EP2503799A1 - Method and system for calculating synthetic head related transfer functions by means of virtual local sound field synthesis - Google Patents
Method and system for calculating synthetic head related transfer functions by means of virtual local sound field synthesis Download PDFInfo
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- EP2503799A1 EP2503799A1 EP11159001A EP11159001A EP2503799A1 EP 2503799 A1 EP2503799 A1 EP 2503799A1 EP 11159001 A EP11159001 A EP 11159001A EP 11159001 A EP11159001 A EP 11159001A EP 2503799 A1 EP2503799 A1 EP 2503799A1
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04S—STEREOPHONIC SYSTEMS
- H04S7/00—Indicating arrangements; Control arrangements, e.g. balance control
- H04S7/30—Control circuits for electronic adaptation of the sound field
- H04S7/302—Electronic adaptation of stereophonic sound system to listener position or orientation
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04S—STEREOPHONIC SYSTEMS
- H04S2420/00—Techniques used stereophonic systems covered by H04S but not provided for in its groups
- H04S2420/01—Enhancing the perception of the sound image or of the spatial distribution using head related transfer functions [HRTF's] or equivalents thereof, e.g. interaural time difference [ITD] or interaural level difference [ILD]
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04S—STEREOPHONIC SYSTEMS
- H04S2420/00—Techniques used stereophonic systems covered by H04S but not provided for in its groups
- H04S2420/11—Application of ambisonics in stereophonic audio systems
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04S—STEREOPHONIC SYSTEMS
- H04S2420/00—Techniques used stereophonic systems covered by H04S but not provided for in its groups
- H04S2420/13—Application of wave-field synthesis in stereophonic audio systems
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04S—STEREOPHONIC SYSTEMS
- H04S7/00—Indicating arrangements; Control arrangements, e.g. balance control
- H04S7/30—Control circuits for electronic adaptation of the sound field
- H04S7/302—Electronic adaptation of stereophonic sound system to listener position or orientation
- H04S7/303—Tracking of listener position or orientation
- H04S7/304—For headphones
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04S—STEREOPHONIC SYSTEMS
- H04S7/00—Indicating arrangements; Control arrangements, e.g. balance control
- H04S7/30—Control circuits for electronic adaptation of the sound field
- H04S7/305—Electronic adaptation of stereophonic audio signals to reverberation of the listening space
Definitions
- the claimed invention relates to a method and system for calculating synthetic outer ear transmission functions by virtual sound field synthesis, preferably local sound field synthesis.
- the invention more particularly relates to such a method and system for use in dynamic virtual binaural auditory environments.
- the spatial auditory perception of humans is essentially based on the evaluation of the differences between the acoustic signals of both ears.
- the differences arise, among other things, from the acoustic properties of the outer ears with respect to a given source location.
- the outer ears essentially comprise the upper body, head and ears.
- the signal from an acoustic source is modified by reflection, diffraction and refraction at the outer ear.
- the acoustic properties of the outer ears can be well characterized by measuring the transmission path from a source to the ear canals.
- the transfer function is usually measured from a loudspeaker to microphones placed in the ear canals.
- These transfer functions are referred to as outer-ear transfer functions ("Head-Related Transfer Function (s)"). They play an important role in the study of human hearing and virtual acoustics.
- the outer ear transmission functions are different from person to person. Furthermore, they depend on the position and characteristics of the source used for the measurement.
- the measurement of the outer ear transmission functions is usually carried out by means of one or more loudspeaker (s). These are typically centered on a circular path or spherical surface with the head. The measurements are then performed sequentially for each speaker position. This procedure results in a set of outer ear transfer functions for different angles at a fixed distance of the source. The measurements are typically performed for a fixed head. Current available data sets usually contain only a single source distance. Often this is measured in the range of 1.5-3 m from the center of the head. But these simple measurements for a distance are usually quite time and resource consuming. Of particular interest are short distances to the source (near field) because the outer ear transfer function significantly changes their properties here.
- virtual sound sources can be generated by filtering a source signal x (t) with the left / right outer ear transmission function (H L and H R ) and presenting the filtered signals by means of headphones.
- the outer ear transmission functions are thereby selected from a database according to the desired position of the virtual source. It is important to consider the current position of the head, eg by a head tracker, so that the virtual sources have a stable position in the room even when the head is rotated. Through so-called crosstalk compensation, the signals can also be reproduced by means of speakers.
- the positions of the virtual sources are limited in principle to the positions that are available in the database of the external vehicle transmission functions. Due to the effort is usually measured only at a fixed distance but for a variety of angles on a circular path / spherical surface. In order to overcome the resulting limitations on the potential positions of virtual sound sources, a number of approaches have been developed to retroactively modify the measured distance (see section below). In addition to the binaural rendering described above, which is based on the use of external toll transfer functions, there are a number of speaker based approaches in virtual acoustics, which are briefly presented below.
- Wave field synthesis allows the physical reconstruction of a sound field over a wide range. It can be used any convex or straight speaker arrangements, which need not necessarily be closed. In the potential listening area, eg within a loudspeaker arrangement, there is no pronounced "sweet spot" over the entire audible frequency range, where the reconstruction of the desired sound field is significantly more accurate than in the rest of the listening area. In practical realizations are great Deviations from the desired sound field over the entire potential listener area available.
- the loudspeaker drive signals can be calculated analytically.
- An essential feature of wave field synthesis is the ability to create so-called focused sources. This is the imitation of the sound field of a sound source located between the listener and the speakers. [5] concerns focused sound sources.
- Ambisonics Another method of virtual acoustics is Ambisonics.
- [3] relates to the traditional formulation of Ambisonics, which method requires circular or spherical arrangements of loudspeakers. With the help of numerical algorithms, the loudspeaker signals are generated, which lead to the reproduction of the desired sound field.
- the limitation of the spatial bandwidth of the drive function necessary in the calculation path has the effect that the reconstruction of the desired sound field in the center of the loudspeaker arrangement is most accurate (“sweet spot"). The further the considered place is from the center, the larger the deviations become.
- EP 2182744 relates to a method of ambisonics wherein sweet spots or the sweet area can be freely placed within a closed speaker assembly.
- the loudspeaker drive signals can be calculated analytically.
- the method is significantly more efficient than other approaches but limited to closed (eg, circular) arrangements.
- the approach presented in [6] is based on the concept of spatially dense virtual secondary sources to improve the accuracy of the synthesis.
- the virtual sources are realized by focused sound sources. This approach can be realized particularly efficiently by the wave field synthesis.
- [11] relates to a method of virtual ambisonics in which a binaural representation of a higher order Ambisonics system is realized.
- virtual speakers are binaurally reproduced by using the corresponding outer ear transmission functions.
- the driving signals of the virtual speakers are calculated by Ambisonics of higher order.
- the virtual loudspeakers and the virtual source are based on the simplified model of the plane wave.
- the distance of a virtual source is realized by a simple time delay.
- the method also includes a simple space model.
- the synthesis of outer ear transfer functions is not considered here.
- the model used for the virtual source does not allow physical consideration of the distance For example, by a curvature of the wavefronts and is therefore not well suited for the synthesis of close sources.
- the known approaches for modifying the (perceived) source distance in outer ear transmission functions can be divided into three classes: (1) weighting of the amplitude, (2) modification of the frequency response, and (3) extrapolation of the measured data.
- the respective outer ear transmission function is frequency independent weighted to model the increasing volume of a source with decreasing distance to the listener.
- the spectral changes in the outer ear transfer functions, especially for near sources are ignored.
- the second class of approaches exactly these spectral changes are modeled by suitable filters. For example, it is known that very close sources cause an increase in frequency response at low frequencies.
- the first and second classes are generally based on psychoacoustic considerations, in contrast to the third class, which are based on physical considerations.
