JP2019016871A - Sound image generating apparatus - Google Patents

Abstract

To suppress noise of an acoustic signal.SOLUTION: A sound image generating apparatus 1 includes: a wavefront synthesis prefilter generation unit 11 for generating a wavefront synthesis prefilter for wavefront synthesis; a window function multiplying unit 12 for multiplying the wavefront synthesis prefilter by a window function; and a filter operation unit 13 for convolving the wavefront synthesis prefilter multiplied by the window function with an acoustic signal.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a sound reproduction technique for creating a virtual sound source / sound image in real space.

  In public viewing and concert venues, voice and music are played from multiple speakers installed at the screening venue. In recent years, efforts have been made to realize more realistic sound reproduction by creating a sound source virtually in real space.

  Regarding sound reproduction technology for creating a virtual sound source in a screening space, Patent Document 1 discloses that a sound signal from an actual sound source is collected by a plurality of microphones in a recording venue, and then the sound signal arrives in the vertical and horizontal directions. By analyzing the direction and using wave field synthesis in the remote screening space, the acoustic signal of the recording venue is physically reproduced from the speaker array, that is, it corresponds to the actual sound source. A method for reproducing a virtual sound source is described.

Further, in Non-Patent Document 1, it is assumed that there is an acoustic sink in the assumed virtual sound field, and a driving signal derived from the first type Rayleigh integration is given to the speaker array in FIG. As shown, a method for creating a virtual sound image (X _s ) on the front surface of the speaker array is described.

JP 2011-244306 A

Sascha Spors, 3 others, “Physical and Perceptual Properties of Focused Sources in Wave Field Synthesis”, 127th Audio Engineering Society Convention paper 7914, October 2009 Hagen Wierstorf, 3 others, “Perception of focused sources in wave field synthesis”, Journal of the Audio Engineering Society, vol. 61, No. 1/2, January, February 2013, p.5-p.16

  The method of Patent Document 1 has high reproducibility in reproducing a virtual sound source in order to faithfully reproduce an acoustic signal at a recording point. However, since not only a speaker array but also a microphone array is required, the scale of the entire system increases. Further, since the recorded sound is to be reproduced faithfully, for example, a sound effect that does not exist on a daily basis as represented by a movie is added as a special effect, making it difficult to edit the audio content performed later.

  On the other hand, the method of Non-Patent Document 1 does not require a microphone array to generate a virtual sound image. In general, as shown in Non-Patent Document 1, an analytically defined digital filter can calculate a filter coefficient with a smaller amount of computation than a technique using sequential optimization or the like. However, since an inverse Fourier transform process or the like is required for each channel of the acoustic signal, there is a problem that the amount of calculation becomes enormous when reproducing a virtual sound source whose position changes in real time.

  Therefore, it is conceivable to use the method of Non-Patent Document 2. The method of Non-Patent Document 1 can be converted into the time domain using the approximation method of Non-Patent Document 2.

As a drive signal (acoustic signal) given to each speaker of the speaker array, the position X _s (x _s , y _s ) of the virtual sound image and the position X _i (x _i , y _i ) of the target i-th speaker are used. Can be defined as

j = √ (−1), k is wave number (k = ω / c), ω is angular frequency (ω = 2πf), f is frequency, c is speed of sound, g ₀ = √ (2π | y _ref −y ₀ | ), | Y _ref −y ₀ | is a distance from the virtual sound image to the speaker array, and H ₁ ⁽¹⁾ is a first-order first-class Hankel function.

  Equation (1) is transformed into the time domain by inverse Fourier transform in the x-axis direction to obtain the following equation known as time domain wavefront synthesis.

  The following expression included in Expression (2) is known as a wavefront synthesis prefilter h (n). n is time.

  Therefore, in the wavefront synthesis technique in the time domain, as shown in Equation (2), if the wavefront synthesis prefilter h (n) in Equation (3) is applied to the acoustic signal scheduled to be output, then for each channel, Since only power multiplication processing and delay processing need be performed, the amount of calculation can be dramatically reduced.

