Classifications

• • 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
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS
  • H04R29/00—Monitoring arrangements; Testing arrangements
  • H04R29/007—Monitoring arrangements; Testing arrangements for public address systems
• • 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

Definitions

• the present invention relates to the determination of an impulse response and to the demonstration of an audio piece in an environment from which an impulse response has been determined.
• WFS Wave-Field Synthesis
• wave field synthesis Due to the enormous demands of this method on computer performance and transmission rates, wave field synthesis has so far been used only rarely in practice. It is only the advances in the areas of microprocessor technology and audio coding that allow this technology to be used in concrete applications. The first products in the professional sector are expected next year. The first wave field synthesis applications for the consumer sector are also expected to be launched in a few years.
• Every point that is captured by a wave is the starting point of an elementary wave that propagates in a spherical or circular manner.
• a large number of loudspeakers that are arranged next to each other can be used to simulate any shape of an incoming wavefront.
• the audio signals of each loudspeaker have to be fed with a time delay and amplitude scaling in such a way that the radiated sound fields of the individual loudspeakers overlap correctly. If there are several sound sources, the contribution to each loudspeaker is calculated separately for each source and the resulting signals are added. If the sources to be reproduced are in a room with reflective walls, then reflections must also be reproduced as additional sources via the loudspeaker array become. The effort involved in the calculation therefore depends heavily on the number of sound sources, the reflection properties of the recording room and the number of speakers.
• the advantage of this technique lies in the fact that a natural spatial sound impression is possible over a large area of the playback room.
• the direction and distance of sound sources are reproduced very precisely.
• virtual sound sources can even be positioned between the real speaker array and the listener.
• wave field synthesis works well for environments whose properties are known, irregularities do occur when the nature changes or when the wave field synthesis is carried out on the basis of an environment condition that does not match the actual nature of the environment.
• An environmental condition can be described by the impulse response of the environment.
• An optimal application of wave field synthesis stands and falls with the fact that the environment in which the demonstration is performed is always optimally captured in order to achieve desired goals, e.g. B. special acoustics, or to introduce no audible interference.
• One possibility would be to equip a concert hall with dummy spectators, for example, whose reflective properties correspond to those of living spectators. Then a corresponding impulse response could be determined, which at least corresponds better to the real situation than if the impulse response of the empty concert hall, i.e. without any listeners, is used for wave field synthesis.
• An alternative to determining a real impulse response is to measure the impulse response of the room shortly before the start of the screening, i.e. if the screening room is already filled with the audience who will actually attend the screening, in order to have a realistic description of the environment that can only be used by the audience actual The situation would deviate significantly, for example if, after the break, many spectators no longer attended the screening, etc.
• the object of the present invention is to provide a concept for determining an impulse response and a concept for demonstrating an audio piece using an ascertained impulse response in order to achieve an accurate impulse response and thus a demonstration with high audio quality.
• the present invention is based on the finding that an exact impulse response determination can be achieved by introducing a test signal for determining the impulse response into an audio signal, so that it is inaudible or almost inaudible and cannot become a nuisance to a listener. The listener still hears the audio signal and is not affected by the impulse response determination. So he won't go for ways seek to be outside of the environment under consideration while determining the impulse response. After no visitor tries to escape the impulse response determination in a screening room, an exact impulse response is achieved, since a realistic determination of the impulse response can take place without disturbing the listener.
• the test signal which is to be introduced into the audio signal is spectrally colored before being introduced into the audio signal using a psychoacoustic masking threshold of the audio signal in order to obtain a colored test signal.
• the colored test signal is then introduced into the audio signal by adding it up spectrally or in the time domain in order to obtain a measurement signal.
• a reaction signal received in response to the measurement signal is then fed with the test signal to a cross-correlation in order to determine the impulse response of a transmission channel between a loudspeaker on the one hand and a microphone on the other hand in a corresponding environment on the basis of this cross-correlation.
• Hiding the test signal in the audio signal according to the invention means that the visitor does not even notice that an impulse response is being determined.
• the described lack of acceptability of such measurements according to the prior art is no longer present in the subject matter according to the invention, which in turn means that all viewers are present when determining the impulse response, so that an accurate impulse response of the surroundings is obtained.
• the test signal is a pseudo-noise signal that has a white spectrum and can therefore be used particularly well for determining the impulse response.
• the spectral coloring can be carried out simply and quickly using the psychoacoustic masking threshold of the audio signal.
• the use of different mutually orthogonal pseudo-noise sequences means that several individual impulse responses can be determined simultaneously in an environment in which there are several loudspeakers and one or more microphones.
