MXPA99004254A - Method and device for projecting sound sources onto loudspeakers - Google Patents

Abstract

For the purpose of spatial reproduction of an audio signal, the latter must be projected onto the positions of the existing loudspeakers. It is desirable in this case not to have to be fixed on a specific loudspeaker configuration for transmitting the audio signal. However, a problem here is that a multiplicity of possible combinations exists. In the method according to the invention, the sound sources (3) are interpreted as acoustic objects for the purpose of projecting them onto an arbitrary loudspeaker configuration (2). Here, an acoustic object consists in that in addition to the audio signal a sound source is assigned an item of spatial information which specifies a virtual, spatial position of the sound source. In order to reproduce an acoustic object, the spatial information of the sound source and the actual position of a loudspeaker are used to calculate the virtual distance from the sound source via the loudspeaker to the hearer (1). Before reproduction, separate processing (7, 8, 9) of theaudio signal for each loudspeaker is then performed for each acoustic object.

Description

METHOD AND DEVICE FOR PROJECTING SOUND SOURCES TO LOUDSPEAKERS DESCRIPTION OF THE INVENTION The invention relates to a method and a device for projection of sound sources on loudspeakers in order, in particular, to allow spatial reproduction of sound sources.

Prior Art It is known from ISO 13818 standard MPEG-2 to a spatial representation for the purpose in a spatial representation by means of multi-nel stereo, also called surround sound, for audio reproduction. Six nels are provided in this case for the sound of multiple nels, of which three nels (left, center, right) are coupled in the space in front of the listener, two nels (left surround, right surround) are coupled in the space behind of the listener, and a sixth nel is provided for the reproduction of low calibrated tones for special effects. The sound nels are duly matrixed, otherwise, to ensure reversible compatibility with MPEG-1 audio signals and, otherwise, also to provide satisfactory possible playback, instead of a complete surround sound speaker configuration, They present a pair of speakers. In this case, the calculated signals are transmitted as the compatible MPEG-1 signals and the remaining signals as well as the additional data.

The invention It is an object of the invention to specify a method for spatial reproduction in virtual sound sources. This object is achieved by means of the method known in claim 1. It is a further object of the invention to specify a device for the application of the method according to the invention. This object is achieved by means of the device specified in claim 8. To reproduce an audio signal, it most often tends to be projected into the existing speaker positions. Few projections can be mentioned in the present by way of example: a) the projection of a mono signal over a pair of stereo speakers. b) the projection of a signal 3/2 (3 speakers in the front / two speakers behind) on a speaker array 2/2 c) the projection of a signal with the position of 3m in distance, 30 ° to the left, 10 ° elevated on a loudspeaker annulus comprising 8 loudspeakers at a distance of 2m with a spacing of 45 ° respectively. d) the projection of two sound sources in the environment on two speakers. It is desirable that you do not have to be fixed in a specific configuration for the transmission of an audio signal. However, the problem arises in this case that there is an unlimited number of possible combinations. In principle, the method according to the invention for projection sound sources on loudspeakers is that the sound sources are interpreted as acoustic objects, an acoustic object consists in addition to the audio signal a sound source it is assigned to a spatial information data unit that specifies a virtual, spatial position of the sound source.

The audio signal is advantageously processed as a function of the associated data unit of spatial information for reproducing an acoustic object. In this case, the spatial position of the loudspeaker is preferably considered additional, the virtual distance of the sound source from the loudspeaker being calculated from the spatial information and the position of the loudspeakers, and which it processes separately from the audio signal for each of the speakers being enhanced by an acoustic object. This is also advantageous when one or more of the following parameters are considered when processing the audio signals: an amplitude attenuation, for example, by wetting or diffraction, a different propagation time for the various acoustic objects and the loudspeaker , - the consideration of the dependence of the loudspeaker level on the spatial arrangement by means of the external ear function. In this case, the processing of the audio signals can be further improved when the frequency dependence of the parameters is also considered. The mathematical functions required for the consideration of the parameters such as, for example, an attenuation function are preferably transmitted and / or stored as a function of the distance and / or deflection angle. It is particularly advantageous when the data of an acoustic object was stored and / or transmitted by means of a stream of compressed data in accordance with MPEG-4 Standard. In principle, the device according to the invention for projection sound sources on the loudspeakers is that an arithmetic unit is provided, which calculates the distance of the virtual acoustic objects from the respective loudspeaker of a data unit of spatial information transmitted with the audio signal and the current position of the speakers. In this case, a memory is preferably provided in which the respective speaker positions and / or arithmetic functions for the considered parameters are stored. This is advantageous for providing actuators n x k for acoustic objects n and speakers k, an actuator performs a process of an audio signal with reference to one of the objects. In this case, a frequency dependent on the parameters is preferably also considered by the actuators, the signals being first resolved in the frequency bands by a divided filter (10), the frequency of individual bands are then processed individually, and the bands of processed frequencies being subsequently recombined by a joined filter (12). It is particularly advantageous when the divided filter and / or the attached filter are part of an audio decoder which is present in any case. In addition, one or more directional microphones may be preferably provided which are used to measure the position of the loudspeaker. Directional microphones are preferably integrated into a remote control Drawings Exemplary embodiments of the invention will be described with the help of the drawings, in which: Figure 1 shows virtual sound sources being projected onto an existing pair of loudspeakers; Figure 2 shows the graphical representation of a model to calculate sound trajectories; Figure 3 shows the block diagram of a presentation circuit of the described model; and Figure 4 shows a section of an audio decoder according to the invention Exemplary Modalities A typical problem that arises is represented in Figure 1. Two sources of virtual sound 3, violin and trumpet, are to be presented on an existing pair of speakers 2 such that the listener 1 has the impression that the violin and the trumpet are placed in the spatial positions represented in Figure 1. A model can be developed by such projection, and is based on the observation if gu i ent-e. That a person is located in a room that has a plurality of windows that are all open. There are several sources of sound outside the room, also acoustic objects finished below, for example, such as a musician in the street, a car horn, etc. The person can locate the various sound sources effectively in acoustic terms, even if they are not visible. This is based on the fact that the sound paths to several windows are different. The model described in the following is based on replacing each window with a loudspeaker. Since the speakers are correctly directed, the same sound field will result, and this could also be identically possible to locate the acoustic objects. A graphic representation of the model is represented in Figure 2. A listener 1 is located in a room in an arbitrary manner whose walls 5 consist of absorbent material, with the result that no soni or can penetrate from the outside and none of the reflections are they produce inside the room. Sources of sound 3 are basically located outside the room. Speakers or windows are taken into account through holes 6 in the walls of the room. This produces different sound trajectories 4 from the sound source 3 to the listener 1 through various loudspeakers or open windows 6. The sound enters the room in this case through all the loudspeakers or. open windows, although each sound path has its own characteristics. A presentation circuit in which the model is converted is illustrated in the block diagram shown in Figure 3. Two acoustic objects 3, "violin and trumpet, are projected in this case in the three existing speakers 2. For each object Acoustic audio signals are now processed as a function of the virtual spatial position of this acoustic object and the current position of each speaker, to allow directing according to the respective virtual sound path.In a generalization for acoustic objects n and k speakers , these are used means that nx k actuators are used, in this case, one or more of the following parameters 7, 8, 9 are considered in each of the actuators according to the virtual sound path. , the latter must first be calculated as a function of the path length, and consideration may also be given for attenuation or absorption. by air. The different functions can be considered in this case depending on the type of sound source or air attenuation. Thus, a spherical sound source loses its acoustic power with the square of the distance, it is said that the received power is given by the following f ormul a. Received power (r): = power t r ansmi tido / r2 On the contrary, a cylindrical sound source such as a train or a street, for example, loses its acoustic power only with simple distance. The respective functions can be stored in this case in the presentation circuit, but in the same way they can be transmitted and stored with the signal. In the same way they can be determined by the respective application or the user. In addition, it is also possible to consider the diffraction that occurs in loudspeakers or open windows. In order to be able to consider these diffraction effects precisely, diffraction should have to be calculated by summing all the sound trajectories by means of a specific geometric hole, taking the frequency and phase under consideration. This gives rise, in approximate terms, to the fact that the propagation of low frequencies takes place in all directions regardless of the angle of incidence, while higher frequencies the amplitude of the audio signal is a function of the angle between the input and the exit from the respective hole. An approximate formula can be used to reduce computing expenses. Such a formula can also, as already described in the case of attenuation, be transmitted at the same time or be established by the application or the user. Since the diffraction effects depend on the frequency, this might be necessary to consider its dependence on the frequency to be able to calculate exactly the diffraction attenuation. In order to realize this technical terms, it is necessary either to use filters with defined time delay groups, or to solve the signals in the frequency bands and process them individually. As shown in Figure 4, in this case the division could be developed by means of a divided filter 10, subsequently so that the process can be developed "by means of several actuators 11 and, finally, the processed signals can be recombined by a filter. 12. This can be particularly well integrated into a typical audio decoder for MPEG, AC3 or ATRAC signals, since in its case the processing is developed in the frequency domain and a split filter has already been provided for this purpose, with the result that there is no need to provide an additional divided filter. An additional parameter is the propagation time (delay) of the signal. This holds here in principle that the first wave of sound that strikes the ear is decisively involved in the perception of direction. For a path length r and a significant speed of the C. sound of approximately 340 m / s is maintained as: Delay (r): = r / c In this case, the length r can be shortened by the shortest distance between the speakers and the listener. This reduces the storage required in the presentation unit.