- the third class of approaches is of particular interest. It is known from the underlying physical description of the sound propagation that the sound pressure and its gradient on the edge of a contour are sufficient to unambiguously determine the sound field within this contour. The method is called extrapolation of a sound field. This basic principle has been applied to the problem of generating synthetic outer ear transmission functions. Due to the underlying spherical geometry, it is advantageous to disassemble the sound fields with respect to so-called spherical harmonics. In [8,9] two methods are shown, which allow the extrapolation of measured outer ear transfer functions from one measured distance to another distance.
- the methods have three major disadvantages: (i) Due to the physical model, the minimum distance of the virtual sources through the head and upper body of the listener is limited and (ii) the numerical complexity is relatively high and (iii) the method is inherently numerically unstable. This is especially true for near virtual sources.
- the concept of the invention relates to the use of methods of sound field synthesis for the calculation or generation of synthetic outer ear transmission functions.
- This calculation is made in accordance with an aspect of the invention by providing a database of pairs of outer ear transmission functions for a plurality of first source positions, each determining at least one pair of outer transmission functions for a first source position by a measurement. Each of these pairs of outer ear transmission functions is interpreted as a virtual speaker at the corresponding first source position. Using the virtual speakers, a method of sound field synthesis for at least one virtual sound source at another source position computes at least one pair of synthetic outer ear transmission functions.
- the virtual speakers can be used as elementary sound sources for generating any sound field by a method of wave field synthesis.
- the drive signals for the virtual loudspeakers with respect to magnitude and phase can be calculated such that a weighted superposition of the elementary sound field produced by each virtual loudspeaker yields the desired sound field in its entirety.
- the desired sound field here is a sound field that results from any virtual sound source that may be placed anywhere in the room. This makes it possible to synthesize a transfer function corresponding to the sound propagation from any virtual sound source. It is therefore a synthetic outer ear transfer function.
- the calculation method can be used to create a database of afore-calculated synthetic outer ear transmission functions for a variety of positions of the virtual sound source. Such a database can be used to model any sound world.
- a space model that simulates propagation paths and properties.
- at least one mirror source is synthesized which belongs to a virtual sound source.
- a method for normal sound field synthesis can be used.
- the calculation can be carried out by virtual local sound field synthesis or other wave field synthesis methods.
- Another aspect of the invention relates to a system for performing a method for computing the generation of synthetic outer ear transmission functions.
- External ear transmission functions characterize the sound propagation from the sound source used in the measurement to the ears of the listener. If an entire data set of outer ear transfer function is now measured for a multiplicity of possible source positions, these source positions can be interpreted as virtual loudspeakers. The weighted superposition of the loudspeaker signals then simulates the influence of the entire ensemble of these virtual loudspeakers on the ear of the listener. If one now controls these virtual speakers with a method of sound field synthesis, the ear signals can be synthesized for virtually any virtual source positions. Head turns can be accounted for by dynamically exchanging the outer ear transfer functions used.
- outer ear transmission functions can be interpolated and extrapolated, and data sets of synthetic outer ear transmission functions can be provided at different distances from the source than those present in the measurement.
- the synthetic outer ear transfer functions for complex source models can be calculated from simple source measurements.
- FIG. 1 is a schematic representation for the measurement of a left and right outer ear transfer function shown (left half of FIG. 1 ) and a block diagram for the use of these outer ear transfer functions for virtual acoustics (right half of FIG. 1 ).
- a loudspeaker located at a certain source position is used, this loudspeaker emitting a source signal x (t).
- the propagating sound waves are shown schematically and reach the left and right ear of a listener, which is positioned in the room in a certain relative position to the speaker.
- the relative position can be described by a specific distance between the loudspeaker and the position of the listener and a specific direction with respect to a spatial coordinate system.
- the relative Position information about the rotational position of the head of the listener relative to the spatial coordinate system include.
- the measurement uses microphones that are placed at the left ear or right ear position of the listener.
- the signal X L (t) detected by the microphone at the position of the left ear is determined by a transfer function h L (t).
- the signal X R (t) recorded with the right microphone at the position of the right ear of the listener is determined by the transfer function h R (t).
- This measurement can be performed for a variety of first source positions.
- a speaker at first source positions on a circular contour 7 as in FIG. 2 be arranged shown.
- the loudspeaker is successively arranged at each of the first source positions and the measurement is carried out and the respective transfer functions are stored with the information about the respective source position and the rotational position of the head in a database.
- a plurality of loudspeakers arranged in a space at respectively associated first source positions may be employed.
- the individual loudspeakers can be operated in succession and the respective source signal x (t) can be emitted and transmitted by sound propagation to the handset present in the room.
- the measured outer ear transmission functions from first source positions used for the calculation of synthetic outer ear transmission functions are provided in a database.
- virtual sound sources can be generated by filtering a source signal x (t) with the left / right outer ear transfer function (H L ( ⁇ ) and H R ( ⁇ ) and presentation of the filtered signals by headphones.)
- an input signal x Depending on the position of the virtual source and the position of the head of the listener, the corresponding outer ear transmission functions are transferred from one HRTF database to the filter devices for the left one (s) corresponding to a particular source signal via two feeders
- the left-ear filter device is adapted to emulate the left-ear transmission functions H L ( ⁇ ).
- the right-ear filter device is adapted to the right ear External ear transmission functions for the right ear H R ( ⁇ ) established.
- the input signal is filtered with the left / right filter unit and directed
- FIG. 2 One embodiment for calculating synthetic outer ear transmission functions is in FIG FIG. 2 shown.
- control signals 5 for the reproduction of the virtual sound source 8 by the virtual loudspeakers 6 in the local area are calculated by an algorithm of the sound field synthesis 2, preferably a local sound field synthesis.
- the virtual speakers 6 are arranged in this example on a circular contour 7, wherein all speakers are directed in the middle of a circle, where schematically a local area 14 is shown in the middle. In the local area 14 is a listener.
- the source type 3 and the source position 4 and, if necessary, the position of the local area 14 are used as additional information.
- Ears are characterized by a left / right outer ear transmission function 10,11. External ear transfer function databases are typically measured on circular / spherical contours 7. The left / right ear signal for the virtual sound source 8 is obtained by the superposition of all the virtual speaker signals 5 filtered with the respective outer ear transmission function 12, 13. Head turns and position changes of the listener may be accounted for by the dynamic replacement of the outer ear transmission functions 12, 13.
- databases of synthetic outer ear transmission functions can also be calculated.
- an impulse is taken as the source signal 1 of a virtual source and the total impulse response is calculated from the virtual sound source 8 to the ears.
- a synthetic data set of outer ear transmission functions can be calculated.
- suitable methods of sound field synthesis are, based on the underlying circular / spherical geometry of measured outer ear transmission functions, for example wave field synthesis and ambisonics of higher order.
- both methods assume a spatially continuous distribution of Speakers (secondary sources) off.
- the outer ear transfer functions are only available at spatially discrete positions. This leads to artifacts in the synthesized ear signals and the synthesized outer ear transmission functions due to spatial discretization. This is the case even if the outer ear transmission functions are relatively finely scanned.
- artifacts occur in a synthetic outer ear transmission function from a frequency of about 10 kHz when the used external transmission functions were measured in 1 degree increments at a distance of the source used in the measurement of 2-3 meters. This will be explained below with reference to FIG. 5 explained in more detail.
- One embodiment of the invention is based on the use of local sound field synthesis for the calculation of synthetic ear signals or outer ear transmission functions in order to avoid or reduce the artifacts of spatial discretization.
- Local sound field synthesis allows a region of higher accuracy to be placed around the listener's head. This will reduce artifacts for better results. This will be explained below with reference to FIG. 6 explained.
- any algorithm can be used for local sound field synthesis, as found in various preferred Ausumngsformen in EP 2182744 , [6] and [7] algorithms described application.
