JPH0229280B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a sound image control device that focuses on correlation coefficients, and more specifically, the present invention relates to a sound image control device that uses a correlation function control device to maintain flat transmission frequency characteristics and to increase the spread of sound images without adding reverberant signals as much as possible. The present invention relates to a sound image control device that controls the sense of depth and sense of depth. Conventionally, there have been two methods for controlling the quality of sound images: (a) a method performed during stereo sound collection, and (b) a method performed during speaker reproduction. First, the simplest method for (a) is to use a pair of microphones, commonly known as a pair of microphones, and change the distance from the sound source to the microphones, the spacing between the microphone heads, and their direction, thereby controlling the stereo feel during playback. This is a convenient method because it allows you to However, when using this method, if the distance between the microphone heads is made too large in order to increase the sense of spaciousness of the sound image, the central sound image becomes unclear, resulting in a so-called hollow state. In addition, various types of so-called stereo microphones, which integrate a pair of unidirectional microphones, have been devised so that sound can be more easily collected using paired microphones. According to this method, even inexperienced users can make stereo recordings with stable localization, but depending on the type of sound source, it may not be possible to sufficiently reproduce the spread of the sound image or the depth. There are basically three types of method (b): (i) A method of applying sound pressure level difference and phase difference only to the signal of the other channel without modifying the signal of one channel, (ii) A method of applying sound pressure level difference and phase difference to the signal of both channels. (iii) use a delay element to electrically create a reverberation component and add it to the signals of both channels. However, in all of these methods, deterioration in sound quality is inevitable because the amplitude-frequency characteristics of the system are not flat. Furthermore, there is a method of obtaining a sense of spaciousness of the sound image using an echo room or a special reverberation device, but when this method is used, the sense of reverberation changes as well as the sense of spaciousness of the sound image. The present invention has been made in consideration of the above-mentioned problems, and when a stereo signal is collected using a pair of microphones or when a stereo signal is reproduced with a narrow speaker spacing, the sound image can be reproduced without changing the microphone head or the spacing between the speakers. The object of the present invention is to provide a sound image control device that can control the spread and depth of the sound image. According to the present invention, the phase lead/lag relationship between output signals is alternately reversed as the frequency changes, without changing the transmission amplitude frequency characteristics between input and output signals, and The correlation coefficient of −
By inserting a correlation function control device which can be arbitrarily varied from 1 to +1 and which can also vary the frequency characteristics of the correlation coefficient into the multi-channel sound collection system or reproduction system, and outputting at least two signals. achieved. The present invention will be explained below using examples. FIG. 1 is a block diagram of a sound image control device according to an embodiment of the present invention. The sound image control device of this embodiment includes a filter 1 having a gain of 1 or less and having the same frequency characteristics.
2, 1' and 2', delay circuits 3 and 3' having the same delay time characteristics, and phase shift circuits 4 and 2 having a phase term twice the position term of the transfer function of filters 1, 2, 1' and 2'. 4', subtracters 5 and 8, and adders 6 and 7, and a correlation function control device with one input channel and two output channels is inserted into the two-channel sound collection system or the reproduction system. do. The correlation coefficient control device subtracts the output signal of the filter 2 from the signal applied to the input terminal IN.
The output signal of the subtracter 5 is input to the adder 6 through the filter 1, and the output signal of the subtracter 5 is input to the delay circuit 3, and the output signal of the delay circuit 3 is input to the subtracter 5 through the filter 2. The output signal of the delay circuit 3 is inputted as an input to an adder 6 through a phase shift circuit 4, and is added to the output signal of the filter 1 by the adder 6 and output to the output terminal _OUT1 . On the other hand, the signal applied to the input terminal IN ₁ and the output signal of the filter 2' are added by the adder 7, and this added signal is input to the filter 1' and the delay circuit 3'. The output signal of filter 2' is input to filter 2' and also input to phase shift circuit 4', the output signal of filter 2' is input to adder 7 as an addition signal, and the output signal of filter 1' is input from the output signal of phase shift circuit 4'. The subtracter 8 subtracts the output signal and outputs the subtracted output signal to the output terminal _OUT2 . In the above sound image control device, the transfer function G ₁ (jω) of the first channel from the input terminal IN to the output terminal OUT ₁ , and the transfer function G ₂ (jω) of the second channel from the input terminal IN to the output terminal OUT ₂ . are expressed by equations (1) and (2) below, respectively. Hereinafter, the transfer function of filters 1, 2, 1' and 2' is g(jω), the delay time of delay circuits 3 and 3' is τ, and the transfer function is e ^-j 〓〓, phase shift circuits 4 and 4' The transfer function of is expressed as e2j∠g(jω). G ₁ (jω) = g(jω) + exp(−jωτ)・exp(2j∠g(jω)
)/1+g(jω)・exp(−jωτ) …(1) G ₂ (jω) =−g(jω)+exp(−jωτ)・exp(2j∠g(jω
))/1−g(jω)・exp(−jωτ) …(2) Also, the amplitude transmissibility |G ₁ (jω)| and G ₂ (jω) are Therefore, the transmission amplitude frequency characteristics of all channels are flat and have no gain, and the spectra of the input signal and output signal are the same. Next, the phase characteristics of the first channel and the second channel are as follows. The phase delay ₁ between the input signal and output signal due to the first channel _{is 1} = ∠G ₁ (jω) = -ωτ + 2∠g (jω) + 2tan ^-1 [|g (jω) | sin
jω)}/1+｜g(jω)cos{ωτ−∠g(jω)}]
...(4) The phase delay ₂ between the input signal and output signal due to the second channel is ₂ = ∠ (jω) = -ωτ + 2∠g (jω) -2 tan ^-1 [|g (jω) | sin{ωτ − ∠g (
jω)}/1+｜g(jω)cos{ωτ−∠g(jω)}]
...(5), and the phase difference ₁₂ between the two channel output signals is ₁₂ = ₁ − ₂ = 2tan ^-1 [|g(jω)|sin{
ωτ−∠g(jω)}/1−|g(jω)| ² ]...(6) As is clear from equation (6), the phase difference ₁₂ is 0<ω<
It vibrates at ∞ and reaches its maximum value at an angular frequency that satisfies ωτ−∠g(jω)=π/2+2nπ, ωτ−∠g(jω)=−π/2+2n
It takes a minimum value at an angular frequency that satisfies π. Also −π＜2tan ^-1 −2 | g (jω) | ² /1− | g (jω) | ²
＜π ＜12＜2tan ^-1 2｜g(jω)｜ ² /1−｜g(jω)
| ² <π, and the amplitude of vibration is defined by |g(jω)|. That is, the fluctuation amplitude of the phase difference ₁₂ is determined by the transfer function g of the filters 1, 2, 1' and 2' in the circuit shown in FIG.
It has a frequency characteristic determined depending on the amplitude characteristic of (jω). For example, when |g(jω)| monotonically increases (decreases) with respect to the angular frequency ω, the vibration amplitude of the phase difference ₁₂ monotonically increases (decreases) with the angular frequency ω. An example of its characteristics is shown in FIG. In FIG. 2, a shows an example of a characteristic in the case of a monotonous decrease, and b shows an example of a characteristic in the case of a monotonous increase. As can be easily inferred from the above phase difference characteristics, when band random noise is applied to the input terminal IN, the correlation coefficient of the output signals output from the output terminals OUT ₁ and OUT ₂ is ' and 2' have frequency characteristics that depend on the amplitude characteristics |g(jω). In fact, when band random noise with center frequency ω ₀ and bandwidth Δω is applied to the input terminal IN, the correlation coefficient Φ5(ω ₀ ) between the output signals is as follows, where the voltage density of the output signal is V(ω). It is expressed by the formula. As is clear from equation (3), V(ω) = (a constant that does not depend on frequency), so equation (7) is Therefore, under the condition of Δω≫1/τ, Φ(ω ₀ )=1−3|g(jω)| ² /1+|g(j
ω) | ² …(8). In other words, as is clear from the above, the correlation coefficient Φ
(φ ₀ ) is determined by equation (8) from the amplitude frequency characteristics |g(jω)| of filters 1, 2, 1', and 2'.
Therefore, by changing the characteristics of filters 1, 2, 1', and 2' in conjunction with each other, the value of the correlation coefficient and its frequency characteristics can be arbitrarily varied, and the quality of the sound image can be controlled. be able to. Further, the maximum value of the correlation coefficient occurs at the position of τ=0, and the sound image is not eccentric. For example, when filters 1, 2, 1', and 2' are constructed with various transfer functions, the frequency characteristic patterns of the correlation coefficients are as shown in Table 1.

[Table] Next, a specific example of the sound image control device based on the principle explained above will be described. FIG. 3 is a block diagram showing this specific embodiment. The sound image control device of this specific embodiment includes attenuators 10, 11, 12, and 13 with a gain g′, a time constant T ₁
Primary low-pass filters 14, 15, 16 having
and 17, first order high pass filters 18, 19, 20 and 21 with time constant T ₂ , first order phase shift circuits 22 and 23 with same time constant T ₁ as the first order low pass filter, same time constant as the first order high pass filter. first order phase shift circuits 24 and 25 with T ₂ ;
The correlation function control device includes delay circuits 26 and 27 having a delay time τ, subtracters 5 and 8, and adders 6 and 7. The sound image control device of the specific embodiment shown in FIG. 3 satisfies all the structural requirements of the sound image control device of the embodiment shown in FIG. In fact, 10 and 1 are connected in series of an attenuator, a first-order low-pass filter, and a first-order high-pass filter.
4 and 18, 12 and 16 and 20, 11 and 15 and 19
And the transfer function of the circuit consisting of 13, 17 and 21 is becomes. If this is set as g(jω), the transfer function of the circuit consisting of 22 and 24, 23 and 25 in which the first-order phase shift circuits are connected in cascade is 1−jωT ₁ /1+jωT ₁ +jωT ₂ −1/1+jωT ₂ =e −2j(tan−1ωT ₁ +tan ⁻¹ ωT ₂ −π/2), which is nothing but e−2j∠g(jω). Therefore, the sound image control device shown in FIG. 3 is a device equivalent to the sound image control device shown in FIG. Therefore, the transmission amplitude frequency characteristic of the sound image control device shown in Fig. 3 is flat, and the correlation coefficient Φ is Φ=1-3(g') ² ε ² T ₂ ² /(1+ε ² T ₁ ² ) (1+ε
² T ₂ ² )/1+(g′) ² ε ² T ₂ ² /(1+ε ² T ₁ ² )(1+ε
² T ₂ ² )…(9). As is clear from equation (9), the correlation coefficient Φ is the gain g′, 1 of the attenuators 10, 11, 12, and 13.
Next low pass filters 14, 15, 16 and 17
time constant T ₁ , first-order high-pass filters 18, 19,
20 and 21 depending on the time constant T ₂ . Therefore attenuators 10, 11, 12 and 13
By appropriately interlocking and varying the circuit constants of the primary low-pass filters 14, 15, 16,
7 and the primary phase shift circuits 22, 23 in conjunction with each other, and/or the circuit constants of the primary high-pass filters 18, 19, 20, 21 and the primary phase shift circuits 24, 25 are varied in conjunction with each other. By varying the correlation coefficient Φ, the frequency characteristics of the correlation coefficient Φ can be changed. Typical frequency characteristics of the correlation coefficient Φ are summarized as follows in correspondence with circuit constants. (i) When T ₁ →0 and T ₂ →∞, the correlation coefficient exhibits a flat characteristic, and Φ=[1-3(g′) ² ]/[1+(g′) ² ]
is given by (ii) When T ₁ → 0, the correlation coefficient shows a high-frequency falling characteristic, and the lowest correlation coefficient Φmin is [1-3
(g′) ² ]/[1+(g′) ² ]. g′＝
An example of the characteristics when the value is 0.55 is shown in curve a in Fig. 4. (iii) When T ₂ →0, the correlation coefficient exhibits a low-frequency falling characteristic, and the lowest correlation value Φmin is [1-3(g') ² ]/
It is given by [1+(g′) ² ]. An example of the characteristics when g'=0.55 is shown in curve b in FIG. (iii) When T ₁ = kT and T ₂ = T/k, the correlation coefficient shows a peak-dip characteristic centered at ω ₀ = 1/T, and the characteristics when k = 2 and g = 0.7. An example is shown by curve C in FIG. Note that changes in the frequency characteristic patterns (i) to (iii) can be selected by a simple switching operation.
