components of the microphone system 500 can be implemented using software executable by one or more computers, such as a computing device having a processor and memory, and / or by hardware (e.g., discrete logic circuits, application specific integrated circuits (ASICs), programmable gate arrays (PGAs), field programmable gate arrays (FPGAs), etc.). For example, some or all components of the beamformer 504 can be implemented using discrete circuit devices and / or using one or more processors (e.g., audio processors and / or digital signal processors) (not shown) executing program code stored in a memory (not shown), the program code configured to perform one or more processes or operations described herein, such as, for example, the method 900 illustrated in FIG. 9. Thus, in an embodiment, the system 500 can include one or more processors, memory devices, computing devices, and / or other hardware components not illustrated in FIG. 5. In a preferred embodiment, system 500 includes at least two separate processors: one for integrating and formatting all of the microphone elements, and one for implementing DSP functions.

[0063] The microphones 502 may include the microphones 102 of the array microphone 100 shown in FIG. 1, or other microphones designed according to the techniques described herein. The beamformer 504 may be in communication with the microphones 502 and may be used to apply an appropriate beamforming technique to the audio signals captured by the microphone elements 502 to create a desired pickup pattern, such as, for example, a primary polar pattern (e.g., cardioid, supercardioid, hypercardioid, etc.) and / or steer the pattern to a desired angle to obtain directivity. For example, in some embodiments, the beamformer 504 may be configured to combine the microphones 502 to form multiple microphone pairs, combine the microphone pairs to form multiple subarrays, and combine the subarrays to create a linear or one-dimensional array output having a directional polar pattern, such as, for example, a cardioid pickup pattern. The output generation unit 506 may be in communication with the beamformer 504 and may be used to process the output signals received from the beamformer 504 for output generation, for example, via a loudspeaker, telecast, etc.

[0064] In an embodiment, the beamformer 504 may include one or more components to facilitate processing of audio signals received from the microphones 502, such as, for example, the sum-difference cardioid forming beamformer 600 of FIG. 6, the subarray combining beamformer 700 of FIG. 7, and / or the linear delay-sum steering beamformer 800 of FIG. 8. In some aspects, the various beamformers 600, 700, and / or 800 may communicate with each other to generate an output for the entire array microphone. In some aspects, the beamformer 504 includes multiple instances of a given beamformer 600, 700, or 800. Other beamforming techniques or combinations thereof may also be performed by the beamformer 504 to provide a desired output.

[0065] 6, a sum-difference beamformer 600 may be configured to combine audio signals captured by a given set or pair of microphones 602 to generate a combined output signal of the microphone pair having a directional polar pattern, according to an embodiment. More specifically, the beamformer 600 may be configured to use a suitable sum-difference technique for each set of first and second microphones 602 positioned orthogonally to a first axis or front face of an array microphone, such as the array microphone 100 of FIG. 1, to form a cardioid element having a narrow lobe (or sound pickup pattern) compared to the fully omnidirectional polar pattern of the individual microphones 602, for example. As an example, the first microphone 602 (or Mic 1) may include one of the first microphones 104 positioned along the first axis 105 of the array microphone 100, and the second microphone 602 (or Mic 2) may include a second microphone 112 positioned on the orthogonal axis of the array microphone 100 so as to overlap with the first microphone 104. The spacing or distance between the first and second microphones 602 along the orthogonal axes can be selected based on the frequency octave covered by the first microphone 602 .

[0066] As shown in FIG. 6, a first audio signal received from a first microphone 602 (e.g., Mic 1) and a second audio signal received from a second microphone 602 (e.g., Mic 2) are provided to a summing component portion 604 of the beamformer 600 and a difference component portion 606 of the beamformer 600. The summing component portion 604 can be configured to calculate a sum of the first and second audio signals (e.g., Mic 1 + Mic 2) to generate a combined or summed output for the pair of microphones 602. The difference component portion 606 can be configured to subtract the second audio signal from the first audio signal (e.g., Mic 1 - Mic 2) to generate a difference signal or output for the first and second microphones 602. As an example, the summing component portion 604 can include one or more adders or other summing elements, and the difference component portion 606 can include one or more inverting summing elements.