- the in EP 2182744 and [6] described algorithms for local sound field synthesis are advantageous because of the underlying geometry of typical data sets of outer ear transmission functions.
- a dynamic binaural synthesis, head orientation, and taken into account realized.
- Dynamic tracking is a key factor in the quality of virtual acoustic environments.
- the advantage of this embodiment lies in an efficient consideration of the listener position compared to solutions, where only the orientation of the head is taken into account. Considering the head position would require a database of outer ear transmission functions measured for many nearby source locations.
- the method can be supplemented by the simulation of a room model.
- the high resolution mirror sources associated with the virtual source may be synthesized using local sound field synthesis.
- the present invention enables efficient consideration of the listener position.
- the virtual source in addition to the typical point source model, is also modeled as a complex directional source, preferably with the method described in [12]. Again, the combination with the local sound field synthesis offers a significant advantage, since the desired directional characteristic is not distorted by the artifacts of the spatial sampling.
- a preferred embodiment inherently involves interpolation of the outer ear transmission functions with respect to the angle.
- the position of the virtual source can be arbitrarily selected with respect to the angular resolution. This allows interpolation of a measured data set.
- the data set of outer ear transfer functions used is measured not only on a circular or spherical contour, but on a contour of any shape.
- the advantage of this embodiment is the efficient measurement of outer ohm transfer functions without geometric constraints.
- FIG. 3 illustrates the processing steps. From the source signal 31, which is generally a Dirac pulse for the calculation of synthetic outer ear transmission functions, 35 signals 44 for the virtual secondary sources are generated by wave field synthesis. As additional information, the source model 32, the positions 33 and emission directions 34 of the virtual secondary sources are used for this purpose. The virtual secondary sources are realized by focused sources again by the wave field synthesis.
- the source signal 31 which is generally a Dirac pulse for the calculation of synthetic outer ear transmission functions
- 35 signals 44 for the virtual secondary sources are generated by wave field synthesis.
- the source model 32, the positions 33 and emission directions 34 of the virtual secondary sources are used for this purpose.
- the virtual secondary sources are realized by focused sources again by the wave field synthesis.
- the signals 45 for the secondary sources are calculated for each of the signals 44 by means of acoustic focusing 40.
- the positions 36 and emission directions 37 of the virtual secondary sources, as well as the positions 38 and emission directions 39 of the secondary sources are used.
- the signals from the secondary sources 45 are then filtered with the data set of the outer ear transfer functions 41 and then summed up. This is done separately with the left / right outer ear transfer functions and then results in the left / right synthetic outer ear transfer function 42/43.
- a data set of outer ear transmission functions can be calculated.
- FIG. 4 a diagram is shown corresponding to a measured set of left outer ear transfer functions.
- the sound source had a distance of 2.5 m and 288 angular steps were measured on a full circle. Shown is the measured head related transfer function (HRTF). Along the abscissa the angle is plotted in degrees. Along the ordinate, the time is plotted in seconds.
- HRTF head related transfer function
- FIG. 5 Figure 12 is a diagram corresponding to the database of synthetic left outer ear transfer functions calculated by wave field synthesis. Shown is the calculated binaural room impulse response (BRIR, binaural room impulse response). The abscissa represents the angle in degrees and the ordinate the time in seconds. The calculation by wave field synthesis was made for a distance of the virtual source of three meters from the listener. The results shown by using Wave Field Synthesis to compute a data set of synthetic outer ear transmission functions are shown here. The spatial sampling artifacts are clearly visible as extra wavefronts after the first wavefront.
- BRIR binaural room impulse response
- FIG. 6 shows a diagram with a database of synthetic left outer ear transmission functions, which were calculated by local wave field synthesis. Again, the calculation was made for a distance of the virtual source of three meters. FIG. 6 thus shows the same situation as FIG. 5 however, local wave field synthesis was used to calculate the synthetic outer ear transmission functions. The zone of increased accuracy was chosen as a circle with a radius of 30 cm around the head. It can be clearly seen that the artifacts of spatial scanning compared to FIG. 5 are no longer available or are significantly reduced.
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Abstract
Description
Die beanspruchte Erfindung bezieht sich auf ein Verfahren und System zur Berechnung synthetischer Außenohrübertragungsfunktionen durch virtuelle Schallfeldsynthese, vorzugsweise lokale Schallfeldsynthese. Die Erfindung bezieht sich im Besonderen auf ein derartiges Verfahren und System zum Einsatz in dynamischen virtuellen binauralen auditorischen Umgebungen.The claimed invention relates to a method and system for calculating synthetic outer ear transmission functions by virtual sound field synthesis, preferably local sound field synthesis. The invention more particularly relates to such a method and system for use in dynamic virtual binaural auditory environments.
Die räumliche auditorische Wahrnehmung des Menschen beruht wesentlich auf der Auswertung der Unterschiede zwischen den akustischen Signalen beider Ohren. Die Unterschiede entstehen unter anderen durch die akustischen Eigenschaften der Außenohren in Bezug auf eine gegebene Quellenposition. Die Außenohren umfassen im Wesentlichen den Oberkörper, Kopf und die Ohrmuscheln. Das Signal einer akustischen Quelle wird durch Reflexion, Beugung und Brechung am Außenohr modifiziert. Die akustischen Eigenschaften der Außenohren können durch die Messung des Übertragungsweges von einer Quelle zu den Ohrkanälen gut charakterisiert werden. Dazu wird meist die Übertragungsfunktion von einem Lautsprecher zu in den Ohrkanälen platzierten Mikrofonen gemessen. Diese Übertragungsfunktionen werden als Außenohrübertragungsfunktionen (englisch "Head-Related Transfer Function(s)") bezeichnet. Sie spielen eine wichtige Rolle bei der Erforschung des menschlichen Gehörs und für die virtuelle Akustik. Im Allgemeinen sind die Außenohrübertragungsfunktionen von Mensch zu Mensch verschieden. Weiterhin hängen sie von der Position und Charakteristik der Quelle ab die zur Messung verwendet wurde.The spatial auditory perception of humans is essentially based on the evaluation of the differences between the acoustic signals of both ears. The differences arise, among other things, from the acoustic properties of the outer ears with respect to a given source location. The outer ears essentially comprise the upper body, head and ears. The signal from an acoustic source is modified by reflection, diffraction and refraction at the outer ear. The acoustic properties of the outer ears can be well characterized by measuring the transmission path from a source to the ear canals. For this purpose, the transfer function is usually measured from a loudspeaker to microphones placed in the ear canals. These transfer functions are referred to as outer-ear transfer functions ("Head-Related Transfer Function (s)"). They play an important role in the study of human hearing and virtual acoustics. In general, the outer ear transmission functions are different from person to person. Furthermore, they depend on the position and characteristics of the source used for the measurement.
Die Messung der Außenohrübertragungsfunktionen wird meist mittels einem oder mehreren Lautsprecher(n) durchgeführt. Diese befinden sich typischerweise auf einer Kreisbahn oder Kugeloberfläche mit dem Kopf im Mittelpunkt. Die Messungen werden dann sequentiell für jede Lautsprecherposition durchgeführt. Dieses Vorgehen resultiert in einem Satz von Außenohrübertragungsfunktionen für verschiede Winkel bei einem festen Abstand der Quelle. Die Messungen werden typischerweise für einen fixierten Kopf durchgeführt. Aktuell verfügbare Datensätze beinhalten meist nur einen einzigen Quellenabstand. Oft befindet sich dieser im Bereich von 1.5-3 m von der Kopfmitte aus gemessen. Allein diese einfachen Messungen für einen Abstand sind meist schon recht zeit- und resourcenaufwendig. Von besonderem Interesse sind kurze Distanzen zur Quelle (Nahfeld) da die Außenohrübertragungsfunktion hier ihre Eigenschaften wesentlich verändern.The measurement of the outer ear transmission functions is usually carried out by means of one or more loudspeaker (s). These are typically centered on a circular path or spherical surface with the head. The measurements are then performed sequentially for each speaker position. This procedure results in a set of outer ear transfer functions for different angles at a fixed distance of the source. The measurements are typically performed for a fixed head. Current available data sets usually contain only a single source distance. Often this is measured in the range of 1.5-3 m from the center of the head. But these simple measurements for a distance are usually quite time and resource consuming. Of particular interest are short distances to the source (near field) because the outer ear transfer function significantly changes their properties here.
