Patent Grant
9961473
If sound is emitted in a room, the sound waves travel across the space until they are reflected at the room boundaries. The reflections are again rebounded and over time a more and more complex pattern of sound waves evolves, the so-called reverberation.
However, in spatial reproduction every sound has a direction of arrival (DOA), i.e., the sound arrives from a certain angular direction given by azimuth and elevation. For a better illustration,
With an increase of time t, depicted at the abscissa, the receiver first perceives direct sound 1002 and afterwards the early reflections 1004 followed by late reverberation 1006. An angular direction is the azimuth angle of the direction of arrival of the sound wave, the azimuth angle depicted as radial dimension. The distance to the receiver is the time of arrival. The darkness of the points depicts the level of perceived level of reflection. Thus,
In the course of audio postproduction, artificial reverberation is added to the sound to enhance the spatial quality. The desired objectives range from enhancement of the musicality, improvement of the sound design to recreation of a physical acoustic space. A realistic acoustic space can be created by the use of multiple loudspeakers, source dependent early reflections and uncorrelated late reverberation. In this sense, it is referred to multichannel as having a high number of audio sources and a high number of output channels.
Practical reverberation algorithms generally fall into one of two categories, although hybrids exist:
1) delay networks, in which the input signal is delayed, filtered and fed back;
2) convolutional, wherein the input signal is simply convolved with a recorded or estimated impulse response of an acoustic space.
Convolutional reverberators reproduce a given acoustics with high precision, but also with high computational costs, i.e., efforts. Multichannel convolutional reverberators have been devised, but the computational costs scale linearly with the number of source and channel pairs.
For low channel applications, i.e., mono and stereo, a wide variety of parametric reverberators was developed. None of these developments, however, have been extended in an efficient manner to a high multichannel reverberator. In particular, they lack flexibility in coping with arbitrary source inputs and loudspeaker setups.
Many artificial reverberators have been developed in recent years, wherein in the following a brief overview of their application in multichannel reverberation is given. The vast majority of the commercially available reverberators have a low number of input and output channels. Whereas they have developed a high standard in usability, computational efficiency and sound quality, they scale inefficiently for high numbers of output channels.
One way to achieve a high number of channels using low channel reverberators is to instantiate multiple similar reverberators. This increases the memory requirements and computational costs considerably. For uncorrelated output channels the reverberators are parameterized differently, so they might become distinctive. It is possible to overcome distinctly receivable reverberators by cross-feeding signals between the reverberators.
However, the DOA of the early reflections cannot be implemented in this way as the desired DOA might be between the output channel of two reverberators. Consequently, there is no explicit way to position multiple sources by the means of the combination of multiple reverberators. Further, the usability for multiple instances can become awkward and complicated.
While convolution-based reverberators can produce a given physical acoustic space with high precision, as it is described, for example, in [1], they scale very inefficiently with a high number of sound sources and output channels. Each pair of sound source and output channel is processed by a separate convolution. Consequently, the number of convolutions to be performed is the product of the number of sound sources and output channels. The impulse responses are difficult to acquire and they lack flexibility in the source and receiver positioning of other room parameters.
In contrast, delay networks-based reverberators allow a wide control over any detail of the reverberated sound. Also, recently delay networks reverberators developed a high standard of sound quality in low channel applications. Currently existing algorithms do not or inefficiently offer a consistent approach to recreate multichannel audio with high efficiency.
Typically, the reverberation is created in two stages: the early reflections and the late reverberation as it is depicted in
The late reverberation is created by the feedback delay network (FDN) 1024. The FDN 1024 is based around a set of N delay lines 1025, labeled as τ1, τ2, . . . , τN and a feedback mixing matrix A to evolve a complex echo pattern over time. The reverberation time and diffusion is controlled by the attenuation filters 1026, labeled as α1, α2, . . . , αN. The implementation of the attenuation filters ranges from a simple lowpass filter, as it is described in [4] to absorbent allpass filters as it is described in [5].
The early reflections are fed into the FDN loop to increase initial density of the delayed reverberation. Delayed reverberation is mixed and added to the panned early reflections. The resulting channels are fed into the loudspeakers 1028 of the reproduction room 1032. Optionally, a channel-dependent equalization filter (EQ) 1034 can be applied to the speaker channels for spectral corrections and speaker dependent frequency response.
In the listening position, all output channels in the reproduction room 160 are delayed and summed up and form the receiver signal. Hence, premixing of the delay line signals as it is typically performed in the prior design, increases the echo density in every output channel, but does not increase the echo density perceived in the room. It rather tends to introduce unpleasant coherence and comb-like filter artifacts. One extreme example, which may occur with a Hadamard mixing matrix, is to distribute the output of a delay line to all output channels, which creates a multichannel mono signal with a phase flip.
Designs of known concepts have no efficient and convenient way to handle multichannel reverberation including spatial cues and direction-dependency. Further, early reflections, which are most important for the spatial perception of the reverberator are rendered separately by known concepts, what is computational costly.
Currently, many different multi-speaker configurations exist, meaning that multichannel reverberations with flexible speaker configurations are highly necessitated. Hence, for example, there is a need for audio reproduction concepts, allowing for multichannel reverberators with a more flexible speaker configuration and/or for an efficient way for obtaining the reverberations.
According to an embodiment, an apparatus for generating a first multitude of output signals based on at least one audio source signal may have: a delay network including a second multitude of delay paths each delay path having a delay line and an attenuation filter, each delay line being configured for delaying delay line input signals and for combining the at least one audio source signal and a reverberated audio signal to obtain a combined signal, wherein the attenuation filter of a delay path is configured for filtering the combined signal from the delay line of the delay path to obtain an output signal, wherein the first multitude of output signals includes the output signal; and a feedback processor configured for reverberating the first multitude of output signals to obtain a third multitude of the reverberated audio signals including the reverberated audio signal; wherein the combined signal includes an audio source signal portion and a reverberated signal portion and wherein the delay line includes a sixth multitude of input taps being configured for receiving the audio source signal or a weighted version of the audio source signal, wherein the apparatus includes an input controller configured for connecting the audio source signal or the weighted version of the audio source signal and one of the sixth multitude of input taps and based on a first position of a virtual audio source in a virtual reproduction room and while not connecting the audio source signal or the weighted version of the audio source signal to a different input tap of the sixth multitude of input taps, and wherein the input controller is configured for disconnecting the audio source signal or the weighted version of the audio source signal from the one of the sixth multitude of input taps based on a second position of the virtual audio source, the second position being different from the first position; or wherein the combined signal includes an audio source signal portion and a reverberated signal portion and wherein the delay line includes a seventh multitude of output taps being configured for providing the combined signal or an intermediate delay line signal, wherein the apparatus includes an output controller configured for connecting an equalization filter to the output signal or top one of the seventh multitude of output taps based on a first reflection characteristic of a virtual reproduction room, while not connecting a different output tap of the seventh multitude of output taps to the equalization filter, and wherein the output controller is configured for disconnecting the equalization filter from the output signal or from the intermediate delay line signal based on a second reflection characteristic of the virtual production room being different from the first characteristic.
