Impulse Response Generation Device and Impulse Response Generation Program

Abstract

To automatically discriminate boundary between initial reflection sound and rear reverberation sound of an impulse response, and to generate from a single impulse response a number of impulse responses that have similar timbre and low correlation with each other.SOLUTION: An impulse response generation device includes: a signal separation section that divides an impulse response into an initial reflection sound and a rear reverberation sound; a time window multiplication section that multiplies the initial reflection sound and the rear reverberation sound by a window function obtained by shifting the window of a predetermined time length multiple times; a random number generator that generates time-shift amounts by random numbers; a time-shifting section that time-shifts the initial reflection sound and the rear reverberation sound based on the time-shift amounts, for each time window; and a signal adding section that adds the time-shifted initial reflection sound and the rear reverberation sound. The signal separation section separates the impulse response into the initial reflected sound and the rear reverberation sound based on the inflection point included in a predetermined section of the decay curve of the impulse response.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to an impulse response generation device and an impulse response generation program, and more particularly to an impulse response generation technique for generating a large number of impulse responses having a timbre similar to a given impulse response and having a low correlation with each other from the given impulse response.

Background Art

[0002] In movie and television sound systems, in addition to the conventional 2-channel (ch) stereo system and 5.1ch surround, in recent years, multi-channel sound systems with a large number of channels such as 7.1ch, 10.2ch, and 22.2ch have been adopted. In the production of multi-channel audio content, in the same manner as the conventional stereo system and 5.1ch audio system, a reverberation addition device is used to give a sense of spatial expansion and a rich sense of presence.

[0003] There are various types of reverberation addition devices, such as those of the IIR (Infinite impulse response) filter type that simulate the reverberation of space by simulation and those of the FIR (Finite impulse response) filter type that generate reverberation using impulse responses measured in an actual space. However, when adding reverberation by convolving an impulse response with a sound source as in the FIR filter type, the number of impulse responses corresponding to the number of channels of the playback system is required. For example, in the case of a 22.2 multi-channel sound system, 22ch of impulse responses are required. Furthermore, considering measuring these impulse responses in a diffuse sound field (a state where sounds with equal timbre and uncorrelated with each other arrive from each arrival direction) such as a concert hall, it is required that they have a similar timbre and a low correlation with each other.

[0004] Although such a large number of impulse responses can be obtained by actual measurement, it is not easy because it is necessary to measure the impulse responses at points that are sufficiently separated from each other, which requires a large-scale measurement system and a long measurement time.

[0005] Therefore, a device has been proposed that generates a large number of impulse responses with similar timbres and low mutual correlations from a given single impulse response (see, for example, Patent Documents 1 and 2, and Non-Patent Documents 1 and 2). The devices described in Patent Documents 1 and 2 separate the impulse response into an early reflection part (a part composed of low-order reverberations from the floor, ceiling, walls, etc. that arrive within a relatively short time after the direct sound arrives) and a late reverberation part (a part that follows the early reflection and repeats multiple reverberations and where individual sounds cannot be separated and heard). Then, predetermined processing is applied to each of the early reflection part and the late reverberation part of the impulse response, and the processed early reflection part and late reverberation part of the impulse response are synthesized and output to generate a large number of impulse responses.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Patent Document 2

Non-Patent Documents

[0007]

Non-Patent Document 1

Non-Patent Document 2

Non-Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0008] In the embodiments described in Patent Documents 1 and 2, in order to generate a large number of impulse responses having similar timbres and low mutual correlation from a given single impulse response, it is necessary to properly use different processing parameters for the early reflection part and the late reverberation part. Therefore, a signal separation unit 10 is provided to separate the early reflection sound and the late reverberation sound and process them separately. In the signal separation units 10 of Patent Documents 1 and 2, the sound in the range where the amplitude of the input impulse response exceeds a predetermined threshold is treated as the early reflection sound, or the early reflection sound and the late reverberation sound are separated by treating a predetermined time from the direct sound as the early reflection sound. However, since the predetermined threshold and the predetermined time vary depending on the acoustic characteristics of the actual sound field from which the impulse response is obtained, it has been necessary for the user to check the waveform of the impulse response that is the source of generation, determine the boundary between the early reflection sound and the late reverberation sound, and perform processing based on that time.

[0009] Therefore, in view of the above problems, an object of the present invention is to automatically discriminate the boundary (length of the early reflection sound) between the early reflection sound and the late reverberation sound of an impulse response, and to provide an impulse response generation device and an impulse response generation program capable of generating a large number of impulse responses having similar timbres and low mutual correlation from a given single impulse response.

Means for Solving the Problems

[0010] To solve the above problems, an impulse response generation device according to the present invention includes a signal separation unit that separates an impulse response into an early reflection sound and a late reverberation sound, a first time window multiplication unit that multiplies the early reflection sound by a first window function obtained by shifting a plurality of times a first time window having a predetermined time length suitable for the early reflection sound, and a second time window multiplication unit that multiplies the late reverberation sound by a second window function obtained by shifting a plurality of times a second time window having a predetermined time length suitable for the late reverberation sound, a first random number generation unit that generates a first time shift amount by a random number based on a distribution width suitable for the early reflection sound, and a second random number generation unit that generates a second time shift amount by a random number based on a distribution width suitable for the late reverberation sound, a first time shift unit that time-shifts, within a time range of the early reflection sound, an output of the first time window multiplication unit regarding the early reflection sound for each first time window based on the first time shift amount, and a second time shift unit that time-shifts, within a time range of the late reverberation sound, an output of the second time window multiplication unit regarding the late reverberation sound for each second time window based on the second time shift amount, and a signal addition unit that adds an output of the first time shift unit regarding the early reflection sound and an output of the second time shift unit regarding the late reverberation sound, wherein the signal separation unit separates the impulse response into the early reflection sound and the late reverberation sound based on an inflection point included in a predetermined section of an attenuation curve of the impulse response. An impulse response generation device, wherein a signal separation unit determines a time range for separating an initial reflected sound and a late reverberation sound according to a reverberation time of the impulse response, using an absolute value of a second derivative of the attenuation curve as an evaluation function, and performs the separation at a time when the evaluation function is maximized within the time range.

