WO2009077152A1 - Capteur de signaux à caractéristique de directivité variable - Google Patents

Capteur de signaux à caractéristique de directivité variable Download PDF

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Publication number
WO2009077152A1
WO2009077152A1 PCT/EP2008/010658 EP2008010658W WO2009077152A1 WO 2009077152 A1 WO2009077152 A1 WO 2009077152A1 EP 2008010658 W EP2008010658 W EP 2008010658W WO 2009077152 A1 WO2009077152 A1 WO 2009077152A1
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Prior art keywords
signal
directivity characteristic
signals
substitution
dipole
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PCT/EP2008/010658
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English (en)
Inventor
Fabian KÜCH
Markus Kallinger
Richard Schultz-Amling
Jukka Ahonen
Ville Pulkki
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Fraunhofer-Gesellschaft Zur Förderung Der Angewandten Forschung_E.V.
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Publication of WO2009077152A1 publication Critical patent/WO2009077152A1/fr

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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS
    • H04R1/00—Details of transducers, loudspeakers or microphones
    • H04R1/20—Arrangements for obtaining desired frequency or directional characteristics
    • H04R1/32—Arrangements for obtaining desired frequency or directional characteristics for obtaining desired directional characteristic only
    • H04R1/326—Arrangements for obtaining desired frequency or directional characteristics for obtaining desired directional characteristic only for microphones
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS
    • H04R1/00—Details of transducers, loudspeakers or microphones
    • H04R1/20—Arrangements for obtaining desired frequency or directional characteristics
    • H04R1/32—Arrangements for obtaining desired frequency or directional characteristics for obtaining desired directional characteristic only
    • H04R1/40—Arrangements for obtaining desired frequency or directional characteristics for obtaining desired directional characteristic only by combining a number of identical transducers
    • H04R1/406—Arrangements for obtaining desired frequency or directional characteristics for obtaining desired directional characteristic only by combining a number of identical transducers microphones

Definitions

  • the present invention relates to the pickup of signals, such as audio signals, and in particular to how a substitution signal may be derived from signals recorded using a known directivity pattern, or directivity characteristic, which substitution signal has a directivity- characteristic which deviates from the former, so as to be able to describe a spatial characteristic of a signal filling up the space.
  • a listener In multi-channel audio reproduction systems, a listener is surrounded by a plurality of loudspeakers.
  • the simplest multi-channel reproduction system is a stereo setup comprising two loudspeakers. Without any additional artificial influences exerted on the sound to be reproduced, a stereo system can reproduce only such sound sources with accurate locatability which are positioned on the line connecting the two loudspeakers of the stereo setup. Sound, or a signal, coming from other spatial directions cannot be reproduced correctly if it concerns spatial orientation. If several loudspeakers are used which are arranged around the listener, several spatial directions may be reproduced correctly, which may result in a more natural spatial sound impression for the listener.
  • this may be accomplished in that the signals picked up are mixed, as early as after or during the pickup, such that, for each of the five reproduction loudspeakers of the ITU system, an audio channel is created which in the reproduction is associated with the respective loudspeaker.
  • the goal is to record the signal picked up by means of DirAC such that it can be reproduced as accurately as possible by means of any multi-channel loudspeaker system, the intention being for the spatial sound impression of the location where the pickup was performed to be reproduced as accurately as possible.
  • the audio signal is recorded using an omnidirectional microphone (W) and a set of microphones which enable determining both an intensity vector of the sound field and the diffuseness of same.
  • W omnidirectional microphone
  • the intensity vector designates the direction from which the sound picked up contributes, with maximum energy, to the signal picked up.
  • the diffuseness describes, in the form of a parameter, the uniformity of the spatial sound impression. If the sound is perceived with identical intensity from all directions, a case of maximum diffuseness has been achieved. However, minimum diffuseness is present when the sound is perceived or recorded only from one single acoustic source from a precisely defined direction. Following the DirAC analysis, the intensity vector also points to this direction.
  • One possibility of recording a signal in this manner consists in using three microphones (X, Y, Z) having dumbbell- shaped directivity characteristics and being aligned such that their maximum directivities run parallel to the axes of a Cartesian coordinate system (see, for example: Craven G. and Gerzon M. "Coincident microphone simulation covering three dimensional space and yielding various directional outputs". United States Patent 4042779).