According to another embodiment, an apparatus for generating a fourth multitude of loudspeaker signals based on at least one audio source signal may have: a delay network including a second multitude of delay paths each delay path having a delay line and an attenuation filter, each delay line being configured for delaying delay line input signals and for combining the at least one audio source signal and a reverberated audio signal to obtain a combined signal, wherein the attenuation filter of a delay path is configured for filtering the combined signal from the delay line of the delay path to obtain an output signal, wherein the first multitude of output signals includes the output signal; and a feedback processor configured for reverberating the first multitude of output signals to obtain a third multitude of the reverberated audio signals including the reverberated audio signal; wherein the delay network includes a fifth multitude of equalization filters being configured for spectrally shaping the first multitude of output signals or intermediate delay line signals to obtain the fourth multitude of loudspeaker signals, the intermediate delay line signals being received from an output tap of the delay line.
According to another embodiment, a sound reproduction system may have: an inventive apparatus for generating a first multitude of output signals; an eleventh multitude of loudspeakers; and a panner configured for receiving a fourth multitude of loudspeaker signals derived from the first multitude of output signals and for panning the fourth multitude of loudspeaker signals to a twelfth multitude of panned loudspeaker signals, the twelfth multitude of panned loudspeaker signals having a number of loudspeaker signals that is equal to a number of loudspeakers of the eleventh multitude of loudspeakers; wherein the panner is configured for maintaining a sound propagation characteristic of a virtual reproduction room associated to the fourth multitude of loudspeaker signals when panning the fourth multitude of loudspeaker signals.
According to another embodiment, a sound reproduction system may have: an inventive apparatus for generating a fourth multitude of loudspeaker signals; an eleventh multitude of loudspeakers; and a panner configured for receiving a fourth multitude of loudspeaker signals derived from the first multitude of output signals and for panning the fourth multitude of loudspeaker signals to a twelfth multitude of panned loudspeaker signals, the twelfth multitude of panned loudspeaker signals having a number of loudspeaker signals that is equal to a number of loudspeakers of the eleventh multitude of loudspeakers; wherein the panner is configured for maintaining a sound propagation characteristic of a virtual reproduction room associated to the fourth multitude of loudspeaker signals when panning the fourth multitude of loudspeaker signals.
According to another embodiment, a method for generating a first multitude of output signals based on at least one audio source signal may have the steps of: delaying and combining the at least one audio source signal and a reverberated audio signal with a delay line to obtain a combined signal; filtering the combined signal from the delay line to obtain an output signal, wherein the first multitude of output signals is obtained from a second multitude of delay paths each delay path having a delay line; and reverberating the first multitude of output signals to obtain a third multitude of the reverberated audio signals including the reverberated audio signal; wherein the combined signal includes an audio source signal portion and a reverberated signal portion and wherein the delay line includes a sixth multitude of input taps being configured for receiving the audio source signal or a weighted version of the audio source signal, the method having the steps of: connecting the audio source signal or the weighted version of the audio source signal and one of the sixth multitude of input taps and based on a first position of a virtual audio source in a virtual reproduction room and while not connecting the audio source signal or the weighted version of the audio source signal to a different input tap of the sixth multitude of input taps, and disconnecting the audio source signal or the weighted version of the audio source signal from the one of the sixth multitude of input taps based on a second position of the virtual audio source, the second position being different from the first position; or or wherein the combined signal includes an audio source signal portion and a reverberated signal portion and wherein the delay line includes a seventh multitude of output taps being configured for providing the combined signal or an intermediate delay line signal, the method having the steps of connecting an equalization filter to the output signal or top one of the seventh multitude of output taps based on a first reflection characteristic of a virtual reproduction room, while not connecting a different output tap of the seventh multitude of output taps to the equalization filter, and disconnecting the equalization filter from the output signal or from the intermediate delay line signal based on a second reflection characteristic of the virtual production room being different from the first characteristic.
According to another embodiment, a method for generating a fourth multitude of loudspeaker signals based on at least one audio source signal may have the steps of: delaying and combining the at least one audio source signal and a reverberated audio signal with a delay line to obtain a combined signal; filtering the combined signal from the delay line to obtain an output signal, wherein the first multitude of output signals is obtained from a second multitude of delay paths each delay path having a delay line; and reverberating the first multitude of output signals to obtain a third multitude of the reverberated audio signals including the reverberated audio signal; spectrally shaping the first multitude of output signals or intermediate delay line signals to obtain the fourth multitude of loudspeaker signals, the intermediate delay line signals being received from an output tap of the delay line; wherein the combined signal includes an audio source signal portion and a reverberated signal portion and wherein the delay line includes a sixth multitude of input taps being configured for receiving the audio source signal or a weighted version of the audio source signal, the method having the steps of: connecting the audio source signal or the weighted version of the audio source signal and one of the sixth multitude of input taps and based on a first position of a virtual audio source in a virtual reproduction room and while not connecting the audio source signal or the weighted version of the audio source signal to a different input tap of the sixth multitude of input taps, and disconnecting the audio source signal or the weighted version of the audio source signal from the one of the sixth multitude of input taps based on a second position of the virtual audio source, the second position being different from the first position; or or wherein the combined signal includes an audio source signal portion and a reverberated signal portion and wherein the delay line includes a seventh multitude of output taps being configured for providing the combined signal or an intermediate delay line signal, the method having the steps of connecting an equalization filter to the output signal or top one of the seventh multitude of output taps based on a first reflection characteristic of a virtual reproduction room, while not connecting a different output tap of the seventh multitude of output taps to the equalization filter, and disconnecting the equalization filter from the output signal or from the intermediate delay line signal based on a second reflection characteristic of the virtual production room being different from the first characteristic.