[0011] Further, it is desirable that the impulse response generation device further includes a time setting unit that selects a plurality of blocks in units of time windows for at least one of the outputs of the first time window multiplication unit regarding the early reflection sound and the second time window multiplication unit regarding the late reverberation sound, deletes them, or selects a plurality of blocks in units of time windows, duplicates each of them, and changes the time length, and the first time shift unit time-shifts, within a time range of the early reflection sound, an output of the time setting unit regarding the early reflection sound for each first time window based on the first time shift amount, and the second time shift unit time-shifts, within a time range of the late reverberation sound, an output of the time setting unit regarding the late reverberation sound for each second time window based on the second time shift amount.

[0013] Also, To solve the above problems, an impulse response generation device according to the present invention includes: a signal separation unit that separates an impulse response into an initial reflected sound and a late reverberation sound; a first time window multiplication unit that multiplies a first window function obtained by shifting a plurality of times a first time window having a predetermined time length suitable for the initial reflected sound, by the initial reflected sound; a second time window multiplication unit that multiplies a second window function obtained by shifting a plurality of times a second time window having a predetermined time length suitable for the late reverberation sound, by the late reverberation sound; a first random number generation unit that generates a first time shift amount by a random number based on a distribution width suitable for the initial reflected sound; a second random number generation unit that generates a second time shift amount by a random number based on a distribution width suitable for the late reverberation sound; a first time shift unit that time-shifts, within a time range of the initial reflected sound, an output of the first time window multiplication unit related to the initial reflected sound, for each first time window, based on the first time shift amount; a second time shift unit that time-shifts, within a time range of the late reverberation sound, an output of the second time window multiplication unit related to the late reverberation sound, for each second time window, based on the second time shift amount; and a signal addition unit that adds an output of the first time shift unit related to the initial reflected sound and an output of the second time shift unit related to the late reverberation sound. The signal separation unit separates the impulse response into the initial reflected sound and the late reverberation sound based on an inflection point included in a predetermined section of an attenuation curve of the impulse response. the impulse response generation device wherein , wherein the signal separation unit determines a time range for separating the early reflection sound and the late reverberation sound based on the reverberation time of the impulse response, using the absolute value of the second derivative of the attenuation curve as an evaluation function, searches for the evaluation function from the later time within the time range, and performs the separation at a time when the evaluation function exceeds a threshold obtained from the maximum value of the evaluation function within the time range and a predetermined threshold coefficient characterized in that

[0014] Also, To solve the above problems, an impulse response generation device according to the present invention includes a signal separation unit that separates an impulse response into an early reflection sound and a late reverberation sound, a first time window multiplication unit that multiplies the early reflection sound by a first window function obtained by shifting a plurality of times a first time window having a predetermined time length suitable for the early reflection sound, and a second time window multiplication unit that multiplies the late reverberation sound by a second window function obtained by shifting a plurality of times a second time window having a predetermined time length suitable for the late reverberation sound, a first random number generation unit that generates a first time shift amount by a random number based on a distribution width suitable for the early reflection sound, and a second random number generation unit that generates a second time shift amount by a random number based on a distribution width suitable for the late reverberation sound, a first time shift unit that time-shifts, within a time range of the early reflection sound, the output of the first time window multiplication unit regarding the early reflection sound for each first time window based on the first time shift amount, and a second time shift unit that time-shifts, within a time range of the late reverberation sound, the output of the second time window multiplication unit regarding the late reverberation sound for each second time window based on the second time shift amount, and a signal addition unit that adds the output of the first time shift unit regarding the early reflection sound and the output of the second time shift unit regarding the late reverberation sound, wherein the signal separation unit separates the impulse response into the early reflection sound and the late reverberation sound based on an inflection point included in a predetermined section of an attenuation curve of the impulse response. the impulse response generation device wherein , wherein the signal separation unit determines a time range for separating the early reflection sound and the late reverberation sound based on the reverberation time of the impulse response, using the absolute value of the second derivative of the attenuation curve as an evaluation function, and when the reverberation time of the impulse response is less than a predetermined time, performs the separation at the time when the evaluation function is maximized within the time range, and when the reverberation time of the impulse response is equal to or more than the predetermined time, performs the separation at the time when the evaluation function has the second largest value within the time range characterized in that.

[0015] The impulse response generation program according to the present invention for solving the above problems causes a computer to function as the above impulse response generation device.

Advantages of the Invention

[0016] According to the impulse response generation device and the impulse response generation program of the present invention, the boundary (the length of the early reflection sound) between the early reflection sound and the late reverberation sound of the impulse response can be automatically discriminated, and a large number of impulse responses having similar timbres and low mutual correlation can be generated from a given single impulse response.

Brief Description of the Drawings

[0017]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Embodiments for Carrying Out the Invention

[0018] Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

[0019] (First Embodiment) FIG. 1 is a diagram showing an example of the configuration of an impulse response generation device according to the first embodiment of the present invention. The impulse response generation device according to the present embodiment includes a signal separation unit 10 that separates an impulse response into an early reflection sound and a late reverberant sound, a time window multiplication unit 20 that multiplies a window function obtained by shifting a time window of a predetermined time length a plurality of times by the early reflection sound and the late reverberant sound, a random number generation unit 30 that generates a time shift amount by a random number, a time shift unit 40 that time-shifts the output of the time window multiplication unit 20 based on the time shift amount, and a signal addition unit 50 that adds the outputs of the time shift unit 40 regarding the early reflection sound and the late reverberant sound. Each functional unit 10 to 50 of the impulse response generation device is configured by a suitable processor such as a CPU or a suitable electric circuit.

[0020] The time window multiplication unit 20 includes a first time window multiplication unit 21 and a second time window multiplication unit 22. The random number generation unit 30 includes a first random number generation unit 31 and a second random number generation unit 32. The time shift unit 40 includes a first time shift unit 41 and a second time shift unit 42. As will be described later, the first time window multiplication unit 21, the first random number generation unit 31, and the first time shift unit 41 perform processing on the initial reflected sound of the impulse response, and the second time window multiplication unit 22, the second random number generation unit 32, and the second time shift unit 42 perform processing on the late reverberation sound of the impulse response.

