JPH03266598A - Acoustic circuit - Google Patents

Abstract

PURPOSE:To faithfully reproduce a surround signal by providing a sum signal generating circuit and a difference signal generating circuit which take the sum and the difference between two encoded signals respectively and delaying the difference signal from the difference signal generating circuit to obtain a delay signal and adding the delay signal and the sum signal from the sum signal generating circuit to obtain a monaural signal. CONSTITUTION:Signals SL and SR of two channels are inputted to a sum signal generating circuit 15 and a difference signal generating circuit 16 through input terminals 11 and 12. The difference signal generating circuit 16 outputs the difference between signals SL and SR, and the difference signal from the circuit 16 is delayed by a delay circuit 17. The sum signal from the sum signal generating circuit 15 and the difference signal delayed by the delay circuit 17 are added by an adder 13, and the result is led out of an output terminal 14 as the monaural signal. The monaural output obtained in this manner includes all channel components where the surround signal is added to signals from each orientation, and the faithful monaural signal is reproduced.

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 audio recorded on the soundtrack is to be played back, a dedicated decoder is used to restore it to four channels.

A stereo signal encoded into two channels by this Dolby surround system has the left, right and center channel signals of the original signal, respectively, and if the surround signal behind R and C1 is S, then the L channel signal = L + S +
CO...(1) R channel signal = R-8+Go
...(2) Here, Co=C/2
...(3).

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

By the way, when a stereo signal to which such a surround signal is distributed is to be reproduced in monaural, conventionally, as shown in FIG. It was.

FIG. 5 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. 5, SL and SR each include a surround signal or represent an R channel signal, and these signals SL.

The SR is inputted to an adder 13 via input terminals 11 and 12, added together by the adder 13, and outputted from an output terminal 14.

In addition, each circuit shown in FIG. 6 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 using the circuit shown in FIG.
It becomes L+R+C. Therefore, the S channel signal component is canceled out.

Further, in the circuit of FIG. 6 or 7, only one channel component (L+S+CO 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 Problem 1) In order to achieve the above object, a sum signal is generated by taking the sum and difference of two encoded signals in which a surround channel signal is distributed to each localization channel signal. 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 delay circuit that adds the sum signal from the sum signal generation circuit and the delay signal from the delay circuit. and an adder that outputs a monaural signal.

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

(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, respectively. The sum signal generation circuit 15 generates a signal SL
, SR. Difference signal generation circuit 16
is a circuit that outputs the difference between signals SL and SR. The difference signal from the difference signal generation circuit 16 is delayed by the delay circuit 17. The sum signal from the sum signal generation circuit 15 and the delay circuit 1
The difference signal delayed in step 7 is added in an adder 13.

The signal added by the adder 13 is derived from the output terminal 14 as a monaural signal.

The operation of the embodiment configured in this way will be explained.

Signals SL and SR applied to input terminals 11 and 12 are added in a sum signal generating circuit 15, and output as a sum signal of (L+R+C) in the case of the Dolby surround system, for example. On the other hand, each of the above signals SL.

The difference of SR is taken in the difference signal generation circuit 16, and (L
-R+28). This difference signal (LR+
25) is delayed by the delay circuit 17 and then added to the sum signal (L+R+C) from the sum signal generating circuit 15. The signal output from this adder 13 is (L+R+C) ten (L-R+28)...(4)
It can be expressed as Note that chi (LR+28) indicates that the difference signal is delayed. Since monaural reproduction is performed in this manner, all components of the Dolby surround system are reproduced, and a reproduction sound field having a sufficient sense of spaciousness (surround effect) is formed even with monaural output.

Furthermore, when the signals SL and SR are monaural signals, the amplitude level of the difference signal from the difference signal generation circuit 16 is approximately zero. Therefore, the sum signal from the sum signal generation 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 (LR). In this case, the output signal from the output terminal 14 is (L+R)+f (L-R)
...(5). Such an output signal can provide a more spacious 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 the ground point, 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 value r2 of resistor 153, resistance value rO of resistor 154
Then, the amplitude level of the output signal becomes, 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 161 through the resistor 162, and a resistor 163 is input to the inverting input terminal of the operational amplifier 1610.
, 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.

Such an operational amplifier circuit has resistors 162. The resistance value of resistor 163 is r tt, and the resistance value of resistor 164.165 is "1".
2, the amplitude level of the output signal is as follows: (7) It can be seen that a difference signal is obtained.

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 ground potential via a resistor 174, 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
When the value of is C, the amplitude level of the output signal is as follows. Note that 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 − order phase shift circuit or other filter circuit may also be used.

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

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of the acoustic circuit according to the present invention, FIG. 2 is a circuit diagram showing an example of the configuration of the sum signal generation circuit used in the above embodiment, and FIGS. 3 and 4 are the same. A circuit diagram showing an example of a difference signal generation circuit and a delay circuit, and FIGS. 5 to 7 are circuit diagrams showing conventional acoustic circuits. 13... Adder, 15... Sum signal generation circuit, 16.
...Difference signal generation circuit, 17...Delay circuit. Figure 4 Figure 5 Figure 5RO
-1 → Figure 6 Figure 7

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. and an adder that adds the sum signal from the sum signal generation circuit and the delay signal from the delay circuit to output a monaural signal. acoustic circuit.