Apparatus and system for use in acoustic metrology and method

Abstract

An apparatus (100) for use in acoustic metrology, comprising: a microphone array structure (110) comprising a plurality of microphones (140) configured to convert acoustic sound into electrical signals; a signal processing system (120) configured to generate synchronized digital output signals; and a digital network interface (130) configured to provide the synchronized digital output signals to a digital network (150) using a synchronization protocol.

Description

[0001] APPARATUS AND SYSTEM FOR USE IN ACOUSTIC METROLOGY AND METHOD

[0002] TECHNICAL FIELD

[0003] Embodiments of the present inventive concept relate to an apparatus and method for use in acoustic metrology, such for example, but not exclusively, sound source localization.

[0004] BACKGROUND OF THE INVENTION

[0005] Microphone arrays are systems consisting of multiple microphones arranged to record acoustic events, commonly used in sound pressure analysis. They can consist of pressure or pressure gradient sensors, with coincident or phased array setups of spherical, linear or planar shape. These arrays serve various purposes, including sound localization, speech recognition, echo cancellation and spatial audio recording. In order to facilitate these demands, subsequent signal processing is paramount. In recent years, machine learning based approaches have come more into focus. Arrays are utilized for spatial filtering, sound intensity analysis, acoustic holography and direction-of-arrival estimation. In acoustic metrology, arrays often incorporate cameras, creating acoustic cameras that visually correlate acoustic information with the visual scenery.

[0006] Acoustic cameras often implement the signal processing of the discrete channels directly on a digital signal processor, making the processing an integral part of the array system. While this approach enables robust industrial applications, the flexibility desired in the research project cannot be realized, as these systems often do not allow for the recording of all raw microphone data. In addition, the non-expandable computing capacity is an obstacle to flexible future applications in which several arrays are to be operated in conjunction or new, more computationally intensive signal processing steps are to be carried out. Other manufacturers rely on proprietary digital transmission mechanisms or record the often numerous signals from analog microphones on dedicated data acquisition systems in order to be able to subsequently carry out the signal processing.

[0007] Thus, there is a significant need for an apparatus for use in acoustic metrology which allows for recording microphone raw data completely and allows for a kind of scalability of the recording in terms of number of microphones captured. Thus, such a concept would enable ms, rm to rely on an expandable computing capacity which permits new and computationally more intensive signal processing.

[0008] SUMMARY OF THE INVENTION

[0009] Such needs are fulfilled, and multiple advantages are provided, by an apparatus for use in acoustic metrology according to claim 1 , a system for use in acoustic metrology according to claim 17 and a method for use in acoustic metrology according to claim 18. Further, specific implementations of the apparatus according to the present inventive concept are defined in the dependent claims.

[0010] In accordance with the present inventive concept, embodiments comprise an apparatus for use in acoustic metrology (e.g. sound based measurements; e.g. sound pressure analyses; e.g. sound source localization; e.g. railway noise analysis; e.g. sound filtering; e.g. beamforming applications; e.g. beamforming for auralization purposes; e.g. acoustic triangulation applications; e.g. speech recognition; e.g. echo cancellation; e.g. spatial audio recording; e.g. acoustic holography ; e.g. direction-of-arrival estimation; e.g. ambisonic applications) comprising a microphone array structure comprising a plurality of microphones, for example miniaturized microphones, MEMS microphones, configured to convert acoustic sound (e.g. from a sound source; e.g. from sound sources) into electrical signals. The apparatus further comprises a signal processing system configured to generate synchronized digital output signals based on the electrical signals. The apparatus further comprises a digital network interface configured to provide the synchronized digital output signals to a digital network using a synchronization protocol, for example transmission protocol, e.g. synchronization and transmission protocol, e.g. audio networking protocols.

[0011] By using a synchronization protocol in providing the synchronized digital output signals to a digital network, the sound capturing is scalable in that the acoustic sound captured by the plurality of microphones of the apparatus is combinable with, or may be added to, sound captured by other microphones such as microphones of another apparatus of the same type, thereby together forming a system comprising more than just one microphone array.

[0012] According to embodiments described herein, the microphone array structure comprising the plurality of microphones may provide an effective mechanism for acoustic sensing, permitting improvements in the range of sound that is detected and minimizing external sources of interferences. The signal processing system of the apparatus then generates the ms, rm synchronized digital output signals using the electrical signals generated by the microphone array structure. By this measure, delays originating in microphones during recording and conversion of sound which lead to signals not being in sync with each other are avoided. That is, the signal processing system generates digital output signals which are coordinated with each other in time based on electrical signals which may not be coordinated with each other in time. As a result, irregularities originating in sound capture by the array structure and in subsequent processing by the signal processing system which permit signals to be mutually asynchronous (i.e. be out of sync) are avoided. Finally, the digital network interface of the apparatus allows the synchronized digital output signals to communicate with the digital network in accordance with a protocol ensuring synchronization of signals during transmission and reception over the network.

[0013] Thus, according to embodiments, the apparatus allows for accessing, recording and a subsequent processing of the raw microphone data thereby facilitating various application use cases. That is, the apparatus permits robust industrial applications as well as the flexibility desired for research purposes. Further, a configurable computing capacity can be selected, which may be optimized for a particular range of tasks. For instance, the computing capacity of the signal processing system may be expanded for applications wherein a plurality of microphone arrays are operated simultaneously, or in conjunction with each other. For instance, the computing capacity of the signal processing unit may be adapted to permit computationally challenging signal processing. This computationally challenging signal processing may be more intensive, or even complex, than the signal processing allowed by the state of the art.

[0014] In accordance with embodiments, additionally or alternatively, the digital network interface is configured to operate according to AES 67.

[0015] In accordance with embodiments, additionally or alternatively, the synchronization protocol comprises Precision Time Protocol, PTP. PTP allows accurate and precise synchronization of clocks in apparatuses, at least one of which is in accordance with embodiments of the present inventive concept. Thus, the apparatus with the help of PTP achieves synchronization communication using optimal bandwidth of the digital network and optimal clock computing resources.

[0016] In accordance with embodiments, additionally or alternatively, the digital network interface is configured to provide the synchronized digital output signals to the digital network using ms, rm User Diagram Protocol, UDP, as a transport protocol. In particular, UDP provides the synchronized digital output signals to the digital network in the form of protocol data units, for example datagrams, wherein the protocol data units are transmitted without requiring acknowledgement information from the receiver, thus permitting communication with minimum latency. Since UDP is a simple protocol with optimal protocol overhead, it permits the digital network interface of the apparatus to be adapted for time-sensitive applications in an efficient manner providing reduced latency and faster communication speeds.

[0017] In accordance with embodiments, additionally or alternatively, the digital network interface is configured to provide the synchronized digital output signals to the digital network using Real-Time Protocol, RTP, as a transport protocol. In particular, RTP provides the synchronized digital output signals to the digital network in the form of protocol data units, for example, packets, wherein the protocol data units are transmitted with real time communication information, thereby allowing synchronization between the transmitter and the receiver, thus providing real-time communication.

[0018] In accordance with embodiments, alternatively or additionally, the apparatus further comprises a power supply module configured to use powered over Ethernet, PoE, technology, for example, for supplying power (e.g. electrical power) to the apparatus. Using PoE, a connection structure such as an Ethernet cable, coupled (e.g. directly or indirectly) to the apparatus provides connectivity to the digital network and electrical power simultaneously. This reduces costs and allows a simple and flexible mechanism for aiding network connectivity and meeting electrical power supply requirements.

[0019] In accordance with embodiments, additionally or alternatively, the plurality of microphones, for example miniaturized microphones, MEMS microphones, are arranged in a multi-armed logarithmic spiral geometry. For example, the multi-armed logarithmic spiral geometry may be an Underbrink spiral geometry.

[0020] In accordance with embodiments, additionally or alternatively, the plurality of microphones, for example miniaturized microphones, MEMS microphones, are configured to provide the electrical signal in a digital pulse density modulated, PDM, manner (e.g. so as to form encoded PDM signals, e.g. so as to form single-bit PDM signals) to the signal processing system. This characteristic of the microphones reduces the component count of the circuit, thus facilitating easier data transmission, that is, transmission of the electrical signals generated by the microphones. ms, rm In accordance with embodiments, additionally or alternatively, the signal processing system comprises a plurality of converter units, for example PDM to PCM converters, each of which is associated with a subset of plurality of microphones (e.g. at least one of the plurality of microphones; e.g. possibly exactly all of the plurality of microphones; e.g. a group formed out of the plurality of microphones) and configured to digitize (e.g. allow direct binary representations for further signal processing; e.g. that is, convert single-bit representations to multi-bit representations) and multiplex (e.g. time-division multiplex; e.g. interleaving within the time domain) the electrical signals of the subset of the plurality of microphones to obtain a multiplex contribution signal (e.g. a serialized data stream; e.g. a time division multiplex, TDM, PCM data stream), and a multi-channel module (e.g. a FPGA module; e.g. a micro-controller unit, MCU; e.g. a digital signal processing, DSP, unit) forming the synchronized digital output signals (e.g. a multi-channel audio signal) out of the multiplex contribution signals (e.g. serialized data streams; e.g. time division multiplex, TDM, PCM data streams) of the plurality of converter units (e.g. PDM to PCM converters).