[0021] The signal separation unit 10 automatically separates the input impulse response h(t) into an initial reflected sound e(t) and a late reverberation sound r(t). The impulse response h(t) serves as a reference for a newly generated impulse response h'(t).

[0022] First, with reference to FIG. 2, which schematically shows the reverberation sound (impulse response) in a diffuse sound field, the initial reflected sound and the late reverberation sound of the reverberation sound will be outlined. The sound emitted from a sound source such as a musical instrument or a speaker first arrives as a direct sound. Next, the initial reflected sound reflected by the floor, ceiling, and walls arrives. In the initial reflected sound part, depending on the conditions, it is composed of low-order reflections that allow each reflected sound to be separated and heard from other sounds. Furthermore, the multiple reflected sounds after repeated reflections gradually arrive as late reverberation sounds that are generally delayed by several milliseconds to 150 milliseconds or more from the direct sound. When it becomes a late reverberation sound, the density of the reflected sound suddenly increases, and the reflected sounds arriving from all directions overlap with each other, becoming a diffuse sound without directivity as a whole. Thus, the reverberation sound is composed of an initial reflected sound and a late reverberation sound with different properties.

[0023] However, particularly in the impulse response measured in an actual sound field, each initial reflected sound also has a temporal spread, and the late reverberation sound and the ambient noise in the sound field also overlap. Therefore, the boundary between the initial reflected sound and the late reverberation sound does not become clear like the waveform in the schematic diagram of FIG. 2. Therefore, in order to automatically separate the initial reflected sound and the late reverberation sound by the signal separation unit 10, it is necessary to automatically determine the time that serves as the boundary between the two.

[0024] Although details will be described later, in this embodiment, a group of reflected sounds obtained by cutting out an impulse response with a window function (time window) having a predetermined shape and time length is randomly shifted (rearranged) within a predetermined time length to generate a large number of impulse responses with low correlation to each other. In order for the generated large number of impulse responses to have low correlation with each other and be reverberant sounds with similar timbres, the time length of the time window and the amount of time shift of the reflected sound group are important parameters, and it has been confirmed by experiments that the optimal values of these parameters are different in the processing of early reflected sounds and late reverberant sounds (Non-Patent Documents 1 and 2). For the early reflected sound part, it is necessary to divide the individual peaks due to low-order reflections with a time window and shift them within the time from the direct sound to the boundary time. Therefore, the signal separation unit 10 of the present application is characterized in that it can automatically discriminate the length of the early reflected sound as the vicinity of the arrival time of the last major low-order reflected sound with an amplitude larger than that of the late reverberant sound after the direct sound arrives.

[0025] The operation of the signal separation unit 10 will be described.

[0026] First, from the input impulse response h(t), the Schroeder decay curve E(t) is obtained by the following equation (1) (Non-Patent Document 3). It is assumed that the direct sound arrives at t = 0.

[0027]

Equation

[0028] The inventors of the present invention confirmed that the slope of the decay of this decay curve E(t) changes at the boundary time between the early reflected sound and the late reverberant sound. From this, a means of searching for the inflection point of the decay curve E(t) from the second derivative function of E(t) is adopted. That is, the absolute value of the second derivative of E(t) is obtained by the following equation (2), and the time at which this value becomes maximum is defined as the length t0 of the desired early reflected sound.

[0029]

Equation

[0030] However, since the slope of the decay of E(t) changes not only immediately after the direct sound arrives or when the level of the late reverberation sound becomes equal to the ambient noise, i.e., at times outside the boundary between the early reflection sound and the late reverberation sound, a time range for searching for the maximum value is determined in advance. In a space with a large room volume, the boundary time between the early reflection sound and the late reverberation sound is large because the average travel distance for the sound wave from the sound source to reach the receiving point after reflection is long, and thus the reverberation time and the boundary time of that space are large values. Generally, the time when the early reflection sound arrives is between several milliseconds and approximately 150 ms after the direct sound arrives. However, in a large space such as an arena or a cave, considering that the early reflection sound may arrive even later, when the reverberation time is T RT and T RT is used, the time range for searching for the maximum value is changed according to T

[0031]

Equation

[0032] The reverberation time T RT is, for example, as described in T 30 (the reverberation time obtained by evaluation in the 30 dB range). The evaluation interval from the initial level to -5 dB to -35 dB of the decay curve E(t) is linearly approximated by the least squares method to obtain the slope, and it is obtained from the time corresponding to a 60 dB decay with that slope.

[0033] Since the actually measured impulse response is discrete-time data by digital processing, the decay curve of the discrete-time system corresponding to Equation (1) is obtained as the following Equation (4) (N is the maximum range of measurement).

[0034]

Equation

[0035] Similarly, an evaluation function regarding the absolute value of the second-order difference of the decay curve corresponding to Equation (2) is defined as Equation (5).

[0036]

Number

[0037] Let the sampling frequency of the measured impulse response be f s Then the length of the early reflection sound t0 = n0 / f s That is, if n0 that satisfies the condition (3) and maximizes the value of the evaluation function in Equation (5) is obtained, t0 can also be determined.

[0038] This method shows an example of discriminating the length of the early reflection sound from the impulse response measured indoors such as in a concert hall or a small booth in a studio.

[0039] Figure 3 shows an example of separating the early reflection sound and the late reverberation sound in a small booth as an example of a small space with a reverberation time of 350 ms (T RT <when it is 1 s). The three graphs in Figure 3 have the time (common up to 0.25 seconds) on the horizontal axis, and from top to bottom are the time waveform of the impulse response, the attenuation curve obtained from Equation (4), and the evaluation function (the second derivative of the attenuation curve) obtained from Equation (5). The dashed line in the graph is the boundary (the length of the early reflection sound) t0 of the early reflection sound and the late reverberation sound discriminated by the above method, and in this example, t0 = 10.4 ms (the time when the evaluation function is maximized between 10 ms and 150 ms).

