WO2010044002A2 - Système de microphone et procédé d’utilisation dudit système - Google Patents

Système de microphone et procédé d’utilisation dudit système Download PDF

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Publication number
WO2010044002A2
WO2010044002A2 PCT/IB2009/054364 IB2009054364W WO2010044002A2 WO 2010044002 A2 WO2010044002 A2 WO 2010044002A2 IB 2009054364 W IB2009054364 W IB 2009054364W WO 2010044002 A2 WO2010044002 A2 WO 2010044002A2
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WO
WIPO (PCT)
Prior art keywords
response
microphone
integrator
monopole
dipole
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Application number
PCT/IB2009/054364
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English (en)
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WO2010044002A3 (fr
Inventor
Rene Martinus Maria Derkx
Cornelis Pieter Janse
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Nxp B.V.
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Publication date
Application filed by Nxp B.V. filed Critical Nxp B.V.
Publication of WO2010044002A2 publication Critical patent/WO2010044002A2/fr
Publication of WO2010044002A3 publication Critical patent/WO2010044002A3/fr

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Classifications

    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS
    • H04R3/00—Circuits for transducers, loudspeakers or microphones

Definitions

  • the invention relates a microphone system, in particular to a steerable superdirectional microphone system. Beyond this, the invention relates to a method operating a microphone system.
  • the invention relates to a computer readable medium. Furthermore, the invention relates to a program element.
  • First-order superdirectional microphones can be constructed out of a linear combination of an omni-directional response and a dipole-response.
  • an integrator is applied to the dipole response.
  • the dipole response has a large noise-gain for the lower-frequencies.
  • a leakage factor can be applied to the integrator, but this may lead to a non-flat response for the lower- frequencies.
  • a microphone system comprising a microphone array comprising a plurality of microphone units each adapted to generate a primary signal indicative of an acoustic wave received from the respective microphone unit, a compensation unit, and a combining unit, wherein the microphone system is adapted to generate at least one dipole response and a monopole response from the primary signals, wherein the compensation unit is adapted to generate a compensated monopole signal from the monopole response, and wherein the combining unit is adapted to combine the compensated monopole signal and the at least one dipole response to an output signal.
  • the microphone array may comprise at least two microphone units, e.g. two, three, four or eight microphone units.
  • the combining unit may be an adding unit which adds the compensated monopole signal and the dipole response.
  • the adding may be a weighted adding, i.e. the compensated monopole signal and/or the dipole response may be multiplied by a weighting factor before adding.
  • the compensated monopole signal and/or the monopole response and/or the dipole response may be amplified before the respective signals are combined. Therefore, one or several amplifiers may be included into the microphone system.
  • a steerable microphone system e.g. a steerable superdirectional microphone system, where the maximum/main- lobe of the superdirectional response can be pointed in any azimuthal direction on the 2D plane.
  • the method may further comprise integrating the at least one dipole response before combining it with the compensated monopole signal.
  • a program element which, when being executed by a processor, is adapted to control or carry out a method according to an aspect of the invention.
  • a computer-readable medium in which a computer program is stored which, when being executed by a processor, is adapted to control or carry out a method according to an aspect of the invention.
  • the term "compensation unit" may particularly denote any kind of unit which is suitable for enabling compensation in any kind.
  • the term compensation unit may also include a compensation filter which is adapted to filter the monopole response in a specific way, e.g.
  • the compensated monopole signal which is an output signal of the compensation unit, may enabling a compensation for some deficiencies of the monopole response and/or of another signal or response.
  • the compensated monopole signal may include the original monopole response in an unchanged or changed form, e.g. amplified, and may further include an additional signal portion derived from or independent from the monopole response. That is, the term "compensated monopole signal" is to understand in a broad sense as any signal which is suitable to compensate for some deficiencies.