• a current impulse response of the surroundings can also be determined during the demonstration of the audio piece. This feature is particularly useful for constantly determining and tracking the impulse response of the environment during the presentation of an audio piece, so that an optimal sound is always obtained, regardless of whether the environment changes or not.
• test signal for determining the impulse response has been spectrally colored using the psychoacoustic masking threshold of the audio signal, so that the test signal is either completely hidden under the masking threshold or by a predetermined amount above the masking threshold, which can vary in time and spectrally, is introduced, so that the visitor may perceive a disturbance in certain cases, but this disturbance is significantly less than in known procedures.
• 1 shows a block diagram of the inventive concept for determining an impulse response
• 2 shows a block diagram of the concept according to the invention for demonstrating an audio piece
• Figure 3 is a schematic representation of an environment with multiple speakers and multiple microphones.
• FIG. 1 shows a block diagram of a device for determining an impulse response in an environment in which a loudspeaker 10 and a microphone 12 are placed.
• An audio signal is used to determine the impulse response and is fed into an audio signal input 14.
• a test signal is used, which is fed into a test signal input 16.
• Any known psychoacoustic model 18 is used to determine the psychoacoustic masking threshold of the audio signal 14.
• a psychoacoustic masking threshold which is calculated by the psychoacoustic model 18, a spectral coloring 20 of the test signal, which is supplied at the input 16, is achieved.
• a spectrally colored test signal is thus present at the output of the device 20 for spectral colors, which is fed to a device 22 for introducing the spectrally colored test signal into the audio signal 14.
• a mode control device 24 is also provided in order to control the device 22 for introduction in order to carry out different measurement modes.
• an output of the device 22 for insertion which is designated by 26 in FIG. 1, there is a measurement signal which is supplied to the loudspeaker 10.
• the Individual possibilities for introducing a signal into an audio signal are disclosed in European patent EP 0 875 107 B1.
• the spectrally colored test signal can be introduced into the audio signal either in the time domain by adding samples. In this case, the spectrally colored test signal must just like the audio ⁇ signal present in the time domain to the sample-wise addition perform.
• a specific time segment of the audio signal or of the test signal can be transformed into the frequency range in order to then carry out a spectral value-wise addition between the transformed audio signal and the transformed test signal.
• the resulting measurement signal in the frequency domain must then be transformed back into the time domain in order to be fed to a loudspeaker as a measurement signal.
• the corresponding details of optional preprocessing and postprocessing relating to a digital / analog conversion in front of the loudspeaker 10 are not shown in FIG. 1, since they are known to those skilled in the art.
• the measurement signal supplied to the loudspeaker 10 is converted by the loudspeaker into a sound signal 28, which is received by the microphone 12 and is referred to as a reaction signal.
• the reaction signal is fed to a cross-correlation device 30, which carries out a cross-correlation between the reaction signal and the spectrally colored test signal or alternatively the immediately present test signal before the spectral coloring.
• post-processing may also be carried out after the cross-correlation, which is effected by a post-processing device 32 in order to obtain the impulse response of the channel between the loudspeaker 10 and the microphone 12.
• a pseudo-noise signal which has a white spectrum is used as the test signal.
• the use of a pseudo-noise signal is inexpensive, since it can be generated easily and quickly at any location, for example if a unit with a feedback shift register is used, which, depending on a specific start value, which is also known in technology as Seed is called, a repeatable pseudo-noise sequence is generated.
• the test signal does not have to be transmitted from a unit 34 assigned to a loudspeaker to a unit 36 assigned to a microphone, but can be generated locally at any point.
• units 34, 36 it is possible to implement units 34, 36 as a single unit.
• the measurement signal for the speaker 10 and the response signal from the microphone 12 would be through cable connections, such as. B. fiber optic cables, or wireless connections to the central unit, which is formed from the units 34 and 36, are transmitted.
• the present invention is particularly useful in multi-speaker systems that use a large number of speakers to reproduce the natural acoustics of the recording room or artificial acoustics designed by the sound engineer.
• a wave field synthesis module is used as a module, as has been shown at the input. Synthesized acoustics or the natural acoustics of the recording room can be reproduced well if the acoustics of the reproduction room do not have too great an influence by "compensating" these acoustics the wave field synthesis is used, for example, to reduce strong reflections of the actual reproduction space by applying an inverse filtering with the spatial impulse response determined according to the invention.
• the procedure according to the invention for determining the impulse response is particularly advantageous, since it can to a certain extent always be carried out, i.e. during a music recorded before an actual performance or even during the actual performance, since the test signal is “hidden” in the audio piece that is comfortable for the listener.
• a pseudo noise signal is therefore preferably embedded in an audio signal for a loudspeaker which is spectrally colored in accordance with the masking threshold of the audio signal which is reproduced by each or each of the loudspeakers.