[0021] In accordance with embodiments, additionally or alternatively, the signal processing system is further configured to provide a plurality of reference clock signals (e.g. frame clock, FCLK, signal; e.g. bit clock, BCLK, signal; e.g. master clock signal; e.g. GPS clock signal) to the converter units (e.g. PDM to PCM converters) using a plurality of clock buffers (e.g. frame clock, FCLK, buffer; e.g. bit clock, BCLK, buffer) so as to mutually synchronize the multiplex contribution signals (e.g. serialized data streams; e.g. time division multiplex, TDM, PCM data streams). In particular, the multi-channel module may be configured to provide any of the plurality of reference clock signals and any of the plurality of clock buffers. By these measures i.e. the use of the clock signals and the clock buffers, the signal processing system establishes that the digital signals generated by itself are mutually synchronous (e.g. time-synchronous) with each other. Further, the clock buffers permit an increased current drive of the clock signals which is in accordance with comparatively long traces, and therefore increased parasitic capacitance, due to a large aperture size of the microphone array structure.

[0022] In accordance with embodiments, additionally or alternatively, the reference clock signals comprise any of a frame clock, FCLK, signal (e.g. configured to indicate samples of each audio channel on a TDM bus associated with the TDM data stream), a bit clock, BCLK, signal (e.g. configured to indicate individual bits of samples of each audio channel on a TDM bus associated with the TDM data stream), and a PDM clock signal, wherein the PDM ms, rm clock signal is configured to each of the plurality of microphones (e.g. miniaturized microphones; e.g. MEMS microphones) using the respective converter units and is derived using the bit clock, BCLK.

[0023] In accordance with embodiments, additionally or alternatively, the signal processing system is configured to provide control signals for the converter units (e.g. PDM to PCM converters).

[0024] In accordance with embodiments, additionally or alternatively, the digital network interface comprises a transceiver module (e.g. an ethernet transceiver module; e.g. ethernet PHY) configured to transmit and receive data, for example, the synchronized digital output signals, to the digital network.

[0025] In accordance with embodiments, additionally or alternatively, the digital network interface further comprises two or more connectors (e.g. RJ45 connectors) configured to connect the transceiver module (e.g. an ethernet transceiver module; e.g. ethernet PHY) to the digital network.

[0026] In accordance with embodiments, additionally or alternatively, the apparatus further comprises a printed circuit board, PCB, structure (e.g. comprising a main PCB and a control PCB) configured to host at least one of the microphone array structure, the signal processing system and the digital network interface.

[0027] In accordance with embodiments, additionally or alternatively, the digital network interface is configured to provide the synchronized digital output signals to the digital network in a manner so that the synchronized digital output signals are provided with timing information which depends on clock information received via the synchronization protocol over the digital network.

[0028] Thus, the embodiments of the present invention enable a system for use in acoustic metrology (e.g. sound based measurements; e.g. sound pressure analyses; e.g. sound source localization; e.g. railway noise analysis; e.g. sound filtering; e.g. beamforming applications; e.g. beamforming for auralization purposes; e.g. acoustic triangulation applications; e.g. speech recognition; e.g. echo cancellation; e.g. spatial audio recording; e.g. acoustic holography ; e.g. direction-of-arrival estimation; e.g. ambisonic applications) comprising a plurality of apparatuses as described above, , wherein the plurality of apparatuses are connected to the same digital network. This enables building distributed ms, rm microphone array networks using the above described system. By combining acoustic triangulation and beamforming, searching and tracking sound sources with entirely unknown locations in a defined area is feasible using such networks for surveillance and security applications. Further, such networks may be utilized for aliasing-free and high- resolution spatial audio capturing systems for higher-order Ambisonics. Advantages are feasible for other industrial use cases, e.g. conference systems and other suitable scenarios.

[0029] BRIEF DESCRIPTION OF THE FIGURES

[0030] Embodiments of the present invention are described herein in brief detail with respect to the appended drawings and figures, in which:

[0031] Fig. 1 shows a schematic block diagram of an apparatus 100 according to embodiments of the present inventive concept;

[0032] Fig. 2a-b shows schematic views of an implementation of a printed circuit board, PCB, structure 200 according to embodiments of the present inventive concept;

[0033] Fig. 3 shows a schematic illustration of an implementation in accordance with embodiments of the present inventive concept;

[0034] Fig. 4 shows a schematic block diagram of signal flow of an apparatus 500 according to embodiments of the present inventive concept.;

[0035] Fig. 5 a schematic block diagram of a system 500 according to embodiments of the present inventive concept;

[0036] DETAILED DESCRIPTION OF THE FIGURES

[0037] In the following description, embodiments are discussed in detail, however, it should be appreciated that the embodiments provide many applicable concepts that can be embodied in a wide variety of the field of pogo cables The specific embodiments discussed are merely illustrative of specific ways to implement and use the present concept, and do not limit the scope of the embodiments. In the following description of embodiments, the same or similar elements or elements that have the same functionality are provided with the same reference ms, rm sign or are identified with the same name, and a repeated description of elements provided with the same reference number or being identified with the same name is typically omitted. In the following description, a plurality of details is set forth to provide a more thorough explanation of embodiments of the disclosure.

[0038] However, it will be apparent to one skilled in the art that other embodiments may be practised without these specific details. In other instances, well-known structures and devices are shown in diagram form rather than in detail in order to avoid obscuring examples described herein. In addition, features of the different embodiments described herein may be combined with each other, unless specifically noted otherwise.

[0039] In the domain of audio broadcasting and live sound recording, the use of local network based audio transmission has established itself as the go-to mechanism. While different protocols have been developed for this purpose over the years, the currently most used interoperability method is the internet protocol (IP) based AES67 standard [1], The standard aims to establish a lowest common denominator, enabling synchronized data exchange between different IP based audio protocols. This mechanism allows for real time, multichannel streaming of digital audio data on standard IP networks and enables the implementation of synchronized, flexible and distributed audio systems. Despite its applicability, the standard has not yet been adopted by the acoustic metrology industry as to the inventors’ knowledge.

[0040] In the following, details on transport and synchronization protocols typically used in network based audio technology are provided.

[0041] I. AES67

[0042] In the domain of audio technology, interoperability is crucial for seamless integration among different systems. AES67 [1], standardized by the Audio Engineering Society (AES), addresses this need by providing a framework for high-performance audio streaming over IP networks. AES67 allows devices from various manufacturers to exchange audio streams seamlessly. It standardizes audio encoding and formatting, supporting uncompressed PCM audio at different sample rates and bit depths. This eliminates the need for transcoding or format conversion, promoting compatibility and flexibility within the audio industry through a vendor-neutral approach. It is used in live sound reinforcement, broadcast production, recording studios, and conferencing systems. Key components of AES67 include its ms, rm transport mechanism, which utilizes the User Datagram Protocol (UDP) [4] for transmitting audio data packets. The Real-Time Protocol (RTP) [5] is another cornerstone of AES67, as it describes the packet format suitable for real time media data transmission. Timing and synchronization are another essential building block in audio streaming. For this purpose, the Precision Time Protocol (PTP) is used for clock synchronization in AES67 systems. The usually deployed PTP version is IEEE 1588-2008 [6], The Session Description Protocol (SDP) [7] is used for session negotiation and description in AES67, providing a standardized format for communicating parameters such as audio stream format and network addresses. Challenges remain, most importantly the lack of standardized control protocols within AES67, which can complicate device management. To address these issues, AES67- compatible solutions by Audinate (Dante) [8] and ALC NetworX (Ravenna) [9] have been proposed and adopted across industries.

[0043] II. PTP

[0044] The Precision Time Protocol (PTP)

[0010] plays a critical role in achieving synchronized audio streaming across networked devices. It enables highly accurate clock synchronization by ensuring that all devices within an AES67 network share a common time reference, which is crucial for maintaining audio coherence and timing precision. PTP achieves clock synchronization through a hierarchical architecture consisting of grandmaster clocks, boundary clocks, transparent clocks and ordinary clocks. Grandmaster clocks serve as primary time references, while boundary and transparent clocks act as intermediaries, synchronizing with grandmasters and distributing time to downstream devices. Ordinary clocks synchronize with boundary clocks or grandmasters to maintain accurate time. Hardware clock synchronization involves precisely aligning the clocks of audio devices to a common time reference using PTP-compatible components. These typically include specialized networking ICs that support PTP synchronization at the hardware level. These devices receive PTP synchronization messages and adjust their internal clocks to match the master clock’s timing. This mechanism also allows for the generation of IP synchronized audio clock signals. Timestamping is another crucial aspect of PTP in AES67. Timestamps are embedded in RTP packets to indicate when the packet was transmitted relative to the master clock’s time. This allows receiving devices to accurately reconstruct synchronized audio streams by aligning packet arrival times with the master clock’s time reference.