[0067] Also as shown, the beamformer 600 further includes a correction component portion 608 for correcting the differential output generated by the difference component portion 606. The correction component portion 608 can be configured to correct the differential output for a gradient response resulting from the difference calculation. For example, the gradient response can impart a 6 dB per octave gradient to the frequency response of the microphone pair. To generate a primary polar pattern (e.g., cardioid) of the microphone pair over a wide frequency range, the differential output must be corrected to have the same magnitude as the summation output. In a preferred embodiment, the correction component portion 608 applies a correction value (c*d) / (j*ω) to the differential output to obtain a corrected differential output of the microphone pair 602 (e.g., (Mic 1 - Mic 2)*(c*d) / (j*ω)), where c corresponds to the speed of sound in air at 20 degrees Celsius, d corresponds to the distance between the first and second microphones (e.g., D2 or an integer multiple thereof), and ω corresponds to the angular frequency. Optionally, a second magnitude correction can be performed to match the sensitivity of the difference component to the sensitivity of the additive component.

[0068] The beamformer 600 also includes a combiner 610 configured to combine or add the sum output generated by the summing component portion 604 and the corrected difference output generated by the correction component portion 608. The combiner 610 thus generates a combined output signal having a directional polar pattern (e.g., cardioid) for the pair of microphones 602, as shown in FIG.

[0069] In some embodiments, the beamformer 600 can be configured to receive audio signals from first and second subarrays instead of individual microphones 602 and combine the first and second subarray signals using the same sum-difference technique as shown in Figure 6. For example, the first and second subarray signals can be summed by a summing component portion 604 and provided to a difference component portion 606 and a correction component portion 608 to calculate a corrected difference for the first and second subarray signals. The resulting summed and corrected difference outputs can be summed or combined together to generate a directional output for the pair of subarrays.

[0070] In one embodiment, the first subarray may be a subarray formed by combining first microphones 104 in a primary layer of the array microphone 100 configured to cover a given frequency octave. Similarly, the second subarray may be formed by combining second microphones 112 arranged in one of the additional layers of the array 100 to overlap with the microphones 104 of the first subarray and cover the same frequency octave. In such a case, the combined directional output generated by the beamformer 600 may be specific to the frequency octave covered by the first and second subarrays. Other combinations of microphones 102 for generating the first and second subarrays are also contemplated.

[0071] The first and second subarray signals can be obtained by combining audio signals captured by the microphones in each subarray. The exact beamforming technique used to combine these microphone signals can vary depending on how the corresponding subarray is formed or how the microphones are arranged within that subarray (e.g., linear array, orthogonal array, broadside array, endfire array, etc.). For example, audio signals received from microphones arranged in a linear array or broadside array can be summed together to generate the subarray signal. In some cases, the beamformer 600 can be in communication with one or more other beamformers to receive the first and second subarray signals. For example, a separate beamformer can be coupled to the microphones of a given subarray to combine the audio signals received from the microphones to generate a combined output signal for that subarray.

[0072] 7, a subarray beamformer 700 may be configured to combine outputs for a given number, n, of microphone pairs 702 (e.g., microphone pair 1 through microphone pair n) according to an embodiment to generate a combined output signal for a subarray formed by the microphone pairs 702. For example, referring to FIG. 2, the microphone pairs 702 may be a plurality of microphone sets forming a first group or subarray 114 for covering a first octave (e.g., the Nth octave), or a plurality of microphone sets forming a second group or subarray 116 for covering a second octave (e.g., the (N-1)th octave), or a plurality of microphone sets forming a third group or subarray 118 for covering a third octave (e.g., the (N-2)th octave). Other combinations of microphone pairs 702 are also contemplated.

