KR102290417B1 - Method and apparatus for 3D sound reproducing using active downmix - Google Patents

Abstract

Receive a plurality of input channel signals including a height input channel signal, generate a parameter for phase alignment based on the plurality of input channel signals, and phase align a first frequency range of the plurality of input channel signals; modify the first downmix matrix based on the parameter for the alignment, modify the second downmix matrix based on the parameter for the phase alignment, to phase align all frequency ranges of the plurality of input channel signals, and downmixing the plurality of input channel signals into a plurality of output channel signals based on one of the first downmix matrix and the modified second downmix matrix, wherein the first frequency range is less than 2.8 kHz and greater than 10 kHz wherein a height input channel signal is identified based on the elevation information, a first modified downmix matrix is used for a general scene and a second modified downmix matrix is used for a highly decorrelated wideband scene. and downmixing is performed by one of a modified first downmix matrix and a modified second downmix matrix selected according to a received flag.

Description

{Method and apparatus for 3D sound reproducing using active downmix}

The present invention relates to a method and apparatus for reproducing a stereophonic sound, and more particularly, to a method and apparatus for reproducing a multi-channel audio signal providing a sense of height.

Thanks to the development of image and sound processing technology, high-definition and high-quality content is being produced in large quantities. Users who have requested high-definition and high-quality content want realistic images and sounds, and accordingly, research on stereoscopic images and stereophonic sounds is being actively conducted.

Stereoscopic sound is a technology that allows a user to feel a sense of space by arranging a plurality of speakers at different positions on a horizontal plane and outputting the same or different sound signals from each speaker. However, actual sound can occur not only at various locations on the horizontal plane, but also at different altitudes. Accordingly, there is a need for a technique for reproducing sound signals generated at different altitudes through speakers arranged on a horizontal plane.

The present invention relates to a method and apparatus for reproducing a stereophonic sound, and to a method for reproducing a stereophonic sound according to a downmix method.

An audio signal rendering method according to an embodiment includes receiving a plurality of input channel signals including a height input channel signal, generating a parameter for phase alignment based on the plurality of input channel signals, the plurality of input channels modifying a first downmix matrix based on the parameter for phase alignment to phase align a first frequency range of a signal, to phase align all frequency ranges of the plurality of input channel signals, the phase alignment modifying a second downmix matrix based on a parameter for wherein the first frequency range includes less than 2.8 kHz and greater than 10 kHz, wherein the height input channel signal is identified based on elevation information, and wherein the modified first downmix matrix is a general the modified second downmix matrix is used for a scene and is used for a highly decorrelated wideband scene, wherein the downmixing comprises the modified first downmix matrix selected according to a received flag and It may be performed by one of the modified second downmix matrices.

An audio signal rendering apparatus according to an embodiment includes a processor and a memory storing at least one instruction executed by the processor, wherein the processor receives a plurality of input channel signals including a height input channel signal, and the plurality of generate a parameter for phase alignment based on the input channel signal of , modify a second downmix matrix based on the parameter for the phase alignment to phase align all frequency ranges of the plurality of input channel signals, and the modified first downmix matrix and the modified second downmix the plurality of input channel signals into a plurality of output channel signals based on one of a downmix matrix, wherein the first frequency range comprises less than 2.8 kHz and greater than 10 kHz, and wherein the height input channel signal comprises: identified based on elevation information, wherein the modified first downmix matrix is used for a general scene and the modified second downmix matrix is used for a highly decorrelated wideband scene, wherein the downmixing is one of the modified first downmix matrix and the modified second downmix matrix selected according to the received flag.

According to an embodiment of the present invention, when performing acoustic signal mixing according to the active-down mixing method, the mixing may be performed so that the sense of height is not reduced.

In an embodiment of the present invention, by applying the active-down mixing method to a low-frequency signal in which the effect of the active-down mixing method can be substantially exhibited, the amount of calculation that may be generated when mixing according to the active-down mixing method is increased and high It is possible to minimize the deterioration of sense.

1 and 2 are block diagrams illustrating an internal structure of a stereophonic sound reproducing apparatus according to an embodiment of the present invention.
3 is a block diagram illustrating internal structures of a 3D renderer and a mixer according to an embodiment of the present invention.
4 and 5 are flowcharts illustrating a 3D sound reproduction method according to an embodiment of the present invention.
6 is an exemplary diagram illustrating an example of an active-down mixing method according to an embodiment of the present invention.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. However, detailed descriptions of well-known functions or configurations that may obscure the gist of the present invention in the following description and accompanying drawings will be omitted. Also, it should be noted that throughout the drawings, the same components are denoted by the same reference numerals as much as possible.

The terms or words used in the present specification and claims described below should not be construed as being limited to conventional or dictionary meanings, and the inventor shall appropriately define his or her invention in terms of the best way to describe it. Based on the principle that it can be done, it should be interpreted as meaning and concept consistent with the technical idea of the present invention. Therefore, the embodiments described in this specification and the configurations shown in the drawings are only the most preferred embodiment of the present invention, and do not represent all the technical ideas of the present invention, so at the time of the present application, various It should be understood that there may be equivalents and variations.

When a part "includes" a certain element throughout the specification, this means that other elements may be further included, rather than excluding other elements, unless otherwise stated. In addition, terms such as "...unit" and "module" described in the specification mean a unit that processes at least one function or operation, which may be implemented as hardware or software, or a combination of hardware and software. .

Hereinafter, with reference to the accompanying drawings, embodiments of the present invention will be described in detail so that those of ordinary skill in the art can easily carry out the present invention. However, the present invention may be embodied in many different forms and is not limited to the embodiments described herein. And in order to clearly explain the present invention in the drawings, parts irrelevant to the description are omitted, and similar reference numerals are attached to similar parts throughout the specification.

Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings.

1 and 2 are block diagrams illustrating an internal structure of a stereophonic sound reproducing apparatus according to an embodiment of the present invention.

The stereoscopic sound reproducing apparatus 100 according to an embodiment of the present invention may output a down-mixed multi-channel audio signal to a channel to be reproduced.

Stereophonic sound is a sound to which spatial information is added, which reproduces not only the pitch and tone of the sound, but also the direction and sense of distance to have a sense of presence, and to allow listeners who are not located in the space where the sound source is located to perceive the sense of direction, distance, and space. it means.

In the following description, a channel of an audio signal may mean the number of speakers from which sound is output. As the number of channels increases, the number of speakers outputting sound may increase. The stereophonic sound reproducing apparatus 100 according to an embodiment of the present invention may render and mix a multi-channel audio signal with a channel to be reproduced so that a multi-channel audio signal with a large number of channels can be output and reproduced in an environment with a small number of channels. . In this case, the multi-channel audio signal may include a channel capable of outputting a high-level sound.

A channel capable of outputting a high-level sound may mean a channel capable of outputting an acoustic signal through a speaker located above a listener's head so as to feel a sense of elevation. The horizontal plane channel may mean a channel capable of outputting an acoustic signal through a speaker positioned on a horizontal plane with the listener.

The above-described environment in which the number of channels is small may mean an environment in which a sound may be output through a speaker disposed on a horizontal plane according to a horizontal plane channel without including a channel capable of outputting a high-level sound.

* Also, in the following description, a horizontal channel may mean a channel including an audio signal that may be output through a speaker disposed on a horizontal plane. The overhead channel may refer to a channel including an audio signal that is disposed on an elevation rather than a horizontal plane and may be output through a speaker capable of outputting an elevation sound.

Referring to FIG. 1 , a stereoscopic sound reproducing apparatus 100 according to an embodiment of the present invention may include a renderer 110 and a mixer 120 . However, not all illustrated components are essential components. The 3D sound reproducing apparatus 100 may be implemented by more components than the illustrated components, or the 3D sound reproducing apparatus 100 may be implemented by fewer than the illustrated components.