  • dumbbell-shaped directivity characteristic such a microphone is also frequently referred to as a dipole (see, for example: G. W. Elko: "Superdirectional microphone arrays" in S. G. Gay, J.
  • the signals W, X, Y and Z may also be determined using a plurality of omnidirectional microphones arranged at different locations within the 3-dimensional space, for example at the corners of an octahedron.
  • a virtual microphone having a directivity characteristic whose maximum points to the direction of the connecting line between the two omnidirectional microphones may be formed, from two spatially separated omnidirectional microphones, in that the signals of the two microphones are subtracted from one another.
  • there are a multitude of applications wherein it is not possible to arrange the microphones in three dimensions within the space.
  • the microphones may only be possible to arrange the microphones in a predetermined orientation on the surface of a plane.
  • the DirAC algorithm may continue to be successfully employed, for example, for recording a spatial audio signal.
  • An example of the sound pickup may be a table microphone arrangement which is normally relatively flat. Put more generally, this may be equated with a case wherein the arrangement of microphones is limited to one plane. If omnidirectional microphones are used, in such an arrangement only microphone signals with directivity characteristics in x and y directions may be generated within the plane by measurement.
  • a further microphone may be arranged, for example, at the center of a rectangular arrangement of omnidirectional signals so as to record an omnidirectional signal W.
  • a speaker for example, who is seated in front of the display in a perpendicular direction or is positioned in front of the plane, or to be able to suitably amplify the signal of the speaker, it is necessary to generate a signal which has a directivity in the z direction, i.e. whose maximum signal energy comes from the z direction.
  • a signal which has a directivity in the z direction, i.e. whose maximum signal energy comes from the z direction.
  • only the signals of the remaining four or five microphones can be used. The subtraction of two microphone signals in a manner analogous with generating the x or y-directional virtual microphone signals is out of the question, since all of the microphones used do not differ from one another with regard to their Z coordinates.
  • a signal with a directivity characteristic which has a maximum in the z direction may be generated by means of known "beam-forming" techniques while using a planar microphone array or a microphone matrix arranged within a plane. Beam-forming is also used with WLAN antennas, inter alia. In this context use is made, for example, of so- called “filter-and-sum beam-formers” (see, for example: G. W. Elko: “Superdirectional microphone arrays” in S. G. Gay, J. Benesty (eds.): “Acoustic Signal Processing for Telecommunication", Chapter 10, Kluwer Academic Press, 2000, ISBN: 978-0792378143; and J. Bitzer, K. U. Simmer: "Superdirective microphone array” in M. Brandstein, D.
  • WLAN frequencies of, e.g., 5.15 GHz to 5.725 GHz this problem does not arise since due to the comparatively small bandwidths of the individual channels (for WLAN 802.11a for example » 0.03 GHz) with a constant phase shift, constructive interference may be achieved for all of the frequencies to be detected.
  • broadband RF signals or audio signals are picked up, application of a constant phase shift with a summation of the signals is no longer practicable.
  • the wavelengths will change from about 15 m to 1.5 cm, so that with common geometrical dimensions (for example with a distance of several cm from neighboring microphones) one can no longer speak of a constant phase shift between the individual microphones for all of the frequencies to be detected.
  • a typical setup could consist of three microphones wherein use is made of two spaced-apart omnidirectional microphones in order to measure the X signal (dipole directivity characteristic) , and of an additional omnidirectional microphone arranged at the center of the two X microphones in order to measure the omnidirectional signal W.
  • a signal having a directivity characteristic in the Y direction In the event of a subsequent DirAC analysis, this signal must additionally have the required dipole directivity characteristic.
  • a signal having a directivity characteristic in the Y direction may be generated by means of conventional beam-forming techniques. However, such a directivity characteristic having a dipole shape cannot be achieved by means of the three microphones discussed above.
  • the amplitude square of a signal generated by means of a beam-forming microphone array is subtracted from the amplitude square of another output signal of a beam-forming microphone array.
  • the directivity of the microphone array may be constantly adjusted, so that the direction of minimum sensitivity of the array corresponds to the direction of the active sound sources.
  • US application 2006/0 115 103 Al addresses interference suppression, or beam forming, of signals recorded with two microphones. Their amplitude values directly added and possibly additionally scaled or provided with an additional phase shift.
  • US application 2006/0171547 addresses the DirAC representation of spatial signals and thus describes a possibility of transmitting the directions of origin of signal components in a reproducible manner without requiring a large transmission bandwidth.