• the measurement of the impulse response can either be carried out simultaneously for all loudspeakers using different PNS sequences for each loudspeaker or sequentially in a so-called round-robin approach. While the first version has a better temporal behavior, the second version gives a better signal-to-noise ratio, i.e. a more precise impulse response. For both measurements, however, it applies that they are imperceptible or barely perceptible to a listener, depending on how hard the spectral coloring is at the psychoacoustic masking threshold. For measurements e.g. B.
• test signal is emitted on average with more energy, which is noticeable in a better signal / noise ratio.
• a device for demonstrating an audio piece in an environment in which a plurality of loudspeakers and a plurality of microphones are placed is shown below with reference to FIG. 2.
• a speaker / microphone array 40 is sketched in FIG. 2.
• the wave field synthesis module calculates audio signals for the loudspeakers in the loudspeaker array 40 on the basis of a supplied audio piece and on the basis of predefined settings for the acoustics of the environment.
• These signals are output via an output 46 of the wave field synthesis module and either directly to the loudspeaker / microphone array 40 fed, as shown by a dashed path 48, or, if an impulse response determination is to be carried out, fed to the impulse response determination device 42, which receives the audio signals on line 46 on the input side and outputs the measurement signals to speaker array 40 via line 50 ,
• the reaction signals are picked up by the microphone array and fed back to the impulse response determination device 42 via the line 50, which is a two-way line, so that the latter can carry out cross-correlation processing which is preferred for the invention and any post-processing which may be necessary.
• Predefined settings in the wave field synthesis module for the acoustics of the environment 52 can then by a current impulse response from the device 42 z. B. has been calculated during the demonstration of the audio piece, updated so that the acoustic settings used by the wave field synthesis module about the environment are constantly updated and better adapted to the actual environment 52. This functionality is represented by a feedback path 54 in FIG. 2.
• the wave field synthesis module 44 can thus be started with predetermined settings for the impulse response and can be updated using the current measurements of the impulse response determination device 42.
• the predefined settings including the position of the loudspeakers, can be measured outside of the demonstration by the impulse response determination device 42 according to the invention, either by using psychoacoustically colored PNS sequences together with music or by not using music, but the pure PNS Sequence is used.
• the microphones away from the loudspeakers is preferred in order to carry out impulse response measurements from which a predefined setting for the wave field synthesis module 44 is calculated, it is preferred to place the microphones between the loudspeakers if, during a demonstration, an adaptation of the wave field synthesis module 44 to be performed.
• the microphones can be fixed or movable in a circular, linear or cruciform configuration. With regard to the microphone movement, the same can be moved in a circle or using an x / y displacement device in space during the measurement. Such procedures are less practical for an impulse response adaptation during the demonstration, so that fixed microphones are preferably preferred between the loudspeakers.
• the microphones can be replaced by loudspeakers in order to reduce the number of components. Due to the fact that it has a membrane and a voice coil, each loudspeaker works as a microphone if it is read out accordingly.
• arbitrarily selected loudspeakers could be used as microphones from time to time in order to carry out an adaptation without having to use extra microphones. If a large number of speakers are used, temporarily switching a few speakers will be unproblematic in terms of audio impression.
• F g. 3 shows a real situation where many speakers and many microphones are used.
• An impulse response can be given for the channel from each speaker to each microphone.
• the channel between loudspeaker 1 (LSI) and microphone 1 (Ml) is referred to as Kll.
• the channel from the first loudspeaker (LSI) to the third microphone (M3) is referred to as K31 etc. If all three loudspeakers send LSI, LS2, LS3 simultaneously, the response signal received by the microphone Ml can be used to send three different impulse responses to calculate.
• the basis for this is that the first loudspeaker (LSI) is impressed with a first pseudo-noise sequence PN1 as part of the measurement signal for the first loudspeaker.
• the second loudspeaker (LS2) receives a second pseudo-noise sequence (PN2).
• the third loudspeaker (LS3) receives a third pseudo-noise sequence (PN3).
• the channel Kll between the first loudspeaker LSI and the first microphone Ml is calculated by carrying out a cross-correlation of the response signal received by the first microphone Ml with the pseudo-noise sequence 1.
• the channel K21 from the second loudspeaker to the first microphone is calculated by correlation with the pseudo-noise sequence 2.
• the channel K31 from the third loudspeaker LS3 to the first microphone Ml is obtained by correlation with the pseudo-noise sequence 3. If all three loudspeakers and all three microphones are operated simultaneously, all nine impulse responses can be calculated. This measurement mode delivers better temporal behavior, since the resulting multidimensional impulse response of the environment, which is determined from the nine individual impulse responses determined by interpolation, is determined on the basis of measurement signals sent simultaneously.