[0073] As shown, the beamformer 700 can receive a combined audio signal for each microphone pair 702 and provide the signal to a combiner network 704 of the beamformer 700. The combiner network 704 can be configured to combine or sum the received signals to generate a combined sub-array output for the microphone pairs 702. In an embodiment, the combiner network 704 can include multiple summers or other summing elements that can sum the various audio signals.

[0074] In some embodiments, the beamformer 700 can communicate with multiple other beamformers, such as, for example, the beamformer 600 shown in FIG. 6, to receive a combined audio signal for each microphone pair 702. For example, the beamformer 600 can be used to combine audio signals generated by the first and second microphones 602 (e.g., Mic 1 and Mic 2) to generate a combined output having a cardioid shaping for that pair of microphones 602. The combined cardioid output of the beamformer 600 can be provided to the beamformer 700 as a combined audio signal for the first microphone pair 702 (e.g., Mic pair 1). A similar technique can be used to provide a combined cardioid output to the beamformer 700 for each of the other microphone pairs 702 in the corresponding subarray. The combiner network 704 can then combine all of the cardioid outputs together to generate a cardioid output for the entire subarray.

[0075] Referring now to FIG. 8, a delay-and-sum beamformer 800 can be configured to steer the entire output of a linear array of microphones 802 towards a desired direction or audio source using an appropriate delay-and-sum technique, according to an embodiment. As shown, the beamformer 800 receives audio signals for the microphones 802 and provides them to a delay network 804. The delay network 804 can be configured to introduce or add an appropriate amount of delay to each of the received audio signals. The delayed signal outputs are then provided to a summing or adding network 806. The adding network 806 combines or aggregates the signals received from the delay network 804 to create a combined output for the entire array that is steered to the desired angle. In an embodiment, the delay network 804 can include multiple delay elements to apply an appropriate amount of delay to each microphone signal, and the adding network includes multiple adders or other summing elements that can sum the outputs received from the multiple delay elements.

[0076] In an embodiment, the microphones 802 can be arranged as a linear or one-dimensional array using techniques described herein, for example, similar to the array microphone 100 shown in FIG. 1. More specifically, the microphones 802 can include a first plurality of microphones (e.g., the first microphone 104) arranged linearly along a first axis, i.e., a front surface, of the array microphone, for example, as shown in FIG. 1, and a second plurality of microphones (e.g., the second microphone 112) arranged orthogonally to the first microphone along one or more different axes perpendicular to the first axis. The first and second microphones can form a plurality of microphone sets or pairs configured to create a linear pattern with respect to the first axis, for example, as shown in FIG. 2. In some cases, the output of each pair of microphones 802 can be combined using a suitable beamforming technique, such as, for example, the beamformer 600. In such a case, the beamformer 800 can be in communication with one or more beamformers 600 to receive a combined audio signal for each of the linearly arranged microphone pairs. In other embodiments, the beamformer 800 can communicate with one or more beamformers 700 to receive combined subarray signals for each of the subarrays formed by grouping linearly arranged microphone pairs based on frequency octave coverage (e.g., subarrays 114, 116, and 118 in FIG. 2).

[0077] The amount of delay introduced by the delay network 804 can be based on the desired steering angle for the entire array, the location of each microphone 802 in the linear array and / or relative to the audio source, how the microphones 802 are paired, grouped, or otherwise arranged in the array, and the speed of sound. As an example, if an audio source is located at a first end of the linear array microphones, sound from the audio source will arrive at a different time at a first set of microphones 802 located at the first end compared to a second set of microphones 802 located at the opposing second end. A delay can be added to the audio signals from the microphones at the second end by the delay network 804 to time-align the audio signals from the microphones at the first end and the second end for proper beamforming. The amount of delay can be equal to the amount of time it takes for sound from the audio source to travel between the first end microphone 802 and the second end microphone 802. In addition to determining the amount of delay, the beamformer 800 can determine which of the microphones 802 or sets of microphones to delay based on, for example, the desired steering angle, the position of the microphone 802 within the array, and the position of the audio source.