[0045] III. UDP ms, rm The User Datagram Protocol (UDP) [4] is a connection less transport protocol that operates at the transport layer of the Internet Protocol (IP) suite. It provides a simple and lightweight method for exchanging datagrams between devices on a network. Unlike the Transmission Control Protocol (TCP), UDP does not establish a connection before transmitting data, making it faster but less reliable. UDP is commonly used for applications where speed and efficiency are prioritized over reliability, such as real-time multimedia streaming, online gaming, and Voice over IP (VoIP) communications. It is also well-suited for scenarios where occasional packet loss or out-of-order delivery is acceptable, as it does not include mechanisms for error correction. UDP packets consist of a header containing source and destination port numbers, along with length and checksum fields for error detection. The absence of connection setup and teardown overhead makes UDP ideal for time-sensitive applications, where low latency and minimal protocol overhead are essential. However, applications built on UDP must incorporate their own mechanisms for reliability, error mitigation, and congestion control if required. In the context of AES67, this is realised through the use of Quality of Service (QoS).

[0046] IV. RTP

[0047] The Real-Time Protocol (RTP) [5] is used for real-time transmission of multimedia data over IP networks. It operates at the transport layer of the Internet Protocol suite and is designed to support real-time communication applications such as audio and video streaming. RTP provides mechanisms for packetizing multimedia data, adding timestamp and sequence number information to packets, and enabling synchronization and delivery control. Each RTP packet encapsulates a payload of multimedia data, along with header fields specifying the type of data, sequence number, and timing information. Timestamps embedded in RTP packets facilitate synchronization of multimedia streams at the receiver’s end, ensuring accurate playback and lip-sync alignment. Sequence numbers enable receivers to detect packet loss, reorder out-of- sequence packets, and discard duplicate or late-arriving packets to maintain stream integrity.

[0048] V. QoS

[0049] Quality of Service (QoS) ensures dependable audio streaming over IP networks. Within AES67, QoS prioritizes audio and timestamping packets to minimize disruptions of AES67 data streams, by incorporating the Differentiated Service CodePoint (DSCP)

[0011] embedded ms, rm in the header of IP packets. This allows for reliable audio transmission over IP, especially in heterogeneous networks with increased overall traffic.

[0050] VI. SDP

[0051] In the context of AES67, the Session Description Protocol (SDP) [7] is used for negotiating and describing audio streams between devices within an IP network. SDP provides a standardized format for communicating key parameters necessary for establishing audio connections, including codec information, network addresses, and synchronization details. SDP facilitates the negotiation of audio stream characteristics between AES67-compatible devices during the session setup phase. It allows devices to exchange information about supported audio formats, sample rates, and channel configurations, ensuring compatibility and interoperability across audio systems. Additionally, SDP includes provisions for conveying timing and synchronization details essential for AES67 operation, like clock sources and timer information.

[0052] VII. Discovery and Advertisement

[0053] AES67 does not specify a mechanism for automatic detection of AES67-compatible devices on the network. The AES67-compatible Ravenna technology leverages the Real-Time Streaming Protocol (RTSP)

[0012] for this purpose, while also adding further control mechanisms. The Dante technology relies on the Session Announcement Protocol (SAP)

[0013] for discovery and advertisement. SAP has become the go-to mechanism for this purpose even outside Dante networks, as this ensures compatibility between Dante devices in AES67-compatibility mode and native AES67 implementations.

[0054] According to embodiments of the present invention, a synchronization protocol is used to provide captured audio signals over a digital network to outside, wherein the synchronization protocol might be PTP and the provision might use AES67 in general.

[0055] The apparatus for use in the field of acoustic metrology described hereinbelow allow sound (e.g. from a sound source; e.g. from sound sources), to be converted to electrical signals with the aid of its microphone array structure, which allows recording, or capturing, sound with a plurality of channels i.e. a very large number of channels each recorded by a corresponding one of the microphones. The plurality of channels help overcome various limitations of existing systems used in acoustic metrology. ms, rm In particular, the microphone array structure having a high bandwidth within the audible frequency range (e.g. ranging from 20 Hz to 20 kHz) may need to show both a large aperture and small minimum distances which results in desiring more single sensors, e.g. microphones, than previously achievable. In order to characterize highly directive sound sources by array measurements, it is beneficial to be able to capture objects from different angles at the same time with synchronized arrays, e.g. the microphone array structure. When examining moving sound sources with a single array, the time frame where a source is located within the observable angular range may be very short. By using multiple synchronized arrays, e.g. the microphone array structure, spaced along the source trajectories, this time frame is enhanced.

[0056] The inventors recognized that beamforming for auralization purposes can be used by defining source models with partial sound sources and their locations and directivities based on measurements of real objects. The obtained models can subsequently be placed in virtual environments. These benefits provides significant advantages for this task compared to existing hardware solutions.

[0057] An apparatus 100 for use in acoustic metrology, in accordance with embodiments of the present inventive concept, is now described with respect to the schematic block diagram of Fig. 1. The apparatus 100 comprises a microphone array structure 110, a signal processing system 120 and a digital network interface 130.

[0058] The microphone array structure 110 comprises a plurality of microphones 140 configured to convert acoustic sound into electrical signals. The plurality of microphones 140 may comprise miniaturized microphones. For example, the microphones may comprise microelectromechanical system, MEMS, microphones. The microphones 140 may comprise at least any of microphones as pressure transducers and microphones as pressure gradient transducers. The microphones 140, or equivalently acoustic sensors, are configured to receive and transform acoustic sound, originating from a sound source or possibly even a plurality of sources, into electrical information such as electrical signals. The sound source, or possibly any of the plurality of sound sources, may be stationary. The sound source, or possibly any of the plurality of sound sources, may be dynamic i.e. non- stationary or moving. Further, the microphones 140, and thus the microphone array structure, may be adapted to receive the acoustic sound from acoustic events, wherein the acoustic events may be dependent or independent of each other. ms, rm Additionally or alternatively, for example, the microphones 140 may comprise using any transduction principle such as electromagnetic (e.g. capacitive), electrostatic, piezoelectric, piezoresistive, optical, spintronic or thermoacoustic mechanisms.

[0059] The plurality of microphones 140 in the microphone array structure 110 may be configured to operate in tandem. That is, the microphones 140, or possibly a subset of the plurality of microphones 140, may be adapted to operate in conjunction as a single unit (e.g. a single acoustic sensing unit). It is also feasible that the microphones 140, or possibly for instance subsets of the plurality of microphones 140, may be adapted to operate as multiple units (e.g. a plurality of acoustic sensing units). These multiple units may operate in a mutually independent manner, or even possibly a mutually dependent manner.

[0060] The microphones 140 may be arranged to comprise an array arrangement, wherein the array arrangement may be planar or linear. For additional examples, the array arrangement may also comprise example, circular, elliptical, parabolic, hyperbolic or spiral shapes. It is a feasible variation of the microphone array structure 110 of the apparatus in accordance with embodiments of the present inventive concept, wherein the array arrangement of the microphones 140 comprises non-planar shapes. That is, the array arrangement may comprise three-dimensional shapes, such as any of cuboid, spherical and ellipsoidal shapes.

[0061] Further, the array arrangement of the microphones 140 may comprise configurations which are optimized depending on a number of the plurality of microphones 140 in the microphone array structure 110. In particular, the number of the plurality of microphones 140 in the microphone array structure 110 may be configured to allow a channel count, wherein the the channel count may be considered as a typical very high value known to persons skilled in the art of acoustic metrology. For example, the number of microphones 140 may be 64 and thus the channel count may be at least 64. In embodiments, the number of microphones may be at least 1 , or at least 2, or at least 4, or at least 8, or at least 16, or at least 32, or at least 64, or at least 128, or at least 256, or at least 512. That is, the number of microphones 140 in the microphone array structure may range from 1 to 512.

[0062] Additionally, or alternatively, the microphones 140 may comprise multi-channel microphones. ms, rm Even further, the array arrangement of the microphones 140 may be configured to arrange positions of the microphones 140 so as to permit the acoustic sound to be incident on the microphone within different angles. By this measure, the microphones are arranged to receive, and thus convert, the acoustic sound with angular information associated with the acoustic sound.

[0063] Additionally, an overall, or primary, dimension associated with the array arrangement may be configured, or selected, to optimize sensing of the acoustic sound. This overall dimension associated with the array arrangement may be considered as an aperture of the array arrangement of the microphones 140 in the microphone array structure 140. Since the large aperture size of the microphone array structure may result in comparatively long traces, and thus may increase the parasitic capacitance, the microphone array structure 140 is configured to optimize its overall dimension i.e. aperture so as to minimize parasitic capacitances, thus providing an improved tradeoff between converting acoustic sound and minimizing losses due to parasitic capacitances.

[0064] The array arrangement of the microphones 140 may be adapted to form a coincident array arrangement. That is, spacing between the microphones 140 in the coincident array arrangement may be configured to permit sensing of acoustic sound in an omnidirectional manner. In other words, the microphones 140 of the coincident array arrangement are configured to receive the acoustic sound from all directions, i.e., for instance, in a substantially isotropic manner, and at the same time, i.e., for instance, in a substantially simultaneous manner.