  • a signal having a predetermined spatial directivity characteristic is generated from a first signal having a known spatial directivity characteristic and from a second signal having a known spatial directivity characteristic in that the first and second signals are initially converted from a temporal to a spectral representation.
  • the spectral representations of the first and second signals are combined, in accordance with a combination rule which depends on the known directivity characteristics of the first and second signals, such that a spectral representation of a signal having the predetermined spatial directivity characteristic is obtained which differs both from the directivity characteristic of the first signal and from that of the second signal.
  • the directivity characteristic is identical for all of the spectral ranges of the signal generated.
  • the amplitude magnitudes of the spectral representations of the input signals are formed before these are combined so as to generate amplitude values for the substitution signal generated.
  • the spectral representation of the signal obtained by the combination may thus have a directivity characteristic which differs from the directivity characteristics of the first and second signals picked up, in particular a directivity characteristic whose maximum gain factor points to a spatial direction which differs from the spatial direction of the maximum sensitivity of the signals having known directivity characteristics.
  • a directivity characteristic which differs from the directivity characteristics of the first and second signals picked up
  • a directivity characteristic whose maximum gain factor points to a spatial direction which differs from the spatial direction of the maximum sensitivity of the signals having known directivity characteristics.
  • the spectral representation of the signal generated is output, or made available for further processing, directly by a signal processor. In further embodiments of the invention, the spectral representation of the signal generated is converted back to the temporal representation so as to obtain a temporal representation of the signal having the predetermined directivity characteristic.
  • audio signals or an audio pickup of pieces of music or of ambient noises or speakers, which are obtained using a 2-dimensional or 1- dimensional microphone array, are processed. Consequently, information on the localization or the position of the audio sources in a direction which is orthogonal with regard to the arrangement of the microphones is also obtained.
  • radio-frequency signals of large bandwidths, or any other signals are processed such that a signal is generated whose maximum contribution to the signal amplitude comes from a predetermined spatial direction, i.e., in other words, which has a predetermined spatial directivity characteristic.
  • a signal having a directivity characteristic is to mean a signal having directionally weighted signal portions, so that there is/are one or several spatial directions from which signal portions having maximum gains or maximum amplitudes are recorded or reconstructed, whereas there are other spatial directions in which the signal portions are attenuated or completely suppressed.
  • a short-time frequency transformation wherein the signals to be transformed or converted are processed block by block, is employed for the conversion to the spectral representation.
  • a filter bank or a frequency transformation may be used wherein each signal component which has a predetermined length and may consist of, e.g., a sequence of a predefined number of signal samples, has a plurality of amplitude and phase values associated with it, as is the case, for example, with short-time Fourier transformation (SFT) .
  • SFT short-time Fourier transformation
  • a continuous signal in a time representation is transformed to a sequence of amplitude and phase factors, or is represented as a sequence of these factors, each signal component, i.e.
  • each independently processed time interval having a plurality of amplitude values P(k, n) associated with it (the index k indicates the analyzed frequency band) .
  • the spectral representations of the transformed signals only the magnitudes of the amplitudes are combined to obtain the signal having a predetermined directivity characteristic.
  • the resulting directivity characteristic may be identical for all of the frequencies of the frequency band to be recorded. This may be the case even when the location where the signals having known directivity characteristics were recorded are not known exactly.
  • the maximum of the sensitivity may thus be obtained for all of the frequencies in the same spatial direction in a simple manner requiring little mathematical effort.
  • the signal thus obtained which has a predetermined spatial directivity characteristic may immediately continue to be used in its spectral representation in order to estimate the spatial direction within the observed frequency band from which the maximum sound energy or signal energy is coming.
  • the spectral representation of the generated signal having the predetermined directivity characteristic is used for directly obtaining, by means of a DirAC analyzer or a DirAC algorithm, the DirAC parametrization in two dimensions or three dimensions.
  • the signal generated substitutes for, or replaces, a signal which is not accessible to direct measurement.
  • the signal generated by means of the signal processor may also be referred to as a substitution signal. Therefore, the terms "substitution signal" and signal having a predetermined directivity characteristic shall be used synonymously below.
  • the intensity vector indicates the energy flux density.
  • the intensity vector has three orthogonal components (e.g. x, y, z), which together reveal the direction of the energy flux.