Another embodiment may have a non-transitory digital storage medium having a computer program stored thereon to perform the method for generating a first multitude of output signals based on at least one audio source signal, the method having the steps of: delaying and combining the at least one audio source signal and a reverberated audio signal with a delay line to obtain a combined signal; filtering the combined signal from the delay line to obtain an output signal, wherein the first multitude of output signals is obtained from a second multitude of delay paths each delay path having a delay line; and reverberating the first multitude of output signals to obtain a third multitude of the reverberated audio signals including the reverberated audio signal; wherein the combined signal includes an audio source signal portion and a reverberated signal portion and wherein the delay line includes a sixth multitude of input taps being configured for receiving the audio source signal or a weighted version of the audio source signal, the method having the steps of: connecting the audio source signal or the weighted version of the audio source signal and one of the sixth multitude of input taps and based on a first position of a virtual audio source in a virtual reproduction room and while not connecting the audio source signal or the weighted version of the audio source signal to a different input tap of the sixth multitude of input taps, and disconnecting the audio source signal or the weighted version of the audio source signal from the one of the sixth multitude of input taps based on a second position of the virtual audio source, the second position being different from the first position; or or wherein the combined signal includes an audio source signal portion and a reverberated signal portion and wherein the delay line includes a seventh multitude of output taps being configured for providing the combined signal or an intermediate delay line signal, the method having the steps of connecting an equalization filter to the output signal or top one of the seventh multitude of output taps based on a first reflection characteristic of a virtual reproduction room, while not connecting a different output tap of the seventh multitude of output taps to the equalization filter, and disconnecting the equalization filter from the output signal or from the intermediate delay line signal based on a second reflection characteristic of the virtual production room being different from the first characteristic, when said computer program is run by a computer.
Another embodiment may have a non-transitory digital storage medium having a computer program stored thereon to perform the method for generating a fourth multitude of loudspeaker signals based on at least one audio source signal, the method having the steps of: delaying and combining the at least one audio source signal and a reverberated audio signal with a delay line to obtain a combined signal; filtering the combined signal from the delay line to obtain an output signal, wherein the first multitude of output signals is obtained from a second multitude of delay paths each delay path having a delay line; and reverberating the first multitude of output signals to obtain a third multitude of the reverberated audio signals including the reverberated audio signal; spectrally shaping the first multitude of output signals or intermediate delay line signals to obtain the fourth multitude of loudspeaker signals, the intermediate delay line signals being received from an output tap of the delay line; wherein the combined signal includes an audio source signal portion and a reverberated signal portion and wherein the delay line includes a sixth multitude of input taps being configured for receiving the audio source signal or a weighted version of the audio source signal, the method having the steps of: connecting the audio source signal or the weighted version of the audio source signal and one of the sixth multitude of input taps and based on a first position of a virtual audio source in a virtual reproduction room and while not connecting the audio source signal or the weighted version of the audio source signal to a different input tap of the sixth multitude of input taps, and disconnecting the audio source signal or the weighted version of the audio source signal from the one of the sixth multitude of input taps based on a second position of the virtual audio source, the second position being different from the first position; or or wherein the combined signal includes an audio source signal portion and a reverberated signal portion and wherein the delay line includes a seventh multitude of output taps being configured for providing the combined signal or an intermediate delay line signal, the method having the steps of connecting an equalization filter to the output signal or top one of the seventh multitude of output taps based on a first reflection characteristic of a virtual reproduction room, while not connecting a different output tap of the seventh multitude of output taps to the equalization filter, and disconnecting the equalization filter from the output signal or from the intermediate delay line signal based on a second reflection characteristic of the virtual production room being different from the first characteristic, when said computer program is run by a computer.
Another embodiment may have a loudspeaker signal obtained by an inventive apparatus for generating a first multitude of output signals.
Another embodiment may have a loudspeaker signal obtained by an inventive apparatus for generating a fourth multitude of loudspeaker signals.
Embodiments of the present invention related to an apparatus for generating a first multitude of output signals based on at least one audio source signal. The apparatus comprises a delay network and a feedback processor. The delay network comprises a second multitude of delay paths, wherein each delay path comprises a delay line and an attenuation filter. Each delay line is configured for delaying input signals of the delay line and for combining the at least one audio source signal and a reverberated audio signal to obtain a combined signal. The attenuation filter of the delay path is configured for filtering the combined signal from the delay line of the delay path to obtain an output signal. The first multitude of output signals comprises the output signal. The feedback processor is configured for reverberating the first multitude of output signals to obtain a third multitude of the reverberated audio signals comprising the reverberated audio signal.
This allows for obtaining delayed (early reflections) and reverberated signals from one FDN, wherein a complexity of the FDN may be almost independent from a number of source signals such that the delayed and reverberated signals are obtained efficiently.
Further embodiments of the present invention relate to an apparatus for generating a fourth multitude of loudspeaker signals based on at least one audio source signal. The apparatus comprises a delay network and a feedback processor. The delay network comprises the second multitude of delay paths, wherein each delay path comprises a delay line and an attenuation filter. Each delay line is configured for delaying delay line input signals and for combining the at least one audio source signal and a reverberated audio signal to obtain a combined signal. The attenuation filter of a delay path is configured for filtering the combined signal from the delay line of the delay path to obtain an output signal. The first multitude of output signals comprises the output signal. The feedback processor is configured for reverberating the first multitude of output signals to obtain a third multitude of the reverberated audio signals comprising the reverberated audio signal. The delay network further comprises a fifth multitude of equalization filters being configured for spectrally shaping the first multitude of output signals or intermediate delay line signals to obtain the fourth multitude of loudspeaker signals. The intermediate delay line signals are received from an output tap of the delay line.
It has been found by the inventors that by combining the audio source signal and reverberated audio signals in a delay line both, the earlier reflections and the late reverberation may be obtained by a feedback delay network. A computational complexity of the proposed concept scales with a number of output signals or loudspeaker signals to be obtained but may be independent or almost independent from a number of audio source signals to be rendered into the output signals, the loudspeaker signals respectively. Further, a spatial information of reflected and/or reverberated audio signals may be maintained.
