Abstract:
The invention relates to a system for simulating stereophonic sound ( 1 ), comprising the following: a core module ( 10 ) having a space simulation module ( 11 ), an echo module and an interface module ( 15 ), a control module ( 20 ), a digital audio delay matrix module ( 21 ), and a digital audio/network system ( 30 ). The invention is characterized in that said system provides an echo and/or directional acoustic irradiation on the basis of a system latency less than 2.5 ms by means of the core module ( 10 ), the control module ( 20 ), and the digital audio network system. A system for simulating stereophonic sound is thus provided, which system operates with a reduced number of loudspeakers and without dedicated components and/or proprietary hardware and provides a plurality of different functions, such as extension of the echo time and directional acoustic irradiation.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application is a U.S. National Phase filing of International Application No. PCT/DE2012/001138, filed on Nov. 28, 2012, designating the United States of America and claiming priority to German Patent Application No. 10 2011 119 642.4, filed Nov. 28, 2011, and this application claims priority to and the benefit of the above-identified applications, which are both incorporated by reference herein in their entireties. 
     FIELD 
     The present disclosure relates to a system for simulating spatial sound, a method and a use of the system for simulating spatial sound which enables an extension of the echo time and/or a directional acoustic irradiation. 
     BACKGROUND 
     In modern audio playback systems individual audio sources can be located in space by the use of a plurality of loudspeakers. 
     In principle there are two different playback concepts for this purpose. In the conventional surround-sound systems which are usual in the cinema and home entertainment sector, the location and space information is already mixed during the audio mixing operation into individual channels to be transmitted separately, and with a playback system consisting of a plurality of loudspeakers the individual channels are played back. In this case the reproducing loudspeakers must be placed at a position relative to the listener predetermined according to the recording in order to achieve an impression of space. 
     More advanced systems for stereo simulations generate the control signals for the individual loudspeakers only during the reproduction, based upon position information of a sound source with respect to the playback space and the space information of a playback environment to be simulated. The systems are based on the wave field synthesis (WFS). This involves a three-dimensional audio playback process for generating virtual acoustic environments. In this case wavefronts emanating from a virtual point are generated, of which the acoustic location is not dependent upon a listener&#39;s position. The WFS is based on the Huygens principle, according to which each wavefront may also be regarded as a superimposition of elementary waves. Thus any wavefront can be synthesised from these elementary waves. For this purpose, by further means a computer program controls individual loudspeakers arranged around the listener for sound wave generation at exactly the time at which a virtual wavefront would have run through its point in space. 
     The mathematical basis for this is the Kirchhoff-Helmholtz integral. This states that the sound pressure is determined at every point within a source-free volume if the sound pressure and sound particle velocity are determined at all points on its surface. Thus every sound field can be reconstructed if the sound pressure and sound particle velocity are reconstructed on all points on the surface of the volume. For this purpose, however, the entire surface of the volume, that is to say all walls, ceilings and preferably floors of the playback space would have to be equipped with closely packed sound generators. Furthermore all sound generators, with their respective signal, would have to be individually controlled. In addition the space would have to be completely soundproof in order to meet the condition of the source-free volume. 
     Thus three-dimensional audio playback systems based on wave field synthesis produce an impression of natural and spatial sound with the aid of many loudspeakers disposed close together. Because of the high requirements with regard to space, number of loudspeakers and computing power, as a rule only proprietary systems produced, which may be appropriate only for a dedicated application (for example extension of the echo time). Furthermore conventional systems have dedicated components for signal transmission, directional processing and spatial processing, which may lead to significantly higher system latencies and to a high system price. In addition various A/D and D/A conversions can have poorer signal-to-noise ratios. 
     A method for controlling a sound reproduction system which is designed in order to produce an impression of spatial sound is known from EP 1 878 308 B1. In this connection a very large number of loudspeakers disposed adjacent to one another (a so-called loudspeaker array) is used for one listener. In this case the orientation of the loudspeakers is 360° in a horizontal arrangement. However, this method may need a very large number of loudspeakers and dedicated hardware. 
     A system for simulating spatial sound is provided, which can operate with a reduced number of loudspeakers and without dedicated components and/or proprietary hardware, and a plurality of different functions, such as extension of the echo time and directional acoustic irradiation. 
     This object is achieved by a system for simulating spatial sound with the features of Claim  1 . Advantageous embodiments and modifications of the disclosure are described in the subordinate claims. 
     A system for simulating spatial sound is provided, which may include the following:
         a core module with a stereo simulation module simulation module, an echo module and an interface module,   a control module,   a digital audio delay matrix module and   a digital audio/network system.       