[0065] Alternatively, the array arrangement of the microphones may be adapted to form a phased array arrangement. This means that spacing between the microphones 140 in the phased array arrangement may be configured to provide offset information (e.g. delays; e.g. phase shifts, or equivalently phase offsets) so as to receive acoustic sound from a particular spatial region i.e. for instance, a particular direction. In other words, the phased array arrangement may permit a phase relationship between the microphones 140 such that acoustic sound from the particular spatial region is enhanced. Further, the phased array arrangement may also be adapted for preferential suppression of acoustic sound from spatial regions, such as spatial regions providing unwanted noise. Feasibly, the phased array arrangement may be configured to provide the offset information as to receive acoustic sound from a plurality of spatial regions (e.g. from multiple directions). ms, rm Thus, the microphone array structure 110 may be configured to determine spatial information, in particular directional information and / or distance information, associated with the acoustic sound. In other words, the microphone array structure 110 may estimate directions from which the acoustic sound is received and / or distances of the source associated with the acoustic sound, thereby performing sound source localization.

[0066] In embodiments, the microphones 140 of the microphone array structure 110 may comprise an analogue interface configured to provide an analogue representation of the electrical signals. The analogue representation of the electrical signals may be provided to the signal processing system 120. Alternatively, or additionally, in embodiments, the microphones 140 of the microphone array structure 110 may comprise a digital interface configured to provide digital representations of the electrical signals. Further, the digital interface may be configured to provide the digital representations of the electrical signals based on the analogue representations of the electrical signals. The digital representation may subsequently be provided to the signal processing system 120.

[0067] For example, in embodiments, the digital interface may be configured to provide pulse density modulation, PDM, representation as the digital representation of the electrical signals. PDM represents the electrical signals by encoding their amplitudes as densities of pulses in a fixed time interval, thereby resulting in a stream of pulses with varying densities directly related to analogue electrical input such as the electrical signals. The stream of pulses with varying densities form the digital representation of the electrical signals. The interface based on PDM reduces component count of the circuits associated with the microphones 140 and thus facilitates easier transmission of the electrical signals. Thus, in accordance with embodiments, the plurality of microphones 140 are configured to provide the electrical signals in a digital pulse density modulated, PDM, manner to the signal processing system 120.

[0068] The above described example of the digital representation is also a native output of a deltasigma modulator. The delta-sigma modulator is currently the quasi-standard mechanism used to convert an analogue audio signal such as the electrical signals into its digital representation. Therefore, in embodiments, the digital interface may comprise a delta-sigma modulator. For another example, the digital interface may comprise protocols based on inter-IC sound, l2S. ms, rm For example, in embodiments, the digital interface may be configured to provide pulse code modulation, PCM, representation as the digital representation of the electrical signals. Additionally, or alternatively, in embodiments, the digital interface may be configured to provide PCM representation based on the PDM representation of the electrical signals. In other words, the digital interface may be configured to convert PDM representation to PCM representation of the electrical signals.

[0069] The signal processing system 120 is configured to generate synchronized digital output signals based on the electrical signals. That is, the signal processing system 120 receives the electrical signals from the microphone array structure 110, wherein the electrical signals may be in an analogue representation (e.g. an analogue format) or a digital representation (e.g. a digital format) such as the digital representation provided by the interface described earlier, and transforms the electrical signals into the synchronized digital output signals as digital output. By this measure, the signal processing system 120 of the apparatus 100 uses the raw microphone data such as the electrical signals and processes, for example digitally processes (e.g. digitizes), the electrical signals for desired applications in acoustic metrology. This processing performed by the signal processing system 120 may vary depending on the desired applications in acoustic metrology.

[0070] The signal processing system 120 may comprise software components and / or hardware components.

[0071] In particular, the signal processing system 120 may be configured to mutually synchronize the electrical signals with each other so as to generate the synchronized digital output signals. In examples, wherein the electrical signals are provided in the analogue representation by the microphones 140, the signal processing system 120 may transform the electrical signals in the analogue representation to a digital representation. The signal processing system 120 may subsequently synchronize the digital representation of the electrical signals (in the analogue representation) to form the synchronized digital output signals. By this measure, digital representations of the electrical signals are mutually coordinated in time domain, which preserves the timing information associated with sound waves of the acoustic sound (e.g. captured acoustic sound; e.g. recorded acoustic sound). This synchronization of the digital representations of the electrical signals may be performed by dedicated components such as any of the software components and the hardware components within the signal processing system 120. ms, rm The signal processing system 120 may comprise software components and / or hardware components.

[0072] The signal processing system 120 may be configured to extract audio information from the electrical signals and use the audio information to generate the synchronized digital output signals. The audio information may comprise spatial-temporal information, or frequency information, related to the sound source, or possibly of a particular sound source among the plurality of sound sources. The extraction of the audio information from the electrical signals may involve noise suppression (e.g. noise cancellation; e.g. echo suppression; e.g. echo cancellation).

[0073] As a non-limiting example, the signal processing system 120 may comprise information filtering units (e.g. digital filters; e.g. spectral filters; e.g. finite impulse response, FIR, filters; e.g. low-pass filter; e.g. band-pass filters; e.g. band-stop filter; e.g. half-band filter) for extracting the audio information from the electrical signals. The information filtering units may perform further processing of the extracted audio information. In particular, the information filtering units may be implemented as parts of the software components and / or the hardware components. Additionally or alternatively, the signal processing system 120 may be configured to extract the audio information using algorithms implemented as any of the software components and / or the hardware components. It is also feasible that the algorithms may be implemented using the software components interfaced with the hardware components.

[0074] The following illustrate a number of non-limiting examples of the aforementioned algorithms, it is noted that the following examples do not preclude or restrict other suitable algorithms known to persons skilled in the art of acoustic metrology: signal strength algorithms; time of arrival algorithms, time difference of arrival algorithms; direction of arrival algorithms, angle of arrival algorithms; time delay estimation algorithms; sound source estimation algorithms; received signal strength indication algorithms; acoustic beamforming algorithms; delay and sum beamforming algorithms; acoustic holography algorithms; near-field acoustic holography algorithms; Fourier-based planar near field acoustic holography algorithms; auralization algorithms; acoustic triangulation algorithms. It is further noted that any of these algorithms may be combined with each other and implemented as embodiments of the signal processing system 120. Understandably, the algorithms may also be used alone without combination, thereby comprising embodiments of the signal processing system 120. Additionally or alternatively, these algorithms may be implemented in external means, such ms, rm as a computer, or even a computational network such as a computing cluster, a data center, a cloud-based computing unit, interfaced with the apparatus 100.

[0075] The digital network interface 130 is configured to provide the synchronized digital output signals to a digital network 150 using a synchronization protocol. Additionally or alternatively, the digital network interface 130 may be configured to provide the synchronized digital output signals to the digital network 150 using a synchronization and transmission protocol, or in other words, equivalently an audio networking protocol. It is also feasible that multiple protocols such as any of the aforementioned protocols are used in conjunction in order to provide the synchronized digital output signals to the digital network 150.

[0076] For instance, the digital network 150 may be a local area network or a wide area network or any computer based network. For example, the digital network 150 may be an Ethernetbased digital network. The digital network 150 may be configured, in particular optimized, for transmission and reception of the synchronized digital output signals. In particular, a structure (e.g. an architecture) of the digital network 150 may be adapted to allocate a specific bandwidth and / or to permit a communication speed for exchanging or sharing the synchronized digital output signals.

[0077] Further, in accordance with embodiments, the digital network interface 130 is configured to provide the synchronized digital output signals to the digital network 150 in a manner so that the synchronized digital output signals are provided with timing information which depends on clock information received via the synchronization protocol over the digital network 150.

[0078] In accordance with embodiments, the digital network interface 130 is configured to operate according to AES 67.

[0079] Thus, the synchronized digital output signals as audio data are provided on the digital network 150 through the use of AES67 [1], The synchronized digital output signals i.e. the audio data embedded in the apparatus 100 may then be acquired on a computational system, such as a computer, by utilizing a network interface unit, such as a standard networking card. The synchronized digital output signals i.e. the audio data may be extracted from IP packets and may be processed further, e.g. for beamforming applications. In addition to the network interface unit (e.g. serial audio interfaces), the signal processing system 120 may be hosted, or implemented, on a printed circuit board structure, thereby ms, rm allowing for communication of control signals via the I2C [2] protocol. The control signals are used in order to configure converter units. For example, bi-directional communication of the synchronized digital output signals as serialized data streams for control purposes may be feasible over the digital network through the use of TCP / IP [3],

[0080] In accordance with embodiments, the synchronization protocol comprises Precision Time Protocol, PTP.

[0081] In accordance with embodiments, the digital network interface 130 is configured to provide the synchronized digital output signals to the digital network 150 using User Diagram Protocol, UDP as a transport protocol.

[0082] In accordance with embodiments, the digital network interface 130 is configured to provide the synchronized digital output signals to the digital network 150 using Real-Time Protocol, RTP as a transport protocol.

[0083] In accordance with embodiments, the digital network interface 130 is configured to provide the synchronized digital output signals to the digital network 150 using Session Description Protocol, SDP, as a session protocol.