[0078] 9 illustrates an example method 900 for generating an output signal for an array microphone including multiple microphones and configured to cover multiple frequency bands, according to an embodiment. All or a portion of the method 900 may be performed by one or more processors (e.g., an audio processor included in the microphone system 500 of FIG. 5 ) and / or other processing devices (e.g., an analog-to-digital converter, an encryption chip, etc.) that are internal or external to the array microphone. Additionally, one or more other types of components (e.g., memory, input and / or output devices, transmitters, receivers, buffers, drivers, discrete components, logic circuits, etc.) may also be utilized in conjunction with the processor and / or other processing components to perform any, some, or all of the steps of the method 900. For example, program code stored in a memory of the system 500 may be executed by an audio processor to perform one or more operations of the method 900.

[0079] In some embodiments, certain operations of method 900 may be performed by one or more of the sum-difference cardioid forming beamformer 600 of Figure 6, the subarray combining beamformer 700 of Figure 7, and the linear delay-sum steering beamformer 800 of Figure 8. The array microphone may be the array microphone 100 described herein, for example, as shown in Figure 1. The microphones included in the array microphone may be, for example, MEMS transducers that are inherently omnidirectional, other types of omnidirectional microphones, electret microphones or condenser microphones, or other types of omnidirectional transducers or sensors.

[0080] Referring back to FIG. 9, the method 900 begins at block 902 with a beamformer or processor receiving audio signals from a plurality of microphones (e.g., microphones 102 in FIG. 1) arranged in a microphone set configured to form a linear pattern along a first axis (e.g., first axis 105 in FIG. 1) and extend orthogonally from the first axis. More specifically, each microphone set may include a first microphone (e.g., one of the first microphones 104 shown in FIG. 1) arranged along the first axis to cover one or more octaves within a plurality of frequency bands covered by the array microphone. Each microphone set may further include a second microphone (e.g., one of the second microphones 112 shown in FIG. 1) arranged on a second axis (e.g., second axis 107 in FIG. 1) orthogonal to the first microphone and perpendicular to the first axis.

[0081] In an embodiment, each second microphone can be positioned in the array microphone such that it overlaps one of the first microphones in terms of placement relative to the first axis and frequency coverage. Specifically, each second microphone can be positioned (along an orthogonal axis) from the overlapping first microphone at a predetermined distance based on the octave covered by the first microphone. As a result, each microphone set can be configured to cover a particular frequency octave. Harmonic nesting techniques can be used to select the placement of the first microphones along the first axis and / or the placement of the second microphones relative to the first microphones.

[0082] The multiple microphone sets can be further arranged to form multiple subarrays. For example, the microphone sets can be grouped based on frequency octaves such that each subarray covers a different octave (e.g., groups 114, 116, and 118 shown in FIG. 2). In some cases, several microphone sets can be located (or co-located) on the same orthogonal axis because they include a common first microphone in addition to different second microphones. In such cases, the first microphone can be configured to cover multiple octaves, and each of the second microphones can be configured to overlap only one of these octaves, for example, by selecting an appropriate distance from the first microphone. As a result, the collocated second microphones can belong to different subarrays even though they are located on the same orthogonal axis.

[0083] In block 904, a processor or beamformer determines the direction of arrival of the audio signals received from the multiple microphones in block 902. The direction of arrival may be measured in degrees or as an angle relative to the first axis 105 of the array microphone 100. The direction of arrival may be determined using one or more beamforming techniques, such as, for example, cross-correlation techniques, inter-element delay calculations, and other suitable techniques.

[0084] In block 906, the processor or beamformer selects one of a plurality of beamforming patterns for processing the received audio signal based on the direction of arrival identified in block 904. For example, the plurality of beamforming patterns may include a broadside pattern, such as beamforming pattern 200 shown in FIG. 2, and at least one oblique pattern, such as beamforming pattern 300 shown in FIG. 3 and / or beamforming pattern 400 shown in FIG. 4. The broadside pattern may be selected when the direction of arrival is perpendicular to the first axis of the array microphone or when the audio source is positioned perpendicular to the array microphone. On the other hand, when the direction of arrival is at an angle to the first axis or when the audio source is positioned to one side of the array, an appropriate oblique pattern may be selected.