  • microphone array may particularly denote any kind of spatial arrangement of a plurality of microphone units wherein each of the plurality of microphone units generate a primary signal.
  • the minimum number of microphone units may be two, while every higher number may be suitable.
  • the microphone units may be arranged in a regular pattern on a 2D plane, e.g. uniformly on a circular array or may be arranged in an irregular pattern, e.g. non-uniformly on a circular array. In case of four microphone units the microphone units may be arranged in a rectangular or square pattern.
  • the microphone system further comprises an integrator which is adapted to integrate the at least one dipole response.
  • an integrator may be a suitable measure to increase the signal level of the dipole response. This may be advantageous in case that primary signals, which are used to generate the dipole signal, e.g. by subtracting two primary signals from each other, may be quite similar in terms of phase-differences, e.g. in case the microphone units are arranged close together, so that the primary signals have potentially a very small phase difference.
  • the integrator is a leaky integrator exhibiting a leakage value.
  • the leakage value may be an input value for the integrator.
  • a weighting factor may be used as an input value for the integrator which weighting factor corresponds to the weight of the monopole response in the combination. That is, a parameter that is used for controlling the integrator may be an integrator leakage parameter while an alternative or additional parameter may be a weighting factor.
  • the compensation unit is adapted to generate the compensated monopole signal in such a way that at low frequencies a flat output signal is achievable for the angle where the superdirectional response has its maximum/main-lobe.
  • the compensation unit may be defined in such a way that for lower frequencies, e.g. between 10 Hz and 1000 Hz or between 100 Hz and 1000 Hz, a unit- response is obtained.
  • the microphone array is a small microphone array.
  • small may particular denote the case in which the distance between adjacent microphone units is smaller than the typical wavelengths of the acoustic waves or sound waves which are measured by the microphone units.
  • the compensation unit is a compensation filter.
  • the compensation filter is a recursive filter.
  • the recursive filter may be formed by:
  • a leakage value of an integrator and/or a weighting factor is used as input values for the compensation filter.
  • the microphone system further comprises an integrator which is adapted to integrate the at least one dipole signal, wherein the compensation filter is a linear combination of at least two compensation filters,
  • the two compensation filters may be a so called Turin integrator and a so called Simpson integrator and/or the integrator may be a so called Al-Alaoui integrator.
  • a gist of an aspect of the invention may be seen in the provision of a microphone system that may exhibit an improved performance in particular in the lower- frequencies range.
  • the microphone system may comprise a small microphone array including at least two microphone units, but preferably more than two microphone units to enable an azimuth steerable microphone system, each generating a primary signal. From the primary signals a monopole response and at least one dipole response may be generated. The dipole response or the dipole responses, e.g.
  • a microphone system may be applied in car-radio chips of Car Entertainment Systems, for example and may be also beneficial for MEMS microphone technology.
  • Fig. 1 schematically illustrates the geometry of a four microphone array.
  • Fig. 2 schematically illustrates a comparison of different discrete-integrators.
  • Fig. 4 schematically illustrates a comparison of different discrete-integrators with leakage factor of 0.95.
  • Fig. 5 schematically illustrates target response for combined monopole/dipole for a leakage factor of 0.95 and a weighting factor of 0.5.
  • Fig. 6 schematically illustrates target response for combined monopole/dipole with compensation filter for a leakage factor of 0.95 and a weighting factor of 0.5.
  • Fig. 7 schematically illustrates a microphone system according to an embodiment.
  • FIG. 1 schematically illustrates the geometry of a four microphone array 100.
  • a (steerable) first-order superdirectional microphone can be implemented via a combined monopole and dipole.
  • four omnidirectional microphone units or microphones in a planar configuration may be used, which are depicted in Fig. 1 as 101, 102, 103 and 104.
  • the spacing between two diagonal microphones e.g. distance between microphone 102 and microphone 104
