JPH0137920B2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention maintains flat transmission frequency characteristics while
The present invention also relates to a sound image control device that controls the sense of spaciousness and depth of a sound image without adding a reverberation signal.

Conventionally, as methods for controlling sound images, there have been two methods: (a) a method performed during stereo sound collection, and (b) a method performed during speaker reproduction.

The simplest method for (a) is to use a pair of microphones, commonly known as a pair of microphones, and to control the stereo feel during playback by changing the distance from the sound source to the microphones, the distance between the microphone heads, and their direction. This is a convenient method because it can be done. 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 collection using a pair of microphones can be performed more easily. According to this, even inexperienced users can make stereo recordings with stable localization, but depending on the type of sound source, the spread of the sound image and the depth may not be sufficiently reproduced.

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.

The present invention has been made in view of the above, and is capable of collecting stereo signals using a pair of microphones or reproducing stereo signals with narrow speaker spacing without changing the microphone head or speaker spacing. It is an object of the present invention to provide a sound image control device that can control the spread and depth of a sound image.

The present invention will be explained below using examples.

FIG. 1 is a block diagram of an embodiment of the sound image control device of the present invention.

In this embodiment, a first circuit A and a second circuit B are independent. The first circuit A is composed of a so-called all-pass circuit 1 with an amplitude transmission rate of "1", an attenuator 3, an adder 5, a subtracter 6, and an adder/subtractor 9, and the input signal applied to the input terminal _IN1 and Add the output signal of the all-pass circuit 1 with the adder 5,
The output signal of adder 5 is attenuated by attenuator 3. A subtracter 6 subtracts the output signal of the attenuator 3 from the input signal applied to the input terminal IN ₁ and inputs the result to the all-pass circuit 1 . Further, the adder/subtractor 9 adds the output signal of the adder 5 and the output signal of the attenuator 3, further subtracts the input signal applied to the input terminal IN ₁ , and the output signal of the adder/subtractor 9 is sent to the output terminal OUT ₁ . Derived as follows.

The second circuit B includes an all-pass circuit 2 having the same characteristics as the all-pass circuit 1, an attenuator 4 having the same gain as the attenuator 3, subtracters 7 and 8,
It consists of an adder/subtractor 10, and the subtracter 7 has an input terminal.
All-pass circuit 2 from the input signal applied to IN ₂
The output signal is subtracted and inputted to the attenuator 4 to be attenuated. A subtracter 8 subtracts the output signal of the attenuator 4 from the input signal applied to the input terminal IN ₂ and inputs the result to the all-pass circuit 2. Input terminal at adder/subtractor 10
The output signal of the subtracter 7 and the output signal of the attenuator 4 are subtracted from the input signal applied to IN ₂ , and the result is delivered to the output terminal OUT ₂ .

If the transfer functions of the first circuit A and the second circuit B are G ₁ (jω) and G ₂ (jω), respectively, then G ₁ (jω) = g + E (jω) / 1 + gE (jω) = E (jω) 1+gE(jω) ^-1 /1+gE(jω) ...(1) G ₂ (jω)=g-E(jω)/1-gE(jω) =E(jω)1-gE(jω) ^-1 /1- gE(jω) …(2) is given. Here, ω is the angular frequency of the input signal applied to input terminals IN ₁ and IN ₂ , E(jω) is the transfer function of all-pass circuits 1 and 2, and g is the attenuator 3 and 4.
is the gain of

The amplitude terms of the transfer functions G ₁ (jω), G _{~ 2} (jω) |G ₁ (jω
)
|, |G ₂ (jω)| are expressed as the transfer function E(jω) of all-pass circuits 1 and 2 as follows: E(jω)=e ^-j 〓 ⁽ 〓 ⁾ …(3) |G ₁ (jω)| =｜e ^-j 〓 ⁽ 〓 ⁾ ｜｜1+ge ^j 〓 ⁽ 〓 ⁾ /1
＋ge ^-j 〓 ⁽ 〓 ⁾ ｜=｜1+g cosφ+jg sinφ／1+g c
osφ−jg sinφ｜=1…(4) ｜G ₂ (jω)｜=｜e ^-j 〓 ⁽ 〓 ⁾ ｜｜1−ge ^j 〓 ⁽ 〓 ⁾ /1
−ge ^-j 〓 ⁽ 〓 ⁾ ｜=｜1−g cosφ−jg sinφ／1−g c
osφ+jg sinφ|=1 (5), and the transmission amplitude frequency characteristics of the first circuit A and the second circuit B are flat.

In addition, the phase terms ₁ and ₂ of the transfer functions G ₁ (jω) and G ₂ (jω)
From equations (1) to (3), ₁ ≡∠G ₁ (jω) = −φ+2tan ^-1 g sinφ/1+g cosφ …(6) ₂ ≡∠G ₂ (jω) = −φ−2tan ^-1 g sinφ /1-g cosφ...(7).