Außenohrübertragungsfunktionen spielen eine wichtige Rolle bei der virtuellen Akustik. Bei der binauralen Wiedergabe können virtuelle Schallquellen durch die Filterung eines Quellsignals x(t) mit der linken/rechten Außenohrübertragungsfunktion (HL und HR) und Darbietung der gefilterten Signale mittels Kopfhörer erzeugt werden. Die Außenohrübertragungsfunktionen werden dabei aus einer Datenbank entsprechend der gewünschten Position der virtuellen Quelle ausgewählt. Dabei ist es wichtig die aktuelle Position des Kopfes zu berücksichtigen, z.B. durch einen Head-Tracker, damit die virtuellen Quellen auch bei Rotation des Kopfes eine stabile Position im Raum haben. Durch sogenannte Übersprechkompensation können die Signale auch mittels Lautsprechern wiedergegeben werden.External ear transmission functions play an important role in virtual acoustics. In binaural reproduction, virtual sound sources can be generated by filtering a source signal x (t) with the left / right outer ear transmission function (H L and H R ) and presenting the filtered signals by means of headphones. The outer ear transmission functions are thereby selected from a database according to the desired position of the virtual source. It is important to consider the current position of the head, eg by a head tracker, so that the virtual sources have a stable position in the room even when the head is rotated. Through so-called crosstalk compensation, the signals can also be reproduced by means of speakers.
Die Positionen der virtuellen Quellen sind prinzipbedingt auf die Positionen beschränkt die in der Datenbank der Außenahrübertragungsfuuktionen zur Verfügung stehen. Aufgrund des Aufwandes wird meist nur in einem fixen Abstand aber für eine Vielzahl von Winkeln auf einer Kreisbahn/Kugeloberfläche gemessen. Um die daraus resultierenden Beschränkungen bezüglich der möglichen Positionen virtueller Schallquellen zu überwinden, wurde eine Reihe von Ansätzen entwickelt, um die gemessene Distanz nachträglich zu modifizieren (siehe Abschnitt weiter unten). Neben der oben beschriebenen binauralen Wiedergabe, die auf der Verwendung von Außenollrübertragungsfunktionen basiert, gibt es noch eine Reihe von Lautsprecher basierter Ansätzen in der virtuellen Akustik, die im Folgenden kurz vorgestellt werden.The positions of the virtual sources are limited in principle to the positions that are available in the database of the external vehicle transmission functions. Due to the effort is usually measured only at a fixed distance but for a variety of angles on a circular path / spherical surface. In order to overcome the resulting limitations on the potential positions of virtual sound sources, a number of approaches have been developed to retroactively modify the measured distance (see section below). In addition to the binaural rendering described above, which is based on the use of external toll transfer functions, there are a number of speaker based approaches in virtual acoustics, which are briefly presented below.
[1] und [2] betreffen Verfahren zur Wellenfeldsynthese. Die Wellenfeldsynthese ermöglicht die physikalische Rekonstruktion eines Schallfeldes über einen ausgedehnten Bereich. Es können beliebige konvexe oder gerade Lautsprecheranordnungen verwendet werden, die nicht zwingend geschlossen sein müssen. In dem potentiellen Hörbereich, z.B. innerhalb einer Lautsprecheranordnung, gibt es keinen ausgeprägten "Sweet Spot" über den gesamten hörbaren Frequenzbereich, wo die Rekonstruktion des gewünschten Schallfeldes signifikant genauer ist als im Rest des Hörbereiches. Bei praktischen Realisierungen sind große Abweichungen vom gewünschten Schallfeld über den gesamten potentiellen Hörerbereich vorhanden. Die Lautsprecheransteuerungssignale können analytisch berechnet werden. Eine wesentliche Eigenschaft der Wellenfeldsynthese ist die Möglichkeit sogenannte fokussierte Quellen zu erzeugen. Dies ist die Imitation des Schallfeldes einer Schallquelle, die sich zwischen dem Zuhörer und den Lautsprechern befindet. [5] betrifft fokussierte Schallquellen.[1] and [2] relate to wave field synthesis methods. Wave field synthesis allows the physical reconstruction of a sound field over a wide range. It can be used any convex or straight speaker arrangements, which need not necessarily be closed. In the potential listening area, eg within a loudspeaker arrangement, there is no pronounced "sweet spot" over the entire audible frequency range, where the reconstruction of the desired sound field is significantly more accurate than in the rest of the listening area. In practical realizations are great Deviations from the desired sound field over the entire potential listener area available. The loudspeaker drive signals can be calculated analytically. An essential feature of wave field synthesis is the ability to create so-called focused sources. This is the imitation of the sound field of a sound source located between the listener and the speakers. [5] concerns focused sound sources.
Ein weiteres Verfahren der virtuellen Akustik ist Ambisonics. [3] betrifft die traditionelle Formulierung von Ambisonics, wobei dieses Verfahren kreisförmige bzw. kugelförmige Anordnungen von Lautsprechern erfordert. Mit Hilfe von numerischen Algorithmen werden die Lautsprechersignale generiert, die zur Wiedergabe des gewünschten Schallfeldes führen. Die im Rechenweg notwendige Beschränkung der räumlichen Bandbreite der Ansteuerungsfunktion bewirkt, dass die Rekonstruktion des gewünschten Schallfeldes im Zentrum der Lautsprecheranordnung am genauesten ist ("Sweet Spot"). Je weiter der betrachtete Ort von Zentrum entfernt ist, desto größer werden die Abweichungen.Another method of virtual acoustics is Ambisonics. [3] relates to the traditional formulation of Ambisonics, which method requires circular or spherical arrangements of loudspeakers. With the help of numerical algorithms, the loudspeaker signals are generated, which lead to the reproduction of the desired sound field. The limitation of the spatial bandwidth of the drive function necessary in the calculation path has the effect that the reconstruction of the desired sound field in the center of the loudspeaker arrangement is most accurate ("sweet spot"). The further the considered place is from the center, the larger the deviations become.
[4] betrifft Erweiterungen der traditionellen Formulierung von Ambisonics. Diese ermöglichen die analytische Berechnung der Lautsprecheransteuerungssignale, die um ein Vielfaches effizienter ist als numerische Verfahren. Jedoch besteht weiterhin die Restriktion, dass der "Sweet Spot" sich im Zentrum der Lautsprecheranordnung befindet, und dass lediglich kreisförmige oder kugelförmige Lautsprecheraufbauten verwendet werden können.[4] concerns extensions of the traditional formulation of Ambisonics. These allow the analytical calculation of loudspeaker drive signals, which is many times more efficient than numerical methods. However, there is still the restriction that the sweet spot is at the center of the speaker assembly, and that only circular or spherical speaker assemblies can be used.
Beide Verfahren, die Wellenfeldsynthese und erweitertes Ambisonics, streben die physikalisch akkurate Wiedergabe in einem möglichst großen Zuhörerbereich an. In der praktischen Realisierung beider Verfahren sind der erreichbaren Genauigkeit allerdings Grenzen gesetzt. Die endliche Anzahl von Lautsprechern führt zu einer Reihe von Artefakten, die zum Teil im gesamten Zuhörerbereich auftreten. Dies hat zu der Entwicklung einer Reihe von Ansätzen geführt, die eine höhere Genauigkeit in einem begrenzten Zuhörerbereich ermöglichen als Wellenfeldsynthese oder Ambisonics.Both methods, wavefield synthesis and advanced ambisonics, aim for physically accurate playback in the widest possible audience. In the practical implementation of both methods, the achievable accuracy, however, limits. The finite number of speakers results in a number of artifacts, some of which occur throughout the listening area. This has led to the development of a number of approaches that allow for higher accuracy in a limited audience than wavefield synthesis or ambisonics.
Der in [6] vorgestellte Ansatz basiert auf dem Konzept räumlich dicht angeordneter virtueller Sekundärquellen um die Genauigkeit der Synthese zu Verbessern. Die virtuellen Quellen werden dabei durch fokussierte Schallquellen realisiert. Dieser Ansatz lässt sich besonders Effizient durch die Wellenfeldsynthese realisieren.The approach presented in [6] is based on the concept of spatially dense virtual secondary sources to improve the accuracy of the synthesis. The virtual sources are realized by focused sound sources. This approach can be realized particularly efficiently by the wave field synthesis.
Der in [7] vorgestellte Ansatz beruht auf einer räumlichen Bandbegrenzung der Allsteuerungssignale der Lautsprecher. Damit wird ein begrenzter Bereich mit erhöhter Genauigkeit der Synthese erreicht, der frei im Hörerbereich platziert werden kann.The approach presented in [7] is based on a spatial band limitation of the control signals of the loudspeakers. Thus, a limited range with increased accuracy of synthesis is achieved, which can be placed freely in the handset area.
[11] betrifft ein Verfahren des virtuellen Ambisonics, bei dem eine binaurale Repräsentation eines Ambisonics Systems höherer Ordnung realisiert wird. Hierbei werden virtuelle Lautsprecher durch Verwendung der entsprechenden Außenohrübertragungsfunktionen binaural wiedergegeben. Die Ansteuerungssignale der virtuellen Lautsprecher werden mittels Ambisonics höherer Ordnung berechnet. Dabei wird bei den virtuellen Lautsprechern und der virtuellen Quelle vereinfacht von dem Modell der ebenen Welle ausgegangen. Die Distanz einer virtuellen Quelle wird durch eine einfache Zeitverzögerung realisiert. Das Verfahren beinhaltet zudem ein einfaches Raummodell. Die Synthese von Außenohrübertragungsfunktionen wird hier nicht betrachtet. Weiterhin erlaubt das verwendete Modell für die virtuelle Quelle keine physikalische Berücksichtigung der Distanz z.B. durch eine Krümmung der Wellenfronten und ist damit für die Synthese naher Quellen nicht gut geeignet.[11] relates to a method of virtual ambisonics in which a binaural representation of a higher order Ambisonics system is realized. In this case, virtual speakers are binaurally reproduced by using the corresponding outer ear transmission functions. The driving signals of the virtual speakers are calculated by Ambisonics of higher order. In this case, the virtual loudspeakers and the virtual source are based on the simplified model of the plane wave. The distance of a virtual source is realized by a simple time delay. The method also includes a simple space model. The synthesis of outer ear transfer functions is not considered here. Furthermore, the model used for the virtual source does not allow physical consideration of the distance For example, by a curvature of the wavefronts and is therefore not well suited for the synthesis of close sources.
Die bekannten Ansätze zur Modifikation der (wahrgenommenen) Quellendistanz bei Außenohrübertragungsfunktionen lassen sich in drei Klassen einteilen: (1) Gewichtung der Amplitude, (2) Modifikation des Frequenzganges und (3) Extrapolation der gemessenen Daten.
Bei der ersten Klasse wird die jeweilige Außenohrübertragungsfunktion frequenzunabhängig gewichtet um die zunehmende Lautstärke einer Quelle mit abnehmender Distanz zum Zuhörer zu modellieren. Bei diesem Ansatz werden die spektralen Änderungen der Außenohrübertragungsfunktionen, speziell für nahe Quellen, ignoriert.
In der zweiten Klasse von Ansätzen werden genau diese spektralen Änderungen durch geeignete Filter modelliert. So ist zum Beispiel bekannt, dass sehr nahe Quellen eine Anhebung des Frequenzganges bei tiefen Frequenzen verursachen.
Die erste und zweite Klasse beruhen im Allgemeinen auf psychoakustischen Überlegungen, im Gegensatz zur dritten Klasse, der physikalische Überlegungen zugrunde liegen. In dem Kontext dieser Erfindung ist die dritte Klasse von Ansätzen von besonderem Interesse. Aus der zu Grunde liegenden physikalischen Beschreibung der Schallausbreitung ist bekannt, dass der Schalldruck und dessen Gradient auf dem Rand einer Kontur ausreichen, um das Schallfeld innerhalb dieser Kontur eindeutig zu bestimmen. Das Verfahren wird als Extrapolation eines Schallfeldes bezeichnet. Dieses Grundprinzip wurde auf das Problem der Generierung von synthetischen Außenohrübertragungsfunktionen angewendet. Aufgrund der zu Grunde liegenden sphärischen Geometrie ist es dabei vorteilhaft, die Schallfelder bezüglich sogenannter sphärischer Harmonische zu zerlegen. In [8,9] sind zwei Verfahren dargestellt, welche die Extrapolation von gemessenen Außenohrilbertragungsfunktionen von einem gemessenen Abstand auf einen anderen Abstand ermöglichen. Die Verfahren haben drei entscheidende Nachteile: (i) Aufgrund des physikalischen Modells ist der minimale Abstand der virtuellen Quellen durch den Kopf und Oberkörper des Zuhörers begrenzt und (ii) die numerische Komplexität ist relativ hoch und (iii) das Verfahren ist inhärent numerisch instabil. Dies gilt besonders für nahe virtuelle Quellen.The known approaches for modifying the (perceived) source distance in outer ear transmission functions can be divided into three classes: (1) weighting of the amplitude, (2) modification of the frequency response, and (3) extrapolation of the measured data.
In the first class, the respective outer ear transmission function is frequency independent weighted to model the increasing volume of a source with decreasing distance to the listener. In this approach, the spectral changes in the outer ear transfer functions, especially for near sources, are ignored.
In the second class of approaches, exactly these spectral changes are modeled by suitable filters. For example, it is known that very close sources cause an increase in frequency response at low frequencies.
The first and second classes are generally based on psychoacoustic considerations, in contrast to the third class, which are based on physical considerations. In the context of this invention, the third class of approaches is of particular interest. It is known from the underlying physical description of the sound propagation that the sound pressure and its gradient on the edge of a contour are sufficient to unambiguously determine the sound field within this contour. The method is called extrapolation of a sound field. This basic principle has been applied to the problem of generating synthetic outer ear transmission functions. Due to the underlying spherical geometry, it is advantageous to disassemble the sound fields with respect to so-called spherical harmonics. In [8,9] two methods are shown, which allow the extrapolation of measured outer ear transfer functions from one measured distance to another distance. The methods have three major disadvantages: (i) Due to the physical model, the minimum distance of the virtual sources through the head and upper body of the listener is limited and (ii) the numerical complexity is relatively high and (iii) the method is inherently numerically unstable. This is especially true for near virtual sources.
Um das Problem der inhärenten Instabilität bei virtuellen Quellen mit geringem Abstand zu lösen, wurde ein Ansatz in [10] vorgeschlagen. Dieser basiert auf der Verwendung von Multipolmodellen löst das Problem der Komplexität und Instabilität nur teilweise.To solve the problem of inherent instability in virtual sources at close range, an approach was proposed in [10]. This is based on the use of multipole models solves the problem of complexity and instability only partially.
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[1]
A.J. Berkhout, D. de Vries, and P. Vogel. Acoustic control by wave field synthesis. Journal of the Acoustical Society of America, Volume 93(5):2764―2778, May 1993 AJ Berkhout, D. de Vries, and P. Vogel. Acoustic control by wave field synthesis. Journal of the Acoustical Society of America, Volume 93 (5): 2764-2778, May 1993 -
[2]
S. Spors, R. Rabenstein, and J. Ahrens. The Theory of Wave Field Synthesis Revisited. In proceedings of 124th Convention of the Audio Engineering Society, May 17-20, Amsterdam, The Netherlands, 2008 S. Spors, R. Rabenstein, and J. Ahrens. The Theory of Wave Field Synthesis Revisited. In proceedings of 124th Convention of the Audio Engineering Society, May 17-20, Amsterdam, The Netherlands, 2008 -
[3]
J. Daniel, Représentation de champs acoustiques, application à la transmission et à la reproduction de scènes sonores complexes dans un contexte multimedia, PhD thesis, Université Paris 6, 2001 J. Daniel, Representation of Acoustics Acoustics, Application for the Transmission and Playback of Matters in Multimedia, PhD thesis, Université Paris 6, 2001 -
[4]
J. Ahrens and S. Spors. Analytical driving functions for higher order Ambisonics. In IEEE International Conference on Acoustics, Speech, and Signal Processing (ICASSP), Las Vegas, Nevada, March 30th―April 4th 2008 J. Ahrens and S. Spors. Analytical driving functions for higher order Ambisonics. In IEEE International Conference on Acoustics, Speech, and Signal Processing (ICASSP), Las Vegas, Nevada, March 30th-April 4th, 2008 -
[5]
S. Spors, H. Wierstorf, M. Geier, and J. Ahrens. Physical and perceptual properties of focused sources in wave field synthesis. In 127th AES Convention. Audio Engineering Society (AES), October 2009 S. Spors, H. Wierstorf, M. Geier, and J. Ahrens. Physical and perceptual properties of focused sources in wave field synthesis. In 127th AES Convention. Audio Engineering Society (AES), October 2009 -
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S. Spors and J. Ahrens. Local sound reproduction by virtual secondary sources. In AES 40th International Conference on Spatial Audio, Tokyo, Japan, October 2010. Audio Engineering Society (AES) S. Spors and J. Ahrens. Local sound reproduction by virtual secondary sources. AES 40th International Conference on Spatial Audio, Tokyo, Japan, October 2010. Audio Engineering Society (AES) -
[7]
J. Ahrens, "The single-layer potential approach applied on sound field synthesis and its extension to nonenclosing distributions of secondary sources," Ph.D. dissertation, Technische Universität Berlin, 2010 J. Ahrens, "The single-layer potential approach applied to sound field synthesis and its extension to non-closing distributions of secondary sources," Ph.D. Dissertation, Technische Universität Berlin, 2010 -
[8]
R. Duraiswami, D. Zotkin, and N. Gumerov, "Interpolation and range extrapolation of hrtfs," in IEEE International Conference on Acoustics, Speech, and Signal Processing (ICASSP), Montreal, Canada, May 2004 R. Duraiswami, D. Zotkin, and N. Gumerov, "Interpolation and Range Extrapolation of Hrtfs," in the IEEE International Conference on Acoustics, Speech, and Signal Processing (ICASSP), Montreal, Canada, May 2004 -
[9]
W. Zhang, T. Abhayapala, and R. Kennedy, "Modal expansion of HRTFs: continuous representation in frequency-range-angle," in IEEE International Conference on Acoustics, Speech, and Signal Processing (ICASSP), Taipei, Japan, 2009 W. Zhang, T. Abhayapala, and R. Kennedy, "Modal Expansion of HRTFs: Continuous Representation in Frequency Range Angle," in the IEEE International Conference on Acoustics, Speech, and Signal Processing (ICASSP), Taipei, Japan, 2009 -
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D. Menzies, "Calculation of near-field head related transfer functions using point source representations," in Ambisonics Symposium, Graz, Austria, June 2009 D. Menzies, "Calculation of near-field head-related transfer functions using point source representations," in Ambisonics Symposium, Graz, Austria, June 2009 -
[11]
M. Noisternig, A. Sontacchi, T. Musil, and R. H¨oldrich, "A 3D Ambisonics based binaural sound reproduction system," in AES 24th International Conference on Multichannel Audio. Banff, Canada: AudioEngineering Society (AES), June 2003 M. Noisternig, A. Sontacchi, T. Musil, and R. H¨richrich, "A 3D Ambisonics based binaural sound reproduction system," in AES 24th International Conference on Multichannel Audio. Banff, Canada: Audio Engineering Society (AES), June 2003 -
[12]
J. Ahrens and S. Spors. Implementation of directional sources in wave field synthesis. In IEEE Workshop on Applications of Signal Processing to Audio and Acoustics, New Paltz, USA, October 2007 J. Ahrens and S. Spors. Implementation of directional sources in wave field synthesis. In IEEE Workshop on Signal Processing to Audio and Acoustics, New Paltz, USA, October 2007
Es ist daher Aufgabe der Erfindung, ein Verfahren und ein System zur Berechung synthetischer Außenohrübertragungsfunktionen bereitzustellen.It is therefore an object of the invention to provide a method and system for calculating synthetic outer ear transmission functions.
Diese Aufgabe wird durch ein Verfahren und System gemäß den unabhängigen Ansprüchen 1 und 10 gelöst. Die abhängigen Ansprüche 2 bis 9 betreffen besondere Ausführungsformen.This object is achieved by a method and system according to
Das Konzept der Erfindung betrifft die Nutzung von Verfahren der Schallfeldsynthese zur Berechnung oder Generierung von synthetischen Außenohrübertragungsfunktionen.The concept of the invention relates to the use of methods of sound field synthesis for the calculation or generation of synthetic outer ear transmission functions.
Diese Berechnung erfolgt gemäß einem Aspekt der Erfindung durch Bereitstellen einer Datenbank von Paaren von Außenohrübertragungsfunktionen für eine Vielzahl von ersten Quellenpositionen, wobei jeweils mindestens ein Paar Außenübertragungsfunktion für eine erste Quellenposition durch eine Messung ermittelt wird. Ein jedes dieser Paare von Außenohrübertragungsfunktionen wird als virtueller Lautsprecher an der entsprechenden ersten Quellenposition interpretiert. Unter Verwendung der virtuellen Lautsprecher werden mittels eines Verfahrens der Schallfeldsynthese für mindestens eine virtuelle Schallquelle an einer weiteren Quellenposition mindestens ein Paar von synthetischen Außenohrübertragungsfunktionen berechnet.This calculation is made in accordance with an aspect of the invention by providing a database of pairs of outer ear transmission functions for a plurality of first source positions, each determining at least one pair of outer transmission functions for a first source position by a measurement. Each of these pairs of outer ear transmission functions is interpreted as a virtual speaker at the corresponding first source position. Using the virtual speakers, a method of sound field synthesis for at least one virtual sound source at another source position computes at least one pair of synthetic outer ear transmission functions.
