APPARATUS AND METHOD FOR GENERATING A FIRST CONTROL SIGNAL AND A SECOND CONTROL SIGNAL BY USING A LINEARIZATION AND/OR A BANDWIDTH EXTENSION

Abstract

An apparatus for generating a first control signal for a first transducer and a second control signal for a second transducer, including: an input interface providing a first audio signal for a first audio channel and a second audio signal for a second audio channel; a signal combiner for determining from the first audio signal and the second audio signal a combination signal including an approximate difference of the first audio signal and the second audio signal; a signal manipulator for manipulating the combination signal to obtain the second control signal; and an output interface for outputting or storing the first control signal based on the first audio signal, or the second control signal, wherein the signal manipulator is configured to delay the combination signal or to amplify or attenuate the combination signal in a frequency-selective manner to counteract a non-linear transducer characteristic over the frequency of the second transducer.

Claims

1. An apparatus for generating a first control signal for a first transducer and a second control signal for a second transducer, comprising: an input interface for providing a first audio signal for a first audio channel and a second audio signal for a second audio channel; a signal combiner for determining from the first audio signal and the second audio signal a combination signal comprising an approximate difference of the first audio signal and the second audio signal; a signal manipulator for manipulating the combination signal to acquire the second control signal; and an output interface for outputting or storing the first control signal based on the first audio signal, or the second control signal, wherein the signal manipulator is configured to delay the combination signal or to amplify or attenuate the combination signal in a frequency-selective manner to counteract a non-linear transducer characteristic over the frequency of the second transducer, or wherein the apparatus is configured to convert at least a part of a spectrum of the first audio signal or the combination signal in a frequency range above 20 kHz to acquire the first control signal comprising the frequency range above 20 kHz.

2. The apparatus according to claim 1, wherein the signal combiner comprises a phase shifter and an adder or a subtractor to determine the combination signal.

3. The apparatus according to claim 1, wherein the signal combiner comprises an attenuation member to attenuate the second audio signal, wherein the approximate difference is formed from the attenuated second audio signal.

4. The apparatus according to claim 1, wherein the output interface comprises a bandwidth extension stage, and wherein at least the part of the spectrum of the first audio signal is converted in a frequency range above 35 kHz by using an amplification factor of greater than or equal to 1 to acquire the first control signal.

5. The apparatus according to claim 4, wherein the bandwidth extension stage is configured to convert the at least one part of the spectrum of the first audio signal by using a harmonic transposition in the frequency range above 20 kHz, wherein the harmonic transposition comprises at least an even-numbered transposition factor equal to 2 or more.

6. The apparatus according to claim 1, wherein the signal manipulator is configured to delay the combination signal such that the Haas effect occurs at a listening position when simultaneously outputting the first control signal by means of the first transducer and the second control signal by means of the second transducer.

7. The apparatus according to claim 1, wherein the signal manipulator is configured to implement a delay of between 10 ms and 40 ms.

8. The apparatus according to claim 1, wherein the signal manipulator comprises a linearization filter configured to reduce or eliminate overshoots in a first set of frequencies due to non-linearity of the second transducer.

9. The apparatus according to claim 8, wherein the linearization filter is configured to not amplify a cancelation in a second set of frequencies, or to amplify it less than it would be required for a full linearization of the cancelation.

10. The apparatus according to claim 1, wherein the signal manipulator comprises the linearization filter configured to comprise a high-pass characteristic and to attenuate signal components of the combination signal below a high-pass cut-off frequency.

11. The apparatus according to claim 10, wherein the high-pass cut-off frequency is in the range of 180 to 250 Hz.

12. The apparatus according to claim 1, wherein the signal combiner is configured to generate from the first audio signal and the second audio signal or from the combination signal a further combination signal that is different from the combination signal, wherein the signal manipulator is configured to manipulate the further combination signal to acquire the fourth control signal, and wherein the output interface is configured to output or store the fourth control signal or a third control signal based on the second audio signal.

13. The apparatus according to claim 12, wherein the signal manipulator is configured to delay the further combination signal or to amplify or attenuate the further combination signal in a frequency-selective manner to counteract a non-linear transducer characteristic over the frequency of a fourth transducer, or wherein the output interface is configured to convert at least a part of a spectrum of the second audio signal in a frequency range above 20 kHz to acquire the third control signal.