Also, the phase difference ₁₂ between the first circuit A and the second circuit B and the cosine of the phase difference ₁₂ which is the correlation coefficient are ₁₂ = ₁ - ₂ = 2tan ^-1 2g sinφ/1 - g ² ...( 8) cos ₁₂ =-1+2(1-g ² ) ² /4g ² sin ² φ+(1-g ²
) ² …(9).

Now, all-pass circuits 1 and 2 satisfy 0≦ω<∞
Assuming that it is a 2n-order phase shift circuit in which the phase changes by 0≧-φ>-2nπ radians, ₁ and ₂ are 0≦ω<∞
becomes a monotonically decreasing function with a value range of 0 to −2nπ, and cos ₁
There are n angular frequencies ω that satisfy =cos ₂ =1. Similarly, ₁₂ oscillates n times in the interval -π< _2tan ^-1 -2g/1-g ² ≦ ₁₂ ≦2tan ^-1 2g/1-g ² <π ...(10), and cos ₁₂ ≧−4g ² −(1−g ² ) ² /4g ² +(1−g ² ) ²
…(11) Vibrate 2n times in the range, minimum value: (cos ₁₂ ) min = −4g ² − (1−g ² ) ² /4g ² + (1−g ² ) ² …(1
2) Maximum value; (cos ₁₂ )max=1...(13) Take each 2n times.

On the other hand, the correlation coefficient between the two systems of the first circuit A and the second circuit B is defined as "the correlation coefficient between the two output signals when a specific band random noise is applied to the input terminal". For example, the first circuit A, the second circuit
The correlation coefficient Φ as a function of the frequency of circuit B is It is expressed as

Here, ω ₀ is the central angular frequency, and Δω is 2π times the bandwidth.

Generally, equation (14) depends on parameters such as the time constants of the all-pass circuits 1 and 2 and the attenuation amounts of the attenuators 3 and 4, but if n is sufficiently large, (ω ₀ −Δω/2) → 0, ( In the limit of ω ₀ +Δω/2)→∞, it is approximated by Φ=1−3g ² /1+g ² (15).

Since cos ₁₂ generally oscillates around the average value Φ, in practical use n may be set sufficiently large to the extent that it can be considered as aurally continuous.

To summarize the above, the sound image control device of this embodiment has (1) the amplitude frequency characteristic |G(jω)| is flat;
Has no gain.

(2) The phase difference ₁₂ between the two channels is such that the phase lead/delay relationship between the two channels repeats inversion as the frequency changes, and oscillates in positive and negative directions around zero.

(3) The correlation coefficient Φ(jω) is
If the parameter of is represented by a, then in general Φ=
If the parameter a is appropriately selected, the correlation coefficient Φ is determined depending only on the amount of attenuation g of the attenuators 3 and 4.

Therefore, by inserting the first circuit A and the second circuit B of this embodiment shown in FIG. The degree of signal correlation can be reduced and the sound image can be controlled.

Next, a specific example of the configuration of this embodiment shown in the block diagram in FIG. 1 will be explained.

FIG. 2 is a circuit diagram showing a specific configuration of this embodiment.

11 is a buffer amplifier. The all-pass circuit 1 is composed of a 2n-order phase shift circuit in which first-order phase shift circuits consisting of operational amplifiers 13 _-1 , 13 _-2 , ...13 _-2o are connected in cascade, and the attenuator 3 is composed of a circuit consisting of an operational amplifier 15 However, the adder 5 is constituted by a circuit consisting of an operational amplifier 17, the subtracter 6 is constituted by a circuit consisting of an operational amplifier 19, and the adder/subtractor 9 is constituted by a circuit consisting of an operational amplifier 21. Configure.

12 is a buffer amplifier. The all-pass circuit 2 has the same operational amplifier 14 as the all-pass circuit 1.
_-1 , 14 _-2 , ...14 _-2o are connected in cascade and have the same characteristics as all-pass circuit 1.
The attenuator 4 is composed of a 2n-order phase shift circuit, and the attenuator 4 is composed of an operational amplifier 16, and a variable resistor V _{R2 that is linked to a variable resistor V R1} connected to the non-inverting input terminal of the operational amplifier _15.
The subtracter 7 is configured with a circuit including an operational amplifier 18, the subtracter 8 is configured with a circuit including an operational amplifier 20, and the adder/subtractor 10 is configured with a circuit including an operational amplifier 22. and configure the second circuit B.

In the circuit shown in FIG. 2, there is considerable freedom in selecting the time constant and the number of stages of the primary phase shift circuit. Two examples will be described below.

Embodiment (i) is a 2n-order phase shift circuit with all the same time constants as all-pass circuits 1 and 2, for example, the transfer function and its phase term are E(jω)=(1-jωT/1-jωT) ²ⁿ ...(16 ) −φ(jω)=4−n tan ⁻¹ ωT (17) This is an example in which a 2n-order phase shift circuit is used. Here, T is the time constant of the first-order phase shift circuit.