     Thus, a plurality of audio signals can be reproduced with regard to amplitude and time with a system latency less than 2.5 ms by means of a plurality of loudspeakers. In this case the system latency encompasses the complete system, from the sound source to the loudspeaker, that is to say also the amplifier, I/O modules, equaliser, signal converter, etc. On the basis of the limited latency period of &lt;2.5 ms the system is significantly easier to handle, in particular when measuring in relation to feedback. In this case, the limited latency period is a prerequisite in order also to provide directional acoustic irradiation in addition to echo or extension of echo. The substantial superiority of this system comes to light primarily in live performances, where synchronicity between the audio signal and the gestures of the actor plays an important role. Furthermore, actors moving in the sound field of the loudspeaker are not perceived as their own echo, as in the case of a system subject to latency. 
     The core module controlled by the control module has a synthetic echo module for generating a synthetic echo and a regenerative echo module for generating a regenerative echo. In this connection the synthetic echo can be mixed as required with the regenerative echo. The regenerative echo module is also controlled inter alia by microphones. 
     The echo or the extension of the echo time and the directional acoustic irradiation in the core module are brought together or merged sequentially or simultaneously. 
     Furthermore the digital audio/network system may include:
         a ceiling-mounted loudspeaker and   a wall-mounted loudspeaker,
 
wherein the loudspeakers are oriented substantially horizontally in bands and the horizontal distance between the loudspeakers is substantially less than or equal to 1.5 m relative to one another. In this case this distance is measured from diaphragm center to diaphragm center. In addition the vertical position of the front and wall-mounted loudspeakers is located slightly above the audience. Thus a representative auditory impression is already achieved in a region (sweet spot) from a distance of likewise 1.5 m from the loudspeaker. With a reduced distance or with half the distance of the loudspeakers from one another of 0.75 m, the sweet spot is significantly increased, so that a representative sound experience is already achieved from 0.75 m. In this way the virtual sources can be located better and thus make a clearer impression. Moreover the focus effect of the sources is improved. Furthermore the listener feels as though he is in the virtual sound environment. If the distance of the loudspeakers from one another is increased and thus the number of loudspeakers is reduced, then effects such as audience area, location, focus and enclosure are also reduced.
       

     In this case the loudspeakers can be oriented on a rectangular, rhomboid or honeycomb matrix. 
     The ceiling-mounted loudspeakers ( 33   c ) can be oriented on a logarithmic matrix R 1  extending in a longitudinal direction of a space ( 50 ). 
     Furthermore, the digital audio/network system may have an I/O module and an amplifier module by which a plurality of loudspeakers can be controlled. With a large number of amplifier modules and I/O modules, in particular up to 512 loudspeakers can be simultaneously controlled individually. 
     The system for simulating spatial sound may have a tracking system which includes a geodata transmitter and a geodata receiver, by which the position of a sound source in live operation is ascertained and delivered to the control module for conversion. 
     By means of the tracking system real movements and/or virtual movements can be converted with the system for simulating spatial sound and made audible for the audience. 
     Due to the configuration of the core module, and thus of the digital audio/network system by means of CAD software, spaces which are treated acoustically so as to have a short echo time and thus good intelligibility of speech, in particular by use of a preset, may have the acoustic attributes for example of a concert hall. Because of the CAD module and the presets the system can be freely scalable and applicable to spaces of all possible sizes and shapes as well as surfaces. Even in the case of greatly split spaces, it is possible to compensate for sound reflections. Symmetry of space is not a prerequisite here. In this case the sound characteristics of a space is simulated and calculated on the basis of the geometric conditions and/or the surface properties, such as for example sound reflection behaviour. 
     The system for simulating spatial sound may have an open network topology and as a result can be quickly installed and uninstalled. Thus the system can be used both in a fixed installation, for example in a concert hall, and also as a mobile installation at festivals and for example large events. Furthermore, as a result the setting up and dismantling is simplified and thus leads to a saving of time and cost. 
     By means of acoustic panels and/or acoustic wall parts it is possible in an acoustically inadequate environment to prevent sound from being reflected and/or to prevent the production of echo chambers which cannot be monitored. For this purpose the acoustic panels and/or acoustic wall parts are appropriately positioned in an acoustically inadequate environment. In this case both passive and also active (anti-noise) panels are used. These may have for example a passive sound insulation at certain points. 
     The system for simulating spatial sound can be used for production of a playback space which corresponds to the generating space acoustically, in particular in the reverberation characteristics. As a result for example a sound characteristic in a building with a long echo, for example a church, in an environment with a short echo, for example an open-air site, can be simulated and vice versa. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention is explained with reference to examples together with the appended drawings. In the drawings: 
         FIG. 1  shows a schematic representation of the system for simulating spatial sound according to one example; 
         FIG. 2  shows a schematic representation of the system for simulating spatial sound with details of the digital audio/network system according to the example of  FIG. 1 ; 
         FIG. 3  shows a schematic representation of a space in plan view for the system for simulating spatial sound according to a the example of  FIG. 1 ; 
         FIG. 4  shows a schematic representation of the system for simulating spatial sound with a stereo simulation according to the example of  FIG. 1 ; 
         FIG. 5  shows a schematic representation of the system for simulating spatial sound with components of the tracking system and a sound source in various positions in relation to an audience according to an example; 
         FIG. 6  shows a schematic representation of the system for simulating spatial sound according to another example; 
         FIG. 7  shows a schematic representation of the arrangement of the loudspeakers on different matrices; and 
         FIG. 8  shows a schematic representation of the correlation between the number of loudspeakers and the size of the sweet spot. 
     
    
    
     DETAILED DESCRIPTION 
       FIGS. 1 to 4  show an example of a system  1  for simulating spatial sound  1  according to certain aspects. 
     As can be seen in  FIG. 1 , the system for simulating spatial sound  1  has a core module  10 , a control module  20 , a CAD module  25  and a digital audio/network system  30 . All components are connected to one another by wiring, for example, by Ethernet wiring, by means of a switch  36 . 
     The control module  20  provides a user interface, calculates spatial parameters and transmits the corresponding data via Ethernet to the core module  10 . 
     The core module  10  which is supplied by the control module  20  with corresponding parameters is responsible for the audio processing and controls the entire digital audio/network system  30 . A plurality of sound sources  34 , in particular up to  32  sound sources  34 , can be managed and controlled. 
     The core module  10  has a stereo simulation module (RSM)  11 , a synthetic echo module  12 , a regenerative echo module  13 , a distributor module  14 , a digital audio delay matrix module  21 , by which three-dimensional echo values are calculated, and an interface module  15 . By the transmitted parameters an echo or an extension of the echo time and/or a directional acoustic irradiation in the stereo simulation module (RSM)  11 , the synthetic echo module  12  and the regenerative echo module  13  for a sound source  34  is calculated and thus a three-dimensional acoustic stereo simulation is provided. In this case the synthetic echo and the regenerative echo are processed sequentially or simultaneously in the core module  10 . For the stereo simulation parameters a plurality of acoustically measured spaces are employed. As a result for example a sound characteristic in a building with a long echo, for example a church, in an environment with a short echo, for example a concert hall, can be simulated and vice versa. Thus acoustically difficult conditions, for example a large stadium, with a sound experience such as that prevailing in a concert hall can be controlled. 
     In addition spatial parameters can be adapted and also simulated by means of the control module  20 . This can take place by means of a 3D-capable CAD system which calculates the sound characteristics of a space on the basis of the geometric conditions and/or the surface properties, such as for example sound reflection behaviour. 
     The digital audio/network system  30  comprises an amplifier module  31 , an I/O module  32 , front loudspeaker  33   a,  wall-mounted loudspeaker  33   b,  in particular a ceiling-mounted loudspeaker  33   c,  a sound source  34 , both fixed microphones  35  and also at least one mobile microphone (not shown), LAN cable  37 , loudspeaker cable  38  and microphone cable  39 . In this case the fixed microphones  35  are used for control of the regenerative echo module  13  for generating a regenerative echo. The mobile microphones are used for example by live actors. In this case a noise which is recorded by the stationary microphones  35  and reproduced by the loudspeakers with a time offset is designated as a regenerative echo. 
     As can be seen from  FIG. 2 , the input or output means, sound source  34  and amplifier  31  are connected by means of the I/O module  32  which in turn is connected by LAN wiring to the switch  36  and thus also to the core module  10 , the control module  20  and the CAD module  25 . 
     Thus all sound sources  34  are made available to the stereo simulation module  11  by means of the interface module  15 . In this case the interface module  15  preferably uses standard Ethernet technology. The management the I/Os takes place centrally in the core module  10 . Corresponding ceiling reflections are also generated here and can be reproduced by means of ceiling-mounted loudspeakers  33   c.  Furthermore an assignment can take place for the horizontal and/or vertical arrangement of front loudspeaker  33   a  and wall-mounted loudspeaker  33   b.    
     Because of the free scalability of the system  1  for simulating spatial sound, even in the case of greatly split spaces, it is possible to compensate for sound reflections. Moreover no symmetry of space or special geometry is presupposed. In this connection an annular band consisting of front loudspeaker  33   a  and wall-mounted loudspeaker  33   b  is mounted in a slightly raised position above the audience  51  at a spacing relative to one another which is optimised for the number and spatial sound. This spacing is variable and may be defined according to the requirements. In a concert hall the spacing for example in a front and central portion of a space  50 , with respect to the audience, is approximately 1.5 m. In a rear portion of the space a large spacing may be chosen on the basis of the directional perception characteristics of a listener selected are being. In addition to the loudspeakers  33   a,    33   b  mounted in a ring on the wall, in particular in the front and central portion of the space  50  the ceiling-mounted loudspeakers  33   c  together with microphones  35  which in particular also control the regenerative echo are mounted on the ceiling. Thus the digital audio/network system  30  can be used both as a system for variable extension of the echo time and also as a system for directional acoustic irradiation. 
       FIG. 4  shows an example application of the ceiling-mounted loudspeakers  33   c,  wherein they are oriented on a logarithmic matrix R 1  extending in the longitudinal direction of the space  50  which is of rectangular construction. In this case in the front portion of the space  50  the spacing of the ceiling-mounted loudspeakers  33   c  is smaller than in a central or rear portion of the space  50 . This reflects the normal listening habits of an audience oriented in the direction of the actors and thus perceiving sound from the front more clearly than sound from the rear, so that the plurality of loudspeakers can be reduced towards the end of the hall. In circular spatial situations the ceiling-mounted loudspeakers can also be oriented on a logarithmic matrix R 1  which extends from the audience to the actors. 
     A fundamental prerequisite for the variable extension of the echo time and the directional acoustic irradiation is a system latency of less than 2.5 ms. This covers the complete signal chain, from the sound source  34  to the loudspeakers. 
     In order to ensure a fast reaction time and a guaranteed data stream, a network, preferably cable-based, preferably an Ethernet topology, in particular according to the 1000BASE-T standard, is provided for the core module  10 , control module  20 , CAD module  25  and digital audio/network system  30 . In this case for the cabling a gigabit cabling, for example to the CAT7 standard, can be chosen which is also suitable for 10 Gbit ethernet. 
     Since the system  1  for simulating spatial sound is intended to control a plurality of loudspeakers  33   a,    33   b,    33   c,  in particular up to 512 loudspeakers, a plurality of amplifier modules  31  may be needed. An amplifier module  31  simultaneously control a plurality of loudspeakers, in particular up to 8 loudspeakers. These amplifier modules  31  are in turn connected to the network by means of an I/O module  32 . In each case an I/O module  32  provides freely combinable channels, in particular up to 16 channels, both for sound sources  34  and also amplifier modules  31 . 
     Because of the required system latency, all network components, core module  10 , control module  20 , CAD module  25  and I/O modules  32  are connected to the network. 
     In order furthermore to keep the latency low and to provide a corresponding dedicated data stream per channel, each network component is connected by means of a port of a switch  36  to which the data stream can be addressed on the basis of the connected network component. Because of the requirements of the network for addressability and prioritisation on the basis of the limited latency, a switch which can evaluate and process higher transport levels of a protocol is used, in particular a layer 3 switch. Furthermore, the transmission of the audio data of the system as audio streams is prioritised for example by means of QoS (quality of service). Accordingly the data traffic for monitoring and management tasks acquires a lower priority than that of the audio streams. Thus a secure and fast transmission of the data packets is ensured. In addition a dedicated bandwidth is provided for each port of the switch  36 . On the basis of the required I/O modules  32  and the necessary bandwidth, in particular from 1.7 to 3.4 Mbit/s or higher per channel, a plurality of switches  36  are provided in the network. In order to adhere to the latency period, the number of hops which a data packet runs through from the transmitter to the receiver is limited to a maximum of 7 hops. 
     With these prerequisites in terms of network and correspondingly further hardware for the further modules used, the absolutely necessary system latency of less than 2.5 ms for the entire system can be achieved. Thus spaces originally configured to be speech-oriented with minimum echo can be converted into orchestral spaces. Furthermore, feedback is almost eliminated. 
     The control module  20  connected by means of the switch  36  to the core module  10  can not only eliminate structurally induced acoustic weak points, such as for example niches, projections, surfaces etc., in existing spaces but also during the planning of a space can simulate the acoustic characteristics of the space which are to be expected. This is possible not only for a listener&#39;s position within the space, but encompasses the entire audience  51 . The adjustment of the system is possible in different ways. For example as can be seen according to  FIG. 3 , the acoustically simulated and as yet non-existent space designated by the letter A can be changed so long as its contour approximates the broken line designated by the letter B. Thus the acoustic characteristics of a non-existent compartment can be simulated simply and quickly and expensive, significant acoustic errors can be avoided. 
     For perfect simulation of real movements and/or virtual movements with the system  1  for simulating spatial sound the core module  10  is controlled in particular by a tracking system  29 . The tracking system  29  has a geodata transmitter  27  and a g  28 . Thus for example the position of an actor (or of the sound source  34 ) is continuously determined and transmitted to the control module  20 . Thus a movement of the actor can be acoustically converted and rendered audible for the audience from every position within the audience  51 . In this connection  FIG. 4  shows a scenario with two different positions of the sound source  34 . 
     This three-dimensional system  1  for simulating spatial sound is universally applicable and is suitable in particular for seated events and for mobile purposes. By the use of standard loudspeakers a cost-effective, compact and efficient system has been developed, which can represent a realistic and three-dimensional sound scenario also without a closed wave field. 
     In this case the specified latency period of less than 2.5 ms relates to the complete signal chain integrated in the system, that is to say transmission by means of the network, echo matrix and processing (RQ, echo, etc.). This is achieved in particular with up to 512 connected loudspeakers. 
     Furthermore the three-dimensional system  1  for simulating spatial sound  1  is convincing due to an extended sweet spot and due to the possibility of live rendering. Thus the system can be used both in planetariums, cinemas and theme parks and also for live acoustic irradiation, for product presentations or three-dimensional audiovisual simulations. 
     Thus the system disclosed herein may offer the following:
         Reduced number of loudspeakers.   Individual control of each loudspeaker in amplitude and time with an algorithm based on the wave field synthesis.   Realistic impression of sound from moving sound sources       

     The examples described herein serve merely for explanation and does not constitute any limitation of the scope of protection. 
       FIG. 6  shows a second embodiment in which a control module  20  one comprises a digital audio delay matrix module  21 . 
       FIG. 7  shows the orientation of the loudspeakers on a rectangular ( FIG. 7 a   ), rhomboid ( FIG. 7 b   ), or honeycomb matrix ( FIG. 7 c   ). 
     In a further example, space geometries, surfaces and entire spaces are simulated in terms of sound by means of a CAD module  25  connected to the core module  10  and/or control module  20 . Thus already before the setting up of a space and/or building structurally induced acoustic weak points, such as for example niches, projections, surfaces etc., can be eliminated and the acoustic characteristics of the space which are to be expected can be simulated. 
     For example, in a further embodiment a digital audio/network system could be controlled by a separate computer. Furthermore, it is also conceivable that a freely scalable echo matrix is controlled by a separate computer. 
     It is also conceivable that ceiling-mounted loudspeakers  33   c  can also be oriented on a logarithmic matrix R 2  extending in a transverse direction of a space  50 . 
     In a further embodiment a smaller spacing than 1.5 m of front and wall-mounted loudspeakers is also conceivable on the basis of variable adjustment possibilities.  FIG. 8  shows the correlation between the number of active loudspeakers and the size of the resulting sweet spot. With an increasing number of active loudspeakers the sweet spot and thus the region of a representative auditory impression is enlarged. On the other hand the number of loudspeakers is reduced to a total of only four active loudspeakers, then the sweet spot is concentrated on a point in the centre of the space, as can also be seen from  FIG. 8   c.    
     For increased safeguarding against failure a redundancy of all important system components is conceivable. In this case all necessary components are doubled. 
     It is also conceivable to use wireless routes for connections of individual components. 
     LIST OF REFERENCE SIGNS 
     
         
           1  system for simulating spatial sound 
           10  core module 
           11  stereo simulation module (RSM) 
           12  synthetic echo module 
           13  regenerative echo module 
           14  distributor module 
           15  interface module 
           20  control module 
           21  digital audio delay matrix module 
           25  CAD module 
           27  geodata transmitter 
           28  geodata receiver 
           29  tracking system 
           30  digital audio/network system 
           31  amplifier module 
           32  I/O module 
           33   a  front loudspeaker 
           33   b  wall-mounted loudspeaker 
           33   c  ceiling-mounted loudspeaker 
           34  sound source 
           35  microphone 
           36  switch 
           37  LAN cable 
           38  loudspeaker cable 
           39  microphone cable 
           50  space 
           51  audience 
         R 1  matrix longitudinal direction 
         R 2  matrix transverse direction