  • the spacing between two diagonal microphones is exactly V2 times the spacing between two non-diagonal microphones (e.g. distance between microphone 101 and 102).
  • the normalized superdirectional microphone-response (with a maximum response/main- lobe on ⁇ radians) maybe formulated as:
  • E 1 the signal picked up by each of the microphone units M 1 , i.e. a primary signal, S the sensitivity of each of the microphones and ⁇ given by:
  • the normalized monopole-response E m ( ⁇ ) may be computed as: fet
  • the overline indicates a normalized response with a maximum response S (equal to the response of a single sensor or microphone unit).
  • the integrator is required to remove the j ⁇ -dependency in the dipole response.
  • the method described above may be the simplest way to construct a steerable first-order microphone (via parameter ⁇ ) with a variable characteristic (via parameter Of 1 ).
  • methods like delay-and-subtract, Linear Constrained Minimum Variance (LCMV) and Generalized Sidelobe Canceller (GSC) may also be modified to obtain steerable capabilities, they may require (FIR) filters that need to be recomputed for different values of ⁇ and Of 1 , which is computationally unattractive.
  • N y ⁇ n ⁇ I)T]
  • N the order of the integrator
  • T f s l with f s the sampling frequency
  • r e ⁇ 0, 1 ⁇ and bk satisfies the symmetry condition:
  • ⁇ 2 ⁇ f I f s lies in the fundamental interval - ⁇ ⁇ ⁇ ⁇ ⁇ .
  • the N'th order optimal discrete integrator coefficients may be chosen in such a way that the integrator response is as close as possible to the ideal (discrete-time) response: ⁇
  • Turin integrator This response Ii is called the Turin (or trapezoid) integrator. It can be seen that for small values of ⁇ , the Turin integrator approximates the ideal integrator. In contrast to the Euler integrator, the phase-shift of this first-order is exactly - ⁇ /2, just as for the ideal integrator.
  • This response I2 is called the Simpson integrator.
  • the phase-shift is exactly - ⁇ /2.
  • the ideal integrator response lies in between responses of the Turin and the Simpson integrator. Therefore, it may be suitable to construct a combined Turin and Simpson integrator that weights the outputs of each individual integrator:
  • IA A( ⁇ ) & • h + 0 « s)- h > OS) where a is the weighting factor.
  • line 302 indicates the result for the Turin integrator
  • line 303 indicates the result for the Simpson integrator
  • line 304 indicates the result for the ideal integrator or ideal response.
  • the response of the Euler integrator poorly matches the ideal response, while this match is improved for the Simpson integrator.
  • the magnitude response well approximates the ideal integrator, the phase response is not perfect, which results in a bad response in Fig. 3.
  • the Simpson integrator rises quickly for frequencies close to the Nyquist frequency. This yields a dominant dipole response (with a large gain-factor) for the Simpson integrator at these frequencies.
  • a leakage-term can be added to discrete time integrators. Such a leakage factor may alleviate the noise-gain problem that occurs for very low frequencies when compensating for the j ⁇ dependency in the dipoles. Without a leakage-factor, the (white) sensor-noise would be amplified enormously which is undesired. Furthermore, adding a leakage term to the integrator may help in improving the numerical-stability for higher order-integrators.
  • FIG. 4 This response of the integrators with leakage term is shown in Fig. 4.
  • a leakage factor ⁇ of 0.95 is used and again f s is set to 48000 Hz.
  • line 402 shows the response for the Turin integrator
  • line 403 shows the response for the Simpson integrator
  • line 404 shows the response for the ideal integrator
  • the curves for the leaky-integrators nicely coincide for the low- frequencies, while for the high-frequencies the Al-Alaoui integrator lies in between the Turin and the Simpson integrator.
  • Fig. 5 schematically illustrates target response for combined monopole/dipole for a leakage factor of 0.95 and a weighting factor of 0.5.
  • Applying the basic principle of a combined monopole/dipole with an integrator with a leakage term may lead to a non-flat target response for a ⁇ ⁇ ⁇ , since for the lower frequencies the monopole is dominant, but is always weighted with ⁇ i.
  • a compensation filter is applied to the monopole to compensate for imperfect target response for lower frequencies.
  • the compensation filter maybe applied as follows:
  • C N ((X I ,Y) is a compensation filter for the monopole component that is defined in such a way that for lower- frequencies, a unit-response is obtained.
  • the compensation filter is a recursive filter, defined as:
  • the compensation filter is constructed out of a linear combination of the compensation filter for the Turin and the Simpson integrator as:
  • the compensation filter nicely flattens the low-frequency response for all the integrator types.
  • line 602 relates to a response of a Turin integrator
  • line 603 relates to the response of a Simpson integrator
  • line 605 relates to the response of an Al-Alaoui integrator.
  • Fig. 7 schematically illustrates a microphone system 700 according to an embodiment.
  • Fig. 7 shows a microphone array 701 comprising four microphone units or elements 702, 703, 704, and 705 which are arranged in a square pattern.
  • Each of the microphone units generates a primary signal which can be used to generate dipole and monopole responses.
  • the primary signals are connected to an adder schematically depicted as box 706 in Fig. 7.
  • An output signal of the adder 706 is amplified by amplifier 707 to generate the monopole response E n .
  • the amplifier may have an amplification factor of 1/4.
  • the monopole response E m is then connected to a compensation unit which may be formed by a compensation filter 708 having as steering inputs the weighting factor ⁇ i and the leakage factor ⁇ , which is indicated by the arrows 709 and 710, to generate a compensated monopole signal which may be amplified by an amplifier 711 and which forms one input of a first combination unit 712, e.g. an adder. Furthermore, the primary signals are connected to two adding or subtracting units 713 and 714 to generate two dipole responses.
  • a compensation filter 708 having as steering inputs the weighting factor ⁇ i and the leakage factor ⁇ , which is indicated by the arrows 709 and 710, to generate a compensated monopole signal which may be amplified by an amplifier 711 and which forms one input of a first combination unit 712, e.g. an adder.
  • the primary signals are connected to two adding or subtracting units 713 and 714 to generate two dipole responses.
  • the primary signal of the first microphone unit 702 and of the third microphone unit 704 is connected to the first subtracting unit 713 in which the primary signal of the first microphone unit is subtracted from the primary signal of the third microphone unit to generate a first dipole response indicated by arrow 715.
  • the primary signal of the second microphone unit 703 and of the fourth microphone unit 705 is connected to the second subtracting unit 714 in which the primary signal of the fourth microphone unit is subtracted from the primary signal of the second microphone unit to generate a second dipole response indicated by arrow 716.
  • the first dipole response 715 is inputted into a first integrator, e.g.
  • a Turin, a Simpson or an Al- Alaoui integrator 717 which has as steering inputs the leakage factor ⁇ as well, and optionally in case of the Al-Alaoui integrator the weighting factor a, to generate a first dipole response E d ⁇ - ⁇ 14) which may then be amplified by another amplifier 718, having an amplification
  • the second dipole response 716 is inputted into a second integrator, e.g. a Turin, a Simpson or an Al-Alaoui integrator 720 which has as steering inputs the leakage factor ⁇ as well, and optionally in case of the Al-Alaoui integrator the weighting factor a, to generate a second dipole response Ed ( ⁇ 14) which may then be amplified by another amplifier
  • a second integrator e.g. a Turin, a Simpson or an Al-Alaoui integrator 720 which has as steering inputs the leakage factor ⁇ as well, and optionally in case of the Al-Alaoui integrator the weighting factor a, to generate a second dipole response Ed ( ⁇ 14) which may then be amplified by another amplifier
  • the second combining unit 719 then combines the two inputs, e.g. adds the same, to generate a total dipole response 722 which may be amplified by another amplifier 723 having as an amplification factor 1- ⁇ i.
  • An output of the amplifier 723 then forms a second input to the first combining unit 712 which then outputs the output signal
  • Es which forms the output of the azimuth steerable superdirectional microphone system 100.
  • more than four microphone units may be used and possibly three dipoles may be generated by using microphones in a 3D geometry, like in a tetrahedron configuration.
  • Fig. 7 schematically shows a complete microphone system with the compensation filter C on the monopole response.
  • the angle ⁇ where a maximum-response of the superdirectional microphone is jl j i obtained, can be varied by recomputing the weights sin( ⁇ H — ) and cos( ⁇ H — ) .
  • the compensation filter C may require the parameter ⁇ i, indicative for the first-order characteristic, and constructible via a weighted combination of the monopole response and the dipole response and the integrator leakage parameter ⁇ , while the block with the integrator I and the compensation- factor T may only require the integrator leakage parameter ⁇ (and also the parameter a, if the Al-Alaoui integrator is used).