Furthermore, by changing the time constant, it is possible to move left and right on the frequency axis while maintaining the frequency characteristic pattern. Moreover, the correlation coefficient is the attenuator 10, 11, 12,
13 and the gain g' can be changed arbitrarily. Here, if the correlation coefficient is 1, there will be a positive correlation and both output signals will be equal, so the sound image will be localized at the center. Furthermore, as the correlation coefficient is made smaller from 1, the two output signals lose their correlation with each other, and the sound image becomes wider. As explained above, according to the present invention, the quality of the sound image can be controlled by changing the correlation coefficient,
You can get the following effects. (i) When used to collect stereo signals,
Normally, output signals from a pair of microphones or a stereo microphone are applied to the sound image control device of the present invention via an amplifier, and the correlation coefficient between the signals of both channels is increased by changing the amount of attenuation of the attenuator.
It can be easily changed from 1 to -1, and even when the correlation coefficient is 0, the time of the reverberation signal added is about 0.1 seconds at most. Therefore, the distance from the sound source to the sound collection point, the distance between the microphone heads,
Without changing the direction of the microphone head, and without adding reverberant signals that would change the reverberation or timbre, the stereo reproduction sound image can be expanded,
It is possible to control the psychological impression of depth. Further, at this time, the sound quality does not deteriorate, and the physical information regarding the directional localization of the original signal does not change. (ii) In the case of a conventional stereo playback device such as a conventional audio multiplex television receiver or a tape recorder with a stereo radio, the distance between the speakers for both left and right channels is narrow, so it is difficult to reproduce a sound field with a rich sense of presence. However, by using the sound image control device of the present invention for speaker reproduction, it is possible to improve the sound image without changing the speaker spacing, degrading the sound quality, or adding reverberation components. The sense of spaciousness and depth can be changed depending on the type of sound source and listener's preference. Further, the effect can be obtained by using it in a place where the volume is small and sound diffusion is not good, such as the inside of a car.

[Brief explanation of drawings]

FIG. 1 is a block diagram of a sound image control device according to an embodiment of the present invention. FIG. 2 is a characteristic diagram showing the phase difference between output signals of the sound image control device shown in FIG. 1. FIG. 3 is a block diagram of a specific embodiment of one embodiment of the present invention. FIG. 4 is a characteristic diagram of the correlation coefficient of a specific example of the embodiment of the present invention shown in FIG. 1, 2, 1' and 2'...filter, 3 and 3'...delay circuit, 4 and 4'...phase shift circuit, 5
and 8...adder, 6 and 7...subtractor, 1
0, 11, 12 and 13...attenuator, 14, 1
5, 16 and 17...first-order low-pass filter,
18, 19, 20 and 21...1st order high pass filter, 22, 23, 24 and 25...1st order phase shift circuit, 26 and 27...delay circuit.

Claims (1)

[Claims] 1. The correlation function control device includes first, second, third, and fourth filters having the same characteristics and a gain of 1 or less, and first and second filters having the same delay time.
and first and second phase shift circuits having a phase angle twice that of the transfer function of the first, second, third and fourth filters, A first signal obtained by subtracting the output signal as a subtraction signal by the input signal applied to the input terminal is input to the first delay circuit and the second filter, and the output signal of the first delay circuit is input to the first delay circuit. input to the filter and the first phase shift circuit, add the output signal of the second filter and the output signal of the first phase shift circuit, derive it from the first output terminal, and output the output of the third filter. A second signal obtained by adding the signal and the input signal applied to the input terminal is inputted to a second delay circuit and a fourth filter, and an output signal of the second delay circuit is inputted to a third filter. and a second phase shift circuit, and the output signal of the fourth filter is subtracted from the output signal of the second phase shift circuit as a subtraction signal to be derived from the second output terminal. Sound image control device.