[0084] It is emphasised that according to embodiments of the present inventive concept the apparatus 100 is suitable for use in acoustic metrology. This means that the apparatus 100 is used in applications involving sound based measurements. That is, applications comprising using acoustic information of an acoustic event or an acoustic environment for facilitating determination, or measurement or estimation, of characteristics, such as acoustic information represented by physical parameters, of the acoustic event or the acoustic environment. For instance, the apparatus 100 may be used for sound source localization. For instance, the apparatus 100 may be used for sound pressure analyses. In particular, the apparatus 100 may be used for railway noise analysis. For example, the apparatus 100 may be used to localize (e.g. localize a single sound source; e.g. localize multiple sound sources) and characterize (e.g. estimate a number of sound sources; e.g. separate sources from each other to allow spatial and temporal source separation) sound sources (e.g. stationary sound sources; e.g. dynamic sound sources). The localization and characterization of the sound sources may be achieved through acoustic beamforming and acoustic holography. ms, rm Although there is an inexhaustible number of applications in acoustic metrology wherein the apparatus 100 may be used, the application proceeds in the following with an exhaustive selection of use cases wherein the apparatus 100 may exemplarily be used. It is emphasised that merely mentioning these use-cases does not restrict or exclude any feasible other applications suitable for the apparatus 100. The apparatus 100 may be used for the following: sound intensity analyses, acoustic instrumentation testing, acoustic speech processing (e.g. acoustic speech recognition), spatial audio processing (e.g. spatial audio recording; e.g. spatial filtering; e.g. direction of arrival estimation), noise reduction (e.g. noise cancellation), echo reduction (e.g. echo cancellation) and ambisonics.

[0085] In accordance with embodiments, the apparatus may additionally comprise acoustic cameras configured to associate (e.g. correlate) acoustic information, such as acoustic sound from a sound source, with visual information. The apparatus may even be interfaced (e.g. combined) with acoustic cameras arranged within the microphone array structure. Additionally or alternatively, the apparatus may be interfaced with the acoustic cameras externally arranged to the microphone array structure. The signal processing system may then be configured to generate synchronized digital output signals based on combinations of the electrical signals, the acoustic information and the visual information.

[0086] Further, the microphone array structure 120 of the apparatus 100 primarily functions as an acoustic signal receiving component, such as receiving or recording the acoustic sound incident on it and subsequently converting it into the electrical signals. Additionally or alternatively, the microphone array structure of the apparatus may also function as an acoustic signal transmitting component, wherein the microphone array structure transmits further acoustic sound so as to generate further acoustic information, such as spatial position of the sound source (or even sound sources) and / or temporal position of the sound source (or even sound sources). For instance, the further acoustic sound may be the acoustic sound incident on the microphone. For instance, the further acoustic sound may be in the form of the electrical signals converted by the microphone array structure. Further, for instance, the further acoustic sound may be in the form of the digital output, such as the synchronized digital output signals, processed by the signal processing system. By this measure, the apparatus may be configured to perform (and improve) sound source localization and sound source characterization.

[0087] Figures 2a and 2b exemplarily show schematic views of an implementation of a printed board circuit structure, PCB structure 200 according to embodiments of the present ms, rm inventive concept. Fig 2a illustrates a front schematic view of the implementation whereas Fig. 2b illustrates a rear schematic view of the same implementation.

[0088] In particular, Figs 2a-b depict the PCB structure 200 configured to host the microphone array structure, the signal processing system and the digital network interface, in accordance with embodiments. The PCB structure 200 comprises a plurality of printed circuit boards, PCBs, 210, 220, specifically a first PCB 210 and a second PCB 220.

[0089] For example, the first PCB 210 may be a main PCB and the second PCB may be a control PCB.

[0090] The second PCB 220 is adapted to host the signal processing system and the digital network interface, and thus, is adapted to provide network connectivity and / or power connectivity to the first PCB 210. In particular, for example, the second PCB 220 may be adapted to provide control signals, power (e.g. electrical power) and a serial audio interface to the first PCB 210.

[0091] Specifically, Fig. 2a shows a front outer surface 230 of the first PCB 210. In particular, the second PCB 220 is arranged on a rear outer surface, which is opposite to the front outer surface 230, of the PCB structure 200. In Fig. 2a, this arrangement of the second PCB 220 is shown with a dashed rectangle. This means that a region comprising the first PCB 210 and a second region comprising the second PCB 220 are at least partially overlapping in a projection perpendicular to the outer surfaces (e.g. the front outer surface 230; e.g. the rear outer surface) of the first PCB.

[0092] Further, the second PCB 220 is connected (e.g. mechanically connected; e.g. attached) to the first PCB 210 using first connection mechanisms. In particular, the the second PCB 220 is mechanically connected to the rear outer surface of the first PCB 210 using pin headers as the first connection mechanisms. Additionally, or alternatively, the first connection mechanisms may comprise any of electrical connectors, mechanical connectors and electro-mechanical connectors. Additionally or alternatively, the first connector mechanisms may be supported by means of soldering technology.

[0093] The first PCB 210 has a larger area than the second PCB 220. Feasibly, an area of the first PCB 210 may be at least 5 times, or at least 10 times, or at least 25 times, or at least 50 times, or at least 100 times larger than an area of the second PCB 220. Alternatively, the ms, rm first PCB 210 may have a smaller area than the second PCB 220. The area of the first PCB 210 may be at least 0.25 times, or at least 0.5 times, or at least 0.75 times smaller than the area of the second PCB 220. In other words, in embodiments, a ratio between the area of the first PCB 210 to the area of the second PCB 220 may comprise in a range from 0.25 to 100, possibly within a tolerance range. In embodiments, the area of the first PCB and the area of the second PCB may be equal.

[0094] It is also depicted in Figs. 2a-b that the first PCB comprises an opening 240 configured to host a camera. The camera may be any image capturing device. Additionally or alternatively, the camera may be an acoustic camera. By this measure, the camera may provide additional visual information and additional acoustic information to an apparatus. Further, the opening 240 may be arranged in a central region of the first PCB 210. For instance, as per Figs a-b, the opening 240 comprises a circular shape. Alternatively, the opening 240 may have any of a square, a rectangular, an elliptical and a polygonal shape. Additionally, or alternatively, the first PCB 210 may comprise a plurality of openings configured to host cameras.

[0095] The first PCB 210 comprises an octagonal shape. To be more specific, the first PCB 210 comprises a regular octagonal shape as illustrated in Figs. 2a and 2b. Alternatively, the first PCB 210 may comprise an irregular octagonal shape. Further, in embodiments, the first PCB and the second PCB may comprise any of a polygonal shape, a circular shape and an elliptical shape. Additionally, or alternatively, the first PCB and the second PCB may comprise solid or skeletal shapes.

[0096] Alternatively, or additionally, although not shown in Figs. 2a-b, the PCB structure 200 may be configured to comprise additional PCBs. Any of the additional PCBs may be inner conductive layers. By this measure, the PCB structure may then form a PCB stack. The inner conductive layers may be configured to host any of the microphones of the microphone array structure. That is, any of the microphones may be arranged on the inner conductive layers of the PCB structure (e.g. the PCB stack). Alternatively, or additionally, the inner conductive layers may be configured to host parts of at least one of the signal processing system and the digital network interface.

[0097] The first PCB 210 and the second PCB 220 may comprise a plurality of traces (e.g. conductive traces) for providing electrical connections. The plurality of traces may be optimized depending on acoustic metrological applications. Additionally, or alternatively, the ms, rm plurality of traces may be optimized for architectural configurations of any of the signal processing system and the digital network interface. Optimizing the traces may relate to adapting any of trace lengths, trace width, trace bends (i.e. number and angles thereof) of the traces.

[0098] Figure 2b exemplarily shows the rear outer surface 250 of the first PCB 210. It is clearly shown that second PCB 220 is arranged on the rear outer surface 250. Although it is not explicitly depicted in Fig 2a, Fig 2b explicitly depicts the plurality of microphones 260 arranged on the first PCB 210. In accordance with embodiments, the plurality of microphones 260 are arranged in a multi-armed logarithmic spiral geometry. For instance, as per Fig. 2b, the microphones 260 are arranged in an Underbrink spiral geometry, wherein the microphones 260 are arranged in nine spiral arms 270-1 , 270-2, 270-3, 270-4, 270-5, 270-6, 270-7, 270-8, 270-9. For example, the first PCB 210 may comprise 64 microphones 260. These 64 microphones may be arranged in 8 spiral arms.

[0099] It is understandable to persons skilled in the art that the microphones 260 of the microphone array structure arranged on the first PCB 210 may also comprise possibly many other suitable shapes, in accordance with already described details of such shapes earlier in the present application, in particular with respect to Fig. 1.

[0100] Further, the microphones 260 are connected (e.g. mechanically connected; e.g. attached) to the first PCB 210 using second connection mechanisms. The second connection mechanisms may comprise any of electrical connectors, mechanical connectors and electro-mechanical connectors. Additionally or alternatively, the second connector mechanisms may be supported by means of soldering technology.