Further embodiments of the present invention relate to a sound reproduction system comprising an apparatus for generating a first multitude of output signals or an apparatus for generating a fourth multitude of loudspeaker signals, a multitude of loudspeakers and a panner configured for receiving loudspeaker signals derived from the output signal and for panning the loudspeaker signals to a multitude of loudspeaker signals that correspond to a number of loudspeakers which may be different from a number of received loudspeaker signals. The panner is configured for maintaining a sound propagation characteristic of a virtual reproduction room associated with the multitude of received loudspeaker signals when panning the received signals to the panned loudspeaker signals.
This allows for a flexible loudspeaker configuration, independent from the generated output signals or loudspeaker signals of the apparatus as those signals may comprise directional information related to the delay lines of the apparatus for generating the output signals or the loudspeaker signals such that those spatial information may be maintained.
Further embodiments of the present invention relate to a method for generating a first multitude of output signals, a method for generating a multitude of loudspeaker signals, to a computer program and to a loudspeaker signal.
Embodiments of the present invention will be detailed subsequently referring to the appended drawings, in which:
Equal or equivalent elements or elements with equal or equivalent functionality are denoted in the following description by equal or equivalent reference numerals even if occurring in different figures.
In the following description, a plurality of details is set forth to provide a more thorough explanation of embodiments of the present invention. However, it will be apparent to those skilled in the art that embodiments of the present invention may be practiced without these specific details. In other instances, well known structures and devices are shown in block diagram form rather than in detail in order to avoid obscuring embodiments of the present invention. In addition, features of the different embodiments described hereinafter may be combined with each other, unless specifically noted otherwise.
The apparatus 100 is configured for generating the output signals 102a-d based on the audio source signals 104a and 104b such that the output signals 102a-d are reflected and/or reverberated versions of the audio source signals 104a and 104b, i.e., the output signals 102a-d are derived from the audio source signals 104a and 104b. An information carried by the output signal 102a-d may vary over time. For example, the output signal may be an early reflection of the audio source signal in a virtual reproduction room 130 at a first time instance and a reverberated version of the audio source signal at a second time instance following the first time instance.
The apparatus 100 comprises four delay lines 106a-d. Each delay path 106a-d comprises a delay line 108a-d and an attenuation filter 112a-d. The delay lines 108a-d are configured for receiving the audio source signals 104a and 104b and a reverberated audio signal 114a-d, i.e., every delay line 108a-d is configured for receiving three signals, two audio source signals and one reverberated audio signal.
As it will be described later and in more detail, every delay line 108a-d is configured for delaying a received (input) signal and for combining the received and delayed signal such that a combined signal 116 is obtained. The combined signal 116 comprises, e.g. by a different time delay, delayed portions of the audio source signals 104a and 104b and of the reverberated signal 114a, 114b, 114c or 114c. The delay lines 108a-d are depicted as schematic blocks labeled as τ1-τ4. Schematically, the delay lines 104a-d may be understood as delaying filters, such as an finite impulse response (FIR) filter transferring a received signal from one direction, e.g., left, to another direction, e.g., right of the schematic filter structure. Simplified, the more “left” a signal is input into the delay line, the more it is delayed. When referring to the delay line 108a, the audio source signal 104a is delayed by a greater time delay than the audio source signal 104b and the reverberated audio signal 114a is delayed by a longer time duration than the audio source signal 104a.
The delay paths 106a-d each comprise the attenuation filter 112a-d labeled as al, a2, a3, a4, respectively. The attenuation filters 116 are configured for providing, i.e., to output, the output signals 102a-d by attenuating the combined signal 116 of the delay line 108a-d and may be implemented, for example as infinite impulse response (IIR) filters. By combining the audio source signal 104a and 104b in a delay line 108a-d and by attenuating the combined signal 116, early reflections of the audio source signals 104a and 104b may be obtained.
The apparatus 100 further comprises a feedback processor 120 configured for reverberating the output signals 102a-d such that the reverberated audio signals 114a-d are obtained. The feedback processor 120 may be understood, for example, as cross-feeding the output signals 102a-d. The cross-feeding may be depicted, for example, as a matrix operation. The delay paths may form a delay network. The feedback processor 120 and the delay network may form a feedback delay network (FDN), wherein the feedback processor 120 is configured for performing a feedback and/or a cross-feeding of the output signals 102 to the delay network.
The apparatus 100 comprises two distributors 118a and 118b, wherein the distributor 118a is configured for receiving the audio source signal 104a and wherein the distributor 118b is configured for receiving the audio source signal 104b. The distributors 118a and 118b are configured for distributing the received audio source signal 104a or 104b into a number of versions (copies) thereof. Simplified, the distributor 118a and 118b are configured for splitting or copying the received audio source signal 104a or 104b. The obtained versions 104a′, 104b′ may comprise no or a low delay with respect to each of the other versions of the respective audio source signal 104a or 104b. A low delay may be, for example, lower than or equal than 20%, than 10% or than 4% of a maximum time delay of the delay lines 108a-d. The distributors 118a and 118b further comprise a plurality or a multitude of amplifiers 122 configured for individually amplifying or attenuating the versions 104a′, 104b′ respectively. the applied gain or attenuation may be correlated, for example, to a strength or a value of the reflection of the sound source in the virtual reproduction room.
The distributor 118a is configured for providing a number of individually, i.e., independent from each other, amplified versions 104a″ of the audio source signal 104a, wherein a number of the versions 104a″ may be equal to a number of delay paths 106a-d such that each delay line 108a-d may receive one of the versions 104a″. The distributor 118b may comprise a multitude of amplifiers 122 configured for independently amplifying the versions 104b′ to obtain a number of independently amplified versions 104b″ of the audio source signal 104b, wherein a number of the obtained versions 104b″ or 104b′ may be equal to the number of delay lines 108a-d such that every delay line 108a-d may receive one of the amplified versions 104b″. As each delay line 106a-d may be associated with a virtual loudspeaker, a gain of each of the amplifiers 122 may influence a characteristic of the reproduced reflection of the sound object reproduced in the virtual reproduction room and reflected at a sound reflecting structure such as a wall.