  • the components of the intensity vector are the same or almost zero in all three spatial directions, one can assume that the signal, or the sound, evenly fills the measuring space, since small or near-zero components of the intensity vector are present from all of the spatial directions within the frequency interval examined.
  • the spectral representation of the generated signal having a predetermined directivity characteristic is converted to a temporal representation, so that a signal is obtained, approximately, as would have been recorded by a virtual microphone having a predetermined directivity characteristic.
  • the phase factors of the conversion to the frequency range of any of the (input) signals having predetermined directivity characteristics may be used so as to obtain as realistic a phase relation as possible between the individual frequency ranges. This may result in that although only the amplitudes were taken into account in the implementation of the directional dependence, a signal is generated whose audible artefacts are hardly perceivable due to the phase information some which has not been taken into account.
  • Fig. 1 shows an embodiment of a signal processor
  • Fig. 2 shows an embodiment of a signal combiner of the signal processor
  • Fig. 3 shows an example of an arrangement of microphones for recording signals for signal processors
  • Fig. 4 shows an example of directivity characteristics of recorded signals
  • Fig. 5 shows an example of a predetermined directivity characteristic of a generated signal
  • Fig. 6A and Fig. 6B show embodiments of an apparatus for generating a signal having a predetermined directivity characteristic
  • Fig. 7 shows an embodiment of deriving a DirAC parametrization
  • Fig. 8 shows an embodiment of a method of generating a signal having a predetermined directivity characteristic.
  • Fig. 1 shows an embodiment of a signal processor 2 comprising a signal converter 4 and a signal combiner 6.
  • the signal processor 2 shown in Fig. 1 serves to generate a signal having a predetermined spatial directivity characteristic (a substitution signal) while using a first signal 8a having a known spatial directivity characteristic, and a second signal 8b having a known spatial directivity characteristic.
  • the signals 8a (Pi) and 8b (P2) may be picked by a microphone or be received by an antenna, for example, and are present in temporal representations.
  • further embodiments of the invention may use more than two signals as input signals, in particular the number of the signals used as input signals in principle having no upper limit.
  • the signal combiner 6 combines the spectral representations of the first signal 8a and of the second signal 8b in accordance with a combination rule so as to generate the signal 10 having a predetermined spatial directivity characteristic.
  • the generated signal 10 may have a directivity characteristic which differs from the directivity characteristics of the signals 8a and 8b.
  • the combination rule used by the signal combiner 6 for generating the signal 10 having a predetermined directivity characteristic exclusively depends on the known directivity characteristics of the first and second signals 8a and 8b.
  • the directivity characteristic be known for each input signal, so as to generate a signal whose directivity characteristic corresponds to the predetermined, or desired, directivity characteristic.
  • the signal processor 2 shown in Fig. 1 thus generates the signal 10, which has a predetermined spatial directivity characteristic, in a spectral representation of same.
  • inventive signal processors are L > 2 signals having known directivity characteristics. These signals may either be (omnidirectional or directional) microphone signals measured directly using the known directivity characteristic, or they may be signals which are tapped by a directivity-pattern output of a microphone array. The manner in which the directivity characteristic was generated is inessential as long as said directivity characteristic is known.
  • Each of the input signals is subdivided into a sequence of discrete time intervals, or signal components (signal blocks) .
  • the signal blocks are converted to a spectral representation, for example to the short-time frequency domain.
  • P ⁇ (k,n) shall designate the 1 th input signal within the -frequency band.
  • the index n designates the quantity, or the number, of the signal block being contemplated of the series of signal blocks into which the input signal was decomposed.
  • the signal may be represented, within each frequency band of interest, as an amplitude, or magnitude,
  • the signal combiner of the signal processor combines the magnitudes
  • This corresponds to a microphone signal having the predetermined spatial directivity characteristic. It is possible, in particular, to keep the directivity characteristic constant or similar within a broad spatial area and a large frequency range.
  • the combination of the magnitudes may be described by the following formula:
  • D(k,n) describes the signal generated (the substitution signal).
  • the function g(.) describes the combination rule in accordance with which the magnitudes of the input signals are combined and which may fundamentally be formed, or composed, of any linear and non-linear functions .
  • one of the phases of the input signals is used as the phase information of the generated signal D(k,n).
  • the combination rule may be defined as follows :
  • a signal combiner 6, which converts the above-described concept, is schematically depicted in Fig. 2.
  • the input signals 8a, 8b and 8c are already- present in their spectral representations.
  • the phase information may be extracted from the first input signal 8a, it being possible, in further embodiments, to use the phase information of any other input signals. Further embodiments may fully dispense with the phase information.
  • the phase information 12 is extracted from the first input signal 8a, the magnitude 14b of the first input signal 8a being formed by a magnitude former 14a. Equivalently, the magnitude values 16b and 18b of the input signals 8b and 8c are formed by the magnitude formers 16a and 18a, respectively.
  • An optional multiplier 24 serves to form the signal D(k,n) by multiplying the magnitude value
  • a signal having a predetermined spatial directivity characteristic may be generated which, in particular, has a directivity characteristic different from those of the input signals.
  • the signal combiner 6 outlined in Fig. 2 thus generates a signal having a predetermined spatial directivity characteristic in a spectral representation.
  • This signal may directly be used further so as to derive, in connection with the input signals 8a to 8c, parameters which describe the fundamental properties of the signal received, or of the audio signal, in the pickup environment. These parameters may be the DirAC parameters, for example, i.e. the direction of the instantaneous intensity per frequency range, and the diffuseness of the signal in each of the frequency ranges contemplated.
  • the generated signal which has a predetermined directivity characteristic and is present in the spectral representation may also be transformed back to a temporal representation.
  • Embodiments of signal combiners only require the knowledge of the directivity characteristics of the microphones, or microphone arrays, used for recording the input signals, and do not a priori make assumptions about the statistics of the input signals, or about the statistics of their spectral compositions. As a result, it becomes possible, in an efficient manner which is based on simple algorithms, to generate a signal having a predetermined spatial directivity characteristic using input signals having known directivity characteristics.
  • Fig. 3 schematically shows a potential microphone setup by means of which the signals W having omnidirectional directivity characteristics, X having dipole-shaped directivity characteristics in the X direction, and Y having dipole-shaped directivity characteristics in the Y direction may be received.
  • Fig. 3 shows a scenario in which five microphones 30a - 3Oe are arranged within a plane. In this context it is assumed that it is impossible, due to geometric boundary conditions, to arrange further microphones outside the plane shown in the top view in Fig. 3.
  • signals having directivity characteristics in the X direction and in the Y direction may be generated by combinations of the signals picked up by the microphones 30a - 30d.
  • the central microphone 3Oe having omnidirectional directivity may be used, for example, for recording an omnidirectional signal W and making it available as an input signal having an omnidirectional directivity characteristic.
  • Fig. 3 is only one of any number of potential examples which enable recording signals having directivity characteristics in the X direction, in the Y direction, and having no specific directivity characteristics, i.e. recording omnidirectional signals W.
  • a signal is generated which has a predetermined spatial directivity characteristic, and on the basis of which, e.g., a DirAC parametrization of the spatial audio signal may be performed, one assumes that an omnidirectional signal W, a signal having a dipole-type directivity characteristic X in the X direction, and a signal Y having a directivity characteristic in the Y direction, as may be obtained, for example, by means of the 2-dimensional microphone array shown in Fig. 3, are available as the input signal.
  • the direction of maximum sensitivity of the signal X(k,n) is the X direction
  • the signal Y(k,n) it is the Y direction, of a Cartesian coordinate system.
  • the signals W, X and Y are to be present in a spectral representation already, i.e. for each frequency range and time block, or signal component, of the signals an amplitude parameter and a phase parameter exist, as was described in the previous paragraphs.
  • Fig. 4 illustrates the directivity characteristic of a signal formed from the amplitudes X(k,n) and Y(k,n) of the input signals X and Y in accordance with the following combination rule:
  • Fig 4 shows a 3-dimensional representation of the directivity characteristic of the signal formed in accordance with the above combination or combination rule. What is represented is the gain factor (the directional weighting factor) with which the signal from the respective spatial direction is contained within the combination signal, as against the position of the source in the X direction 40 and in the Y direction 42.
  • a gain factor of 1 signifies that the signal is recorded in an unattenuated manner, i.e. with an amplitude, or intensity, which is not reduced by the combination of the two individual signals X and Y.
  • the gain factor is constantly zero along the Z axis, since neither the X signal nor the Y signal, or the microphones associated with this signal, are/is sensitive in this direction.
  • the above-mentioned combination of the X signals and Y signals results in a directivity which corresponds to the torus shown in Fig. 4, whose axis of rotation is the Z axis. If one further takes into account that the directivity characteristic of an omnidirectional signal W has no maximum, i.e.