Hereinafter, the components will be described in turn.

According to an embodiment of the present invention, the 3D sound reproducing apparatus 100 may render, mix, and output a multi-channel audio signal as a channel to be reproduced. For example, the multi-channel audio signal may be a 22.2 channel signal, and the channel to be reproduced may be a 5.1 or 7.1 channel. The stereophonic sound reproducing apparatus 100 performs rendering by determining a channel to correspond to each channel of the multi-channel audio signal, and mixes the rendered audio signals by combining the signal of each channel corresponding to the channel to be reproduced and outputting it as a final signal. can

The renderer 110 may render a multi-channel audio signal according to a channel and a frequency. The renderer 110 may perform 3D (dimensional) rendering and 2D (dimensional) rendering of a multi-channel audio signal according to an overhead channel and a horizontal plane channel, respectively.

The renderer 110 may render an overhead channel that has passed a head related transfer filter (HRTF) transformation filter in 3D rendering methods according to frequencies in different ways. The HRTF transform filter is not only a simple path difference such as a difference in level between the two ears and a time difference between the two ears, but also a complex path characteristic such as diffraction from the head surface and reflection by the pinna in the direction of sound arrival. It transforms the tone of the sound arriving from the other direction by applying the deformation of the tone that occurs in the changing phenomenon. The HRTF transformation filter may process the audio signals included in the overhead channel so that the stereophonic sound can be recognized by changing the sound quality of the audio signal.

The renderer 110 renders a low-frequency signal among overhead channel signals according to an Add to the closest channel method, and a high-frequency signal is rendered according to a multichannel panning method. can do. According to the multi-channel panning method, a signal of each channel of the multi-channel audio signal may be respectively rendered to at least one horizontal plane channel by applying a gain value set differently for each channel to be rendered to each channel signal. Signals of each channel to which the gain value is applied may be combined through mixing and output as a final signal.

Since the low-frequency signal has strong diffraction properties, according to the multi-channel panning method, each channel of the multi-channel audio signal is not divided into several channels and rendered, but only one channel can be rendered to have similar sound quality for listeners to hear. Accordingly, the stereophonic sound reproducing apparatus 100 according to an embodiment of the present invention renders a low-frequency signal according to the add-to-closest-channel method, so that sound quality that can be generated by mixing several channels into one output channel deterioration can be prevented. That is, when several channels are mixed into one output channel, the sound quality may be amplified or reduced and deteriorated according to interference between the respective channel signals, so that sound quality deterioration may be prevented by mixing one channel to one output channel.

According to the add-to-close channel method, each channel of the multi-channel audio signal may be rendered to the nearest channel among channels to be reproduced instead of being divided into multiple channels for rendering.

Also, the stereophonic sound reproducing apparatus 100 may widen a sweet spot without degrading sound quality by performing rendering in a different method according to a frequency. That is, by rendering a low-frequency signal having strong diffraction characteristics according to the add-to-closest channel method, it is possible to prevent deterioration in sound quality that may occur when several channels are mixed into one output channel. The sweet spot refers to a predetermined range in which a listener can optimally listen to an undistorted stereophonic sound. As the sweet spot is wider, the listener can optimally listen to the undistorted stereophonic sound over a wide range, and when the listener is not located in the sweet spot, the listener can listen to the sound with distorted sound quality or sound image.

The mixer 120 may combine the signals of the horizontal channels and the corresponding channels by the renderer 110 and output them as a final signal. The mixer 120 may mix signals of each channel for each predetermined section. For example, the mixer 120 may mix signals of each channel for each frame.

The mixer 120 according to an embodiment of the present invention may mix signals rendered according to frequencies in an active downmix method. More specifically, the mixer 120 may mix low-frequency signals in an active-down mixing method. In addition, with respect to the high-frequency signal, the mixer 120 determines the amplitude of the final signal or the gain to be applied to the final signal based on the power values of the signals rendered to each channel to be reproduced (Power preserving module) can be mixed with In addition, the mixer 120 may mix high-frequency signals according to other methods other than the method in which the phase of each signal is corrected and mixed, not limited to the power conservation method.

The active-down mixing method refers to a method of mixing by correcting a phase of each signal when downmixing using a covariance matrix between signals added to a channel to be mixed. For example, the phase of each signal may be corrected based on a signal having the greatest energy among downmixed signals. According to the active-down mixing method, the phase of each signal is corrected so that constructive interference between the signals to be combined can be made, thereby preventing distortion of sound quality due to destructive interference that may occur during mixing. In particular, when sound signals are mixed according to the active-down mixing method, it is possible to prevent the tone of the mixed sound signal from changing or the sound from disappearing due to destructive interference caused by the mismatch of phases of the respective signals.

On the other hand, a virtual rendering technology that passes an overhead channel signal through an HRTF transform filter and reproduces a stereophonic sound signal through multi-channel panning is a high-level stereophonic sound by reproducing a synchronized sound source through left and right surround speakers. This can be output. In particular, as a synchronized sound source is reproduced through the left and right surround speakers, the same amount of a binaural signal is provided, so that a sense of height can be imparted to the sound image.

However, when downmixing signals according to the active-down mixing method, since phases of the signals may be different, a sense of height may not be provided as the synchronization of signals between channels is out of sync. For example, if the synchronization of the signals to the overhead channel is out of sync during the mixing process, the sense of height that can be recognized according to the time difference between the two ears is reached, so the sound quality deteriorates due to the application of the active down mix. can be

Accordingly, the mixer 120 produces a low-frequency signal according to the active-down mixing method in that the time difference between the two ears is hardly recognized for the low-frequency signal with strong diffraction, and the phase overlap phenomenon is prominent in the low-frequency component. can be mixed In addition, the mixer 120 may mix a high-frequency signal with a strong sense of height, which can be recognized according to a time difference between the two ears, according to a mixing method in which the phase is not corrected. For example, the mixer 120 may mix high-frequency signals while minimizing distortion of sound quality due to destructive interference by preserving energy canceled by destructive interference occurring according to a power conservation method.

In addition, in an embodiment of the present invention, in the QMF (quadrature mirror filter) filter bank, band components above a specific crossover frequency are regarded as high frequency and the rest are considered as low frequency, so that the low frequency signal and the high frequency signal are implemented in such a way that Rendering and mixing may be performed respectively. The QMF filter may refer to a filter that divides an input signal into a low frequency and a high frequency and outputs it.

In addition, active-down mixing can be performed for each frequency band, and it has a very high amount of computation, such as having to calculate covariance between channels for down-mixing. The amount of computation can be reduced. For example, when an active-down mix is applied to a signal sampled at 48 kHz by the acoustic signal reproducing apparatus 100 and only a sound of 3 kHz or less is applied in the QMF filter bank and a power conservation module is applied to a sound of a frequency higher than that, the amount of computation is approximately It can be reduced by 1/3.

In addition, in the case of a substantially recorded sound source, the more high-frequency signals, the less the probability that one channel signal is in phase with another channel, so unnecessary calculations are sometimes performed during mixing by active-down mixing.

Referring to FIG. 2 , the stereoscopic sound reproducing apparatus 200 according to an embodiment of the present invention may include a sound analyzer 210 , a renderer 220 , a mixer 230 , and an output unit 240 . The 3D sound reproducing apparatus 200, the renderer 220, and the mixer 230 of FIG. 2 correspond to the 3D sound reproducing apparatus 100, the renderer 210, and the mixer 220 of FIG. 1 , and overlapping descriptions are omitted. decide to do However, not all illustrated components are essential components. The 3D sound reproducing apparatus 200 may be implemented by more components than the illustrated components, or the 3D sound reproducing apparatus 200 may be implemented by fewer than the illustrated components.

Hereinafter, the components will be described in turn.

The sound analyzer 210 may analyze the multi-channel audio signal, select a rendering mode, and separate and output some signals included in the multi-channel audio signal. The acoustic analysis unit 210 may include a rendering mode selection unit 211 and a rendering signal separation unit 212 .

The rendering mode selector 211 may determine whether there are many transient signals, such as a clap sound or a rain sound, in the multi-channel audio signal for each predetermined section. In the following description, an audio signal having many transient, that is, an instantaneous and temporary signal, such as an applause sound or a rain sound, will be referred to as an applause signal.

The stereoscopic sound reproducing apparatus 200 according to an embodiment of the present invention may separate the applause signal and process channel rendering and mixing according to the characteristics of the applause signal.

The rendering mode selector 211 may select the rendering mode as either a general mode or an applause mode according to whether the applause signal is included in the multi-channel audio signal. The renderer 220 may render according to the mode selected by the rendering mode selector 211 . That is, the renderer 220 may render the applause signal according to the selected mode.

The rendering mode selector 211 may select a normal mode when the applause signal is not included in the multi-channel audio signal. According to the normal mode, the overhead channel signal may be rendered by the 3D renderer 221 , and the horizontal channel signal may be rendered by the 2D renderer 222 . That is, rendering may be performed without considering the applause signal.

The rendering mode selector 211 may select the applause mode when the applause signal is included in the multi-channel audio signal. According to the applause mode, the applause signal may be separated, and rendering may be performed on the separated applause signal.

The rendering mode selector 211 determines whether the applause signal is included in the multi-channel audio signal for each predetermined section using applause bit information included in the multi-channel audio signal or separately received from another device. can Applause bit information includes bsTsEnable or bsTempShapeEnableChannel flag information according to the MPEG-based codec, and a rendering mode may be selected by the rendering mode selection unit 211 based on the above-described flag information.

Also, the rendering mode selector 211 may select a rendering mode based on the characteristics of the multi-channel audio signal of a predetermined section to be determined. That is, the rendering mode selector 211 may select the rendering mode according to whether the characteristic of the multi-channel audio signal of the predetermined section has the characteristic of the audio signal including the applause signal.

The rendering mode selector 211 determines whether a non-tonal wideband signal exists in a plurality of input channels in a multi-channel audio signal of a predetermined section, and whether the level of the signal is similar for each channel, and whether the signal level is similar for each channel. It may be determined whether the applause signal is included in the multi-channel audio signal based on at least one condition of whether the impulse form is repeated and whether the correlation between channels is low. .

The rendering mode selection unit 211 may select the rendering mode as the applause mode when it is determined that the applause signal is included in the multi-channel audio signal in the current section.

The rendering signal separating unit 212 may separate the applause signal included in the multi-channel audio signal from the general sound signal when the applause mode is selected by the rendering signal selector 211 .

When the bsTsdEnable flag in the MPEG USAC series is used, 2D rendering may be performed like a horizontal channel signal according to flag information regardless of the elevation of the corresponding channel. In addition, the overhead signal may also be mixed by being assumed to be a horizontal channel signal according to flag information. That is, the rendering signal separation unit 212 may separate the applause signal included in the multi-channel audio signal of a predetermined section according to the flag information, and the separated applause signal may be 2D rendered like the horizontal channel signal. there is.

When the flag is not used, the rendering signal separation unit 212 may analyze a signal between channels to separate the applause signal component. The separated applause signal among the overhead signals may be 2D rendered, and the remaining signals other than the applause signal may be 3D rendered.

The renderer 220 may include a 3D renderer 221 that renders an overhead signal according to a 3D rendering method and a 2D renderer 222 that renders a horizontal plane channel signal or applause signal according to a 2D rendering method.