There is a transfer function, also called the external ear function, which is dependent on the direction and frequency, between a sound source and the human eardrum. In simple terms: the sound from the front is filtered di f ercially by the muscles of the ear that sound from behind. The external ear function could be considered if the desire is to radiate a virtual sound source, placed at the angle x, by means of a speaker that is provided at the angle z. This requires the level of differential signal between the virtual and speaker positions to be determined and the signal to be filtered appropriately. Since the external ear function is not the same for all people, it is conceivable to enable the user to select between different external ear functions for the purpose of a particularly good correction. Here, also the filters can be realized by means of actuators in the frequency plane of an audio decoder. The current speaker position must be determined to determine the path length between the virtual acoustic object and the current speaker position. Various methods are designed for this. Thus, the user could measure the space coordinates of the respective speaker boxes using a meter rule or the like, and enter the corresponding distance data in an input device that retransmits this data to the presentation circuit. The input can be improved here by means of a board in the appropriate device, or a remote control, also being possible, if appropriate, to monitor the input data or for the user to be guided by an on-screen display in a deployed device or in a focus screen. It is also possible to measure the speaker system with the help of one or more directional microphones, to save the user the mechanical measurement of distances. The distance of the loudspeaker from the directional microphone or the microphones can be determined in this case by means of the reproduction by means of the loudspeakers to a test sequence with pulses and by the measurement of the propagation time. The angles of the individual loudspeakers can be determined by means of the directional characteristic of the directional microphones. This is then possible to measure the speaker configuration automatically. In particular, this is properly seen in this case to integrate the microphones into a remote control. The entire virtual path length is then maintained from the position of the virtual acoustic object, and as described above, the position was determined for the respective speaker. Several possibilities of representation are conceivable in this case for the two positions. Thus, this can be done, for example, by means of Cartesian coordinates, that is, a distance specification in all three directions in space, or by spherical coordinates, that is, a distance specification and the specification of the horizontal and, if the vertical angle is appropriate. While the position of the speaker could remain unchanged in most cases, a change in the virtual position of the acoustic objects can occur frequently by all means. This will be the case, in particular, as long as the audio signals are reproduced in the accompaniment with the video signals. Thus, for example, in a characteristic film an actor or a vehicle can move in the focus screen or disappear from the screen and this changes its spatial position. It is concessionable in the same way as in computer games that have sound production, a game participant is moved by the player, for example with the help of a game lever, and that the reproduction of a sound signal, which is assigned to the game participant, is adapted according to the position prescribed or altered by the player. The invention can be used to transmit, but also for recording and playing digital audio signals, for example in accordance with standard MPEG-4, MPEG-2 or AC3. This can be both audio signal reproduction, for example by means of a CD player, DAB or ADR receivers, and the reproduction of the audio signals together with the video signals, for example a DVD player or a digital television receiver. In addition, the request is also conceivable in the case of interactive systems such as video, telephones or computer games.