[0101] A diameter of the first PCB 210 may be 45 cm, resulting in the aperture associated with the microphone array structure to be 45 cm. The diameter of the first PCB 210 may be adapted (e.g. selected) to optimize sensing of the acoustic sound by the microphone array structure.

[0102] The second PCB 220 is connected to a connection structure 280, such as a cable, as shown in Fig. 2b. The connection structure 280 may be an ethernet cable, thus providing network as well as power connectivity using the powered over Ethernet technology. For example, the connection structure 280 may be a coaxial cable or a fibre optic cable. ms, rm Although not shown in Figs. 2a-b, the first PCB 210 may comprise a plurality of mounting holes configured to connect mounting structures. The mounting holes may be arranged so as to allow mechanical support by connecting the first PCB 210 to the mounting structures. The arrangement of the mounting holes on the first PCB 210 may depend on the mounting structures. For example, an apparatus may be mechanically fixed to the mounting structure such as mounting posts through the use of the plurality of mounting holes on the first PCB 210. 1 / 4 inch threaded rods may then fit the mounting holes, allowing for the use of standard mounting equipment.

[0103] Figure 3 exemplarily shows a schematic illustration of an implementation of the second PCB 300 (e.g. a control PCB). Details of the second PCB 300 described herein with respect to Fig. 3 may be combined with details of the second PCB described with respect to Figs. 2a- b.

[0104] As exemplarily shown in Fig. 3, the second PCB 300 comprises a multi-channel module 310, a power supply module 320 and the digital network interface 330. In accordance with embodiments, the power supply module 320 is configured to use powered over Ethernet, PoE, technology. The power supply module 320 is further configured to use PoE technology for supplying power (e.g. electrical power) to an apparatus according to embodiments of the present inventive concept as well as providing (e.g. interfacing) communication with the digital network.

[0105] The digital network interface 330, denoted by a dashed rectangle, comprises a transceiver module 340 and two connectors 350-1 , 350-2. In embodiments, the transceiver module 340 is configure to transmit and receive data, for example the synchronized digital output signals formed by the multi-channel module 310, to the digital network. For example, the transceiver module 340 may be an ethernet based transceiver module. The ethernet based transceiver module may be a ethernet PHY.

[0106] In embodiments, the two connectors 350-1 , 350-2, and possibly more connectors, are configured to connect the transceiver module 340 to the digital network. For example, the two connectors 350-1 , 350-2 may be ethernet connectors, for instance RJ45 connectors. For instance, the connectors 350-1 , 350-2 may be fiber optic connectors. For instance, the connectors may be coaxial connectors. For instance, the connectors may be USB connectors. It is to be noted that listing the exemplarily connectors does not preclude or ms, rm exclude other connectors from consideration as embodiments of the present inventive concept.

[0107] Although not depicted in Fig. 3, it is feasible that in implementations, the second PCB 300 may comprise a network interface unit for providing communication of a computational system, such as a computer, to the digital network. By this measure, the synchronized digital output signals, which have been provided to the digital network using the digital network interface 330, are communicated (e.g. exchanged; e.g. shared) with the computational system. The network interface unit may arranged on the second PCB 300. Additionally or alternatively, in implementations, the network interface unit may even be comprised in the digital network interface 330. For, the network interface unit may comprise a network interface controller, NIC, i.e. a network card.

[0108] Further shown in Fig. 3, the second PCB 300 comprises a power switch 360 configured to control (e.g. activate and deactivate) the electrical power supplied to an apparatus according to embodiments of the present inventive concept. In particular, the power switch 360 may be interfaced with the power supply module 320. Additionally or alternatively, the power switch 360 may be configured to control the power (e.g. electrical power) when supplied to the apparatus using external means, such as an external power system.

[0109] Furthermore, the second PCB 300 comprises a plurality of mounting holes 370, four mounting holes 370 as shown in Fig. 3, for facilitating connection (e.g. mechanical connection; e.g. mechanical attachment) to the first PCB.

[0110] Further details about the multi-channel module 310 are presented below in the present application, in particular with respect to Fig. 4. These details may be combined with the implementation described herein with respect to Fig. 3.

[0111] Figure 4 exemplarily shows a schematic block diagram of signal flow of an apparatus 500 according to embodiments of the present inventive concept. The schematic block diagram depicts the signal flow as shared by the first PCB block 404 and the second PCB block 408, representing the respective first PCB and the respective second PCB as parts of the signal processing system of the apparatus 400. The first PCB block 404 and the second PCB block 408 have been depicted with dashed rectangles. ms, rm The first PCB block 404 comprises a plurality of microphones represented by eight blocks 410a-h, a plurality of converter units represented by eight blocks 420a-h and two clock buffers 424, 426. The arrows 432a-h denote an exemplary signal flow of the electrical signals in a digital PDM manner, i.e. the digital representation of the electrical signals, flowing out of the microphone blocks 410a-h and flowing into the respective converter units 420a-h. The second PCB block 408 comprises a multi-channel module 450, a transceiver module 460 and connectors 470.

[0112] In particular, each microphone block corresponds to eight microphones i.e. the first block 410a denotes a first subset of microphones i.e. microphones 1-8, the second block 410b denotes a second subset of microphones i.e. microphones 9-16, the third block 410c denotes a third subset of microphones i.e. microphones 17-24, the fourth block 41 Od denotes a fourth subset of microphones i.e. microphones 25-32, the fifth block 41 Oe denotes a fifth subset of microphones i.e. microphones 33-40, the sixth block 41 Of denotes a sixth subset of microphones i.e. microphones 41-48, the seventh block 410g denotes a seventh subset of microphones i.e. microphones 49-56 and the eight block 41 Oh denotes an eighth subset of microphones i.e. microphones 57-64. That is, the first PCB comprises 64 microphones arranged into eight subsets.

[0113] In accordance with embodiments, and as per the schematic signal flow block diagram of Fig. 4, the signal processing system comprises the plurality of converter units 420a-h, each of which is associated with the subset of plurality of microphones 410a-h and configured to digitize and multiplex the electrical signals of the subset of the plurality of microphones 410a-h to obtain a multiplex contribution signal; and the multi-channel module 450 forming the synchronized digital output signals out of the multiplex contribution signals of the plurality of converter units 420a-h.

[0114] For instance, the multi-channel module 450 may be any of a field-programmable gate array, FPGA, module, a micro-controller unit, MCU and a digital signal processing, DSP, unit.

[0115] Although not shown in Fig. 4, each microphone of the plurality of microphones comprises the interface for providing the digital representation of the electrical signals to the signal processing system. In particular, each microphone comprises the PDM based interface which provides digital representations of the electrical signals. For instance, the digital representations provided by the microphones 410a-h may be single-bit PDM data and may be derived by oversampling from the electrical signals. ms, rm As shown in Fig. 4, the first block 410a of the first subset of microphones is associated with a first converter unit 420a, the second block 410b of the second subset of microphones is associated with a second converter unit 420b, the third block 410c of the third subset of microphones is associated with a third converter unit 420c, the fourth block 41 Od of the fourth subset of microphones is associated with a fourth converter unit 420d, the fifth block 41 Oe of the fifth subset of microphones is associated with a fifth converter unit 420e, the sixth block 41 Of of the sixth subset of microphones is associated with a sixth converter unit 420f, the seventh block 410g of the seventh subset of microphones is associated with a seventh converter unit 420g and the eight block 41 Oh of the eight subset of microphones is associated with an eight converter unit 420h.

[0116] The converter units 420a-h are further configured to digitize the electrical signals, or to be specific, the digital representations (e.g. PDM signals) of the electrical signals. This means that the converter units allow direct binary number representations of the electrical signals for further signal processing within the signal processing system. Possibly, the converter units may be configured to convert single-bit representations of the electrical signals to multi-bit representations of the electrical signals. For instance, the the digital representations are converted into pulse code modulated, PCM; representations (e.g. PCM signals). Thus, in accordance with embodiments, the plurality of converter units 440a-h comprise PDM to PCM integrated circuits, ICs.

[0117] As shown in Fig. 4, each of the eight converter units (i.e. eight dedicated PDM to PCM ICs) 440a-h are configured to receive (e.g. accept) eight PDM representations of the electrical signals (i.e. PDM signals or PDM data) since each converter unit (i.e. PDM to PCM IC) is associated with the subset comprising eight microphones. Each of the converter units 440a- h i.e. PDM to PCM ICs is further configured to multiplex the electrical signals of the subset to obtain a multiplex contribution signal. In other words, each converter units 440a-h is further configured to convert the digital representations of the electrical signals to the multiplex contribution signal. In particular, for example, the multiplex contribution signal is a time-division multiplexed, TDM, PCM data stream, wherein the TDM PCM data stream comprises serialized PCM data of the respective eight microphones (i.e. serialized PCM data of eight audio channels of the respective eight microphones).

[0118] Once the electrical signals of the plurality of microphones 410a-h for the plurality of converter units 420a-h have been converted, i.e. digitized and subsequently multiplexed in ms, rm this instance, to obtain the multiplexed contribution signals as serialized data streams, the multiplexed contribution signals are acquired by the multi-channel module 450, for example an FPGA module. This means that the converter units 420a-h and the multi-channel module 450 are interfaced with a plurality of data lanes between them, each transporting multiple multiplexed contribution signals.