The 3D renderer 221 may render the overhead signal in different ways depending on the frequency. The 3D renderer 221 may render a low-frequency signal according to the add-to-closest channel method and render a high-frequency signal according to the 3D rendering method. Hereinafter, the 3D rendering method refers to a method of rendering an overhead signal, and the 3D rendering method may include a multi-channel panning method.

The 2D renderer 222 may render the horizontal channel signal or the applause signal according to at least one of a 2D rendering method, an add-to-closest channel method, and an energy boost method. Hereinafter, the 2D rendering method refers to a method of rendering a horizontal channel signal, and the 2D rendering method may include a downmix equation or a VBAP method.

The mixer 230 may calculate the rendered signals for each channel and output a final signal. The mixer 230 according to an embodiment of the present invention may mix signals rendered according to frequencies in an active downmix method. Accordingly, the stereophonic sound reproducing apparatus 200 according to an embodiment of the present invention can reduce tone distortion that may occur due to destructive interference by mixing low-frequency signals in an active-down mixing method. In addition, the stereophonic sound reproducing apparatus 200 mixes high-frequency signals other than the low-frequency signals according to, for example, the power conservation module in addition to the active-down mixing method to prevent a decrease in the sense of height that may be caused by the application of the active-down mix. can

The output unit 240 may finally output the signal mixed by the mixer 230 through the speaker. In this case, the output unit 240 may output the sound signal through different speakers according to the channel of the mixed signal.

3 is a block diagram illustrating internal structures of a 3D renderer and a mixer according to an embodiment of the present invention. The 3D renderer 301 and the mixer 302 of FIG. 3 correspond to the 3D renderer 221 and the mixer 230 of FIG. 2 , and overlapping descriptions will be omitted. However, not all illustrated components are essential components. The 3D renderer 301 and the mixer 302 may be implemented by more components than the illustrated components, and the 3D renderer 301 and the mixer 302 may be implemented by fewer components.

Hereinafter, the components will be described in turn.

Referring to FIG. 5 , the 3D renderer 301 may include an HRTF transformation filter 310 , an LPF 320 , an HPF 330 , an add-to-closest channel 340 , and a multi-channel panning 350 . there is.

The HRTF transformation filter 310 may perform HRTF transformation filtering on an overhead channel signal among multi-channel audio signals.

The LPF 320 may separate and output a low frequency component among the HRTF transform-filtered overhead channel signals.

The HPF 320 may separate and output a high-frequency component among the HRTF transform-filtered overhead channel signals.

The add-to-close channel 340 may render a channel closest to the low-frequency component of the overhead channel signal when it is projected onto the horizontal plane of each channel.

The multi-channel panning 350 may render a high-frequency component of the overhead channel signal according to the multi-channel panning method.

Also, referring to FIG. 3 , the mixer 302 may include an active-down mixing module 360 and a power conservation module 370 .

The active-down mixing module 360 may mix low-frequency components of the overhead channel signals rendered by the add-to-close channel 540 among the signals rendered by the 3D renderer 301 in an active-down mixing method. The active-down mixing module 360 may mix low-frequency components according to an active-down mixing method of correcting the phases of signals added for each channel in order to induce constructive interference.

The power conservation module 370 may mix high-frequency components of the overhead channel signals rendered by the multi-channel panning 350 among the signals rendered by the 3D renderer 301 according to the power conservation method. The power conservation module 370 may mix the high frequency component in a power conservation method of determining the amplitude of the final signal or a gain to be applied to the final signal based on the power values of the signals rendered to each channel. The power conservation module 370 according to an embodiment of the present invention may mix a signal of a high frequency component in the power conservation method described above, but is not limited thereto, and may also be mixed according to another method.

The mixer 302 may output a mixed 3D sound signal by adding the signals mixed by the active-down mixing module 360 and the power conservation module 370 .

Hereinafter, a method of reproducing a stereophonic sound according to the active-down mixing method described above will be described in detail with reference to FIGS. 4 and 5 .

4 and 5 are flowcharts illustrating a 3D sound reproduction method according to an embodiment of the present invention.

Referring to FIG. 4 , in step S401 , the stereophonic sound reproducing apparatus 100 may obtain a multi-channel audio signal to be reproduced.

In operation S403 , the stereophonic sound reproducing apparatus 100 may render for each channel. The 3D sound reproducing apparatus 100 according to an embodiment of the present invention may render according to a frequency, but the present invention is not limited thereto, and may be rendered in various ways.

In operation S405, the stereophonic sound reproducing apparatus 100 may mix the signals rendered in operation S403 in an active-down mixing method according to frequencies. In more detail, the stereophonic sound reproducing apparatus 100 may mix low-frequency components in an active-down mixing method and high-frequency components in another method. For example, the stereophonic sound reproducing apparatus 100 applies a gain determined according to the power value of the rendered signals for each channel to the high-frequency component, so that the energy canceled by the destructive interference is mixed so as to be preserved in a power conservation method. can be mixed

Accordingly, the stereophonic sound reproducing apparatus 100 according to an embodiment of the present invention can minimize a decrease in the sense of height that may occur when the active-down mixing method is applied to a high-frequency component.

FIG. 5 is a flowchart illustrating in more detail a method of rendering and mixing for each frequency in the stereophonic sound reproduction method illustrated in FIG. 4 .

Referring to FIG. 5 , in step S501 , the stereophonic sound reproducing apparatus 100 may obtain a multi-channel audio signal to be reproduced. In this case, when the applause signal is inserted, the stereophonic sound reproducing apparatus 100 may separate the applause signal and process the channel rendering and mixing according to the characteristics of the applause signal.

In operation S503, the stereophonic sound reproducing apparatus 100 divides the stereophonic sound signal obtained in operation S501 into an overhead channel signal and a horizontal channel signal, and performs rendering and mixing, respectively. That is, the 3D sound reproducing apparatus 100 may perform 3D rendering and mixing of the overhead channel signal and 2D rendering and mixing of the horizontal channel signal.

In operation S505 , the stereophonic sound reproducing apparatus 100 may filter the overhead channel signal with an HRTF transformation filter to provide a sense of height.

In operation S507, the stereophonic sound reproducing apparatus 100 may perform rendering and mixing processing by separating the overhead channel signal into high frequency and low frequency signals.

In operation S509 , the stereophonic sound reproducing apparatus 100 may render a high-frequency signal among the overhead channel signals according to a 3D rendering method in operation S511 . The 3D rendering method may include a multi-channel panning method. Multi-channel panning may mean that each channel signal of a multi-channel audio signal is distributed to channels to be reproduced. In this case, each channel signal to which the panning coefficient is applied may be distributed to channels to be reproduced. In the case of a high-frequency signal, the signal may be distributed to a surround channel in order to provide a characteristic that an interaural level difference (ILD) between the two ears decreases as the sense of height increases. In addition, the direction of the acoustic signal may be determined by the number of the plurality of channels to be panned with the front channel.

In operation S513, the stereophonic sound reproducing apparatus 100 may mix the high-frequency signal rendered in operation S511 by a method other than the active-down mixing method. For example, the stereophonic sound reproducing apparatus 100 may mix the rendered high-frequency signal according to the power conservation module.

Also, in operation S515 , the stereophonic sound reproducing apparatus 100 may render a low-frequency signal among the overhead channel signals according to the above-described add-to-closest channel method. When many signals in one channel, that is, several channel signals of a multi-channel audio signal are mixed, sound quality may be deteriorated as sound quality is canceled or amplified due to different phases. According to the add-to-close channel method, the stereophonic sound reproducing apparatus 100 may map each channel to the closest channel when projected onto the horizontal plane in order to prevent the above-described sound quality deterioration.

When the multi-channel audio signal is a frequency signal or filter bank signal, the bin or band corresponding to the low frequency is the add-to-close channel method, and the bin or band corresponding to the high frequency is the multi-channel method. It may be rendered according to a channel panning method. A bin or a band may mean a signal period of a predetermined unit in the frequency domain.

In operation S521, the stereophonic sound reproducing apparatus 100 may mix the signals of the horizontal plane channel rendered in operation S519 according to the power conservation module.

In operation S523, the stereophonic sound reproducing apparatus 100 may output a final mixed signal of the overhead channel signal and the horizontal channel signal.

6 is an exemplary diagram illustrating an example of an active-down mixing method according to an embodiment of the present invention.

When the signal 610 and the signal 620 are mixed, the phases of the respective signals do not match, so destructive interference may occur and sound quality may be distorted. Accordingly, according to the active-down mixing method, the phase of the signal 610 having relatively low energy may be corrected to match the signal 620 , and each signal may be mixed. Referring to the mixed signal 630 , as the phase of the signal 610 is shifted backward, constructive interference may occur.

According to an embodiment of the present invention, when performing acoustic signal mixing according to the active-down mixing method, the mixing may be performed so that the sense of height is not reduced.

In an embodiment of the present invention, by applying the active-down mixing method to a low-frequency signal in which the effect of the active-down mixing method can be substantially exhibited, the amount of calculation that may be generated when mixing according to the active-down mixing method is increased and high It is possible to minimize the deterioration of sense.

The method according to an embodiment of the present invention can be implemented as computer-readable codes on a computer-readable recording medium (including all devices having an information processing function). The computer-readable recording medium includes all types of recording devices in which data readable by a computer system is stored. Examples of computer-readable recording devices include ROM, RAM, CD-ROM, magnetic tape, floppy disk, and optical data storage device.

Although the foregoing description has focused on novel features of the invention as applied to various embodiments, those skilled in the art will recognize the apparatus and method described above without departing from the scope of the invention. It will be understood that various deletions, substitutions, and changes are possible in the form and details of Accordingly, the scope of the present invention is defined by the appended claims rather than by the above description. All modifications within the scope of equivalents of the claims are included in the scope of the present invention.

Claims (2)

receiving a plurality of input channel signals comprising a height input channel signal;
generating a parameter for phase alignment based on the plurality of input channel signals;
modifying a first downmix matrix based on the parameter for phase alignment to phase align a first frequency range of the plurality of input channel signals;
modifying a second downmix matrix based on the parameter for phase alignment to phase align all frequency ranges of the plurality of input channel signals; and
downmixing the plurality of input channel signals into a plurality of output channel signals based on one of the modified first downmix matrix and the modified second downmix matrix;
wherein the first frequency range includes less than 2.8 kHz and greater than 10 kHz;
the height input channel signal is identified based on altitude information;
the modified first downmix matrix is used for a general scene and the modified second downmix matrix is used for a highly decorrelated wideband scene;
and the downmixing is performed by one of the modified first downmix matrix and the modified second downmix matrix selected according to a received flag. An audio signal rendering apparatus comprising:
processor; and
a memory for storing at least one instruction executed by the processor;
the processor
receiving a plurality of input channel signals including a height input channel signal;
generating a parameter for phase alignment based on the plurality of input channel signals;
modify a first downmix matrix based on the parameter for phase alignment to phase-align a first frequency range of the plurality of input channel signals;
modify a second downmix matrix based on the parameter for phase alignment to phase align all frequency ranges of the plurality of input channel signals, and
downmix the plurality of input channel signals into a plurality of output channel signals based on one of the modified first downmix matrix and the modified second downmix matrix;
wherein the first frequency range includes less than 2.8 kHz and greater than 10 kHz,
the height input channel signal is identified based on altitude information;
the modified first downmix matrix is used for a general scene and the modified second downmix matrix is used for a highly decorrelated wideband scene;
and the downmixing is performed by one of the modified first downmix matrix and the modified second downmix matrix selected according to a received flag.

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