Die virtuellen Lautsprecher lassen sich als Elementarschallquellen zur Generierung eines beliebigen Schallfeldes durch ein Verfahren der Wellenfeldsynthese verwenden. Mittels eines solchen Verfahrens lassen sich die Ansteuersignale für die virtuellen Lautsprecher hinsichtlich Betrag und Phase so berechnen, dass eine gewichtete Superposition des von jedem virtuellen Lautsprecher hervorgerufenen Elementarschallfeldes das gewünschte Schallfeld in seiner Gesamtheit ergibt. Das gewünschte Schallfeld ist hierbei ein Schallfeld, das sich von einer beliebigen virtuellen Schallquelle, die an einem beliebigen Ort im Raum platziert sein kann, ergibt. Dadurch ist es möglich, eine Übertragungsfunktion, welche der Schallausbreitung von einer beliebigen virtuellen Schallquelle entspricht, zu synthetisieren. Es handelt sich mithin um eine synthetische Außenohrübertragungsfunktion. Die Berechnungsmethode lässt sich zur Erstellung einer Datenbank mit apriori berechneten synthetischen Außenohrübertragungsfunktionen für eine Vielzahl von Positionen der virtuellen Schallquelle verwenden. Auf eine solche Datenbank kann zur Modellierung beliebiger Klangwelten zurückgegriffen werden.The virtual speakers can be used as elementary sound sources for generating any sound field by a method of wave field synthesis. By means of such a method, the drive signals for the virtual loudspeakers with respect to magnitude and phase can be calculated such that a weighted superposition of the elementary sound field produced by each virtual loudspeaker yields the desired sound field in its entirety. The desired sound field here is a sound field that results from any virtual sound source that may be placed anywhere in the room. This makes it possible to synthesize a transfer function corresponding to the sound propagation from any virtual sound source. It is therefore a synthetic outer ear transfer function. The calculation method can be used to create a database of afore-calculated synthetic outer ear transmission functions for a variety of positions of the virtual sound source. Such a database can be used to model any sound world.
Gemäß einem weiteren Aspekt der Erfindung wird ein Raummodell bereitgestellt, wobei Ausbreitungswege und ―eigenschaften simuliert werden. Bevorzugt wird mindestens eine Spiegelquelle synthetisiert, die zu einer virtuellen Schallquelle gehört. Dazu kann ein Verfahren zur normalen Schallfeldsynthese eingesetzt werden. Allgemein ist die Berechnung durch virtuelle lokale Schallfeldsynthese oder andere Verfahren der Wellenfeldsynthese durchführbar.According to another aspect of the invention, a space model is provided that simulates propagation paths and properties. Preferably, at least one mirror source is synthesized which belongs to a virtual sound source. For this purpose, a method for normal sound field synthesis can be used. In general, the calculation can be carried out by virtual local sound field synthesis or other wave field synthesis methods.
Ein weiterer Aspekt der Erfindung betrifft ein System zum Durchführen eines Verfahrens für die Berechnung der Generierung synthetischer Außenohrübertragungsfunktionen.Another aspect of the invention relates to a system for performing a method for computing the generation of synthetic outer ear transmission functions.
Außenohrübertragungsfunktionen charakterisieren die Schallausbreitung von der bei der Messung verwendeten Schallquelle zu den Ohren des Zuhörers. Wird jetzt ein gesamter Datensatz von Außenohrübcrtragungsfunktion für eine Vielzahl von möglichen Quellpositionen gemessen, so können diese Quellpositionen als virtuelle Lautsprecher interpretiert werden. Durch die gewichtete Superposition der Lautsprechersignale kann dann der Einfluss des gesamten Ensembles dieser virtuellen Lautsprecher am Ohr des Zuhörers simuliert werden. Steuert man nun diese virtuellen Lautsprecher mit einem Verfahren der Schallfeldsynthese an, so können die Ohrsignale für nahezu beliebige virtuelle Quellenpositionen synthetisiert werden. Kopfdrehungen können durch das dynamische Austauschen der verwendeten Außenohrübertragungsfunktionen berücksichtigt werden.External ear transmission functions characterize the sound propagation from the sound source used in the measurement to the ears of the listener. If an entire data set of outer ear transfer function is now measured for a multiplicity of possible source positions, these source positions can be interpreted as virtual loudspeakers. The weighted superposition of the loudspeaker signals then simulates the influence of the entire ensemble of these virtual loudspeakers on the ear of the listener. If one now controls these virtual speakers with a method of sound field synthesis, the ear signals can be synthesized for virtually any virtual source positions. Head turns can be accounted for by dynamically exchanging the outer ear transfer functions used.
Mit diesem erfindungsgemäßen Verfahren lassen sich Außenohrübertragungsfunktionen inter-und extrapolieren und Datensätze von synthetischen Außenohrübertragungsfunktionen können mit anderen Distanzen der Quelle als denen bei der Messung vorliegenden bereitgestellt werden. Zusätzlich lassen sich die synthetischen Außenohrübertragungsfunktionen für komplexe Quellenmodelle aus Messungen einfacher Quellen berechnen.With this inventive method, outer ear transmission functions can be interpolated and extrapolated, and data sets of synthetic outer ear transmission functions can be provided at different distances from the source than those present in the measurement. In addition, the synthetic outer ear transfer functions for complex source models can be calculated from simple source measurements.
Das Verfahren und das zugeordnete System der Erfindung werden detaillierter im Folgenden anhand von Ausführungsbeispielen und den Zeichnungen beschrieben.The method and the associated system of the invention will be described in more detail below with reference to exemplary embodiments and the drawings.
Es zeigen:
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eine schematische Darstellung für die Messung einer linken/rechten Außenohrübertragungsfunktion und Nutzung dieser für die virtuelle Akustik,Figur 1 -
einen schematischen Aufbau für die Beschreibung des Wirkprinzips eines Verfahrens der Schallfeldsynthese für die Generierung synthetischer Außenohrübertragungsfunktionen einer Ausführungsform,Figur 2 -
ein Blockschaltbild einer Ausführungsform eines Systems für die Berechung synthetischer Außenohrübertragungsfunktionen mittels der lokalen Wellenfeldsynthese einer Ausführungsform,Figur 3 -
ein Diagramm mit einen gemessenen Datensatz von linken Außenohrübertragungsfunktionen,Figur 4 -
ein Diagramm mit einer Datenbank von synthetischen linken Außenohrübertragungsfunktionen, welche durch Wellenfeldsynthese berechnet wurden, undFigur 5 -
ein Diagramm mit einer Datenbank von synthetischen linken Außenohrübertragungsfunktionen, welche durch lokale Wellenfeldsynthese berechnet wurden.Figur 6
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FIG. 1 a schematic representation for the measurement of a left / right outer ear transmission function and use of this for the virtual acoustics, -
FIG. 2 1 shows a schematic structure for the description of the operating principle of a method of sound field synthesis for the generation of synthetic outer ear transmission functions of an embodiment, -
FIG. 3 3 is a block diagram of an embodiment of a system for calculating synthetic outer ear transmission functions by means of the local wave field synthesis of an embodiment, -
FIG. 4 a diagram with a measured data set of left outer ear transmission functions, -
FIG. 5 a diagram with a database of synthetic left outer ear transfer functions, which were calculated by wave field synthesis, and -
FIG. 6 a diagram with a database of synthetic left outer ear transfer functions, which were calculated by local wave field synthesis.
In
Diese Messung kann für eine Vielzahl von ersten Quellenpositionen durchgeführt werden. Beispielsweise kann ein Lautsprecher an ersten Quellenpositionen auf einer kreisförmigen Kontur 7 wie in
Die für die Berechnung von synthetischen Außenohrübertragungsfunktionen verwendeten gemessenen Außenohrübertragungsfunktionen von ersten Quellpositionen werden in einer Datenbank bereitgestellt. In der rechten Hälfte von
Eine Ausführungsform zur Berechnung von synthetischen Außenohrübertragungsfunktionen ist in
Mit dem beschriebenen Verfahren können auch Datenbanken von synthetischen Außenohrübertragungsfunktionen berechnet werden. Dazu wird als Quellsignal 1 einer virtuellen Quelle ein Impuls genommen und die gesamte Inpulsantwort von der virtuellen Schallquelle 8 zu den Ohren berechnet. Durch Variation der Quellenposition, z.B. auf einer kreis- bzw. kugelförmigen Kontur 9 kann ein synthetischer Datensatz von Außenohrübertragungsfunktionen berechnet werden.With the described method, databases of synthetic outer ear transmission functions can also be calculated. For this purpose, an impulse is taken as the
Prinzipiell geeignete Verfahren der Schallfeldsynthese sind, aufgrund der zugrundeliegenden zirkulären/sphärischen Geometrie gemessener Außenohrübertragungsfunktionen, zum Beispiel die Wellenfeldsynthese und Ambisonics höherer Ordnung. In ihrer theoretischen Grundlage gehen beide Verfahren von eine räumlich kontinuierlichen Verteilung von Lautsprechern (Sekundärquellen) aus. In der Praxis sind die Außenohrdbertragungsfunktionen allerdings nur an räumlich diskreten Positionen verfügbar. Dies führt zu Artefakten in den synthetisierten Ohrsignalen bzw. den synthetisierten Außenohrübertragungsfünktionen aufgrund der räumlichen Diskretisierung. Dies ist selbst dann der Fall wenn die Außenohrübertragungsfunctionen relativ fein abgetastet werden. Zum Beispiel treten in einer synthetischen Außenohrübertragungsfunktion ab einer Frequenz von ca. 10 kHz Artefakte auf, wenn die verwendeten Außenobrübertragungsfünktionen in 1 Grad Schritten bei einer Distanz der bei der Messung verwendeten Quelle von 2-3 Meter gemessen wurden. Dies wird nachstehend anhand von
Eine Ausführungsform der Erfindung basiert auf Verwendung der lokalen Schallfeldsynthese zur Berechnung synthetischer Ohrsignale bzw. Außenohrübertraguugsfunktionen, um die Artefakte der räumlichen Diskretisierung zu vermeiden bzw. zu verringern. Durch die lokale Schallfeldsynthese kann ein Bereich höherer Genauigkeit um den Kopf des Zuhörers gelegt werden. Dadurch werden werde die Artefakte verringert und bessere Ergebnisse erzielt. Dies wird nachstehend anhand von
Prinzipiell kann jeder Algorithmus zur lokalen Schallfeldsynthese genutzt werden, so finden in verschiedenen bevorzugten Ausfühmngsformen die in
Aufgrund einer typischerweise kleinen Apertur von beispielsweise etwa 20 cm der lokalen Zone 14 ist es nicht erforderlich, ein Verfahren zur lokalen Schaltfeldsynthese wie es in
In einer Ausführungsform wird durch das Nachführen der virtuellen Quellposition mit der Kopfposition des Zuhörers eine dynamische binaurale Synthese, die Kopforientierung und - position berücksichtigt, realisiert. Das dynamische Nachführen ist für die Qualität virtueller akustischer Umgebungen ein entscheidender Faktor. Der Vorteil dieser Ausführungsform liegt in einer effizienten Berücksichtigung der Hörerposition im Vergleich zu Lösungen, wo lediglich die Orientierung des Kopfes berücksichtigt wird. Für eine Berücksichtigung der Kopfposition wäre eine Datenbank von Außenohrübertragungsfunktionen nötig, die für viele nahe beieinander liegende Quellenpositionen gemessen wurde.In one embodiment, by tracking the virtual source position with the listener's head position, a dynamic binaural synthesis, head orientation, and taken into account, realized. Dynamic tracking is a key factor in the quality of virtual acoustic environments. The advantage of this embodiment lies in an efficient consideration of the listener position compared to solutions, where only the orientation of the head is taken into account. Considering the head position would require a database of outer ear transmission functions measured for many nearby source locations.
Das Verfahren kann durch die Simulation eines Raummodells ergänzt werden. Zum Beispiel können die zur virtuellen Quelle gehörigen Spiegelquellen mit hoher Auflösung durch Verwendung der lokalen Schallfeldsynthese synthetisiert werden. Die vorliegende Erfindung ermöglicht eine effiziente Berücksichtigung der Hörerposition.The method can be supplemented by the simulation of a room model. For example, the high resolution mirror sources associated with the virtual source may be synthesized using local sound field synthesis. The present invention enables efficient consideration of the listener position.
In einer Ausführungsform wird die virtuelle Quelle neben dem typischen Punktquellenmodell auch als Quelle mit komplexer Richtcharakteristik modelliert, vorzugsweise mit dem in [12] beschriebenen Verfahren. Auch hier bietet die Kombination mit der lokalen Schallfeldsynthese einen wesentlichen Vorteil, da die gewünschte Richtcharakteristik nicht durch die Artefakte der räumlichen Abtastung verfälscht wird.In one embodiment, in addition to the typical point source model, the virtual source is also modeled as a complex directional source, preferably with the method described in [12]. Again, the combination with the local sound field synthesis offers a significant advantage, since the desired directional characteristic is not distorted by the artifacts of the spatial sampling.
Eine bevorzugte Ausführungsform beinhaltet inhärent eine Interpolation der Außenohrübertragungsfunktionen bezüglich des Winkels. Die Position der virtuellen Quelle kann bezüglich der Winkelauflösung beliebig gewählt werden. Dies ermöglicht eine Interpolation eines gemessenen Datensatzes.A preferred embodiment inherently involves interpolation of the outer ear transmission functions with respect to the angle. The position of the virtual source can be arbitrarily selected with respect to the angular resolution. This allows interpolation of a measured data set.
In einer Ausführungsform wird der verwendete Datensatz von Außenohrübertragungsfunktionen nicht lediglich auf einer zirkulären oder sphärischen Kontur, sondern auf einer Kontur beliebiger Gestalt gemessen. Der Vorteil dieser Ausführungsform ist die effiziente Messung von Außenohmbertragungsfünktionen ohne geometrische Einschränkungen.In one embodiment, the data set of outer ear transfer functions used is measured not only on a circular or spherical contour, but on a contour of any shape. The advantage of this embodiment is the efficient measurement of outer ohm transfer functions without geometric constraints.
Ein weiteres Ausführungsbeispiel wird anhand von
In
Die Erfindung wurde anhand von Beispielen und der Figuren näher erläutert, wobei diese Darstellung die Erfindung nicht einschränken soll. Es versteht sich, dass Fachleute Änderungen und Abwandlungen machen können, ohne den Umfang der folgenden Ansprüche zu verlassen. Insbesondere umfasst die Erfindung Ausführungsformen mit jeglicher Kombination von Merkmalen der verschiedenen Ausführungsformen, die hier beschrieben sind.The invention has been explained in more detail with reference to examples and the figures, this representation is not intended to limit the invention. It is understood that those skilled in the art can make changes and modifications without departing from the scope of the following claims. In particular, the invention includes embodiments with any combination of features of the various embodiments described herein.
Claims (10)
wobei die Vielzahl von weiteren Quellenpositionen, an denen das jeweils mindestens eine Paar von synthetischen Außenohrübertragungsfunktionen berechnet wird, auf einer weiteren kreisförmigen Kontur oder kugelförmigen Kontur angeordnet sind, wobei die weitere kreisförmige Kontur oder kugelförmige Kontur vorzugsweise verschieden ist von der ersten kreisförmigen Kontur oder der ersten kugelförmigen Kontur, und wobei besonders bevorzugt eine erste Distanz von der Position eines Zuhörers zur ersten kreisförmigen Kontur oder ersten kugelförmigen Kontur verschieden ist von einer weiteren Distanz von der Position des Zuhörers zur weiteren kreisförmigen Kontur oder weiteren kugelförmigen Kontur.The method of any one of claims 1 to 3, wherein the plurality of first source locations at which each of the at least one pair of outer tube transfer functions is measured are disposed on a first circular contour or a first spherical contour, and
wherein the plurality of further source positions at which the respective at least one pair of synthetic outer ear transfer functions is calculated are arranged on a further circular contour or spherical contour, wherein the further circular contour or spherical contour is preferably different from the first one circular contour or the first spherical contour, and particularly preferably a first distance from the position of a listener to the first circular contour or first spherical contour is different from a further distance from the position of the listener to another circular contour or other spherical contour.
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