[0119] Thus, the multi-channel module 450 effectively performs functions of a data acquisition system permitting synchronous exchange of the acquired data in real time or otherwise.

[0120] As per the configuration of Fig. 4, for example, there are 8 data lanes (e.g. PCM data lanes) each transporting multiplexed contribution signals formed out of 8 electrical signals provided by 8 microphones. The bit clock frequency fscLK is determined by the product of sampling frequency with number of bits per channel and number of channels. For example, for 8 channels at a sampling frequency of 48 kHz, when the number of bits per channel is chosen to be 32 bit, the bit clock frequency is 12, 288 MHz, in accordance with the following equation. fBCLK = 12.288 MHz = 32 bit ■ 48000 Hz ■ 8 channels (1)

[0121] It is noted that in the above example, although the PCM representations of the electrical signals of the microphones may be 24 bit wide, the multiplex contribution signals may be packed into 32 bit wide units, or word slots.

[0122] The arrows 472a-h denote an exemplary signal flow of the multiplex contribution signals, for example the serialized PCM data of eight audio channels of the respective eight microphones, flowing out of the respective converter units 420a-h and flowing into the multichannel module 450. For instance, the multi channel module 450 comprises 64 channels corresponding to each of the plurality of microphones.

[0123] In accordance with embodiments, the signal processing system is further configured to provide a plurality of reference clock signals to the converter units 420a-h using a plurality of clock buffers, i.e. the clock buffers 424, 426 as shown in Fig. 4, so as to mutually synchronize the multiplex contributions signals. Arrows 486a-h, 488a-h denote an exemplary signal flow of the reference clock signals from the clock buffers 424, 426 to the converter units 420a-h. In particular, the arrows 486a-h denote the bit clock signal flow and the arrows 488a-h denote the frame clock signal flow. By this measure, the multiple ms, rm multiplex contributions signals provided by the converter units 420a-h are mutually synchronized, or in other words, mutually coordinated with each other with respect to time.

[0124] In accordance with embodiments, the reference clock signals comprise a frame clock signal, FCLK, a bit clock signal, BCLK, and a PDM clock signal, wherein the PDM clock signal is provided to each of the plurality of microphones 41 Oa-h using the respective converter units 420a-h and is derived using the bit clock signal, BCLK. The arrows 484a-h denote an exemplary signal flow of the PDM clock signals from the respective converter units 420a-h to the respective microphones 41 Oa-h.

[0125] It is shown that the multi-channel module 450 provides the FCLK signal and the BCLK signal on the second PCB block 408. Multiple copies of the reference clock signals i.e. FCLK signal and the BCLK signal are provided to the converter units 420a-h using the FCLK buffer 224 and the BCLK buffer 426. The FCLK buffer 224 is configured to provide copies of the FCLK signal to the converter units 420a-h, which is denoted by arrows flowing from the FCLK buffer 424 and into the respective converter units 420a-h in Fig. 4. The BCLK buffer 426 is configured to provide copies of the BCLK signal to the converter units 420a-h, which is denoted by arrows flowing from the BCLK buffer and into the respective converter units 420a-h in Fig. 4.

[0126] The frame clock signal FCLK, their signal flow denoted by arrow 480, and the bit clock BCLK signal, their signal flow denoted by arrow 482, permit sampling, in particular synchronous sampling, by the plurality of converter units 420a-h with use of the clock buffer, achieving a synchronous operation of the signal processing unit. In particular, the buffers 424, 426 allow an increased current to drive the clock signals.

[0127] For instance, the multi channel-module 450 may additionally comprise a combiner unit, wherein the multi channel-module 450 is configured to form the synchronized digital output signals out of the multiplex contribution signals using the combiner unit. The multi-channel module 450 may be configured, for example programmed, to adapt and process the synchronized digital output signals based on a particular acoustic metrological application. Additionally or alternatively, the synchronized digital output signals may be transformed so as to be exchangeable with the digital network.

[0128] The frame clock signal FCLK is configured to indicate samples of each audio channel on the combiner unit (e.g. a serialized TDM bus) associated with the multiplex contribution ms, rm signal. The bit clock signal is configured to indicate individual bits of the combiner unit. The PDM clock signal is provided to the subset of microphones 410a-h by the respective converter units 420a-h, wherein the PDM clock signal is derived by the bit clock signal BCLK copies of the respective converter units 420a-h, for example the PCM bit clock signal.

[0129] The multi-channel module 450 may provide other reference clock signals in addition to the FCLK signal and the BCLK signal. Thus, the multi-channel module 450 may allow synchronized and distributed clocking schemes to be interfaced with the apparatus. It is also feasible that such synchronized and distributed clocking schemes are provided via the digital network, for example any standard IP network.

[0130] In accordance with embodiments, the multi-channel module 450 may be further configured provide the control signals for the converter units 420a-h.

[0131] According to Fig. 4, the second PCB 408 also comprises the transceiver module 460 interfaced with the multi-channel module 450 and connectors 470 interfaced with the transceiver module 460. The synchronized digital output signals provided by the multichannel module 450 are exchanged by the transceiver module 460 to the digital network and the connectors 470 are configured to connect the transceiver module 460 to the digital network.

[0132] Figure 5 exemplarily shows a schematic block diagram of a system 500 for use in acoustic metrology (e.g. sound based measurements; e.g. sound pressure analyses; e.g. sound source localization; e.g. railway noise analysis; e.g. sound filtering; e.g. beamforming applications; e.g. beamforming for auralization purposes; e.g. acoustic triangulation applications; e.g. speech recognition; e.g. echo cancellation; e.g. spatial audio recording; e.g. acoustic holography ; e.g. direction-of-arrival estimation; e.g. ambisonic applications) in accordance with embodiments of the present inventive concept. The system 500 comprises a plurality of apparatuses 510, 520 in accordance with embodiments of the present inventive concept, and in accordance with embodiments and details thereof, wherein the plurality of apparatuses 510, 520 are connected to a same digital network 530.

[0133] In particular, the plurality of apparatuses comprise a first apparatus 510 and a second apparatus 520 connected to the network 530, wherein the first apparatus 510 and the second apparatus 520 are configured to exchange acoustic information, such as first synchronized digital output signals of the first apparatus and second synchronized digital ms, rm output signals of the second apparatus, with the digital network 530. This means that the first apparatus 510 and the second apparatus 520 although not directly connected with each other may exchange the acoustic information with each other through the digital network 530.

[0134] Additionally or alternatively, the plurality of apparatuses 510, 520 may be connected, e.g. directly connected, with each other. For example, the plurality of apparatuses 510, 520 may be connected to the same local area network, LAN. For example, the plurality of apparatuses 510, 520 may be connected to the same Ethernet-based network such as the Internet.

[0135] Further, the apparatuses 510, 520 may be connected so as to synchronize their respective synchronized digital output signals with each other. In embodiments, possibly, the microphone array structures of the apparatuses 510, 520 may be arranged to be connected with each other. Additionally or alternatively, the apparatuses 510, 520 may also be configured to share the same signal processing system. It is also feasible that the apparatuses 510, 520 are configured to share the same digital network interface.

[0136] By these measures, the system 500 may be configured to build distributed microphone array networks. Details described with respect to embodiments of the present inventive concept may be combined with regard to the system 500.

[0137] The signal processing systems of the system 500 may then be interfaced with implementations of acoustic triangulation and acoustic beamforming algorithms. In particular, embodiments of the system 500 wherein the implementations of combinations acoustic triangulation and acoustic beamforming algorithms may be preferable. Such embodiments may allow localizing and characterizing sound sources with unknown locations in a specific spatial region, thereby permitting surveillance and security applications, in addition to numerous acoustic metrological applications. Such embodiments of the system 500 may also be used for realizing spatial audio capturing systems with aliasing-free and high resolution properties for higher-order Ambisonic applications. Such embodiments may also be beneficial in industrial use-cases such as conference systems.

[0138] Implementation alternatives ms, rm Although some aspects have been described in the context of an apparatus, it is clear that these aspects also represent a description of the corresponding method, where a block or device corresponds to a method step or a feature of a method step. Analogously, aspects described in the context of a method step also represent a description of a corresponding block or item or feature of a corresponding apparatus. Some or all of the method steps may be executed by (or using) a hardware apparatus, like for example, a microprocessor, a programmable computer or an electronic circuit. In some embodiments, one or more of the most important method steps may be executed by such an apparatus.

[0139] Depending on certain implementation requirements, embodiments of the invention can be implemented in hardware or in software. The implementation can be performed using a digital storage medium, for example a floppy disk, a DVD, a Blu-Ray, a CD, a ROM, a PROM, an EPROM, an EEPROM or a FLASH memory, having electronically readable control signals stored thereon, which cooperate (or are capable of cooperating) with a programmable computer system such that the respective method is performed. Therefore, the digital storage medium may be computer readable.

[0140] Some embodiments according to the invention comprise a data carrier having electronically readable control signals, which are capable of cooperating with a programmable computer system, such that one of the methods described herein is performed.