14. The apparatus according to claim 1, wherein the signal combiner is configured to subtract the second audio signal from the first audio signal in the time domain to acquire the combination signal, wherein the signal manipulator comprises: a delay stage configured to delay the combination signal, a linearization filter to at least partially linearize the non-linear frequency response of the second transducer, and an attenuation member to attenuate a level of the combination signal, and wherein the output interface comprises a bandwidth extension stage to convert at least a part of a spectrum of the first audio signal in a frequency range above 20 kHz by using an amplification factor greater than or equal to 1 to acquire the first control signal comprising the frequency range above 20 kHz.

15. The apparatus according to claim 1, wherein the signal combiner is configured to subtract the first audio signal from the second audio signal in the time domain to acquire the further combination signal, wherein the signal manipulator comprises: a further delay stage configured to delay the further combination signal, a further linearization filter to at least partially linearize a non-linear frequency response of the fourth transducer, and an attenuation member to attenuate a level of the further combination signal, and wherein the output interface comprises a further bandwidth extension stage to convert at least a part of a spectrum of the second audio signal in a frequency range above 20 kHz by using an amplification factor of greater than or equal to 1 to acquire the third control signal.

16. The apparatus according to claim 1, wherein the input interface is configured to acquire a first reception audio signal or a second reception audio signal, and wherein the input interface comprises a bandwidth extension stage to convert at least a part of a spectrum of the first input audio signal or the second input audio signal in a frequency range above 20 kHz by using an amplification factor of greater than or equal to 1 to acquire the first audio signal or the second audio signal.

17. The apparatus according to claim 1, wherein the signal manipulator comprises: a bandwidth extension stage to convert at least a part of a spectrum of the combination signal or a signal derived from the combination signal in a frequency range above 20 kHz by using an amplification factor greater than or equal to one to acquire a manipulated signal the second control signal is based on.

18. A loudspeaker system, comprising: a first transducer, a second transducer, a third transducer, and a fourth transducer; and an apparatus for generating according to claim 1, wherein the apparatus for generating is configured to: generate the first control signal for the first transducer by using the first audio signal, generate the second control signal for the second transducer by using the combination signal, generate a third control signal for the third transducer by using the second audio signal, and generate a fourth control signal for the fourth transducer by using a further combination signal, wherein the first transducer and the third transducer are configured to generate a translational sound signal, and wherein the second transducer and the fourth transducer are configured to generate a rotatory sound signal.

19. The loudspeaker system according to claim 18, wherein the first transducer and the second transducer are arranged at a first position with respect to a listening position, wherein the first position is determined by the first audio channel, wherein the third transducer and the fourth transducer are arranged at a second position with respect to the listening position, wherein the second position differs from the first position and is determined by the second audio channel.

20. The loudspeaker system according to claim 18, wherein the second transducer or the fourth transducer comprises: a first sound generator with a first membrane and a first front side and a first rear side, a second sound generator with a second membrane and a second front side and a second rear side, wherein the first sound generator and the second sound generator are arranged with respect to each other such that the first front side and the second front side are directed towards each other, and wherein the first sound generator and the second sound generator may be fed with the second audio signal and the fourth audio signal, respectively.

21. The loudspeaker system according to claim 20, wherein the second transducer and the fourth transducer each comprises a phase shifter to introduce a phase difference between a first feed signal for the first sound generator and a second feed signal for the second sound generator.

22. The loudspeaker system according to claim 21, wherein the phase shifter is configured to generate a phase angle of between 150 and 210.

23. The loudspeaker system according to claim 18, wherein the second transducer comprises a frequency response that is non-linear, and wherein the signal manipulator is configured to at least partially linearize the second frequency response when generating the second audio signal, or wherein the fourth transducer comprises a fourth frequency response that is non-linear, and wherein the signal manipulator is configured to at least partially linearize the fourth frequency response when generating the fourth control signal.

24. A method for generating a first control signal for a first transducer and a second control signal for a second transducer, comprising: providing a first audio signal for a first audio channel and a second audio signal for a second audio channel; determining from the first audio signal and the second audio signal a combination signal comprising an approximate difference of the first audio signal and the second audio signal; manipulating the combination signal to acquire the second control signal; and outputting or storing the first control signal based on the first audio signal, or the second control signal, wherein manipulating is configured to delay the combination signal or to amplify or attenuate the combination signal in a frequency-selective manner to counteract a non-linear transducer characteristic over the frequency of the second transducer, or wherein at least a part of a spectrum of the first audio signal or the combination signal is converted in a frequency range above 20 kHz to acquire the first control signal comprising the frequency range above 20 kHz.