  However, in the method of Non-Patent Document 2, since the calculated wavefront synthesis pre-filter h (n) has power at the skirt portion other than the center of the filter (described later), reverb (resonance sound) is generated in the output acoustic signal. , Noise such as reverberation sound), and the subjective quality is deteriorated.

  The present invention has been made in view of the above circumstances, and an object thereof is to suppress noise in an acoustic signal.

  In order to solve the above problems, a sound image generating apparatus according to claim 1 includes a window function multiplying unit that multiplies a wavefront synthesis prefilter for wavefront synthesis by a window function, and the wavefront synthesis premultiplied by the window function. And a filter operation unit that convolves the filter with the acoustic signal.

  The sound image generation device according to claim 2 is the sound image generation device according to claim 1, wherein the window function multiplying unit has a time range including the maximum amplitude value of the wavefront synthesis prefilter within a time range of the wavefront synthesis prefilter. A window function of a time range smaller than the range is multiplied, and the filter operation unit convolves the acoustic signal with a wavefront synthesis prefilter only for the time range multiplied by the window function.

  According to the present invention, noise of an acoustic signal can be suppressed.

It is a figure which shows the structure of a sound image production | generation apparatus. It is a figure which shows the original shape of a wavefront synthetic | combination prefilter. It is a figure which shows the shape of a Hanning window. It is a figure which shows the shape of a wavefront synthetic | combination prefilter. It is a figure which shows the sound pressure distribution of the past and this invention. It is a figure which shows the positional relationship of a speaker array and a virtual sound source.

  In order to solve the above problems, the present invention is characterized by multiplying a wavefront synthesis prefilter by a window function. Thereby, since the power of the skirt part of the wavefront synthesis prefilter is suppressed, it is possible to suppress the reverberation noise of the output acoustic signal.

  Further, the present invention is limited to the vicinity of the central portion including the maximum amplitude value of the wavefront synthesis prefilter, and is multiplied by a window function in a time range smaller than the time range of the wavefront synthesis prefilter, and the window function is multiplied. Only the wavefront synthesis prefilter limited to the specified time range is taken out and used as a new wavefront synthesis prefilter. Thereby, since the time length of the wavefront synthesis prefilter is shortened, the delay time associated with the convolution calculation processing of the wavefront synthesis prefilter can be reduced.

  Hereinafter, an embodiment for carrying out the present invention will be described with reference to the drawings.

[First Embodiment]
FIG. 1 is a diagram illustrating a configuration of a sound image generating apparatus 1 according to the first embodiment. The configuration shown in FIG. 1 is a basic configuration example in the case of performing time domain wavefront synthesis. The sound image generation device 1 includes a wavefront synthesis prefilter generation unit 11 that generates a wavefront synthesis prefilter for wavefront synthesis, a window function multiplication unit 12 that multiplies the wavefront synthesis prefilter by a window function, and the window function A filter calculation unit 13 that convolves the wavefront synthesis pre-filter with the acoustic signal, a delay adjustment unit 14 that adjusts a delay amount of the acoustic signal, a gain multiplication unit 15 that multiplies the acoustic signal after the delay amount adjustment by a gain, It is configured with. The delay adjustment unit 14 and the gain multiplication unit 15 have the same number as the number of speakers in the speaker array, and perform arithmetic processing independently for each speaker.

  Next, the operation of the sound image generating device 1 will be described.

Step S1;
First, the wavefront synthesis prefilter generation unit 11 generates a wavefront synthesis prefilter h (n). Hereinafter, a method of generating the wavefront synthesis prefilter h (n) will be described again.

For example, an acoustic signal to be given to each speaker of the speaker array is expressed by using the virtual sound image position X _s (x _s , y _s ) and the i th target speaker position X _i (x _i , y _i ) 4).

Here, j = √ (−1), k is the wave number (k = ω / c), ω is the angular frequency (ω = 2πf), f is the frequency, c is the speed of sound, and g ₀ = √ (2π | y _ref − y ₀ |) and | y _ref −y ₀ | are distances from the virtual sound image to the speaker array, and H ₁ ⁽¹⁾ is a first-order first-class Hankel function.