[0141] Generally, embodiments of the present invention can be implemented as a computer program product with a program code, the program code being operative for performing one of the methods when the computer program product runs on a computer. The program code may for example be stored on a machine-readable carrier.

[0142] Other embodiments comprise the computer program for performing one of the methods described herein, stored on a machine-readable carrier.

[0143] In other words, an embodiment of the inventive method is, therefore, a computer program having a program code for performing one of the methods described herein, when the computer program runs on a computer.

[0144] A further embodiment of the inventive methods is, therefore, a data carrier (or a digital storage medium, or a computer-readable medium) comprising, recorded thereon, the computer program for performing one of the methods described herein. The data carrier, ms, rm the digital storage medium or the recorded medium are typically tangible and / or non- transitionary.

[0145] A further embodiment of the inventive method is, therefore, a data stream or a sequence of signals representing the computer program for performing one of the methods described herein. The data stream or the sequence of signals may, for example, be configured to be transferred via a data communication connection, for example via the Internet.

[0146] A further embodiment comprises a processing means, for example a computer, or a programmable logic device, configured to or adapted to perform one of the methods described herein.

[0147] A further embodiment comprises a computer having installed thereon the computer program for performing one of the methods described herein.

[0148] A further embodiment according to the invention comprises an apparatus or a system configured to transfer (for example, electronically or optically) a computer program for performing one of the methods described herein to a receiver. The receiver may, for example, be a computer, a mobile device, a memory device or the like. The apparatus or system may, for example, comprise a file server for transferring the computer program to the receiver.

[0149] In some embodiments, a programmable logic device (for example a field programmable gate array) may be used to perform some or all of the functionalities of the methods described herein. In some embodiments, a field programmable gate array may cooperate with a microprocessor in order to perform one of the methods described herein. Generally, the methods are preferably performed by any hardware apparatus.

[0150] The apparatus described herein may be implemented using a hardware apparatus, or using a computer, or using a combination of a hardware apparatus and a computer.

[0151] The apparatus described herein, or any components of the apparatus described herein, may be implemented at least partially in hardware and / or in software.

[0152] The methods described herein may be performed using a hardware apparatus, or using a computer, or using a combination of a hardware apparatus and a computer. ms, rm The methods described herein, or any components of the apparatus described herein, may be performed at least partially by hardware and / or by software. The above-described embodiments are merely illustrative for the principles of the present invention. It is understood that modifications and variations of the arrangements and the details described herein will be apparent to others skilled in the art. It is the intent, therefore, to be limited only by the scope of the impending patent claims and not by the specific details presented by way of description and explanation of the embodiments herein. ms, rm REFERENCES

[0153] [1] AES67-2023: AES standard for audio applications of networks - High-performance streaming audio-over-IP interoperability. Standard, Audio Engineering Society, Inc., 2023, originally published 2013.

[0154] [2] l2C-bus specification and user manual. Protocol, NXP Semiconductors, 2021, originally published 1982.

[0155] [3] Wesley Eddy. Transmission Control Protocol (TCP). RFC 9293, August 2022.

[0156] [4] J. Postel. User Datagram Protocol. RFC 768, August 1980.

[0157] [5] Henning Schulzrinne, Stephen L. Casner, Ron Frederick, and Van Jacobson. RTP: A Transport Protocol for Real-Time Applications. RFC 3550, July 2003.

[0158] [6] IEEE Standard for a Precision Clock Synchronization Protocol for Networked Measurement and Control Systems. IEEE Std 1588-2008 (Revision of IEEE Std 1588-2002), pages 1-269, 2008.

[0159] [7] Ali C. Begen, Paul Kyzivat, Colin Perkins, and Mark J. Handley. SDP: Session Description Protocol. RFC 8866, January 2021.

[0160] [8] Audinate Dante, https: / / www.getdante.com / . Last accessed 2024-05-09.

[0161] [9] Ravenna Network, https: / / www.ravenna-network.com / . Last accessed 2024-05-09.

[0162]

[0010] IEEE standard for a precision clock synchronization protocol for networked measurement and control systems. IEEE Std 1588-2019 (Revision of IEEE Std 1588-2008), pages 1-499, 2020.

[0163]

[0011] Fred Baker, Jozef Babiarz, and Kwok Ho Chan. Configuration Guidelines for DiffServ Service Classes. RFC 4594, August 2006.

[0164]

[0012] Anup Rao, Rob Lanphier, and Henning Schulzrinne. Real Time Streaming Protocol (RTSP). RFC 2326, April 1998.

[0165]

[0013] Mark J. Handley, Colin Perkins, and Edmund Whelan. Session Announcement Protocol. RFC 2974, October 2000. ms, rm

Claims

1. CLAIMS1. An apparatus (100; 510; 520) for use in acoustic metrology, comprising: a microphone array structure (110) comprising a plurality of microphones (140; 260; 410a-h) configured to convert acoustic sound into electrical signals; a signal processing system (120) configured to generate synchronized digital output signals based on the electrical signals; a digital network interface (130; 330) configured to provide the synchronized digital output signals to a digital network (150; 530) using a synchronization protocol.

2. The apparatus (100; 510; 520) of claim 1 , wherein the digital network interface (130) is configured to operate according to AES 67.

3. The apparatus (100; 510; 520) of claims 1 or 2, wherein the synchronization protocol comprises Precision Time Protocol, PTP.

4. The apparatus (100; 510; 520) of any of claims 1 to 3, wherein the digital network interface (130; 330) is configured to provide the synchronized digital output signals to the digital network (150; 530) using User Diagram Protocol, UDP as a transport protocol.

5. The apparatus (100; 510; 520) of any of claims 1 to 4, wherein the digital network interface (130; 330) is configured to provide the synchronized digital output signals to the digital network (150; 530) using Real-Time Protocol, RTP as a transport protocol.

6. The apparatus (100; 510; 520) of any of claims 1 to 5, further comprising a power supply module (320) configured to use powered over Ethernet, PoE, technology.

7. The apparatus (100; 510; 520) of any of claims 1 to 6, wherein the plurality of microphones (140; 260; 410a-h) are arranged in a multi-armed (270-1 , ... , 270-9) logarithmic spiral geometry.

8. The apparatus (100; 510; 520) of any of claims 1 to 7, wherein the plurality of microphones (140; 260; 410a-h) are configured to provide the electrical signals in a digital pulse density modulated, PDM, manner to the signal processing system (120). ms, rm9. The apparatus (100; 510; 520) of any of claims 1 to 8, wherein the signal processing system (120) comprises a plurality of converter units (420a-h), each of which is associated with a subset of plurality of microphones (140; 260; 410a-h) and configured to digitize and multiplex the electrical signals of the subset of the plurality of microphones (140; 260; 410a-h) to obtain a multiplex contribution signal, and a multi-channel module (310; 450) forming the synchronized digital output signals out of the multiplex contribution signals of the plurality of converter units (420a-h).

10. The apparatus (100; 510; 520) of claim 9, wherein the signal processing system is further configured to provide a plurality of reference clock signals to the converter units (420a-h) using a plurality of clock buffers (424, 426) so as to mutually synchronize the multiplex contribution signals.

11. The apparatus (100; 510; 520) of claim 10, wherein the reference clock signals comprise any of a frame clock, FCLK, signal, a bit clock, BCLK, signal, and a PDM clock signal, wherein the PDM clock signal is provided to each of the plurality of microphones (140; 260; 410a-h) using the respective converter units (420a-h) and is derived using the bit clock, BCLK, signal.

12. The apparatus (100; 510; 520) of any of claims 1 to 11 , wherein the signal processing system (120) is configured to provide control signals for the converter units (420a-h).

13. The apparatus (100; 510; 520) of any of claims 1 to 12, wherein the digital network interface (130; 330) comprises a transceiver module (340; 460) configured to transmit and receive data, for example the synchronized digital output signals, to the digital network (150; 530).

14. The apparatus (100; 510; 520) of claim 13, wherein the digital network interface further comprises two or more connectors (350-1 , 350-2; 470) configured to connect the transceiver module (340; 460) to the digital network (150; 530). ms, rm15. The apparatus (100; 510; 520) of any of claims 1 to 14, further comprising a printed circuit board, PCB, structure (200) configured to host at least one of the microphone array structure (110), the signal processing system (120) and the digital network interface (130; 330).

16. The apparatus (100; 510; 520) of any of claims 1 to 15, wherein the digital network interface (130; 330). is configured to provide the synchronized digital output signals to the digital network (150; 530) in a manner so that the synchronized digital output signals are provided with timing information which depends on clock information received via the synchronization protocol over the digital network (150; 530).

17. A system (500) for use in acoustic metrology, comprising one or more apparatuses (100; 510; 520) according to one of claims 1 to 16, wherein the one or more apparatuses are connected to a same digital network (150; 530).

18. A method (600) for use in acoustic metrology, comprising: converting (610) acoustic sound into electrical signals using a microphone array structure comprising a plurality of microphones; generating (620) synchronized digital output signals based on the electrical signals using a signal processing system; and providing (630) the synchronized digital output signals to a digital network using a synchronization protocol in a digital network interface. ms, rm

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