The versions (copies) and the amplified versions of the audio source signal 104a and 104b carry an unchanged information with respect to the mono signal, i.e., to the audios source signal 104a and 104b. In terms of the further processing for delaying, attenuating and the like, those signals may be regarded as unchanged.
The structure of the apparatus 100 allows for, over time, that each output signal 102a-d comprises a reflected and a reverberated portion of the audio source signals 104a and 104b as it will be described in the following example:
The delay line 108a is configured for receiving the audio source signal 104a, an amplified version 104a″ thereof respectively, and an amplified version 104b″ of the audio source signal 104b. The audio source signal 104b is delayed by a shorter time delay than the audio source signal 104a as it is indicated by the input of the audio source signal 104b being arranged closer to the output of the delay line 108a when compared to the input of the audio source signal 104a. For example, when the delay line 108a comprises a plurality of delay blocks, the audio source signal 104a may be delayed by a higher number of delay blocks when compared to the audio source signal 104b. The combined signal 116 thus comprises a portion derived from the delayed audio source signal 104b and a portion of the audio source signal 104b which is delayed for a longer time. The combined signal 116 is provided to the attenuation filter 112a. The output signal 102a may be described as a delayed and attenuated and thus reflected version of the audio source signals 104a and 104b.
As indicated by the inputs at different actual positions and therefore time delays of the delay lines 108a-d, the inputs receiving the audio source signals 104a and 104b, the amplified versions 104a″ and 104b″ respectively, each version 104a″ may be delayed by a different time delay when compared to other delay lines 108a-d. Accordingly, each version 104b″ of the audio source signal 104b may be delayed by a different time delay when compared to the other delay lines 108a-d. Thus, a multitude of reflected signals may be obtained.
The output signals 102a-d are reverberated by the feedback processor 120 and then provided to the delay paths 106a-d. The reverberated signals 114a-d are delayed by the delay lines 108a-d and combined with the audio source signals 104a and 104b. This allows for obtaining reverberated portions in the output signals 102a-d.
Further audio source signals may be fed into the delay network, i.e., into the plurality of delay paths 106a-d. A processing of the further audio source signals may be obtained without a further arrangement of delay paths and thus without providing extra memory or filter stages. Alternatively, only one audio source signal may be processed, i.e., delayed and reverberated.
A time delay of the audio source signal 104a and 104b, i.e., a position of the signal input with respect to the delay line 108a-d may be adjusted or set according to a position of a virtual loudspeaker 132a-d in a virtual reproduction room 130. The virtual reproduction room 130 may be parameterized as a reference scene in which audio objects shall be reproduced or generated. The virtual loudspeakers 130a-d are arranged at virtual positions in the virtual reproduction room and comprise virtual radiation characteristics, such as a direction and/or a radiation pattern. The position and/or direction of sound propagation of the virtual loudspeakers 132a-d (the direction of sound arrival) in the virtual reproduction room 130 are related (parameterized) by the FDN, by the delay lines 108a-d respectively. Simplified, the virtual reproduction room 130 may be used to acquire the parameters for the delay lines 108a-d, the attenuation filters 112a-d and the feedback processor 120.
A delay time of a delay line 108a-d may correspond to a distance of a virtual loudspeaker 132a-d to a sound reflecting structure of the virtual reproduction room. A reverberation time of the virtual reproduction room may correspond to attenuation factors of the attenuation filters 112a-d. The attenuation factors of the attenuation filters 112a-d and/or the reverberation time may be frequency dependent, i.e., a first frequency may be reverberated with a first reverberation time, different from a second reverberation time by which a second frequency, different from the first frequency, is reverberated. For example, the higher the attenuation is, the shorter a reverberation time may be. Thus, the filter coefficients of the attenuation filters 112a-d may be related to a reverberation time of the audio source signal with respect to the virtual reproduction room 130. The filter coefficients may be time variant, e.g., based on a time variant virtual reproduction room 130.
Thus, the virtual loudspeakers 132a-d are associated with an information comprising a virtual direction of sound propagation in the virtual reproduction room 130. Each virtual loudspeaker 132a-d may be adjusted independently with respect to other virtual loudspeakers 132a-d. By varying a time delay of the delay line 108a-d, a position of a corresponding virtual loudspeaker 132a-d in the virtual reproduction room 130 may be influenced or vice versa. Thus, the virtual loudspeaker setup may be realized in any desired form, for example, the virtual loudspeakers 132a-d may be distributed equally in the virtual reproduction room 130. Alternatively, the virtual loudspeakers 132a-d may be distributed unequally, for example and with respect to a position of a listener, a left, right, front or back area of the listener may comprise a higher density of loudspeakers when compared to other sections of the virtual reproduction room 130.
A floor, a ceiling, walls and/or other sound reflecting objects may also be parameterized by or in the virtual reproduction room. Thus, a virtual sound object emitting a sound in the virtual reproduction room with a sound propagation characteristic, such as a direction, may be reproduced by the virtual loudspeakers 130a-d. Sound propagation characteristics of the virtual reproduction room, such as sound reflections and/or sound attenuation at walls or the like may be transferred at least partially into parameters of the delay network. For example, a distance between a virtual loudspeaker and a wall of the virtual reproduction room may be transferred in a time of travel (time delay) before the sound wave is reflected. The time delays of the delay lines 108a-d may refer to a delay of a propagated sound in the virtual reproduction room before arriving at a virtual listening position. Each delay path 106a-d may be related to a virtual loudspeaker 130a-d in the virtual reproduction room 130. This allows for a scaling of the apparatus 100 based on a number of virtual loudspeakers 130a-d instead of based on a number of reproduced sound sources.
Based on a variable position of a virtual audio source in the virtual reproduction room 130 also time delays may vary, for example, when the virtual audio source is moving closer to a wall, then the emitted sound is reflected earlier. The apparatus 100 comprises an input controller 140 configured for connecting the audio source signals 104a and 104b, amplified versions 104a″ and 104b″ respectively, with different inputs of the delay lines 108a-d, wherein the different inputs are related to a different time delay between the respective input and the output. Simplified, the input controller 140 is configured for receiving parameters related to a necessitated or aimed time delay and for adapting the time delay by which the audio source signal is delayed by the delay line 108a-d.