[0040] Figure 4 shows an example of separating the early reflection sound and the late reverberation sound in a concert hall as an example of a relatively large space with a reverberation time of 1.7 s (T RT ≧1 s). The three graphs in Figure 4 are the same as in Figure 3, with the time (common up to 1 second) on the horizontal axis, and from top to bottom are the time waveform of the impulse response, the attenuation curve obtained from Equation (4), and the evaluation function obtained from Equation (5). The dashed line in the graph is the boundary (the length of the early reflection sound) t0 of the early reflection sound and the late reverberation sound discriminated by the above method, and in this example, t0 = 78 ms (the time when the evaluation function is maximized between 50 ms and 300 ms).

[0041] As shown by the dashed lines on the impulse response waveforms of FIGS. 3 and 4, the last peak portion of the main early reflection sound can be discriminated, and it is thereby shown that the separation between the early reflection sound and the late reverberation sound can be automatically performed.

[0042] In this embodiment, in the case of dividing the reverberation time into two cases of less than 1 s and greater than or equal to 1 s according to condition (3), a time range for searching for the boundary (length of the early reflection sound) t0 between the desired early reflection sound and the late reverberation sound is set. However, in order to cope with various acoustic spaces, this classification may be increased.

[0043] Also, in a sound field with an extremely large room volume or a sound field having a structure in which a plurality of rooms with greatly different volumes are connected, the early reflection may arrive with a large time delay, and as a result, there is a sound field in which a plurality of inflection points occur in the time range for searching for the decay curve. As an example, FIG. 5 shows an example in which the reverberation time is 8.6 s and the decay curve has two inflection points. The first inflection point in the time range to be searched is 80 ms indicated by the dotted line, and the second inflection point is 99 ms indicated by the dashed-dotted line. In a sound field where two inflection points occur in this way, it is desired to define the second inflection point as the boundary between the early reflection sound and the late reverberation sound.

[0044] In this case, the maximum value of the evaluation function of formula (5) within the time range for separating the early reflection sound and the late reverberation sound of condition (3) is E max , the threshold coefficient is set as α (0 <α <1), and the value of α is appropriately determined. The evaluation function of formula (5) is searched from the later time of the search time range, and the time when it exceeds the threshold α·E max is set as t0, so that the second (later) inflection point can be detected as t0. In the example of FIG. 5, when α = 0.5 and the value of the evaluation function is searched from 300 ms to 50 ms ahead in time, the 99 ms of the second inflection point can be detected as the boundary t0 as the point exceeding the threshold. This method can also be applied to the separation between the early reflection sound and the late reverberation sound of the impulse response in FIGS. 3 and 4.

[0045] Or, increase the classification according to the reverberation time T RT For example, the reverberation time T RTIf it is less than 5 seconds, as described above, the time t0 when the evaluation function is maximized within the time range separated into the initial reflected sound and the late reverberation sound determined by the reverberation time according to Equation (5) is used as the reverberation time T RT If it is 5 seconds or more, within a predetermined time range of the value of the evaluation function (for example, 50 ms ≤ t0 ≤ 300 ms), the value of the evaluation function may be searched and the time t0 when it becomes the second largest value may be used. When there are a plurality of maximum values or second largest values of the evaluation function within the time range that are the same, it is desirable to adopt the later time as t0.

[0046] As described above, the signal separation unit 10 automatically separates the sound from the direct sound to the length t0 of the initial reflected sound as the initial reflected sound e(t) and the sound after t0 as the late reverberation sound r(t) based on the characteristics of the waveform of the impulse response h(t). Then, the signal separation unit 10 outputs the initial reflected sound e(t) to the first time window multiplication unit 21 and outputs the late reverberation sound r(t) to the second time window multiplication unit 22.

[0047] Hereinafter, the processing of the first time window multiplication unit 21, the first random number generation unit 31, and the first time shift unit 41 for the initial reflected sound e(t) will be described in detail.

[0048] The first time window multiplication unit 21 multiplies the initial reflected sound e(t) by a window function We n (t) (n = 1, 2,... k) obtained by shifting a time window We(t) of a predetermined time length Tw a plurality of times (k times) to output e n (t)=We n (t)×e(t) (n = 1, 2,... k) is generated. Note that, as the time window, a Hanning window with little change in the amplitude-frequency characteristic due to window multiplication can be used. Also, a Hamming window, a Blackman window, etc. may be used as the window. When the window function We n (t) is obtained by shifting the time window We(t) at equal intervals Ted, the output e n (t) is represented by Equation (6). The first time window multiplication unit 21 outputs the output e n (t) to the first time shift unit 41.

[0049]

Equation

[0050] The first random number generator 31 generates a time shift amount by a random number. The first time shift unit 41 generates an output e´(t) by time-shifting the output e(t) of the first time window multiplication unit 21 for the initial reflected sound e(t) within the time range of the initial reflected sound e(t) for each time window based on the time shift amount. Here, when the time shift amount N(n) generated by the first random number generator 31 is a random number of a uniform distribution taking an integer value of the distribution width N, the output e´(t) obtained by time-shifting the output e(t) represented by Equation (6) is represented by the following Equation (7). n (t) is time-shifted within the time range of the initial reflected sound e(t) to generate an output e´(t). Here, if the time shift amount N * (n) generated by the first random number generator 31 is a random number of a uniform distribution taking an integer value of the distribution width N, the output e n (t) time-shifted is represented by the following Equation (7).

[0051] [Number]

[0052] The first time shift unit 41 controls so that n + N n (n) satisfies 1 ≦ n + N * (n) ≦ k in order to time-shift the output e * (t) of the first time window multiplication unit 21 within the time range of the initial reflected sound e(t). When e´(t) goes out of the range of the initial reflected sound e(t), the first time shift unit 41 causes the first random number generator 31 to generate a time shift amount by a random number again, and time-shifts the output e n (t) of the first time window multiplication unit 21 within the time range of the initial reflected sound e(t). The first time shift unit 41 outputs the generated e´(t) to the signal addition unit 50.