[0085] In an embodiment, the processor or beamformer may access a database (e.g., a look-up table) stored in the memory of the microphone system 500 to determine which pattern to use. The database may store a direction of arrival value or a range of values ​​associated with each pattern. For example, the first oblique pattern 300 may be selected if the direction of arrival is approximately 45 degrees to the first axis or within a preset range of approximately 45 degrees (e.g., 0 degrees to 60 degrees). The second oblique pattern 400 may be selected if the direction of arrival is approximately 135 degrees to the first axis or within a preset range of approximately 135 degrees (e.g., 120 degrees to 180 degrees). Additionally, the broadside pattern 200 may be selected if the direction of arrival is within a preset range of approximately 90 degrees (e.g., 61 degrees to 121 degrees). Other suitable techniques for selecting an appropriate beamforming pattern based on the detected direction of arrival may also be used.

[0086] In some embodiments, method 900 proceeds from block 906 to block 908 where a beamformer or processor applies an appropriate beamforming technique to steer the array output towards a desired direction or audio source. For example, all or part of the steering process in block 908 may be performed by the linear delay-and-sum steering beamformer 800 of FIG. 8 or using other delay-and-sum techniques to steer the output of a linear array microphone to a desired angle. As shown in FIG. 9, the steering technique may be performed prior to combining the received audio signals to achieve the desired directional output with the beamforming pattern selected in block 906.

[0087] In block 910, the beamformer or processor combines the received audio signals according to a selected beamforming pattern to generate a directional output for each microphone set. In an embodiment, combining the received audio signals includes, for each microphone set, combining an audio signal received from a first microphone with an audio signal received from a second microphone and generating a directional output using a sum-and-difference beamforming technique. Thus, all or a portion of block 910 may be performed by the sum-and-difference beamformer 600 of FIG. 6 or by otherwise applying a sum-and-difference cardioid forming technique to the received audio signals for each microphone set.

[0088] In some embodiments, the microphones of each layer of the array microphone may first be combined according to the octave covered to form one or more on-axis subarrays for that layer (e.g., nests 106, 108, 110 in the primary layer shown in FIG. 1). In such a case, a sum-and-difference technique such as the beamformer 600 may be applied to pairs of subarrays instead of pairs of microphones. For example, the sum-and-difference beamformer 600 may be used to combine the first subarray 106 from the primary layer of the array microphone 100 shown in FIG. 1 with a first secondary layer added orthogonal to the first axis 105 to overlap the microphone 104 of the first nest 106. This process may be repeated for each of the remaining secondary layers of the array microphone.

[0089] At block 912, the beamformer or processor aggregates all the beamforming outputs generated at block 910 to provide an overall or single array output for the array microphone. As described herein, the microphones of the array microphone may be arranged into subarrays using one or more different techniques. At block 912, the outputs of such subarrays may be aggregated or combined to generate an overall array output, regardless of how they are generated. Method 900 may end once a single array output has been provided.

[0090] As an example, in an embodiment where microphones are combined into microphone sets in block 910 to improve directivity, in block 912, the microphone sets may be further combined into various subarrays based on the frequency octave covered by each set. In such an embodiment, all or a portion of block 912 may be performed by the subarray combining beamformer 700 of FIG. 7 to aggregate the directional outputs for each of the microphone pairs in a given subarray to generate an overall subarray output for that subarray. This process may be repeated for each subarray or each octave of the array microphone. The aggregation process in block 912 may further include aggregating or combining the various subarray outputs to generate a single array output.

[0091] 9 and described herein as having a particular chronological order, in other embodiments, one or more of the blocks may be performed out of order or according to a different order. For example, the steering process of block 908 may be performed after block 910 and / or block 912 in some embodiments. More specifically, in such cases, the steering technique may be applied to the array output after the received audio signals are combined to form microphone sets, after the microphone sets are combined to form sub-arrays, or after the sub-arrays are combined to form a single array output.