  • a signal having a predetermined spatial directivity characteristic (a dipole aligned in the Z direction) is generated by the above relationship, provided that the directivity characteristics of the input signals X, Y and W are known.
  • the phase ⁇ w (k,n) may be selected in correspondence with the phase of the omnidirectional signal W(k,n), so that the generated signal which is extended by a piece of phase information exhibits the following form:
  • Fig. 5 illustrates the gain factor in dependence of the angle ⁇ (52) between the
  • the continuous line 54 describes the directivity characteristic of a conventional dipole.
  • the dotted curve 56 illustrates the directivity characteristic of the signal Z(k,n), which by means of the above combination rule was combined, or derived, from the signals W, X ' and Y.
  • the phase information is no longer complete due to the combination, which makes itself felt in that the directivity characteristic of the so-called homophasic dipole 56 is equivalent to that of the "classic" dipole only for the angles of 0 to 90° and 270 to 360°.
  • the absolute magnitude of the directional gain factors in the range between 90° and 270° is identical to the absolute magnitude of the classic dipole, but no negative signs occur. If, as for example in the DirAC parametrization, one requires only that information which states the spatial direction from which the maximum intensity is recorded, this loss of information is acceptable.
  • Figs. 6A and 6B once again schematically illustrate, respectively, embodiments of an apparatus for generating a signal having a predetermined directivity characteristic, and a system for generating a DirAC parametrization on the basis of a first signal X having a directivity characteristic in the X direction, a second signal Y having a directivity characteristic in the Y direction, and an omnidirectional signal W.
  • Fig. 6A and 6B once again schematically illustrate, respectively, embodiments of an apparatus for generating a signal having a predetermined directivity characteristic, and a system for generating a DirAC parametrization on the basis of a first signal X having a directivity characteristic in the X direction, a second signal Y having a directivity characteristic in the Y direction, and an omnidirectional signal W.
  • FIG. 6A schematically shows an embodiment of a signal processor 2 which has a first signal X, a second signal Y and a third signal W supplied to it.
  • the directivity characteristics of the signals correspond to the embodiment described further up, so that, by means of the signal processor 2, a signal Z having a predetermined spatial directivity characteristic may be generated wherein the maximum directional weighting factor occurs in the Z direction.
  • the signals X, Y and W which are initially picked up by microphones in a temporal representation, are converted to a spectral representation, whereupon a signal Z having the predetermined directivity characteristic is formed by the above-described combination of the magnitude values.
  • the spectral representation of the signals X, Y and W may alternatively be supplied, along with the spectral representation of the specific signal Z, to a DirAC analyzer 60, which, as was described above, generates the parameters characteristic for the
  • DirAC parametrization of an acoustic spatial signal namely a direction vector 62 and a diffuseness parameter 64.
  • these parameters enable preferring random spatial directions in a subsequent reproduction, or reproducing signals only from the random spatial directions, or faithfully reproducing the sound field as well.
  • a DirAC parametrization may be performed using a substitution signal having a predetermined directivity characteristic and being generated by an embodiment of a signal processor, for example how the DirAC parameters (a direction vector or direction information and a diffuseness value ⁇ may be formed.
  • FIG. 7 shows, in a Cartesian coordinate system comprising the axes X, Y and Z, seven omnidirectional microphones at the corners of an octahedron and at the center thereof, by means of which omnidirectional microphones the complete information required for the DirAC parametrization or analysis, i.e. signals with directivities in X, Y and Z as well as an omnidirectional signal W, may be obtained.
  • the signals having directivity characteristics may be obtained from the difference between two omnidirectional microphones spaced apart from each other in the respective spatial direction.
  • Fig. 7 shows, in a Cartesian coordinate system comprising the axes X, Y and Z, seven omnidirectional microphones at the corners of an octahedron and at the center thereof, by means of which omnidirectional microphones the complete information required for the DirAC parametrization or analysis, i.e. signals with directivities in X, Y and Z as well as an omnidirectional signal W, may be obtained.
  • a signal having the directivity characteristic in the X direction may be obtained by subtracting the signals of the microphones 70a and 70b, said signals possibly having been suitably normalized in a frequency-dependent manner.
  • a signal having a directivity characteristic in the Y direction may be obtained by subtracting the signals of the microphones 72a and 72b, said signals possibly having been suitably normalized in a frequency-dependent manner.