Claims (15)

1. A method for projection of sound sources on loudspeakers, characterized in that the sound sources are interpreted as acoustic objects, an acoustic object is that in addition to the audio signal or sound source a spatial information data unit is assigned that specifies a virtual, spatial position or sound source.

2. The method according to claim 1, characterized in that the audio signal is processed as a function of the associated data unit of the spatial information in order to reproduce an acoustic object.

3. The method of agreement. with claim 2, characterized in that the spatial position of the loudspeakers is additionally considered, the virtual distance of the loudspeaker sound source being calculated from the spatial information and the position of the loudspeakers, and processed separately from the audio signal for each of the speakers being executed by an acoustic object.

4. The method according to claim 2 or 3, characterized in that one or more of the following parameters are considered when processing the audio signals: amplitude attenuation, for example by means of wetting or diffraction, - a different propagation time for the various acoustic objects and loudspeakers, - consideration of the dependence of the loudspeaker level on the spatial coupling by means of external ear function.

5. The method according to claim 4, characterized in that the frequency depends on the parameters that are also considered in the projection of the audio signals.

6. The method according to claim 5, characterized in that the mathematical functions required for the consideration of the parameters such as, for example, an attenuation function are transmitted and / or stored as a function of the distance and / or the angle of deflection.

7. The method according to one of the preceding claims, characterized in that the data of an acoustic object are stored and / or transmitted by means of a stream of compressed data according to the MPEG-4 is tuned.

8. A device for projecting sound sources onto the speaker, characterized in that the sound sources are interpreted as acoustic objects, nxk actuators being provided by acoustic objects n and speakers k and an actuator performs the process of an acoustic object with reference to one of the at tceces.

9. The device "according to claim 8, characterized in that an actuator contains at least one of the following units: - a unit to match the amplitude, a unit of delay time to correct the propagation times different one unit for the consideration of the external ear function.

10. The device according to the rei indication 9, characterized in that a frequency dependent on the parameters is also considered by the actuators, the signals are first resolved in frequency bands by a filter-divided, the individual frequency bands then being processed individually , and the frequency bands processed subsequently being recombined by a -bonded filter.

11. The device according to the indication 10, characterized in that the divided filter and / or the attached filter are part of an audio decoder that is present in any case.

12. The device according to one of claims 8 to 11, characterized in that an arithmetic unit is provided which calculates the distance of the virtual acoustic objects from the respective speakers of a spatial information data unit transmitted with the audio signal and the current position of the speakers.

13. The device according to one of the rei indications 8 to 12, characterized in that a memory is provided in which the respective speaker positions and / or mathematical functions are stored for consideration of parameters.

14. The device according to one of the rei indications 8 to 13, characterized in that one or more of the directional microphones are provided, which are used to measure the position of the t or z t.

15. The device according to claim 14, characterized in that the directional microphone or the directional microphones is / are integrated in a remote control. SUMMARY For the purpose of spatial reproduction of an audio signal, the latter must be projected over the positions of the existing speakers. It is desirable in this case not to have to be set in a specific speaker configuration for the transmission of the audio signal. However, a problem here is that there is a multiplicity of possible combinations. In the method according to the invention, the sound sources (3) are interpreted as acoustic objects for the purpose of projecting them onto an arbitrary speaker configuration (2). Here, an acoustic object consists in that in addition to the audio signal, a spatial information data unit is assigned to a sound source that specifies a virtual, spatial position of the sound source. In order to reproduce an acoustic object, the spatial information of the sound source and the current position of a speaker are used to calculate the virtual distance from the sound source through the speaker to the listener (1) . Before playback, separate processing (7,8,9) of the audio signal is performed for each speaker for each acoustic object. Figure 3