[0092] According to an embodiment, the array microphone 100 shown in FIG. 1 and described herein can generate a substantially consistent frequency response across a variety of settings or orientations, including, for example, whether placed on a table or other horizontal surface, mounted on a ceiling, or mounted horizontally on a wall. In particular, regardless of the orientation of the array, the lobes of the array microphone 100 can be aimed at a desired sound source with increased rear rejection and steering control or separate front acceptance, thus improving the ability of the array to reject unwanted sound sources and room reflections and provide a high signal-to-noise ratio (SNR). At the same time, slight or small differences in behavior may occur between certain directions due to the placement of the microphone 102 relative to the audio source.

[0093] 10A and 10B show an exemplary environment 1000 in which an array microphone 100 is placed on a table 1002, or other horizontal or substantially flat surface, according to an embodiment. The table 1002 can be, for example, a conference room table, with multiple audio sources 1004 (e.g., human speakers) positioned or seated around the table 1002. In such an environment 1000, the array microphone 100 can be positioned such that the front surface 120 faces one side of the table 1002 and the rear surface 122 faces the opposite side of the table 1002, as shown in FIG. 10B. Because the array microphone 100 is independent of the direction of arrival in the xy plane, the array microphone 100 can direct a broadside polar pattern towards either of the two sides of the table, allowing sound sources (e.g., other speakers or unwanted noise sources) coming from the opposite side of the table to be separated. Additionally, the array microphone 100 can steer a main lobe or sound beam to any angle around the table 1002 using the beamforming techniques described herein. As a result, the array microphone 100 can be used to simultaneously generate multiple individual audio channels, each tuned to capture a particular speaker or audio source 1004, while rejecting room noise, other talker noise, and other unwanted sounds. In this manner, the array microphone 100 can provide not only improved directionality, but also improved signal-to-noise ratio (SNR) and acoustic echo cancellation (AEC) characteristics.

[0094] 11A is a polar plot 1100 of the vertical directivity of the array microphone 100 of FIG. 10A, according to an embodiment. More specifically, the polar plot 1100 illustrates the frequency response of the array microphone 100 at 1900 Hz, perpendicular to the table 1002, for a zero degree azimuth of the array microphone 100, or in an unsteered (or broadside) state. As shown, the vertical directivity response of the array microphone 100 forms a cardioid polar pattern with a main lobe 1102 that is narrower than the full 360 degree pickup pattern of the individual omnidirectional microphones 102. As a result, the array microphone 100 can better reject unwanted sound sources, for example, at the rear of the array.

[0095] 11B is a polar plot 1110 of the horizontal directivity of the array microphone 100 of FIG. 10B, according to an embodiment. More specifically, the polar plot 1110 illustrates the frequency response of the array microphone 100 at 1900 Hz for a zero degree orientation of the array microphone 100 or in an unsteered (or broadside) state, in the plane of the table 1002. As shown, the horizontal directivity response of the array microphone 100 forms a unidirectional or cardioid polar pattern with a main lobe 1112 narrower than 180 degrees. This narrow lobe 1112 can be directed or steered toward individual audio sources 1004 seated around the table 1002 with more precision and without picking up unwanted noise or room reflections.

[0096] FIG. 12 is a polar plot 1200 of both the horizontal and vertical directivity of the array microphone 100 of FIGS. 10A and 10B for 2500 Hz, according to an embodiment. Specifically, curve 1202 illustrates the frequency response of the array microphone 100 for 2500 Hz in the plane of the table 1002, in a non-steered or broadside condition (e.g., pointed at a talker located at 0 degrees). Curve 1204 illustrates the frequency response of the array microphone 100 for 2500 Hz perpendicular to the table 1002, also in a broadside condition. As shown, the vertical response illustrated by curve 1202 forms a cardioid polar pattern with a main lobe narrower than the full 360 degree pickup pattern of an individual omnidirectional microphone 102. Also as shown, the horizontal directivity response illustrated by curve 1204 forms a unidirectional or array polar pattern with a main lobe narrower than 180 degrees. Typically, for harmonic subarrays, the higher the frequency, the more directivity (i.e., the narrower the beamwidth). This is shown at least in Figures 11A, 11B, and 12, where the horizontal directivity response curve 1202 to 2500 Hz has a narrower beamwidth than the horizontal directivity response curve 1112 to 1900 Hz.

[0097] 13 illustrates an exemplary environment 1300 in which an array microphone 100 is mounted or attached horizontally to a wall 1302 or other vertical or upright surface, according to an embodiment. The wall 1302 can be a conference room or other environment with one or more audio sources (not shown) seated or positioned in front of the wall 1302. For example, an audio source (e.g., a human speaker) can be seated at a table (not shown) and facing the wall 1302 for a conference call, telecast, webcast, etc. In such a case, the array microphone 100 can be positioned horizontally on the wall below a television or other display screen (not shown), such that the front surface 120 of the array microphone 100 is directed toward a bottom surface 1304 (or floor) of the wall 1302 and the back surface 122 of the array microphone 100 is directed toward a top surface 1306 (or ceiling) of the wall 1302, as shown in FIG.

[0098] FIG. 14 is a plot 1400 of the directional response of the array microphone 100 shown in FIG. 13, according to an embodiment. More specifically, the plot 1400 illustrates the normalized sensitivity of the array microphone 100 for 94 dB SPL (sound pressure level) at zero degree azimuth, i.e., in a non-steered (or broadside) state, of the array microphone 100. As shown by segment 1402, the microphone sensitivity is significantly higher directly in front of the array microphone 100, i.e., in a direction substantially perpendicular to the front face 120 of the array. In an embodiment, segment 1402 represents a focused sound beam (or lobe) generated perpendicular to the array microphone 100 or directed straight from the wall 1302 toward the opposite side of the room. This sound beam can be generated by combining the audio signals received from the microphones 102 of each microphone set using a delay-and-sum forming technique. For example, beamformer 800 of FIG. 8 can be used to apply exact and / or optimized delay-and-sum beamforming techniques to create resultant directional beams configured to reject unwanted noise and reflections from the ceiling and floor within the octave covered by the microphones being summed.

[0099] As shown by segment 1404, there is significantly less microphone sensitivity on the left and right sides of the array microphone 100. In an embodiment, segment 1404 may represent nulls formed on either side of the array 100 due to placement of the array microphone 100 on the wall 1302. In particular, when mounted on the wall 1302, the array microphone 100 may eliminate or ignore sounds coming from the extreme left and right sides because the array geometry naturally creates nulls on the left and right sides, and the use of a delay-and-sum network allows for null creation within the axis of the array 100. As shown by segment 1406 of plot 1400, microphone sensitivity may be significantly higher in either direction in the plane of the microphone 102.

[0100] Thus, the techniques described herein provide an array microphone that has a narrow one-dimensional form factor and improved frequency-dependent directivity in multiple dimensions, thus resulting in improved signal-to-noise ratio (SNR) and wideband audio applications (e.g., 20 Hertz (Hz)≦f≦20 Kilohertz (kHz)). The microphones of the array microphone are arranged in harmonically nested orthogonal pairs configured to create a linear pattern in front of the array microphone and overlap the linear pattern in one or more orthogonal layers to enhance directionality. One or more beamforming techniques can be used to generate directional outputs of each microphone pair and combine the directional outputs to form a cardioid polar pattern for the entire array, for example, when the array microphone is placed on a horizontal surface. When the array microphone is mounted on a vertical surface, the microphones can be combined to generate a focused narrow beam pointed straight ahead, i.e., perpendicular to the vertical surface. As a result, despite being composed of low-profile microphones (e.g., MEMS microphones), the array microphone can provide improved rear rejection and front acceptance isolation in both wall-mounted and table-mounted orientations.