25. The method according to claim 24, comprising: measuring the non-linear transducer characteristic over the frequency of the second transducer; calculating a linearization filter to at least partially linearize the non-linear transducer characteristic over the frequency of the second transducer to acquire a calculated linearization filter; and using the calculated linearization filter to amplify or attenuate the combination signal in a frequency-selective manner.

26. A non-transitory digital storage medium having a computer program stored thereon to perform the method for generating a first control signal for a first transducer and a second control signal for a second transducer, comprising: providing a first audio signal for a first audio channel and a second audio signal for a second audio channel; determining from the first audio signal and the second audio signal a combination signal comprising an approximate difference of the first audio signal and the second audio signal; manipulating the combination signal to acquire the second control signal; and outputting or storing the first control signal based on the first audio signal, or the second control signal, wherein manipulating is configured to delay the combination signal or to amplify or attenuate the combination signal in a frequency-selective manner to counteract a non-linear transducer characteristic over the frequency of the second transducer, or wherein at least a part of a spectrum of the first audio signal or the combination signal is converted in a frequency range above 20 kHz to acquire the first control signal comprising the frequency range above 20 kHz, when said computer program is run by a computer.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Embodiments of the present invention will be detailed subsequently referring to the appended drawings, in which:

[0035] FIG. 1 shows an apparatus for generating a first control signal and a second control signal according to an embodiment of the present invention;

[0036] FIG. 2 shows a detailed illustration of the signal manipulator of FIG. 1 according to an advantageous embodiment;

[0037] FIG. 3 shows a detailed illustration of the signal combiner of FIG. 1 according to an advantageous embodiment, as well as an illustration of incorporating a bandwidth extension stage for each control signal for a translational transducer;

[0038] FIG. 4 shows an alternative implementation of the apparatus for generating with a different arrangement of the bandwidth extension stages compared to FIG. 3;

[0039] FIG. 5a shows a schematic illustration of the effect of a bandwidth extension stage according to an embodiment;

[0040] FIG. 5b shows a schematic illustration of an effect of a bandwidth extension stage according to a further embodiment;

[0041] FIG. 6 shows a schematic illustration of the loudspeaker side of a loudspeaker system for a 2-channel output format;

[0042] FIG. 7a shows an exemplary non-linear frequency response of a transducer with a comb filter effect;

[0043] FIG. 7b shows a schematic frequency response of a linearization filter to at least partially linearize the frequency response of FIG. 7a;

[0044] FIG. 8a shows a schematic illustration of another non-linear frequency response of a rotatory transducer;

[0045] FIG. 8b shows a schematic illustration of a frequency response of a linearization filter; and

[0046] FIG. 8c shows a schematic illustration of a linearized frequency response due to the linearization filter and the rotatory sound transducers used.

DETAILED DESCRIPTION OF THE INVENTION

[0047] FIG. 1 shows an apparatus for generating a first control signal 411 for a first transducer and a second control signal 412 for a second transducer. The apparatus includes an input interface 100 for providing a first audio signal 111 for a first audio channel and a second audio signal for a second audio channel. In addition, the apparatus includes a signal combiner 200 for determining from the first audio signal 111 and the second audio signal 112 a combination signal including an approximate difference of the first audio signal 111 and the second audio signal 112. This combination signal is shown at 211.

[0048] In advantageous embodiments, the signal combiner is further configured to generate a further combination signal 212 that also represents a difference between the first and the second audio signal and is derived from the first audio signal and the second audio signal or from the first combination signal 211. In embodiments, the second combination signal 212 differs from the first combination signal 211 and differs, in particular, by 180 degrees, i.e. it has an opposite sign.

[0049] Similar to the advantageously used further combination signal 212, the combination signal 211 is also supplied to a signal manipulator 300 configured to manipulate the combination signal in order to obtain therefrom a manipulated combination signal, illustrated at 311 and corresponding to the second control signal 412. In special embodiments, the second control signal 412 is therefore transmitted from the signal manipulator by using the output interface 400 and is output or stored by the output interface. Furthermore, the output interface is configured to output the first control signal 411 for the first transducer in addition to the second control signal for the second transducer as well. The first control signal 411 is obtained by the output interface directly from the input interface and corresponds to the first audio signal 111, or is derived by the output interface 400 from the first audio signal, e.g., by using a bandwidth extension stage, i.e. a spectral enhancer, described later.

[0050] In advantageous embodiments, the signal manipulator 300 is configured to delay the combination signal, i.e. to feed it into a delay stage, or to amplify or attenuate the combination signal in a frequency-selective manner, i.e. to feed it into a linearization filter, in order to at least partially counteract a non-linear transducer characteristic over the frequency of the second transducer.