The output signals 102a-d may be stored, for example, on or in a data memory, for example a hard drive, a digital video disc (DVD), the internet or other media. Alternatively, the input signals 102a-d may be provided to a equalizing network 141 comprising equalization filters 142a-d configured for spectrally shaping the output signals 102a-d. A spectral shaping of the equalization filters 142a-d may be implemented according to sound propagation characteristics and/or a direction of a sound propagation of the emitted sound in the virtual reproduction room. For example, when walls of the virtual reproduction room 130 are adapted to attenuate high frequencies, the equalization filters 142a-d may be implemented according to such a characteristic and may allow for sound adjustment according to a sound direction.
Output signals 144a-d of the equalization filters 142a-d may thus be configured for reproducing the virtual reproduction scene comprising the virtual audio objects, the virtual reproduction room 130 and the virtual loudspeakers 132a-d as when the virtual reproduction room 130 and the virtual loudspeakers 132a-d were real. The obtained signals 144a-d may be stored on a storage medium and/or provided to a panner 150 of the audio system 1000, wherein the panner 150 is configured for providing (real) loudspeaker signals 152a-f in a number according to a number of real loudspeakers 162 in a real reproduction room 160. Simplified, the panner 150 is configured for panning a number of loudspeaker signals 144a-d having a number according to a number of the virtual loudspeakers 132a-d to a number of loudspeaker signals 152a-f having a number according to a number of real loudspeakers 162a-f. In general, a number of real loudspeakers 152a-f may be higher or lower than a number of virtual loudspeakers 132a-d. A number of real loudspeakers may depend on a user setup and may be even unknown, when generating the output signals 102a-d and/or the loudspeaker signals 144a-d. Thus, the generation of the output signals 102a-d and/or of the loudspeaker signals 144a-d may be regarded as being independent from the reproduction room. A number of output signals 102a-d, delay paths 106a-d and equalization filters 142a-d for filtering the output signals may thus be equal. Simplified, the delay lines 106a-d are associated to a direction of sound propagation of the early reflections in the virtual reproduction room 130. Filter parameters of the equalization filters 142a-d may be adapted based on the direction of sound propagation.
Reproducing an audio scene may comprise reproducing of direct sound, i.e., an unreflected signal from the reproduced audio object to the listener. The audio reproduction system 1000 may comprise equalization filters 143a and 143b configured for equalizing, i.e., spectrally shaping, the audio source signal 104a and/or 104b, to obtain spectrally shaped audio source signals 145a and 145b. The panner 150 may be configured for receiving the audio source signals 104a and 104b and/or the spectrally shaped signals 145a and 145b. The panner 150 may further be configured for providing the loudspeaker signals 152a-f based on the loudspeaker signals 144a-d and on the audio source signals 104a and 104b the spectrally shaped versions thereof, respectively. Simplified, the panner 150 may provide the loudspeaker signals 152a-d comprising an information related to the direct sound, to the early reflections and to the late reverberations.
Although the equalization filters 152a-d were described as being configured for receiving the output signal 102a-d, the equalization filters 142a-d may also be configured for receiving an intermediate delay line signal, which is, for example, not attenuated by the attenuation filters 112a-d. Such a scenario is described later and allows for obtaining loudspeaker signals 144a-d and therefore loudspeaker signals 152a-d comprising reverberated signals in an absence of reflected portions.
The apparatus 100 may comprise an output controller 170 configured for connecting an equalization filter 142a-d to an output tap of a delay line 108a-d. At the output tap the intermediate delay line signal may be obtained. Based on changed sound reflection characteristics of the virtual reproduction room, the output controller 170 is further configured for disconnecting the equalization filter 142a-d from the output tap of the delay line 108a-d and/or for connecting the equalization filter 142a-d to another output tap. According to an embodiment, at most one output tap is connected to the equalization filter 142a-d. Both, the input controller 140 and the output controller 170 may be configured to connect only one input tap of a delay line, only one output tap respectively.
The apparatus 200 comprises a delay network 202 comprising the delay paths 106a-d. The delay network 202 and the feedback processor 120 form a FDN, wherein the feedback processor 120 is configured for performing a feedback and/or a cross-feeding of the output signals 102 to the delay network 202.
In other words, in
The number of delay lines and the number of sources are scalable from one to higher integers. In prior designs such as the one depicted in
A direct assignment of the delay lines to virtual directions of the virtual loudspeakers 132a-d may provide an advantageous solution when compared to known concepts. Vice versa, an angular direction is assigned to each filtered delay line output, the output signals 102a-d, and therefore to the delay line 108a-d itself. This one-to-one correspondence between a delay line 108a-d and a virtual speaker 130a-d, e.g., the delay line 108a to the virtual speaker 130a, may be regarded as important or even most important when compared to prior designs, a spatial design can be introduced into the FDN framework. Similarly, the attenuation filters 112a-d and the output equalization filters 142a-d may correspond to spatial directions.
The channel directions as indicated by the virtual loudspeakers 132a-d in the virtual reproduction room 130 are then panned to the desired output loudspeaker setup in the actual reproduction room 160. Every virtual speaker 132 may be understood as a point source on a sphere around the listener, which can be reproduced by the physical speakers with weighted gains depending on their relative position. For example, a Vector-Based Amplitude Panning (VBAP) as described in [6] may be employed as a simple and effective choice. Alternatively, especially in a scenario utilizing a high number of loudspeakers such as at least 20, at least 30 or at least 50, a panning may be performed as a so-called hard panning, i.e., the loudspeaker signal 144a-d is provided to the closest real loudspeaker 162a-f, i.e., having the closest distance to a virtual loudspeaker 132a-d that would emit the sound signal.
The intermediate step of a virtual reproduction room allows for a high or even maximal flexibility in the choice of loudspeaker setups and maintains the spatial and acoustic features of the reverberation with a good level or maybe even as best as possible. The resulting mixing matrix, i.e., the feedback processor 120, is very sparse in terms of computational complexity for multichannel loudspeaker setups.
The delay lines 108a-d are positioned to discretize the panning sphere around the listening position. The particular positioning may be panned on the sound design, e.g., they can be placed equally spaced on the sphere or certain sections of the sphere may be enhanced by the number of delay lines.