  Then, by transforming Equation (4) into the time domain by inverse Fourier transform in the x-axis direction, Equation (5) known as time domain wavefront synthesis can be obtained.

  Expression (6) forming a part of the right side of Expression (5) is the wavefront synthesis prefilter h (n). The wavefront synthesis prefilter generation unit 11 generates a wavefront synthesis prefilter h (n) using the equation (6). n is time.

  The wavefront synthesis prefilter h (n) is illustrated in FIG. By using Expression (6), for example, a wavefront synthesis prefilter h (n) having power (amplitude value) within a time range of 0 to about 250 can be generated. However, as described in “Problems to be Solved by the Invention”, the wavefront synthesis prefilter h (n) includes power also in the skirt portion other than the filter center. In the case of the wavefront synthesis prefilter h (n) illustrated in FIG. 2, there is power in a time range of 0 to about 100 and a time range of about 170 to about 250.

Step S2;
Next, the window function multiplying unit 12 generates a window function w (n) having the same time length as the time length of the wavefront synthesis prefilter h (n) generated in step S1, and the window function w (n) is The wavefront synthesis prefilter h (n) is multiplied to generate an improved wavefront synthesis prefilter h (n) {h above “h”} shown in Expression (7).

  For example, the Hanning window function w (n) is generated as the window function w (n). The Hanning window function w (n) is illustrated in FIG. “1” is the maximum power with the same time length (0 to about 250) as the time length (0 to about 250) of the wavefront synthesis prefilter h (n) illustrated in FIG. By multiplying the Hanning window function w (n) shown in FIG. 3 by the wavefront synthesis prefilter h (n) shown in FIG. 2, the improved wavefront in which the power at the skirt portion is suppressed as shown in FIG. A combined prefilter h (n) {h can be generated on “h”}.

  In addition to the Hanning window function, a Hamming window function or the like may be used as the window function. In addition, since it is only necessary to suppress the power of the skirt portion of the original wavefront synthesis prefilter h (n), each power in the time range of 0 to about 100 and about 170 to about 250 is set to “0” and about 100 A standard window function with a power in the time range of about 170 to “1” may be used.

Step S3;
Next, as shown in Expression (8), the filter calculation unit 13 applies the improved wavefront synthesis prefilter h () generated in step S2 to the acoustic signal s (n) input to the sound image generation device 1. n) Fold “∧” on {h. In addition, the convolution calculation process itself which performs the said convolution is a well-known technique.

Step S4;
Next, as shown in Expression (9), the delay adjustment unit 14 positions the virtual sound source with respect to the acoustic signal s (n) {s “s” on s} that has been subjected to the convolution process in step S3. Add a delay amount determined by X _s and speaker position X _i .

Step S5;
Next, as shown in the equation (10), the gain multiplication unit 15 adjusts (adds, subtracts) the gain of the acoustic signal s (n) {s “·”} added to the delay amount in step S4. Etc.). The gain-adjusted acoustic signal y (n) becomes a drive signal for driving the speaker.

  By repeating step S4 and step S5 for the number of speakers, all acoustic signals necessary for time-domain wavefront synthesis can be obtained. Note that the position of the virtual sound image can be dynamically changed by temporally changing the parameters of the delay adjustment unit 14 and the gain multiplication unit 15. In addition, when the sound image generation apparatus 1 receives sound image position information in which the position of the virtual sound image is designated together with the acoustic signal, the sound image generation apparatus 1 adjusts the parameters so that the position of the generated virtual sound image matches the designated position. You can also.

  According to the first embodiment, since the window function is multiplied by the wavefront synthesis prefilter, the power (amplitude value) of the skirt portion of the wavefront synthesis prefilter is suppressed, and the reverberation noise of the acoustic signal is suppressed. Can do.