[0101] The process illustrations or blocks in the figures should be understood as representing modules, segments, or portions of code that contain one or more executable instructions for performing particular logical functions or steps in the process, and alternative implementations are within the scope of embodiments of the invention that can perform functions in orders different from those illustrated or discussed, including substantially simultaneously or in reverse order, depending on the functionality involved, as will be appreciated by those skilled in the art.

[0102] The present disclosure is intended to describe how to make and use various embodiments in accordance with the technology, rather than to limit its true intended fair scope and spirit. The foregoing description is not intended to be exhaustive or to be limited to the precise form disclosed. Modifications or variations are possible in light of the above teachings. The embodiments have been chosen and described to provide the best explanation of the principles of the described technology and its practical application, and to enable those skilled in the art to utilize the technology with various embodiments and variations suitable for the particular applications contemplated. All such modifications and variations are within the scope of the embodiments as determined by the appended claims, as may be amended during the pendency of the application of this invention, when interpreted in accordance with the breadth to which they are fairly, legally and equitably entitled, and all equivalents thereof.

Claims

1. A plurality of microphone sets arranged in a linear array pattern along a first axis, the linear array pattern arranging the plurality of microphone sets in a harmonic nested configuration, the linear array pattern configured to cover a plurality of frequency bands including a first octave, a second octave, and a third octave, each microphone set including a first microphone arranged along the first axis and a second microphone arranged along a second axis orthogonal to the first axis for additional directionality in one or more covered octaves. Equipped with a distance between adjacent first microphones along the first axis selected from a first group of integer multiples of a first value, and within each microphone set, a distance between the first microphone and the second microphone along the second axis selected from a second group of integer multiples of a second value, the first value being different from the second value; the plurality of microphone sets are configured to form a first subarray for covering the first octave, a second subarray for covering the second octave, and a third subarray for covering the third octave, each subarray including seven microphone sets; Array microphone.

2. The plurality of microphone sets are arranged at the same position on the same second axis. The array microphone according to claim 1 .

3. the co-located microphone sets include the same first microphone but different second microphones; The array microphone according to claim 2 .

4. The second value is determined based on frequency values ​​included in the plurality of frequency bands. The array microphone according to claim 1 .

5. the first value is determined based on a linear aperture size of the array microphone; The array microphone according to claim 1 .

6. a distance between adjacent microphones in the second subarray along the first axis is twice the distance between adjacent microphones in the first subarray along the first axis; The array microphone according to claim 1 .

7. a distance between adjacent microphones in the second subarray along the second axis is twice the distance between adjacent microphones in the first subarray along the second axis; The array microphone according to claim 1 .

8. a distance between adjacent microphones of the third subarray along the first axis is four times the distance between adjacent microphones of the first subarray along the first axis; The array microphone according to claim 1 .

9. a distance between adjacent microphones in the third subarray along the second axis is four times the distance between adjacent microphones in the first subarray along the second axis; The array microphone according to claim 1 .

10. each said microphone being a microelectromechanical system (MEMS) microphone; The array microphone according to claim 1 .

11. The array microphone further includes a front surface configured to have a length and width determined by an overall dimension of the first microphones and the distance between adjacent first microphones, the first microphones being linearly arranged along the length of the array microphone. The array microphone according to claim 1 .

12. The first microphone of the plurality of microphone sets forms an upper layer, and the second microphone of the plurality of microphone sets forms a plurality of secondary layers spatially disposed behind the upper layer. The array microphone according to claim 1 .

13. The method of claim 12, wherein the total depth of the array microphone is determined by the number of secondary layers and the distance between the first microphone and the second microphone in each set. The array microphone according to claim 12.

14. Each secondary layer is configured to provide the additional directionality for a selective one of the first octave, the second octave, and the third octave. The array microphone according to claim 12.

15. Each second microphone overlaps with one of the first microphones in terms of its arrangement relative to the first axis. The array microphone according to claim 1 .

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