Depending on the target loudspeaker setup, certain sections of the sphere can be omitted and others can be condensed, e.g., for: loudspeaker setups like 5.1+4 or 22.2 large parts of the lower hemisphere can be omitted, or depending on the application it may be favorable to place more delay lines in the front, the natural stage direction. Such an area is denoted as “front” in
The input taps 302a-d are arranged sequentially and with a delay block 304a-d between two input taps 302a-d. Thus, a signal received at the input tap 302a is forwarded to the delay block 304a, delayed and then forwarded to the second input tap 302b. When the first input tap 302a receives the reverberated audio signal 114a and when the second input tap 302b receives the audio source signal 104a, the reverberated audio signal 114a is combined with the audio source signal 104a at the second input tap. A last output tap, e.g., the outtap 306c may be the output of the filter providing the combined signal 116, such that a “last” intermediate delay line signal, e.g., 308c, may be the combine signal.
Alternatively or in addition, for example, when the third input tap 302c receives the audio source signal 104b, at the third input tap 302c the reverberated audio signal 114a, the audio source signal 104a and the audio source signal 104b are combined. Each of the signals 114a, 104a and 104b is delayed by a different time delay, i.e., by a different number of delay blocks 304a-c. A signal combined at an input tap 302a-d may be amplified or attenuated by a gain factor or an attenuation factor k1-k3. Subsequent amplified or attenuated signals are combined at output taps 306a-c, wherein at the output taps 306a-c intermediate delay line signals 308a-c may be obtained. For example, the output controller 170 may connect or disconnect one of the output taps 306a-c or an output of the attenuation filter 112a with or from the equalization filter 142a such that the equalization filter 142a may receive one of the intermediate delay line signals 308a-c or the output signal 102a.
A delay time from the input tap 302i to the filter output, i.e., until the attenuation filter 112i receives the combined signal 116 may be regarded as a reflection delay. An output signal 102i of the attenuation filter 112i, for example one of the output signals 102a-d, is forwarded to the equalization filter 142i such that the loudspeaker signal 144i comprises a reverberated portion and a reflected portion. When the filters of the delay line 108i and/or of the attenuation filter 112i are, for example, in an initial or basic state, then the reverberated signal 114i may be also static and/or initial, for example in a zero-state. When the audio source signal 104 is applied to the system and the delay line 108i receives the amplified version thereof, then the loudspeaker signal 144i may first only comprise the reflected portion as the reverberated signal 114i is different from the zero-state in the next iteration. Simplified, the audio source signal first travels once through parts of the delay line 108i such that the loudspeaker signal 144i is based on the delayed (reflected) audio source signal. Then, the output signal 102i is reverberated and combined with the audio source signal such that in a following time interval the loudspeaker signal 144i is based on reflected and reverberated portions.
In other words, for every source, intaps, i.e., input taps, up to a number of delay lines can be chosen in a way that the first reflections are determined in gain, delay and approximated direction and all reflections are filtered by the attenuation filter. The proposed apparatus and method comes with reduced computational cost compared to known prior methods. In the case that spatial early reflections are not desired, an alternative approach as depicted in
r=A*oor, alternatively rT=oT*AT
wherein r denotes a vector comprising the reverberated signals 114a-d, A denotes the reverberation matrix, o denotes the output signals 102a-d and xT denotes a transposed version of x.
The sub-room 136b may be, for example, a back or a second, different side of the virtual reproduction room 130 when compared to the sub-room 136a. The sub-room 136a may be parameterized by a parameter block U1 (comprising a subset of the parameters a11-a44). The sub-room 136b may be parameterized by a parameter block U2 (comprising an at least partially different subset of the parameters a11-a44). Parameter blocks V1 and V2 denote an acoustic coupling from the first sub-room 136a to the second sub-room 136b, from the second sub-room 136b to the first sub-room 136a respectively. The matrix A may be structured according to the parameter blocks U1, U2, V1 and V2. The sub-rooms 136a and 136b may also be two different rooms comprising an acoustic coupling between each other, for example, two rooms connected by a door. This allows for an easy parameterization of the virtual reproduction room 130. The parameterization may be obtained based on the maintained directional information of the reflections and/or of the reverberations.
In other words, the feedback matrix A is often chosen to control the reflection density. Every entry in the matrix indicates the gain from one delay line to another. The more dense the matrix is, the more dense the reverberation tail will be. The proposed apparatus and method allow for subdividing the matrix A into directional sections to control the directional propagation of the reflections over time. The virtual direction of the delay lines are known, so that a matrix entry indicates the propagation from one direction to another, e.g., a diagonal entry keeps the direction. For homogeneous rooms, where every direction is mixed with each other, uniform matrix gains may be appropriate. Two acoustically coupled rooms, e.g., a room and a neighboring hallway can be implemented by a 2×2 block matrix.
The diagonal blocks U1 and U2 control the mixing of, for example, the front and the back room, respectively. The non-diagonal blocks V1 and V2 may control the leakage between the coupled rooms.
Accordingly, the attenuation filters and/or the equalization filters related to virtual loudspeakers arranged in different sub-rooms may be adjusted differently, i.e., it may be that they implement different reverberation characteristics.
In other words,
In other words, to place a certain reflection in direction and time, the closest delay line to the desired direction of arrival may be chosen and the intap is placed in the delay line with appropriate distance. The direction of the early reflection is approximated by the angular delay line distribution and may reflect the lowered DOA perception for early reflections. Compared to known methods, no matter how many input sources are rendered, no extra memory is needed for external delay lines. Also, the dedicated panning unit for the early reflections can be omitted. In known methods, typically extra processing of the early reflection output needs to be done to avoid unattenuated early reflections. The computational costs for the extra intaps are practically equal to the cost of the early reflection outtaps.
Typically, the overall spectral power of a reverberation made to be adjusted, for example by a spectral shaping as it is described for the equalization filters 142a-d in
The proposed concept presents techniques for spatial multichannel parametric reverberation. It is based on the Feedback Delay Network as the most general representative of the delay network reverberators.
The proposed concept introduces a spatial interpretation of the delay lines. The intermediate level of a virtual listening room gives weighted flexibility with target loudspeaker setups via a panning algorithm. Therefore, an integrated technique for early reflections is applicable. At the same time, the computational costs can be maintained and direction-of-arrival can be controlled. Further, the proposed method allows for efficient adjustment of the direction dependent spectral power, mixing and reverberation time. The proposed concept allows the creation of spatial reverberation for playback in 3D multichannel speaker setups. Thus, the proposed concept provides techniques for spatial multichannel parametric reverberation. A novel delay networks multichannel reverberator is proposed, which allows the positioning of high numbers of sound sources with a high number of loudspeakers, while maintaining computational efficiency. The proposed concept introduces a spatial interpretation of the delay lines and an integrated technique for processing early reflections. Further, the proposed concept allows for an efficient adjustment of the direction dependent spectral power, mixing and reverberation time.
The attenuation filters of the FDN and/or the equalization filters may be implemented as IIR-filters having a low number of filter coefficients such as at most 200, at most 100 or at most 50 and/or a low order of the filter, such as, for example, at most of order 8, order 5 or order 3 or lower. Attenuation factors of the attenuation filters may be adjusted based on a frequency selective reverberation time of the combined signal. Filter coefficients of the equalization filters may be based on a frequency selective spectral energy of the output signal, the intermediate delay line signal respectively. In addition, the filter coefficients of the attenuation filters and/or of the equalization filter may be set according to a direction of arrival of the sound to be implemented.
Although above described embodiments relate to a number of four and sixteen delay lines, other embodiments relate to a different number of delay lines and therefore virtual loudspeakers, for example, at least three, at least eight, twelve or sixteen.
Although the above embodiments refer to a realization of the feedback processor such that the feedback processor is configured for performing matrix-based operations, the feedback processor may alternatively or in addition be configured for performing other types of operation such as a convolution operation related to a matrix (e.g. related to IIR- or FIR-filters), a transformation, a difference, a division and/or non-linear operations.
Although the above embodiments refer to a reproduction room comprising six loudspeakers, a reproduction room may also comprise a different number of loudspeakers, for example, at least two, at least four, ten or more.
Although the above embodiments relate to delay lines being implemented as FIR filters, delay lines may also be realized as different types of filters and/or without attenuation or gain parameters. For example, a multitude of delay blocks may be implemented digitally such that the delay line may be characterized by a simple number of delay blocks for delaying signals.
Although the above embodiments relate to a virtual reproduction room comprising two sub-rooms or one room, the virtual reproduction room may also comprise three or more sub-rooms. Accordingly, the matrix A may also comprise a different number of parameter blocks which may be separated or combined (partially overlapping) with each other and wherein a number of parameter blocks and/or delay paths may be based on a number of coupling paths between the sub-rooms. However, although the matrix A is depicted as being quadratic, based on the coupling parameters, the matrix A may also be non-quadratic and/or comprise one or more sub-room related matrices having a non-quadratic form.
Although some aspects have been described in the context of an apparatus, it is clear that these aspects also represent a description of the corresponding method, where a block or device corresponds to a method step or a feature of a method step. Analogously, aspects described in the context of a method step also represent a description of a corresponding block or item or feature of a corresponding apparatus.
The inventive encoded audio signal can be stored on a digital storage medium or can be transmitted on a transmission medium such as a wireless transmission medium or a wired transmission medium such as the Internet.
Depending on certain implementation requirements, embodiments of the invention can be implemented in hardware or in software. The implementation can be performed using a digital storage medium, for example a floppy disk, a DVD, a CD, a ROM, a PROM, an EPROM, an EEPROM or a FLASH memory, having electronically readable control signals stored thereon, which cooperate (or are capable of cooperating) with a programmable computer system such that the respective method is performed.
Some embodiments according to the invention comprise a data carrier having electronically readable control signals, which are capable of cooperating with a programmable computer system, such that one of the methods described herein is performed.
Generally, embodiments of the present invention can be implemented as a computer program product with a program code, the program code being operative for performing one of the methods when the computer program product runs on a computer. The program code may for example be stored on a machine readable carrier.
Other embodiments comprise the computer program for performing one of the methods described herein, stored on a machine readable carrier.
In other words, an embodiment of the inventive method is, therefore, a computer program having a program code for performing one of the methods described herein, when the computer program runs on a computer.
A further embodiment of the inventive methods is, therefore, a data carrier (or a digital storage medium, or a computer-readable medium) comprising, recorded thereon, the computer program for performing one of the methods described herein.
A further embodiment of the inventive method is, therefore, a data stream or a sequence of signals representing the computer program for performing one of the methods described herein. The data stream or the sequence of signals may for example be configured to be transferred via a data communication connection, for example via the Internet.
A further embodiment comprises a processing means, for example a computer, or a programmable logic device, configured to or adapted to perform one of the methods described herein.
A further embodiment comprises a computer having installed thereon the computer program for performing one of the methods described herein.
In some embodiments, a programmable logic device (for example a field programmable gate array) may be used to perform some or all of the functionalities of the methods described herein. In some embodiments, a field programmable gate array may cooperate with a microprocessor in order to perform one of the methods described herein. Generally, the methods are performed by any hardware apparatus.
While this invention has been described in terms of several advantageous 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.
| Number | Date | Country | Kind |
|---|---|---|---|
| 14192213 | Nov 2014 | EP | regional |
This application is a continuation of copending International Application No. PCT/EP2015/075141, filed Oct. 29, 2015, which is incorporated herein by reference in its entirety, and additionally claims priority from European Application No. EP 14192213.8, filed Nov. 7, 2014, which is also incorporated herein by reference in its entirety. The present invention relates to an apparatus for generating output signals based on at least one audio source signal, to an apparatus for generating a multitude of loudspeaker signals based on the at least one audio source signal, to a sound reproduction system, a method for generating the output signals and to a computer program. The present invention further relates to a loudspeaker signal and to techniques for spatial multichannel parametric reverberation.
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| Dahl, Luke et al., “A Reverberator Based on Absorbent All-Pass Filters”, Proceedings of the COST G-6 Conference on Digital Audio Effects (DAFX-00), Dec. 2000, 6 pages. |
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| Number | Date | Country | |
|---|---|---|---|
| 20170238119 A1 | Aug 2017 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | PCT/EP2015/075141 | Oct 2015 | US |
| Child | 15585792 | US |