  • a signal having a directivity characteristic in the Z direction may be obtained by subtracting the signals of the microphones 74a and 74b, said signals possibly having been suitably normalized in a frequency-dependent manner.
  • the omnidirectional microphone 76 (W) arranged at the center serves to pick up a signal W(k,n) having an omnidirectional characteristic, as is required for a DirAC analysis.
  • the signal having an omnidirectional characteristic may alternatively also be calculated as a mean value of all of the microphone signals or as a mean value of the external microphone signals.
  • indices k indicate the contemplated spectral range in each case
  • index n describes the contemplated signal component, or signal block, of the block-wise frequency analysis (e.g. short- time Fourier transformation SFT) used by way of example here.
  • SFT short- time Fourier transformation
  • the angle ⁇ designates the azimuth 79a
  • the angle ⁇ designates the elevation 79b, i.e. those angles which unambiguously describe the direction of the sound source 78 in relation to the origin of the coordinate system.
  • the diffuseness ⁇ is determined as follows in the DirAC analysis:
  • the signal Z(k,n) may be generated by means of an embodiment of a signal processor, as was described above.
  • This signal will have the directivity characteristic illustrated with reference to Fig. 5. Therefore, the signal thus generated may be used, in the frequency range, directly for deriving the DirAC parameters.
  • the intensity vector for the DirAC parametrization in the Z direction consequently results as:
  • An elevation angle 79b indicating the position of the sound source 78 in the Z direction may consequently be derived even in the case where there is no signal which has been picked up generically and has a directivity characteristic in the Z direction. This is possible in that the intensity
  • the directivity characteristic of the signal generated may correspond to that of a homophasic dipole due to the fact that the phase information is not taken into account in the combination rule. Therefore, unambiguous association of the position of the sound source 78 is possible only within the half-plane with positive Z values.
  • the diffuseness parameter results in that the value I 1 is replaced by the intensity / 2 derived above.
  • a DirAC analysis is also possible if one is only interested in the 2-dimensional analysis of the sound field.
  • the omnidirectional microphone 76 may be dispensed with, since, as will be shown below, a substitution signal having a torus-shaped directivity characteristic may be generated from the X and Y signals, which substitution signal enables determining the 2- dimensional DirAC parameters of interest, namely azimuth 79a and the diffuseness parameter ⁇ 2D .
  • a signal W ⁇ (k,n) is formed as a substitution signal having a predetermined directivity characteristic, the signal W ⁇ (k,n) having a torus-shaped directivity characteristic, as was already described above.
  • the signal W ⁇ (k,n) may be represented from the signals X and Y as follows :
  • the phase parameter is optional.
  • the "2-dimensional intensity" may be formed as follows:
  • the azimuth angle 79a may be directly determined, in accordance with the following formula, from the X and Y intensities :
  • the "2-dimensional" overall energy value may be calculated, in accordance with the following formula, by means of the generated signal having a predetermined directivity characteristic (signal W ⁇ having a torus-shaped directivity characteristic) :
  • the diffuseness parameter ⁇ may thus be calculated, in accordance with the following formula, also in the 2- dimensional case by using the substitution signal W T/ which was generated by means of an embodiment of a signal processor:
  • an acoustic analysis may occur at least within the X-Y plane, for example with the DirAC parametrization, since, as will be described below, a signal Y(k,n) having a predetermined, dipole-type directivity characteristic may be generated from the signals W and X.
  • the following combination rule may be modified in order to determine, in accordance with the following relation, the magnitude values of the signal to be generated:
  • the directivity characteristic of the signal thus generated corresponds to a torus whose axis of rotation is the X axis.
  • the directivity characteristic thus generated therefore meets the preconditions for a subsequent DirAC analysis .
  • phase factor may correspond to the phase factor of the omnidirectional signal W(k,n), so that, if phase information is desired, the combination rule may be extended in order to form the generated signal such that it may be described in accordance with the following formula:
  • the signal ⁇ (k,n) thus generated has a directivity characteristic which corresponds to a homophasic dipole within the X-Y plane.
  • a subsequent DirAC analysis will lead to a correct determination of the intensity vector within the half-plane of the X-Y plane, which includes the positive Y axis. Consequently, even in the case of a 1-dimensional microphone array, a DirAC analysis may be performed which enables highly flexible further processing of the signal analyzed if embodiments of inventive signal processors can be used for generating an additional signal having a predetermined spatial directivity characteristic.