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  • Physics & Mathematics (AREA)
  • Engineering & Computer Science (AREA)
  • Acoustics & Sound (AREA)
  • Signal Processing (AREA)
  • Circuit For Audible Band Transducer (AREA)
  • Measurement Of Velocity Or Position Using Acoustic Or Ultrasonic Waves (AREA)

Abstract

L’invention concerne un système de microphone comportant un ensemble de microphones comprenant une pluralité d’unités microphones, chacune des unités étant conçue pour générer un signal primaire indiquant la réception d’une onde acoustique émanant de l’unité microphone concernée, une unité de compensation, et une unité de combinaison. Le système de microphone est conçu pour générer au moins une réponse dipôle et une réponse monopôle à partir des signaux primaires. L’unité de compensation est conçue pour générer un signal monopôle compensé à partir de la réponse monopôle. L’unité de combinaison est conçue pour combiner le signal monopôle compensé et la ou les réponses dipôles en un signal de sortie.
PCT/IB2009/054364 2008-10-16 2009-10-06 Système de microphone et procédé d’utilisation dudit système WO2010044002A2 (fr)

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EP08105589.9 2008-10-16
EP08105589 2008-10-16

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WO2010044002A2 true WO2010044002A2 (fr) 2010-04-22
WO2010044002A3 WO2010044002A3 (fr) 2010-07-08

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Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US8855326B2 (en) 2008-10-16 2014-10-07 Nxp, B.V. Microphone system and method of operating the same

Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE19948907A1 (de) * 1999-10-11 2001-02-01 Siemens Audiologische Technik Verfahren zur Signalverarbeitung in einer Hörhilfe sowie Hörhilfe
EP1278395A2 (fr) * 2001-07-18 2003-01-22 Agere Systems Inc. Réseau de microphones adaptatifs différentiels du second ordre
WO2005048648A2 (fr) * 2003-11-12 2005-05-26 Oticon A/S Systeme de microphone
WO2007106399A2 (fr) * 2006-03-10 2007-09-20 Mh Acoustics, Llc Reseau de microphones directionnels reducteur de bruit

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE19948907A1 (de) * 1999-10-11 2001-02-01 Siemens Audiologische Technik Verfahren zur Signalverarbeitung in einer Hörhilfe sowie Hörhilfe
EP1278395A2 (fr) * 2001-07-18 2003-01-22 Agere Systems Inc. Réseau de microphones adaptatifs différentiels du second ordre
WO2005048648A2 (fr) * 2003-11-12 2005-05-26 Oticon A/S Systeme de microphone
WO2007106399A2 (fr) * 2006-03-10 2007-09-20 Mh Acoustics, Llc Reseau de microphones directionnels reducteur de bruit

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
BUCK M: "ASPECTS OF FIRST-ORDER DIFFERENTIAL MICROPHONE ARRAYS IN THE PRESENCE OF SENSOR IMPERFECTIONS" EUROPEAN TRANSACTIONS ON TELECOMMUNICATIONS, WILEY & SONS, CHICHESTER, GB, vol. 13, no. 2, 1 March 2002 (2002-03-01), pages 115-122, XP001123749 ISSN: 1124-318X *

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US8855326B2 (en) 2008-10-16 2014-10-07 Nxp, B.V. Microphone system and method of operating the same

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