• the loudspeaker 1 is first operated and at the same time all three microphones calculate the three channels K1, K12 and K13 by correlating the received signal with the pseudo-noise sequence 1. Then, at a subsequent time, the same is done for the loudspeaker 2 and finally the same is done for the loudspeaker 3.
• the different impulse responses are thus determined one after the other, with as many impulse responses being ascertained simultaneously as there are microphones.
• a discrete-time test signal p (t) is applied to the channel.
• the channel outputs a received signal y (t) which, as is known, corresponds to the convolution of the input signal and with the channel impulse response.
• a matrix notation is used.
• a channel impulse response with only two values ho and hi is assumed without restricting generality.
• the channel impulse response h 0 , hi can be written as a channel impulse response matrix H (t), which has the band structure shown in FIG. 5, the remaining elements of the matrix being filled with zeros.
• the excitation signal p (t) is written as a vector, it being assumed here that the excitation signal has only three samples p 0 , pi, p 2 without restricting the generality. It can be shown that the convolution shown in FIG. 4 corresponds to the matrix-vector multiplication shown in FIG. 5, so that a vector y results for the output signal.
• the cross correlation can be written as the expected value E ⁇ ... ⁇ of the multiplication of the output signal y (t) by the conjugate-complex-transposed excitation signal p * ⁇ .
• the expected value is calculated as the limit value for N against infinity via the summation of individual products for different excitation signals pi shown in FIG. 5.
• the multiplication and subsequent summation results in the cross-correlation matrix, which is shown at the top left in FIG. 5, the latter being weighted with the effective value of the excitation signal p, which is represented by ⁇ p 2 .
• the first line of the channel impulse response matrix is taken, for example, whereupon the individual components are divided by ⁇ p 2 in order to immediately obtain the individual components of the channel impulse response h o , hi.
• the spectral coloring can be represented by digital filtering, the filter being described by a filter coefficient matrix Q.
• the correlation matrix H also results on the output side, but is now weighted with the expected value over Q x Q H.
• the cross-correlation concept for calculating the impulse response is an iterative concept, as is the case for the summation approach for the expected value is evident.
• the first multiplication of the reaction signal by the conjugate-complex-transposed excitation signal already provides a first, very rough estimate for the channel impulse response, which becomes better and better with each further multiplication and summation.
• the entire matrix H (t) is calculated by the iterative summation approach, it turns out that the elements of the band matrix H (t) set to zero in the top left in FIG. 5 gradually decrease towards zero, while in the middle, that is the band of the matrix, the coefficients of the channel impulse response h (t) remain and assume certain values.
• B. calculate a row of the matrix H (t) in order to obtain the entire channel impulse response.
• the concept according to the invention is not limited to the procedure for calculating the cross-correlation described with reference to FIG. 5. All other methods for calculating the cross-correlation between a measurement signal and a reaction signal can also be used. Other methods of determining an impulse response instead of cross correlation can also be used.
• the length of the pseudo-noise sequences used should be dimensioned depending on the expected impulse response of the channel under consideration. For larger acoustic environments, impulse responses with a length of a few seconds are conceivable. This fact must be taken into account by selecting an appropriate length of the pseudo-noise sequences for correlation.
• the method according to the invention for determining the impulse response or the method according to the invention for demonstrating an audio piece can be implemented in hardware or in software.
• the I ple- Menting can be done on a digital storage medium, in particular a floppy disk or CD with electronically readable control signals, which can interact with a programmable computer system so that the corresponding method is carried out.
• the invention thus also consists in a computer program product with program code stored on a machine-readable carrier for carrying out the method according to the invention when the computer program product runs on a computer.
• the invention can thus be implemented as a computer program with a program code for performing the method if the computer program runs on a computer.

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• Physics & Mathematics (AREA)
• Engineering & Computer Science (AREA)
• Acoustics & Sound (AREA)
• Signal Processing (AREA)
• Stereophonic System (AREA)
• Electrophonic Musical Instruments (AREA)
• Circuit For Audible Band Transducer (AREA)
• Soundproofing, Sound Blocking, And Sound Damping (AREA)
• Measurement Of Mechanical Vibrations Or Ultrasonic Waves (AREA)
• Measuring Pulse, Heart Rate, Blood Pressure Or Blood Flow (AREA)

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• 2002
  • 2002-11-21 DE DE10254470A patent/DE10254470B4/de not_active Expired - Fee Related
• 2003
  • 2003-11-06 WO PCT/EP2003/012449 patent/WO2004047486A2/fr active IP Right Grant
  • 2003-11-06 AU AU2003283370A patent/AU2003283370A1/en not_active Abandoned
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