  • the following considerations reveal the manner in which a subsequent DirAC analysis (2-dimensional case) may be performed, even in the case of a linear microphone array, by means of the signal ⁇ (k,n) generated above.
  • the intensity vector for the DirAC analysis is calculated for the X component as it is done in the normal case, since this component is directly available along with an omnidirectional signal.
  • the intensity I 2D ⁇ thus generated and the measured intensity / 2£)Jt may be used.
  • a diffuseness parameter ⁇ 2D may be derived from the following relations, even if only such microphones can be used which are arranged linearly one behind the other in a spatial direction:
  • information on the spatial composition of the signal may therefore also be given even if this may be recorded only with a 1-dimensional receiver array.
  • phase information is desired, combining the magnitude of the signal generated with one of the phase factors of the spectral representations of one, of the input signals .
  • inventive signal processors enables the more flexible use of microphones, or microphone arrays, with regard to determining parameters for the spatial reconstruction of an ambience of sound which is to be picked up, or of a signal picked up.
  • the spatial selectivity of microphone arrays in that, for example, the spatial area wherein the directional weighting factor is large may be restricted. This may be achieved, for example, in that the output signals of the microphone arrays having known directivity characteristics are processed by means of embodiments of inventive signal processors.
  • Fig. 8 shows an embodiment of a method of generating a signal having a predetermined spatial directivity characteristic.
  • a signal generation step 100 a first signal having a known spatial directivity characteristic 8a, and a second signal having a known spatial directivity characteristic 8b are provided.
  • the temporal representations of the first and second signals are converted, in a transformation step, to a spectral representation of the first signal 8a and to a spectral representation of the second signal 8b.
  • the spectral representation of the first signal 8a and the spectral representation of the second signal 8b are combined, in accordance with a combination rule, such that a spectral representation, resulting from the combination, of the signal to be generated has the predetermined spatial directivity characteristic, the predetermined directivity characteristic differing from the directivity characteristics of the first and second signals.
  • the spectral representation of the generated signal is converted to a temporal representation in order to obtain a signal having a predetermined spatial directivity characteristic which may be reproduced, for example, by means of a loudspeaker.
  • a parameterization, or spectral representation, of the spatial properties of the audio signal picked up is derived from the generated signal having a predetermined spatial directivity characteristic 10 and from the input signals 8a and 8b.
  • the inventive method of generating a signal having a predetermined spatial directivity characteristic may be implemented in hardware or in software.
  • the implementation may be effected on a digital storage medium, in particular a disk or a CD having electronically readable control signals, which may cooperate with a programmable computer system such that the inventive method of generating a signal having a predetermined spatial directivity characteristic is performed.
  • the invention thus also consists in a computer program product having a program code, stored on a machine-readable carrier, for performing the inventive method, when the computer program product runs on a computer.
  • the invention may therefore also be realized as a computer program having a program code for performing the method, when the computer program runs on a computer.

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  • Health & Medical Sciences (AREA)
  • Otolaryngology (AREA)
  • Physics & Mathematics (AREA)
  • Engineering & Computer Science (AREA)
  • Acoustics & Sound (AREA)
  • Signal Processing (AREA)
  • Circuit For Audible Band Transducer (AREA)

Abstract

Processeur de signaux servant à produire un signal de substitution (10) présentant une caractéristique de directivité spatiale prédéfinie en utilisant un premier signal (8a) présentant une caractéristique de directivité spatiale connue et un second signal (8b) présentant une caractéristique de directivité spatiale connue. Les premier et second signaux sont convertis en une représentation spectrale. Dans un processeur de signaux, les représentations spectrales des premier et second signaux sont converties conformément à un critère combinatoire dans le but d'obtenir des paramètres d'amplitude d'une représentation spectrale du signal de substitution présentant une caractéristique de directivité prédéfinie (10). Les valeurs absolues des paramètres d'amplitude des représentations spectrales des premier et second signaux sont combinées conformément au critère combinatoire, de sorte que la caractéristique de directivité prédéfinie diffère des caractéristiques de directivité des premier (8a) et second (8b) signaux.
PCT/EP2008/010658 2007-12-17 2008-12-15 Capteur de signaux à caractéristique de directivité variable WO2009077152A1 (fr)

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