[0053] FIG. 6 is a diagram showing an outline of generating a new impulse response by time shift. FIG. 6(a) shows an impulse response serving as a reference for generating a new impulse response, and a window function We(t) with a window width Tw arranged at a predetermined interval Ted is multiplied by the initial reflected sound e(t). Here, the output e(t) of the first time window multiplication unit 21 corresponding to the nth window function indicated by hatching n (t) is multiplied by the initial reflected sound e(t). Here, the output e nFor (t), the first random number generator 31 generates, for example, a time shift amount (-2, -1, 0, 1, 2) with a width N = 5 by random numbers. As shown in Fig. 6(b), the first time shift unit 41 shifts the output e n (t) corresponding to the n-th window function based on the time shift amount (for example, -1). In this way, by shifting the output of the first time window multiplication unit 21 for each time window based on random numbers, an impulse response h'(t) is generated that has a timbre similar to the initial reflected sound e(t) of a given impulse response h(t) and has low mutual correlation and has an initial reflected sound e'(t).

[0054] The processing of the second time window multiplication unit 22, the second random number generator 32, and the second time shift unit 42 for the late reverberation sound r(t) is the same as the processing of the first time window multiplication unit 21, the first random number generator 31, and the first time shift unit 41 for the initial reflected sound e(t), respectively. Note that parameter values such as the length of the window function (window width) and the range of random numbers of the time shift amount (distribution width) can be individually set to values suitable for each of the initial reflected sound e(t) and the late reverberation sound r(t). That is, in the first time window multiplication unit 21, a first time window with a predetermined time length suitable for the initial reflected sound is used, in the second time window multiplication unit 22, a second time window with a predetermined time length suitable for the late reverberation sound is used, the first random number generator 31 generates a first time shift amount based on a distribution width suitable for the initial reflected sound, and the second random number generator 32 generates a second time shift amount based on a distribution width suitable for the late reverberation sound.

[0055] The second time window multiplication unit 22 multiplies the late reverberation sound r(t) by window functions Wr n (t) (n = 1, 2,... m) obtained by shifting a plurality of time windows Wr(t) with a predetermined time length Tr to generate outputs r n (t) (n = 1, 2,... m). The second random number generator 32 generates a time shift amount by random numbers. The second time shift unit 42 shifts the output r of the second time window multiplication unit 22 regarding the late reverberation sound r(t) for each time window based on the time shift amount nOutput r'(t) is generated by time-shifting (t) within the time range of the late reverberation sound r(t). When r'(t) goes outside the range of the late reverberation sound r(t), the second time-shifting unit 42 causes the second random number generation unit 32 to generate a time-shifting amount that falls within the range of the late reverberation sound r(t) again. The second time-shifting unit 42 outputs the generated r'(t) to the signal addition unit 50.

[0056] The signal addition unit 50 adds the output e´(t) of the first time-shifting unit 41 regarding the early reflection sound e(t) and the output r'(t) of the second time-shifting unit 42 regarding the late reverberation sound r(t) to generate a new impulse response h'(t).

[0057] Thus, according to this embodiment, the signal separation unit 10 automatically separates the impulse response into the early reflection sound and the late reverberation sound. The time window multiplication unit 20 multiplies the window functions obtained by shifting a time window of a predetermined time length a plurality of times by the early reflection sound and the late reverberation sound. The random number generation unit 30 generates the time-shifting amount by a random number. The time-shifting unit 40 time-shifts the output of the first time window multiplication unit 21 regarding the early reflection sound within the time range of the early reflection sound for each time window based on the time-shifting amount, and time-shifts the output of the second time window multiplication unit 22 regarding the late reverberation sound within the time range of the late reverberation sound. The signal addition unit 50 adds the outputs of the time-shifting unit 40 regarding the early reflection sound and the late reverberation sound to generate a new impulse response. As a result, it becomes possible to generate a large number of impulse responses having timbres similar to a given impulse response in advance and having low correlation with each other, and to provide impulse responses of sufficient quality for use in reverberation addition in a multi-channel acoustic system. In particular, according to this embodiment, it becomes possible to accurately and automatically separate the early reflection sound and the late reverberation sound, and to generate a large number of impulse responses having low correlation between the early reflection sound and the late reverberation sound, and to obtain a sense of spread that cannot be obtained from the same impulse response when the impulse response is convolved.

[0058] (Second Embodiment) FIG. 7 is a diagram showing an example of the configuration of an impulse response generation apparatus according to the second embodiment of the present invention. The impulse response generation apparatus according to the present embodiment includes a signal separation unit 10 that separates an impulse response into an initial reflected sound and a late reverberation sound, a time window multiplication unit 20 that multiplies a window function obtained by shifting a time window of a predetermined time length a plurality of times by the initial reflected sound and the late reverberation sound, a time setting unit 60 that changes the impulse response to an arbitrary time length, a random number generation unit 30 that generates a time shift amount by a random number, a time shift unit 40 that time-shifts the output of the time setting unit 60 based on the time shift amount, and a signal addition unit 50 that adds the outputs of the time shift unit 40 regarding the initial reflected sound and the late reverberation sound. Each functional unit 10 to 60 of the impulse response generation apparatus is configured by a suitable processor such as a CPU or a suitable electric circuit.

[0059] The time window multiplication unit 20 includes a first time window multiplication unit 21 and a second time window multiplication unit 22, the time setting unit 60 includes a first time setting unit 61 and a second time setting unit 62, the random number generation unit 30 includes a first random number generation unit 31 and a second random number generation unit 32, and the time shift unit 40 includes a first time shift unit 41 and a second time shift unit 42. As will be described later, the first time window multiplication unit 21, the first time setting unit 61, the first random number generation unit 31, and the first time shift unit 41 perform processing on the initial reflected sound of the impulse response, and the second time window multiplication unit 22, the second time setting unit 62, the second random number generation unit 32, and the second time shift unit 42 perform processing on the late reverberation sound of the impulse response.

[0060] The signal separation unit 10 has the same configuration as the signal separation unit 10 of the first embodiment, and automatically separates the input impulse response h(t) into an initial reflected sound e(t) and a late reverberation sound r(t). That is, the signal separation unit 10 first obtains the attenuation curve E(t) of the shredder from the input impulse response h(t). Since the actual impulse response is discrete-time data by digital processing, the attenuation curve of the discrete-time system is obtained by Equation (4). Next, in order to obtain the inflection point of the attenuation curve, an evaluation function regarding the absolute value of the second-order difference of the attenuation curve is obtained from Equation (5). Then, n0 that maximizes the value of the evaluation function of Equation (5) is obtained and determined as the length t0 of the initial reflected sound.

[0061] In determining the length t0 of the initial reflected sound, the time range for searching for the maximum value is changed according to the reverberation time T RT and the maximum value of the evaluation function is searched under the condition of (3) to obtain the length t0 of the initial reflected sound. Alternatively, the maximum value E of the evaluation function in Equation (5) within the time range for separating the initial reflected sound and the rear reverberation sound of condition (3) max is set, the value of α is appropriately determined with the threshold coefficient being α (0 < α < 1), the evaluation function in Equation (5) is searched from the later time of the search time range, and the time when it exceeds the threshold α·E max is set as t0, and the length t0 of the initial reflected sound may be obtained. Also, when the reverberation sound T RT is long, the time when the evaluation function becomes the second largest value may be set as the length t0 of the initial reflected sound.

[0062] In this way, the signal separation unit 10 automatically separates the sound from the direct sound to the length t0 of the initial reflected sound as the initial reflected sound e(t) and the sound after t0 as the rear reverberation sound r(t). Then, the initial reflected sound e(t) is output to the first time window multiplication unit 21, and the rear reverberation sound r(t) is output to the second time window multiplication unit 22.

[0063] Next, the processing of the first time window multiplication unit 21, the first time setting unit 61, the first random number generation unit 31, and the first time shift unit 41 for the initial reflected sound e(t) will be described in detail.

[0064] The first time window multiplication unit 21 is the same as the first time window multiplication unit 21 of the first embodiment, and the window function We n (t) (n = 1, 2,... k) obtained by shifting the time window We(t) of a predetermined time length Tw a plurality of times (k times) is multiplied by the initial reflected sound e(t) to output e n (t)=We n (t)×e(t) (n = 1, 2,... k) is generated. When the window function We n (t) is obtained by shifting the time window We(t) at equal intervals Ted, the output e n (t) is represented by Equation (6). The first time window multiplication unit 21 outputs e nOutput (t) to the first time setting unit 61.

[0065] The first time setting unit 61 deletes or duplicates, for each time window, the output of the first time window multiplication unit 21 regarding the initial reflection sound e(t) (length t0) of the input impulse response h(t) to generate a new initial reflection sound e'(t) of length t. e When shortening the reverberation time (t e <t0), the first time setting unit 61 appropriately deletes the block after multiplying the window function of the original initial reflection sound e(t), and when lengthening the reverberation time (t e >t0), the first time setting unit 61 appropriately duplicates the block after multiplying the window function of the original initial reflection sound e(t) to generate a new initial reflection sound e'(t). Regarding the method of deletion or duplication, for example, it may be performed on equally spaced blocks, or on randomly selected blocks. Also, blocks in any continuous section may be deleted or duplicated. As will be described later, an impulse response h'(t) with a changed reverberation time is generated from the new initial reflection sound e'(t) and the new late reverberation sound r'(t).

[0066] FIG. 8 is a diagram showing an outline of the process when shortening the reverberation time. When the initial reflection sound e(t) is e1~e12, the new initial reflection sound e'(t) is represented by, for example, e1, e3, e4, e6, e7, e9, e10, e12 where the blocks e2, e5, e8, e11 in time window units are deleted. Thereby, the first time setting unit 61 can generate a new initial reflection sound e'(t) with a length that is 2 / 3 of the original length.

[0067] FIG. 9 is a diagram showing an outline of the process when lengthening the reverberation time. When the initial reflection sound e(t) is e1~e12, the new initial reflection sound e'(t) is represented by, for example, e1, e2, e3, e3, e4, e5, e6, e6, e7, e8, e9, e9, e10, e11, e12, e12 where the blocks e3, e6, e9, e12 in time window units are duplicated. Thereby, the first time setting unit 61 can generate a new initial reflection sound e'(t) with a length that is 4 / 3 of the original length.

[0068] The first random number generation unit 31 is the same as that in the first embodiment, and generates a time shift amount by a random number. Here, the time shift amount N * (n) generated by the first random number generation unit 31 is a random number of a uniform distribution taking an integer value with a distribution width N.

[0069] The first time shift unit 41, based on the time shift amount, shifts each component e' of the initial reflected sound e'(t) after the time length change, which is the output of the first time setting unit 61, n (t) within the time range of the initial reflected sound e'(t) to generate the output e''(t).

[0070] The outline of generating a new impulse response by time shift is the same as that in FIG. 6. That is, the output e' corresponding to the n-th window function n (t) [corresponding to the component shown by the hatching in FIG. 6(a)] is time-shifted based on the time shift amount N * (n) from the first random number generation unit 31 [FIG. 6(b)]. In this way, by time-shifting based on a random number for each time window, an initial reflected sound e''(t) is generated that has a timbre similar to that of the initial reflected sound e'(t) of the impulse response h'(t) and has a low correlation with each other.

[0071] Note that the first time shift unit 41 shifts each output e' n (t) regarding the initial reflected sound e'(t) after the time length change within the time range of the initial reflected sound. Therefore, n + N * (n) is controlled such that 1 ≤ n + N * (n) ≤ (t e -Tw + Ted) / Ted. When e''(t) goes outside the range of the initial reflected sound e'(t), the first time shift unit 41 causes the first random number generation unit 31 to generate a time shift amount by a random number again, and shifts the output e' of the first time window multiplication unit 21 within the time range of the initial reflected sound e'(t). n (t). The first time shift unit 41 outputs the generated e''(t) to the signal addition unit 50.

[0072] The processing of the second time window multiplication unit 22, the second time setting unit 62, the second random number generation unit 32, and the second time shift unit 42 for the late reverberation sound r(t) is the same as the processing of the first time window multiplication unit 21, the first random number generation unit 31, and the first time shift unit 41 for the early reflection sound e(t), respectively. Note that parameter values such as the length of the window function (window width) and the range of the random numbers of the time shift amount (distribution width) can be individually set to values suitable for each of the early reflection sound e(t) and the late reverberation sound r(t). That is, the first time window multiplication unit 21 uses a first time window with a predetermined time length suitable for the early reflection sound, the second time window multiplication unit 22 uses a second time window with a predetermined time length suitable for the late reverberation sound, the first random number generation unit 31 generates a first time shift amount based on a distribution width suitable for the early reflection sound, and the second random number generation unit 32 generates a second time shift amount based on a distribution width suitable for the late reverberation sound.

[0073] The second time window multiplication unit 22 multiplies the late reverberation sound r(t) by window functions Wr(t) (n = 1, 2, … m) obtained by shifting a plurality of time windows Wr(t) with a predetermined time length Tr, respectively, and outputs r(t) (n = 1, 2, … m). n (t) (n = 1, 2, … m) is generated. The second time setting unit 62 deletes or duplicates, for each time window, the output of the second time window multiplication unit 22 regarding the late reverberation sound r(t) (length t1) of the input impulse response h(t) to generate a new late reverberation sound r'(t) with a length t. n (t) (n = 1, 2, … m). When shortening the reverberation time (t < t1), the second time setting unit 62 appropriately deletes blocks of the original late reverberation sound r(t), and when lengthening the reverberation time (t > t1), r the second time setting unit 62 appropriately duplicates blocks of the original late reverberation sound r(t) to generate a new late reverberation sound r'(t). The second random number generation unit 32 generates a time shift amount by a random number. The second time shift unit 42, based on the time shift amount, for each time window, each component r' of the late reverberation sound r'(t) after the time length change r <t1) for the late reverberation sound r(t) of the input impulse response h(t) to generate a new late reverberation sound r'(t) with a length t. When shortening the reverberation time (t < t1), the second time setting unit 62 appropriately deletes blocks of the original late reverberation sound r(t), and when lengthening the reverberation time (t > t1), r >t1) for the late reverberation sound r(t) of the input impulse response h(t) to generate a new late reverberation sound r'(t) with a length t. When shortening the reverberation time (t < t1), the second time setting unit 62 appropriately deletes blocks of the original late reverberation sound r(t), and when lengthening the reverberation time (t > t1), nOutput r''(t) is generated by time-shifting (t) within the time range of the rear reverberation sound r'(t). When r''(t) is outside the range of the rear reverberation sound r'(t) after the time length change, the second time-shifting unit 42 causes the second random number generation unit 32 to generate a time-shifting amount that is within the range of the rear reverberation sound r'(t) again. The second time-shifting unit 42 outputs the generated r''(t) to the signal addition unit 50.

[0074] The signal addition unit 50 adds the output e''(t) of the first time-shifting unit 41 regarding the early reflection sound e(t) and the output r''(t) of the second time-shifting unit 42 regarding the rear reverberation sound r(t), and generates a new impulse response h''(t).

[0075] In this embodiment, a time-shifting unit 40 that shifts the reverberation component for each time window is provided in the subsequent stage of the time setting unit 60 that changes the length of the reverberation time. However, the time-shifting unit 40 and the related random number generation unit 30 may be omitted, and a configuration may be adopted in which a new impulse response h'(t) is generated directly from the output of the time setting unit 60. In this case, the signal addition unit 50 adds the output e'(t) of the first time setting unit 61 regarding the early reflection sound e(t) and the output r'(t) of the second time setting unit 62 regarding the rear reverberation sound r(t), and generates a new impulse response h'(t).

[0076] Thus, according to this embodiment, the signal separation unit 10 automatically separates the impulse response into the early reflection sound and the rear reverberation sound. The time window multiplication unit 20 multiplies the window function obtained by shifting a time window of a predetermined time length a plurality of times by the early reflection sound and the rear reverberation sound. The time setting unit 60 deletes or duplicates the output of the time window multiplication unit 20 regarding at least one of the early reflection sound or the rear reverberation sound for each time window to change the time length. By adding the early reflection sound and the rear reverberation sound with the changed time length, it becomes possible to generate a large number of impulse responses having a timbre similar to a given impulse response and having an arbitrary reverberation time with low mutual correlation, and to provide impulse responses of sufficient quality and various types for use in reverberation addition in a multi-channel acoustic system.

[0077] Furthermore, the random number generation unit 30 generates a time shift amount by a random number, and the time shift unit 40 time-shifts the output of the first time setting unit 61 regarding the initial reflected sound within the time range of the initial reflected sound for each time window based on the time shift amount. As a result, it becomes possible to generate a large number of impulse responses with low correlation of the initial reflected sound, and it is possible to obtain a sense of spread that cannot be obtained from the impulse response of the same initial reflected sound when the impulse responses are convolved. The same applies to the late reverberant sound.

[0078] In the above-described embodiment, the configuration and operation of the impulse response generation device have been described. However, the present invention is not limited to this, and it may be configured as a method for generating a large number of impulse responses. That is, it may be configured as an impulse response generation method in an impulse response generation device that sequentially includes the processing steps in each part of the impulse response generation device according to the data flow in FIG. 1 or FIG. 7.

[0079] Note that a computer can be suitably used to function as the above-described impulse response generation device. Such a computer can be realized by storing a program describing the processing contents for realizing each function of the impulse response generation device in the storage unit of the computer and reading and executing this program by the CPU of the computer. Note that this program (impulse response generation program) can be recorded on a computer-readable recording medium.

[0080] The above-described embodiment has been described as a representative example, but it is obvious to those skilled in the art that many changes and substitutions can be made within the spirit and scope of the present invention. Therefore, the present invention should not be construed as being limited by the above-described embodiment, and various modifications or changes are possible without departing from the scope of the claims. For example, the functions included in each block, each step, etc. described in the embodiment can be rearranged so as not to be logically contradictory, and a plurality of constituent blocks, steps, etc. can be combined into one or divided.

Explanation of Reference Numerals

[0081] 10 Signal separation unit 20 Time window multiplication unit 21 First time window multiplication unit 22 Second time window multiplication unit 30 Random number generation unit 31 First random number generation unit 32 Second random number generation unit 40 Time shift unit 41 First time shift unit 42 Second time shift unit 50 Signal addition unit 60 Time setting unit 61 First time setting unit 62 Second time setting unit

Claims

1. A signal separation unit that separates an impulse response into an initial reflected sound and a late reverberation sound, a first time window multiplication unit that multiplies the initial reflected sound by a first window function obtained by shifting a first time window having a predetermined time length suitable for the initial reflected sound a plurality of times, and a second time window multiplication unit that multiplies the late reverberation sound by a second window function obtained by shifting a second time window having a predetermined time length suitable for the late reverberation sound a plurality of times, a first random number generation unit that generates a first time shift amount by a random number based on a distribution width suitable for the initial reflected sound, and a second random number generation unit that generates a second time shift amount by a random number based on a distribution width suitable for the late reverberation sound, a first time shift unit that time-shifts the output of the first time window multiplication unit related to the initial reflected sound within the time range of the initial reflected sound for each first time window based on the first time shift amount, and a second time shift unit that time-shifts the output of the second time window multiplication unit related to the late reverberation sound within the time range of the late reverberation sound for each second time window based on the second time shift amount, a signal addition unit that adds the output of the first time shift unit related to the initial reflected sound and the output of the second time shift unit related to the late reverberation sound, An impulse response generation device comprising: wherein the signal separation unit separates the impulse response into the initial reflected sound and the late reverberation sound based on an inflection point included in a predetermined section of the attenuation curve of the impulse response. The signal separation unit uses the absolute value of the second derivative of the attenuation curve as an evaluation function to determine a time range for separating the initial reflected sound and the late reverberation sound according to the reverberation time of the impulse response, and performs the separation at the time when the evaluation function is maximized within the time range. An impulse response generation device characterized by this.

2. A signal separation unit that separates an impulse response into an initial reflected sound and a late reverberation sound, a first time window multiplication unit that multiplies the initial reflected sound by a first window function obtained by shifting a first time window having a predetermined time length suitable for the initial reflected sound a plurality of times, and a second time window multiplication unit that multiplies the late reverberation sound by a second window function obtained by shifting a second time window having a predetermined time length suitable for the late reverberation sound a plurality of times, a first random number generation unit that generates a first time shift amount by a random number based on a distribution width suitable for the initial reflected sound, and a second random number generation unit that generates a second time shift amount by a random number based on a distribution width suitable for the late reverberation sound, A first time shift unit that time-shifts the output of the first time window multiplication unit related to the early reflection sound within the time range of the early reflection sound for each first time window based on the first time shift amount, and a second time shift unit that time-shifts the output of the second time window multiplication unit related to the late reverberation sound within the time range of the late reverberation sound for each second time window based on the second time shift amount, A signal addition unit that adds the output of the first time shift unit related to the early reflection sound and the output of the second time shift unit related to the late reverberation sound, An impulse response generation device comprising: a signal separation unit that separates the impulse response into the early reflection sound and the late reverberation sound based on an inflection point included in a predetermined section of the attenuation curve of the impulse response, The signal separation unit uses the absolute value of the second derivative of the attenuation curve as an evaluation function to determine a time range for separating the impulse response into the early reflection sound and the late reverberation sound based on the reverberation time of the impulse response, searches for the evaluation function from the later time of the time range, and performs the separation at a time when the evaluation function exceeds a threshold obtained from the maximum value of the evaluation function within the time range and a predetermined threshold coefficient. An impulse response generation device characterized by this.

3. A signal separation unit that separates an impulse response into an early reflection sound and a late reverberation sound, A first time window multiplication unit that multiplies the first window function obtained by shifting a plurality of times a first time window having a predetermined time length suitable for the early reflection sound by the early reflection sound, and a second time window multiplication unit that multiplies the second window function obtained by shifting a plurality of times a second time window having a predetermined time length suitable for the late reverberation sound by the late reverberation sound, A first random number generation unit that generates a first time shift amount by a random number based on a distribution width suitable for the early reflection sound, and a second random number generation unit that generates a second time shift amount by a random number based on a distribution width suitable for the late reverberation sound, A first time shift unit that time-shifts the output of the first time window multiplication unit related to the early reflection sound within the time range of the early reflection sound for each first time window based on the first time shift amount, and a second time shift unit that time-shifts the output of the second time window multiplication unit related to the late reverberation sound within the time range of the late reverberation sound for each second time window based on the second time shift amount, A signal addition unit that adds the output of the first time shift unit related to the early reflection sound and the output of the second time shift unit related to the late reverberation sound, An impulse response generation device comprising: a signal separation unit that separates the impulse response into an initial reflected sound and a late reverberation sound based on an inflection point included in a predetermined section of an attenuation curve of the impulse response. The signal separation unit uses the absolute value of the second derivative of the attenuation curve as an evaluation function to determine a time range for separating the initial reflected sound and the late reverberation sound according to the reverberation time of the impulse response. When the reverberation time of the impulse response is less than a predetermined time, the separation is performed at a time when the evaluation function is maximized within the time range. When the reverberation time of the impulse response is equal to or greater than the predetermined time, the separation is performed at a time when the evaluation function has the second largest value within the time range. **Claim 4**: The impulse response generation device according to any one of Claims 1 to 3, further comprising a time setting unit that selects a plurality of blocks in time window units for at least one of the outputs of the first time window multiplication unit related to the initial reflected sound and the second time window multiplication unit related to the late reverberation sound, deletes them, or selects a plurality of blocks in time window units, duplicates each of them, and changes the time length. The first time shift unit time-shifts the output of the time setting unit related to the initial reflected sound within the time range of the initial reflected sound for each first time window based on the first time shift amount. The second time shift unit time-shifts the output of the time setting unit related to the late reverberation sound within the time range of the late reverberation sound for each second time window based on the second time shift amount. **Claim 5** An impulse response generation program for causing a computer to function as the impulse response generation device according to any one of Claims 1 to 4.

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