  In order to confirm the effect, a computer simulation of a sound field using a single frequency (1 kHz) sine wave was performed. The conventional sound pressure distribution and the sound pressure distribution of this embodiment are shown in FIG. In the figure, “x... X” indicates 40 speakers arranged at 10 cm intervals on the x-axis, and coordinates (0, 2) indicate the position (focus sound source) of the virtual sound image. Even when the wavefront synthesis prefilter is multiplied by the window function, it can be understood that the sound field distribution generated by the focal sound source is not deteriorated as compared with the conventional case.

[Second Embodiment]
The second embodiment aims to reduce the delay time associated with the convolution calculation processing of the wavefront synthesis prefilter. In order to achieve the object, the window function multiplied by the wavefront synthesis prefilter in the window function multiplication unit 12 is a window function having a time length shorter than the time length of the wavefront synthesis prefilter, and the window function is multiplied. Generate a wavefront synthesis prefilter only for time length.

  The configuration of the sound image generation device 1 according to the present embodiment is the same as the configuration of the first embodiment. However, in addition to the function described in the first embodiment, the window function multiplying unit 12 generates a window function having a time length shorter than the time length of the original wavefront synthesis prefilter, and the original wavefront synthesis prefilter The time range including the maximum amplitude value is multiplied by the window function, and only the wavefront synthesis prefilter for only the time range multiplied by the window function is taken out to have an improved wavefront synthesis prefilter. The functions other than the window function multiplying unit 12 are substantially the same as those in the first embodiment.

  Next, the operation of the sound image generation device 1 according to this embodiment will be described.

  After step S1 described in the first embodiment, the window function multiplying unit 12 first has a window function w (p) having a time length L shorter than the time length of the wavefront synthesis prefilter h (n) generated in step S1. ) {P = 1,..., L} is generated.

  Next, the window function multiplying unit 12 specifies a time point at which the absolute value of the amplitude of the wavefront synthesis prefilter h (n) is maximum, and specifies a time range in which the time point is in the center. For example, the p value is added to each predetermined start time t, and the time when the maximum amplitude value of the wavefront synthesis prefilter is located in the center from each time range of (t + 1), (t + 2),..., (T + L) Identify the range.

  Next, as shown in Expression (11), the window function multiplying unit 12 multiplies the wavefront synthesis prefilter within the specified time range by the window function w (p) of the time length L, and the window function w ( A wavefront synthesis prefilter having a shorter time length than the improved wavefront synthesis prefilter used in the first embodiment, which is composed only of the time range multiplied by p), is generated.

  The subsequent processing is the same as the processing after step S3 described in the first embodiment. In the filter calculation part 13, the process which convolves the acoustic signal with the wavefront synthetic | combination pre filter whose time length is shorter than 1st Embodiment is performed.

  According to the second embodiment, a time range including the maximum amplitude value of the wavefront synthesis prefilter is multiplied by a window function having a time length shorter than the time length of the wavefront synthesis prefilter, and the window function is multiplied. Therefore, the time length of the wavefront synthesis prefilter is shortened and the delay time associated with the convolution calculation processing of the wavefront synthesis prefilter can be reduced.

  Finally, the sound image generation device 1 described in each embodiment can be realized by a circuit or a computer having the above functions.

DESCRIPTION OF SYMBOLS 1 ... Sound image generation apparatus 11 ... Wavefront synthetic | combination pre-filter production | generation part 12 ... Window function multiplication part 13 ... Filter operation part 14 ... Delay adjustment part 15 ... Gain multiplication part

Claims (2)

A window function multiplier that multiplies a wavefront synthesis prefilter for wavefront synthesis by a window function;
A filter operation unit for convolving the wavefront synthesis prefilter multiplied by the window function into an acoustic signal;
A sound image generating apparatus comprising: The window function multiplying unit multiplies the time range including the maximum amplitude value of the wavefront synthesis prefilter by a window function of a time range smaller than the time range of the wavefront synthesis prefilter,
The filter operation unit
The sound image generating apparatus according to claim 1, wherein a wavefront synthesis prefilter only for a time range multiplied by the window function is convoluted with the acoustic signal.