In this case, the transmission amplitude frequency characteristics |G ₁ (jω)|, |G ₂ (jω)| and phase frequency characteristics ₁ and ₂ of the first circuit A and the second circuit B are n=10, g = 0.7, the result will be as shown in Figure 3.

In Figure 3, the dashed-dotted lines are |G ₁ (jω)|, |G ₂
(jω)|, the solid line indicates ₁ , and the broken line indicates ₁ .

Further, the cosine cos ₁₂ of the phase difference is as shown in FIG. In Fig. 4, the dashed line indicates the minimum value of ₂ , that is, the value of equation (12), and in this example, (-
0.7657).

Example (ii) is a 2n-order phase shift circuit in which the time constants of the first-order phase shift circuit are two types, T and 10T, and the transfer function and phase term are E(jω)=(1−jωT/1+jωT・1 −j10ωT/1
+j10ωT) ⁿ ...(18) -φ(jω)=-2n(tan ^-1 ωT+tan ^-1 10ωT)...(19) This is an example of the case where a 2n-order phase shift circuit is used.

In this case, the transmission amplitude frequency characteristics |G ₁ (jω)|, |G ₂ (jω)| and phase frequency characteristics ₁ and ₂ of the first circuit A and the second circuit B are n=10, g If =0.7, the result will be as shown in FIG.

In Fig. 5, the dashed-dotted lines are |G ₁ (jω)|, |G ₂
(jω)|, the solid line indicates ₁ , and the broken line indicates ₂ .

Further, the cosine cos ₁₂ of the phase difference is as shown in FIG. In FIG. 6, the dashed line indicates the minimum value of ₁₂ , which in this example is (-0.7657).

In the above embodiments (i) and (ii), the cosine of the phase difference
Although the intervals between the peak values of cos ₁₂ are different, the correlation coefficient Φ can be practically approximated by the equation (15): Φ=1−3g ² /1+g ² . Therefore, by interlocking the attenuators 3 and 4, which are components of the first circuit A and the second circuit B, and changing 0≦g<1, the correlation coefficient between the two channels can be set to 1≧Φ. It can be arbitrarily changed within the range >-1, and the sound image can be controlled.

As explained above, according to the present invention, the following effects can be obtained.

(i) When used to collect stereo signals,
The output signal of a normal pair of microphones or a stereo microphone is 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 adjusted from +1 to -1 by changing the amount of attenuation of the attenuator. can be easily changed. Therefore, it is possible to control the spread of the stereo reproduced sound image and the psychological impression of depth without changing the distance from the sound source to the sound collection point, the interval between the microphone heads, or the direction. 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) When used for speaker playback, compared to the case of a normal stereo playback device such as an audio multiplex television receiver or a tape recorder with stereo radio, the distance between the speakers for both left and right channels is Due to the narrow spacing, it was not possible to reproduce a sound field with a rich sense of presence, but by using the sound image control device of the present invention, it is possible to do so without changing the speaker spacing and without deteriorating the sound quality. without adding reverberation components,
The sense of spaciousness and depth of the sound image can be changed depending on the type of sound source and the listener's preference.

[Brief explanation of drawings]

FIG. 1 is a block diagram of one embodiment of the present invention. Second
The figure is a circuit diagram showing a specific configuration of a sound image control device according to an embodiment of the present invention. FIG. 3, FIG. 4, FIG. 5, and FIG. 6 are characteristic diagrams for explaining the operation of an embodiment of the present invention. 1 and 2...all-pass circuit, 3 and 4...attenuator, 5...adder, 6, 7 and 8...subtractor, 9
and 10...addition/subtraction device.

Claims (1)

[Claims] 1 comprising a first n-order phase shift circuit and a first attenuator,
Adding the input signal applied to the input terminal with the output signal of the first n-order phase shift circuit to obtain a first signal, inputting the first signal to the first attenuator,
The output signal of the first attenuator is subtracted from the input signal applied to the input terminal and input to the first n-order phase shift circuit, and the output signal of the first attenuator and the first signal are subtracted from the input signal applied to the input terminal. a first circuit configured to obtain a second signal by adding the signals, and derive a signal obtained by subtracting the input signal applied to the input terminal from the second signal to the output terminal; an n-th phase shift circuit and a second attenuator, the output signal of the second n-th phase shift circuit is subtracted from the input signal applied to the input terminal, and a third
, the third signal is input to the second attenuator, and the output signal of the second attenuator is subtracted from the input signal applied to the input terminal to obtain the second n-th signal. a second circuit configured to input to the phase shift circuit and derive to an output terminal a signal obtained by subtracting the third signal and the output signal of the second attenuator from the input signal applied to the input terminal; A sound image control device comprising: