JPH03266599A - Acoustic circuit - Google Patents

Abstract

PURPOSE:To faithfully reproduce a surround signal by adding the output signal of a voltage controlled amplifier which compares signal levels of a sum signal and a difference signal with each other to control the level of a delay signal and that of a voltage controlled amplifier, which controls the level of the sum signal by the inverted signal of the control signal from a comparator, to obtain a monaural signal. CONSTITUTION:Signals SL and SR are inputted to a sum signal generating circuit 15 and a difference signal generating circuit 16, and the sum signal from the sum signal generating circuit 15 is inputted to a voltage controlled amplifier 22 and level detected by a level detecting circuit 18. The difference signal from the difference signal generating circuit 16 is inputted to a delay circuit 17 and level detected by a level detecting circuit 19. The difference signal from the delay circuit 17 is inputted to a voltage controlled amplifier 23, and outputs from level detecting circuits 18 and 19 are supplied to a comparator 20, and voltage controlled amplifiers 22 and 23 are controlled by the output of the comparator. Outputs of voltage controlled amplifiers 22 and 23 are added by an adder 13 to obtain the monaural signal. Thus, signals of two channels are faithfully reproduced as the monaural signal without losing the surround component.

Description

DETAILED DESCRIPTION OF THE INVENTION [Structure of the Invention] (Industrial Application Field) The present invention relates to an audio circuit that reproduces monaurally a stereo signal including a surround signal in each channel signal.

(Prior Art) A surround signal refers to a signal component that gives a sense of the sound source direction or reverberation of an original signal in a reproduced sound field, and there are surround signal reproduction methods such as the Dolby surround method and the phase shift method.

For example, the Dolby surround system was proposed in 1975 as a sound system for movies. This Dolby Surround system converts the signals of the total mouth channels (left, center, right) in front of the movie viewer and one channel behind the viewer into stereo signals of L and R channels. When the audio is encoded and recorded on a film soundtrack, and the sound recorded on the soundtrack is played back, it is restored to four channels using a dedicated decoder.

The stereo signal encoded using this Dolby Surround system consists of the left, right and center channel signals of the original signal, L, R, and C, and the rear surround signal as S.
Then, L channel signal = L + S + Go ... (1) R
Channel signal=R-8+Go...(2) Here, C0=C/2...(3).

These stereo signals are restored to four channels using a special decoder at movie theaters, so you can watch movies with powerful sound.

By the way, in the case of monaural reproduction of a stereo signal to which such surround signals are distributed, conventionally, as shown in FIG. It was a signal.

Figure 6 shows an L channel signal including a surround signal and an R channel signal including a surround signal.
This is a circuit that outputs the sum of the channel signal and the output as a monaural signal. That is, in FIG. 6, SL and SR each include a surround signal and represent an R channel signal, and these signals SL and SR are input to an adder 13 via input terminals 11 and 12, and are input to an adder 13 by the adder 13. The sum is added and output from the output terminal 14.

In addition, each circuit shown in FIG. 7 has an R channel signal SL.
, SR, only the L channel signal SL is led from the terminal 11 to the output terminal 14, and the circuit shown in FIG. It is something that guides.

However, when a surround system signal is reproduced monaurally by the circuit shown in FIG. 6, the monaural signal appearing at the output terminal 14 becomes L+R+C obtained by adding the above equations (1) and (2). Therefore, the S channel signal component is canceled out.

Further, in the circuit of FIG. 7 or FIG. 8, only one channel component (L+S+GO or R-8+Go) L is reproduced.

(Problems to be Solved by the Invention) As described above, in the conventional method of monaurally reproducing two channel signals to which surround signals are distributed, it is not possible to reproduce the surround components as they are. In recent years, an increasing number of playback systems are creating sounds that place emphasis on the S channel component, so there has been a drawback that fidelity will be poor if the S channel component cannot be played back.

SUMMARY OF THE INVENTION An object of the present invention is to provide an audio circuit for monaural reproduction that faithfully reproduces surround signals.

[Structure of the Invention] (Means for Solving the 1m! Problem) In order to achieve the above object, a sum signal that calculates the sum and difference of two encoded signals in which a surround channel signal is distributed to each localization channel signal is provided. a generation circuit and a difference signal generation circuit; a delay circuit that delays the difference signal from the difference signal generation circuit to obtain a delayed signal; and a comparator that compares signal levels from the sum signal generation circuit and the difference signal generation circuit. , a voltage control amplifier that controls the level of the delayed signal from the delay circuit with a control signal from a comparator, and a voltage that controls the level of the sum signal from the sum signal generation circuit with an inverted signal of the control signal from the comparator. It includes a control amplifier and an adder that adds the output signals from each of the voltage control amplifiers and outputs a monaural signal.

(Operation) According to the above configuration, the sum signal of the two encoded signals to which the surround signals are distributed is an output in which the signals of the respective localization channels are mixed. The difference signal is mainly composed of surround components. Therefore, the obtained monaural output includes all channel components in which the surround signal is added to the signal from each localization.

(Example) Hereinafter, the present invention will be described in detail with reference to illustrated examples.

FIG. 1 is a block diagram showing an embodiment of an acoustic circuit according to the present invention.

In FIG. 1, 2 shown in equations (1) and (2) above
Channel signals SL and SR are input to a sum signal generation circuit 15 and a difference signal generation circuit 16 via input terminals 11 and 12. The sum signal generation circuit 15 generates a signal SL.

This is a circuit that outputs the sum of SR. The difference signal generation circuit 16 is a circuit that outputs the difference between the signals SL and SR.

The sum signal from the sum signal generation circuit 15 is sent to the voltage controlled amplifier 22.
The level of the signal is detected by the level detection circuit 18. The difference signal from the difference signal generation circuit 16 is input to the delay circuit 17 and its level is detected by the level detection circuit 19. The difference signal from delay circuit 17 is input to voltage controlled amplifier 23 .

Each detection output from the level detection circuit 18.19 is fed to a comparator 20, the output of which controls the voltage controlled amplifier 22.23. In this case, voltage controlled amplifier 23 is directly controlled by the output of comparator 20, while voltage controlled amplifier 22 is controlled via inverting circuit 21.

Each output of the voltage control amplifiers 22 and 23 is connected to an adder 13.
are inputted to , added to the output terminal 14 , and output from the output terminal 14 .

The operation of the embodiment configured as described above will be explained using an example of a signal encoded by the Dolby surround system.

The signals SL and SR encoded by the Dolby surround system are outputted as a sum signal (L+R〇) by the sum signal generation circuit 15, which is supplied to the level detection circuit 18 and the voltage control amplifier 22. . Further, the difference between the signals SL and SR is taken by the difference signal generation circuit 16 and outputted as a difference signal (L-R+28).
The signal is supplied to a delay circuit 17 and a level detection circuit 19.

The level detection circuit 18 rectifies and smoothes the sum signal and outputs a level detection output proportional to the level of the sum signal, and the level detection circuit 19 rectifies and smoothes the difference signal and outputs a level detection output proportional to the level of the difference signal. do. Level detection circuit 1
The levels of the level detection outputs from 8.19 are compared in a comparator 20.

Here, the sum signal mainly consists of left and right and center channel signals of the original sound source, and the difference signal mainly consists of the L-R signal and the surround signal. The L-R signal is normally a signal that contributes to the sense of presence in a sound field in the same way as a surround signal, and after all, the difference signal can be regarded as a surround signal. Further, the sum signal is generally a localization signal (anallancer, etc.), and when vibrated by a speaker, the sound quality differs from that of a surround signal. Therefore, in this embodiment, the level of the sum signal and the level of the difference signal are compared, and the ratio of the sum signal and the difference signal included in the output signal is changed depending on the magnitude thereof.

As a result, when the sum signal is large, an output signal is obtained in which the proportion of the sum signal is larger than the difference signal, and when the difference signal is large (
For signals in which the main signal is the cheers of the audience, etc., an output signal is obtained in which the proportion of the sum signal is smaller than that of the difference signal.

Now, if the sum signal has a higher level than the difference signal, comparator 2
Assuming that the output of 0 exhibits a logic "1'' and the amplification factor of the voltage controlled amplifier 23 is controlled to be α, the amplification factor of the voltage controlled amplifier 22 is 1-α.

The output signal from the adder 13 at this time is (1-α)
(L+R+C) +αf (1-R+28) (4) If α is a positive coefficient of 0.5 or less, the output signal will have a large proportion of the sum signal. In addition, f (L−R+28
) indicates that the difference signal is delayed.

Further, when the sum signal has a lower level than the difference signal, the output of the comparator 20 is inverted to logic "O", and the voltage control amplifier 2
The amplification factor of 2 is α, and the amplification factor of voltage control amplifier 23 is 1−α.
Switch to As a result, when the surround signal is large, the output signal has a large proportion of the difference signal. Since monaural reproduction is performed in this manner, all components of the surround system are reproduced, creating a reproduction sound field with a sufficiently spacious feeling even with monaural output. Moreover, in this embodiment, the ratio in the output signal can be changed depending on the magnitude of the surround signal and each localization signal.

Note that when the signals SL and SR are monaural signals, the amplitude level of the difference signal output from the difference signal generating circuit 16 is approximately zero. Therefore, the sum signal from the sum signal generating circuit 15 is outputted as is from the output terminal 14, so that the same effect as before can be obtained.

Further, when the signals SL and SR are stereo signals, the sum signal generation circuit 15 outputs a sum signal (L+R), and the difference signal generation circuit 16 outputs a difference signal (L-R). Difference signal (
LR) is delayed by the delay circuit 17 and is derived as a delayed output signal CH (LR). The sum signal from the sum signal generating circuit 15 and the delayed signal from the delay circuit 17 are added by the adder 13 and output from the output terminal 14. The output signal of this output terminal 14 is (L+R)+f (L-R)...(5)
becomes. Therefore, this embodiment can provide a more expansive feeling than the conventional method of monaural reproduction of a stereo signal.

FIG. 2 shows a specific example of the circuit configuration of the sum signal generating circuit 15 used in FIG.

In FIG. 2, the sum signal generation circuit 15 includes an operational amplifier (
Each resistor 15 is connected to the inverting input terminal of the operational amplifier) 151.
2. Input the signals SL and SR through 153, connect the non-inverting input terminal to ground potential, connect the resistor 154 between the inverting input terminal and the output terminal of the operational amplifier 151, and input the sum signal from the output terminal of the operational amplifier 151. I am trying to derive the following.

Such an operational amplifier circuit sets the resistance value of the resistor 152 to r
l, resistance fir2 of resistor 153, resistance value r of resistor 154
, ), the amplitude level of the output signal of the operational amplifier 151 becomes 2, and it can be seen that a sum signal is obtained.

FIG. 3 shows a specific example of the circuit configuration of the difference signal generating circuit 16 used in FIG. 1.

In FIG. 3, the difference signal generation circuit 16 includes an operational amplifier 1
A signal Sb is input to the non-inverting input terminal of the operational amplifier 61 via the resistor 162, and a resistor 163 is input to the inverting input terminal of the operational amplifier 161.
, the non-inverting input terminal is connected to the ground potential via a resistor 164, a resistor 165 is connected between the inverting input terminal and the output terminal of the operational amplifier 161, and the sum signal is input from the output terminal. I am trying to derive it.

In such an operational amplifier circuit, the resistance value of the resistor 162.163 is r tt and the resistance value of the resistor 164.165 is r 1
2, the amplitude level of the output signal is connected to the ground potential through , a resistor 175 is connected between the inverting input terminal and the output terminal of the operational amplifier 171, and a delayed signal is derived from the output terminal.

In such an operational amplifier circuit, the resistance value of the resistor 172.174 is r, the resistance value of the resistor 175 is r, and the capacitor 173 is
If the value of is C, then the amplitude level of the output signal is as follows: (7) It can be seen that a difference signal is obtained.

Note that even if a circuit configuration other than this is used, the sum signal generation circuit 1
It goes without saying that 5 can be achieved.

FIG. 4 shows a specific example of the circuit configuration of the delay circuit 17 used in FIG. 1.

In FIG. 4, the delay circuit 17 connects the differential signal generating circuit 16 to the inverting input terminal of the operational amplifier 171 via a resistor 172.
and input the difference signal from the operational amplifier 171 to the non-inverting input terminal of the operational amplifier 171 via the capacitor 173,
The non-inverting input terminal is connected to the resistor 174 by Cφ r
It becomes C.r. S is a complex variable in the transfer function.

Equation (8) above indicates that the circuit shown in FIG. 4 is a phase shift circuit in which the amplitude characteristic is constant over the entire frequency band and only the phase characteristic is a function of frequency.

Note that although the above circuit configuration shows a phase shift circuit, it goes without saying that similar effects can be obtained with a circuit that adds a certain delay to an input signal. Further, in the above circuit configuration, a − order phase shift circuit is shown, but a higher order phase shift circuit or other filter circuit may be used.

FIG. 5 shows a specific circuit configuration example of the inversion circuit 21 used in FIG. 1.

In FIG. 5, the inverting circuit 21 inputs the comparison output from the comparator 20 to the inverting input terminal of the operational amplifier 211 via the resistor 212, connects the non-inverting input terminal of the operational amplifier 211 to the ground potential, and connects the non-inverting input terminal of the operational amplifier 211 to the ground potential. Inverting input terminal
A resistor 213 is connected between the output terminals, and a sum signal is derived from the output terminals. A comparison output from the comparator 20 is supplied to an inverting input terminal of an operational amplifier 211 via a resistor 212.

Here, if the resistance value of the resistor 212 is r 31 and the resistance value of the resistor 213 is r 32, then the amplitude level of the output signal of the operational amplifier 211 is 3t (9). Here, if r32=r31, a signal obtained by inverting the comparison output is obtained.

Further, although specific circuit configurations of the level detection circuits 18 and 19, the comparator 20, and the voltage control amplifiers 22 and 23 are not listed, those having similar configurations may be used.

[Effects of the Invention] As described above, according to the present invention, it is possible to perform faithful monaural reproduction of two-channel signals related to a certain sound field to which surround signals are distributed without losing the surround components, and to output monaural signals. The effect is that you can enjoy the surround effect.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of an acoustic circuit according to the present invention, FIG. 2 is a circuit diagram showing a configuration example of a sum signal generation circuit used in the above embodiment, and FIGS. This figure is a circuit diagram showing an example of a difference signal generating circuit, a delay circuit, and an inverting circuit, and FIGS. 6 to 8 are diagrams showing conventional acoustic circuits. 13... Adder, 15... Sum signal generation circuit, 16.
...Difference signal generation circuit, 17...Delay circuit, 18.19
...Level detection circuit, 20...Comparator, 21...
Inverting circuit, 22.23...voltage control amplifier. /15 3rd plot m-" 4th figure 1 L-111111" 5th figure

Claims (1)

[Scope of Claims] A sum signal generation circuit and a difference signal generation circuit that calculate the sum and difference of two encoded signals in which a surround channel signal is distributed to each localization channel signal, and a difference signal from the difference signal generation circuit. a delay circuit that obtains a delayed signal by delaying the signal, a comparator that compares signal levels from the sum signal generation circuit and the difference signal generation circuit, and a control signal from the comparator that compares the level of the delayed signal from the delay circuit. a voltage controlled amplifier to control, a voltage controlled amplifier to control the level of the sum signal from the sum signal generation circuit with an inverted signal of the control signal from the comparator, and a monaural signal by adding the output signals from each of the voltage controlled amplifiers. An acoustic circuit comprising: an adder that outputs a signal.