[0051] Alternatively or additionally, the output interface is configured to feed the first audio signal 111 into a bandwidth extension stage so as to obtain the first output signal 411. Therefore, the apparatus for generating a first control signal 411 and a second control signal 412 includes three aspects that may be used together or independent from one another.

[0052] The first aspect consists of generating the manipulated signal from the combination signal by using a delay, which utilizes the Haas effect.

[0053] The second aspect consists of the signal manipulator 300 using the linearization filter in order to at least partially compensate a heavily non-linear frequency response of the rotatory transducer in the sense of a predistortion. The third aspect consists of the signal manipulator performing any other type of manipulation such as an attenuation or high-pass filtering or any other processing, wherein the output interface performs a bandwidth extension for the first audio signal.

[0054] This bandwidth extension using a bandwidth extension stage is particular in that at least a part of a spectrum of the first audio signal in a frequency range above 20 kHz is converted by using an amplification factor of more than 1 or equal to 1, i.e. without amplification, in order to obtain the first control signal including the frequency range above 20 kHz. In contrast to a conventional bandwidth extension, which is typically configured to extend a signal band-limited to perhaps 4 or 8 kHz in a frequency range of up to perhaps 16 or 20 kHz, further using attenuation to synthesize a decreasing performance characteristic of an audio signal, the inventive bandwidth extension differs in that it determines spectral values for a frequency range above 20 kHz, i.e. for an inaudible range, and in that this spectral range is not attenuated, but converted amplification factor larger than 1 or equal to 1 in order to bring into the non-audible spectral range signal energy that is then radiated by the membranes of the corresponding transducers in order to provide a high-quality audio signal experience. This audio signal experience consists of conditioning, so to speak, the air carrying the sound energy in the audible range by sound energy in the non-audible range so that certain signals very rich in harmonics are clearly audible despite a great distance, such as the scream of the parrot in the jungle or a triangle in an orchestra.

[0055] In advantageous embodiments, all three aspects are implemented, as will be described later. However, only one aspect of the three aspects can be implemented, or any two aspects of the three aspects.

[0056] Advantageously, the first input signal 102 and the second input signal 104 introduced into the input interface 100 represent a left audio channel and a right audio channel. The first audio signal 411 and the second audio signal 412 then represent the control signals for the first and the second transducers placed on the left side with respect to a listening position. The apparatus for generating is further configured to generate the control signals, i.e. the third control signal 413 for a third transducer and the fourth control signal 414 for the fourth transducer, for the right side as well. The third control signal 413 is formed analogously to the first control signal 411, and the fourth control signal 414 is formed analogously to the second control signal 412. The first control signal 411 and the third control signal 413 are supplied to conventional translational transducers, and the control signals 412 and 414 are supplied to rotatory transducers, i.e. transducers that emit a sound field with rotating sound particle velocity vectors, as will be described with reference to FIG. 6.

[0057] FIG. 2 shows an advantageous implementation of the signal manipulator 300 in order to calculate the second control signal 311/412 from the combination signal 211. In addition, FIG. 2 also shows the implementation of the signal manipulator 300 in order to generate the fourth control signal 312 and 414 from the further combination signal 212. In order to generate the second control signal, in advantageous embodiments, the signal combiner includes a variable attenuation member 301, a delay stage 302, and a linearization filter 303. It is to be noted that the order of the blocks 301, 302, 303 is arbitrary. There may also be a single element that unites the functionalities of the linearization filter, the delay, and the attenuation. The attenuation may be adjusted, or is set to a predefined value that is between 3 and 20 dB, advantageously between 6 and 12 dB, e.g. at 10 dB.

[0058] Analogously, the signal manipulator 300 is configured to subject the combination signal 212 to an attenuation by an attenuation stage 321, to subject it to a delay 322, and to feed it into a linearization filter 323. All three elements may be integrated in a single filter that implements the attenuation that is typically constant across the entire frequency range, the delay that is also constant across the entire frequency range, and a linearization filter that attenuates, or amplifies, at least in a frequency-selective manner. It is to be noted that a partial set of the elements can be used as well, i.e. only attenuation and linearization without delay, or only delay without attenuation and linearization, or only attenuation without delay and linearization. In advantageous embodiments, all three aspects are implemented.

[0059] For the delay, in particular, a delay is used that is large enough that a precedence effect, or a Haas effect, or an effect of the first wave front, occurs between the non-delayed signal given by the first control signal 411, and the second control signal subject to the delay. The signal for the rotatory transducer, i.e. the second in control signal 412, is delayed such that a listener initially perceives the wave front due to the first control signal 411 and therefore carries out localization of the left channel. The rotatory component, which is essential for the audio quality, however, which does not carry any particular information with respect to the localization, is perceived slightly later and, due to the Haas effect, is not perceived as its own signal. Useful delay values for the delay stage 302 or 322 are advantageously between 10 and 40 ms, particularly advantageously between 25 ms and 35 ms, and in particular at 30 ms.

[0060] FIG. 3 shows an advantageous implementation of the signal combiner 200 to calculate an approximate difference represented by the combination signal 211 or the further combination signal 212. To this end, the signal combiner 200 includes a phase shifter 201, a downstream attenuation member 202, and an adder 203. In addition, the first audio signal 111 and the second audio signal 112 are used. The first audio signal 111 is phase-shifted by the phase shifter 201, is attenuated depending on the setting of the attenuation member 202, and is then added to the first audio signal 112 in order to obtain the further combination signal 212. In addition, the signal combiner 200 includes a further adder 223, a further phase shifter 221, and a further attenuation member 222, wherein the second audio signal 112 is phase-shifted by the phase shifter 221, the phase-shifted signal is possibly attenuated and then combined with the first audio signal 111. If the phase shifters 201 and 221 carry out a phase shift by 180, which is advantageous, and if the attenuation member 202, 222 are set such that the attenuation is zero, i.e. these potentiometers are fully turned up, the combination signal 211 is the result of the subtraction of the second audio signal 112 from the first audio signal 111, i.e. when the first audio signal 111 is the left channel and the right audio signal 112 is the right channel, the combination signal 211 is L-R. Analogously, the further combination signal 212 is R-L in this example.

[0061] The implementation of a phase shift of 180 is achieved particularly easily by plugging in a corresponding jack carrying the audio signal in a reverse manner. Different phase shifts that differ from 180, i.e. in a range of 150 to 210, may also be achieved by correct phase shifter elements and may be of advantage in certain implementations. The same applies to certain attenuation settings of the attenuation members 202, 222, which, according to the implementation, are used to affect the combination signal in that, when forming the difference, the signal that is subtracted is attenuated in contrast to the signal from which the subtraction is carried out. Thus, a subtraction factor x between zero and 1 can be formed, as will be described in FIG. 6.

[0062] In addition to a special implementation of the signal combiner 200, FIG. 3 further shows an advantageous embodiment of the bandwidth extension of the translational signal, wherein this bandwidth extension is advantageously carried out in the output interface 400. To this end, the output interface 400 includes a first bandwidth extension stage 402 and a second bandwidth extension stage 404. The first bandwidth extension stage 402 is configured to subject the first audio signal 111 to a bandwidth extension in the non-audible range above 20 kHz, whereas the bandwidth extension stage 404 is configured to subject the second audio signal, i.e. the right channel for example, to a bandwidth extension in the non-audible range above 20 kHz as well.

[0063] The result of the bandwidth extension is the first audio signal for the first transducer, i.e. the rotatory transducer, e.g. on the left side with respect to a listening position, and the third control signal obtained at the output of the bandwidth extension stage 404 is the control signal for the translational transducer on the right side with respect to the listening position. Both control signals 411, 413 are now provided with signal energy at frequencies above 20 kHz, in contrast to the audio signals 111, 112, wherein these signal components are advantageously present in the control signals up to 40 kHz and particularly advantageously even up to 80 kHz or above.

[0064] Even though FIG. 3 shows an implementation in which a bandwidth extension is only carried out with the translational signal, in other embodiments, a bandwidth extension may be carried out with the rotatory signal, as is illustrated at 304 and 324 in FIG. 4. Alternatively to the bandwidth extension stages 304, 324, a bandwidth extension could be provided in the input interface 100. To this end, a bandwidth extension stage 121 for a first input signal 102 is provided so as to generate the first audio signal 111 from the first input signal 102. In addition, the input stage 100 is provided in order to generate the second audio signal 112 from the second input signal 104. In contrast to the implementation of FIG. 3, these two audio signals have a frequency range that goes far beyond 20 kHz. If the bandwidth extension is already carried out in the input interface, further bandwidth extensions in the output interface 400, as is illustrated in FIG. 3, or in the signal manipulation elements 300a, 300b are not required, since all signals already have a high bandwidth in the subsequent signal processing. However, due to the efficiency of processing, an implementation as illustrated in FIG. 3 is advatangeous, wherein only the control signals for the translational transducers, i.e. the first control signal 411 and the third control signal 413, are subjected to the bandwidth extension, since the high frequencies are of particular significance for the propagation. Thus, all other processing stages can be performed in the input interface, in the signal combiner, and in the signal manipulator with the band-limited signal, saving processing resources, since all elements apart from the bandwidth extension stages 402, 404 in FIG. 3 can operate with band-limited signals.

[0065] FIG. 5 shows a first implementation of the bandwidth extension stage 402, 404, or the optional elements 121, 122 or 304, 324 of FIG. 4. In particular, the bandwidth extension stage is configured to generate a bandwidth extension above the range of 20 kHz, i.e. in the non-audible range, which goes up to 80 kHz in FIG. 5a. To this end, advantageously, a harmonic bandwidth extension is carried out, wherein each frequency in the range between 10 and 20 kHz of the audio signal is multiplied with the factor 2, for example, in order to generate a frequency range of between 20 kHz and 40 kHz. In addition, an amplification by means of an amplification member 407 that implements an amplification of greater than 1, as is illustrated by the dotted line in FIG. 5a, is advantageously carried out in the bandwidth extension stage. The harmonic bandwidth extension unit 404 together with the amplifier 407 therefore generates in the corresponding audio signal a signal component that is between 20 and 40 kHz and even has a higher signal energy than the range from the baseband between 10 and 20 kHz. In order to reach an even higher range of between 40 kHz and 80 kHz, a further transposer 406 that multiplies the frequencies each with 4 is provided, wherein the output signal is again advantageously multiplied with an amplification factor of greater than 1, wherein this amplifier having the amplification factor of greater than 1 is shown at 408 in FIG. 5a. It is to be noted that the frequency axis is broken through at the corresponding positions, since the range between 40 kHz and 80 kHz is twice as long as the range between 20 kHz and 40 kHz, which is in turn twice as long as the range between 10 kHz and 20 kHz, due to the harmonic bandwidth extension by the elements 404, 406. Although transposing factors that are odd-numbered, i.e. 1, 3, 5 and 7, can be used in principle, it has been shown that even-numbered transposing factors, as achieved by the transposer 404, 406, generate a more realistic audio signal impression. In addition, according to the implementation, the baseband may not be attenuated and amplified, i.e. it is taken as it is. However, since loudspeakers typically have a lower transducer efficiency, or a decreasing with higher frequencies, at frequencies above 20 kHz, this lower, or decreasing, transducer efficiency is compensated with an amplified transposed spectral range. Thus, it is advantageous that the amplifier 408 for the range between 40 and 80 kHz amplifies more than the amplifier 407 for the range between 20 kHz and 40 kHz.

[0066] While FIG. 5a shows a first implementation of the bandwidth extension, FIG. 5b shows a second implementation of the bandwidth extension, operating on the basis of the technique of mirroring, i.e. mirroring the transposed spectral range at the cross-over frequency (transition frequency), which is advantageous in that in case of a non-constant signal progression in the baseband, as is illustrated in FIG. 5b, there is no discontinuity at the transposition location, i.e. at 20 kHz, if an amplification factor of 1 is used. Mirroring, or up-sampling, may be easily done in the time domain by introducing one or several zeroes as additional sample values into an audio signal between two sample values. If amplification is carried out, only a small discontinuity is created. This discontinuity can be left as is or, if required, it can be attenuated by using average values for the amplification factors in a certain spectral transition area.

[0067] FIG. 6 shows a loudspeaker system including a first transducer 521 for the first control signal 411 and a second transducer 522a, 522b for the second control signal 412. In addition, the loudspeaker system comprises a third transducer 523 for the third control signal 413 and a fourth transducer 524a, 524b for the fourth control signal 414. All control signals may be amplified by respective amplifiers 501, 502, 503, 504, e.g., in a manner as input by a user interface via a volume control. The transducers 521, 523 represent the translational and, so to speak, conventional transducers that, in contrast to normal transducers, are characterized by being able to output sound energy in the range above 20 kHz as well, where they advantageously are intended to emit up to 80 kHz or above. The decreasing efficiency at higher frequencies is compensated by the amplification due to the amplification members 407, 408.

[0068] In an advantageous embodiment illustrated in FIG. 6, the rotatory transducers 522a, 522b, or 524a, 524b, are implemented such that the transducers each include two individual transducers with a front side and a rear side, wherein the two front sides, as illustrated in FIG. 6, are directed towards each other. Between the front sides, i.e. between the membranes, there may be no distance or only such a distance that the membranes are able to deflect and generate, in the intermediate space between the membranes, sound that is able to exit along the edges of the membranes as a rotation. Such a transducer has a very good efficiency in the generation of rotating sound, i.e. a sound field with rotating sound particle velocity vectors. However, the frequency response is heavily non-linear. Thus, the linearization filter 303, 323 is provided to generate a signal via a predistortion, so to speak, which, if it is output by the non-linear frequency response of the transducer 522a, 522b, or 524a, 524b, has a relative linear transmission characteristic or signal characteristic. FIG. 7a shows an exemplary spectrum as it may occur in transducers for rotatory signals. FIG. 7b shows an exemplary frequency response of the linearization filter 303, 323. In the advantageous implementation of the linearization filter, the overshoots 701, 702, 703, 704, 705 are lowered, whereas the indentations 706 to 710 are left as is so that, in the frequency ranges where the indentations are located, the frequency response of the linearization filter is at the 0 dB reference line and, in the range of the overshoots, the overshoots are at least partially lowered, that is by 6 dB if the overshoot itself has a height of 6 dB, as is illustrated in the exemplary frequency response in FIG. 7a. The linearization filter is further configured to provide a high-pass characteristic with respect to a cut-off frequency f.sub.g, which is only schematically shown in FIG. 7b and which has a size of between 100 and 500 Hz and which is advantageously at 200 Hz. This means that the first overshoot 711 in FIG. 7a is fully attenuated.

[0069] FIG. 8a shows an alternative frequency response of a rotatory sound transducer, which may be created by the construction of the rotatory sound transducers as illustrated in FIG. 6. Strong overshoots and very strong plunges are shown. The linearization is particularly configured such that only the overshoots, which are shown in a hatched manner in FIG. 8a, are to be attenuated, whereas the plunges are approximately to be left as is. This leads to a frequency response of a linearization filter as illustrated in FIG. 8b. The entire linearized frequency response is schematically shown in FIG. 8c, where it can be seen that the linearized frequency response is not completely linearized, but when comparing FIG. 8c and FIG. 8a, it runs significantly more linearly, since the strong overshoots have been cut off.

[0070] It has been shown that strongly overshooting frequency ranges in the rotation signal have an interfering effect, whereas indentations in the rotation signal at certain tones, leading to certain tones in the rotation signal being hidden, are not perceived to be interfering. Thus, the plunges in the frequency response of the loudspeakers, i.e. in FIG. 8a or 7a, do not have to be lifted. This simultaneously avoids that a signal still present in the attenuated indentation, which may also be an artefact signal, is too heavily amplified by strong amplification factors at certain frequencies. According to the invention, cutting off only the overshoots, or at least partially reducing the overshoots, and leaving the plunges, achieves a particularly efficient and high-quality means to provide the corresponding control signal for the rotatory sound transducer 522a, 522b, or 524a, 524b. Advantageously, corresponding phase shifters 506, 508 are built into the rotatory sound transducers, which, according to the implementation, provide a phase shift of 180, however, which may be set to other values, which are advantageously between 150 and 210. With respect to FIG. 3, it has been noted that the attenuation members 202, 222 may be set so as to obtain an approximate difference. This is illustrated in FIG. 6 at L-x-R and R-x-L. If the corresponding attenuation member 202, 222 is set to an attenuation of zero, i.e. no attenuation at all, the factor x in FIG. 6 is equal to 1. However, if the attenuation member 202, 222 is set to a factor of half the attenuation, for example, the factor x is 0.5. However, if the attenuation member 202, 222 is set to full attenuation, the difference is no longer formed, and the first transducer 522a, 522b emits only the left signal. However, it is advantageous to set an attenuation of the attenuation member 202, 222 to a maximum of 0.25 so that the corresponding signal is a difference signal, even though, compared to the channel from which the subtraction is carried out, the subtracted channel is reduced with respect to its amplitude or power or energy.

[0071] In a further implementation, the apparatus for generating the first control signal and the second control signal, and in particular for generating the third and the fourth control signals, is implemented as a signal processor or software in order to generate the control signals for the individual loudspeakers, e.g. in a mobile device, such as a mobile telephone, and to then output them via a wireless interface. Alternatively, the transducers as illustrated in FIG. 6, including the amplifiers 502 to 504, are implemented together with the apparatus as illustrated in FIG. 1 into a loudspeaker unit that additionally includes the transducer 521 and the transducer 522a, 522b in a special carrier. Then, for example, this loudspeaker unit may be placed as it is at a left reproduction position with respect to a listening position. The same may be done for another loudspeaker unit including the elements 523, 524a, 524b as well as the corresponding part of the apparatus for generating the control signals so that a loudspeaker unit is provided for the right position with respect to a defined listening position. Accordingly, loudspeaker units may be used for further channels than the two stereo channels, e.g. for a center channel, for a left rear channel, for a right rear channel, in the case of a 5.1 system. In the case of higher systems, a transducer for rotatory sound and a transducer for translational sound that are driven with the separate control signals may be used at corresponding further positions, such as a ceiling loudspeaker.

[0072] A advantageous embodiment of the present invention is located within a mobile telephone. In particular, the control apparatus is loaded as a hardware element or as an app, or program, on the mobile telephone. The mobile telephone is configured to receive the first audio signal and the second audio signal or the multi-channel signal from any source that may be local or in the internet, and to generate the control signals depending thereon. These signals are transmitted by the mobile telephone to the sound generator with the sound generator elements either in a wired or wireless manner, e.g. by means of Bluetooth or Wi-Fi. In the latter case, the sound generating elements have to have a battery supply, or a power supply in general, in order to achieve the corresponding amplifications for the wireless signals received, e.g. according to the Bluetooth format or the Wi-Fi format.

[0073] Even though some aspects have been described within the context of a device, it is understood that said aspects also represent a description of the corresponding method, so that a block or a structural component of a device is also to be understood as a corresponding method step or as a feature of a method step. By analogy therewith, aspects that have been described within the context of or as a method step also represent a description of a corresponding block or detail or feature of a corresponding device. Some or all of the method steps may be performed while using a hardware device, such as a microprocessor, a programmable computer or an electronic circuit. In some embodiments, some or several of the most important method steps may be performed by such a device.

[0074] Depending on specific implementation requirements, embodiments of the invention may be implemented in hardware or in software. Implementation may be effected while using a digital storage medium, for example a floppy disc, a DVD, a Blu-ray disc, a CD, a ROM, a PROM, an EPROM, an EEPROM or a FLASH memory, a hard disc or any other magnetic or optical memory which has electronically readable control signals stored thereon which may cooperate, or cooperate, with a programmable computer system such that the respective method is performed. This is why the digital storage medium may be computer-readable.

[0075] Some embodiments in accordance with the invention thus comprise a data carrier which comprises electronically readable control signals that are capable of cooperating with a programmable computer system such that any of the methods described herein is performed.

[0076] Generally, embodiments of the present invention may be implemented as a computer program product having a program code, the program code being effective to perform any of the methods when the computer program product runs on a computer.

[0077] The program code may also be stored on a machine-readable carrier, for example.

[0078] Other embodiments include the computer program for performing any of the methods described herein, said computer program being stored on a machine-readable carrier.

[0079] In other words, an embodiment of the inventive method thus is a computer program which has a program code for performing any of the methods described herein, when the computer program runs on a computer.

[0080] A further embodiment of the inventive methods thus is a data carrier (or a digital storage medium or a computer-readable medium) on which the computer program for performing any of the methods described herein is recorded. The data carrier, the digital storage medium, or the recorded medium are typically tangible, or non-volatile.

[0081] A further embodiment of the inventive method thus is a data stream or a sequence of signals representing the computer program for performing any of the methods described herein. The data stream or the sequence of signals may be configured, for example, to be transmitted via a data communication link, for example via the internet.

[0082] A further embodiment includes a processing unit, for example a computer or a programmable logic device, configured or adapted to perform any of the methods described herein.

[0083] A further embodiment includes a computer on which the computer program for performing any of the methods described herein is installed.

[0084] A further embodiment in accordance with the invention includes a device or a system configured to transmit a computer program for performing at least one of the methods described herein to a receiver. The transmission may be electronic or optical, for example. The receiver may be a computer, a mobile device, a memory device or a similar device, for example. The device or the system may include a file server for transmitting the computer program to the receiver, for example.

[0085] In some embodiments, a programmable logic device (for example a field-programmable gate array, an FPGA) may be used for performing some or all of the functionalities of the methods described herein. In some embodiments, a field-programmable gate array may cooperate with a microprocessor to perform any of the methods described herein. Generally, the methods are performed, in some embodiments, by any hardware device. Said hardware device may be any universally applicable hardware such as a computer processor (CPU), or may be a hardware specific to the method, such as an ASIC.

[0086] While this invention has been described in terms of several embodiments, there are alterations, permutations, and equivalents which fall within the scope of this invention. It should also be noted that there are many alternative ways of implementing the methods and compositions of the present invention. It is therefore intended that the following appended claims be interpreted as including all such alterations, permutations and equivalents as fall within the true spirit and scope of the present invention.