JPH0414920A - Sound signal processing circuit - Google Patents

Abstract

PURPOSE:To realize a 2-channel stereo signal without a sense of disorder by adding a front middle sound signal in (3-1)4-channel stereo signal to left/right sound signals in phase and adding a rear sound signal to the left/right sound signals in opposite phase. CONSTITUTION:A front left signal in (3-1)4-channel stereo signals is outputted to an output terminal A from a sound signal demodulation circuit 14, a front right signal is outputted to an output terminal B, a front middle signal is outputted to an output terminal C and a rear signal is outputted to an output terminal D. The signals are inputted to a mixture circuit 15, where they are mixed at a prescribed rate, the front middle sound signal is added respectively in phase to the front left sound signal and the front right sound signal, and the rear sound signal is added respectively in opposite phase to the front left sound signal and the front right sound signal. Thus, the rear sound signal has a sound image having a sense of spread and the front middle sound signal is a sound image located in the middle thereby obtaining a 2-channel stereo signal without a sense of disorder.

Description

[Detailed Description of the Invention] [Object of the Invention] (Industrial Application Field) The present invention relates to an audio signal processing circuit that is effective when converting a high-definition television signal so that it can be played back on a conventional television receiver. .

(Prior Art) Recently, a high-definition television system has been developed that has a different aspect ratio from the current television system and a significantly larger number of scanning lines than the current system. The aspect ratio is 16 compared to the current NTSC system, which is 4=3.
．． 9, the reproduced video is on a horizontally long screen, and the visual sense of presence is enhanced.

Stereo systems are being researched to enhance the sense of presence of audio signals for such screens. For example, 1986
In 2010, Kengo Ogushi and others gave a presentation at the National Conference of the Television Society entitled ``Study of audio formats suitable for high-definition.''
Published by name.

According to this result, in addition to the conventional stereo system, a 4-channel stereo system with speakers placed in the front center and rear (3-1.) is considered to be appropriate.

The above-mentioned high-definition broadcasting is not yet widespread at present, and it may take some time before it becomes widespread. In addition, a dedicated receiver is required to receive and play back the NoVision system signal, and this receiver performs signal processing that is completely different from current television receivers. There is no compatibility with

Therefore, a conversion device has been developed that receives a high-definition broadcast signal and converts it into a current television system signal so that it can be played back even on current television receivers.

When considering audio signals here, current television receivers and stereo playback devices mainly use a 2-channel stereo playback system using left and right speakers, and are compatible with high-definition (3-), 4-channel stereo playback systems. I can't do it.

Furthermore, when converting a high-definition signal into an NTSC signal and recording it on a video tape recorder (hereinafter referred to as VTR), since the audio is stereo, it is only possible to record audio from the front center and the rear.

(Problem to be Solved by the Invention) Even if it is possible to convert a high-definition system signal into a current television system signal, there is a problem in that current stereo system devices cannot handle audio signals. Furthermore, there is a problem in that current equipment cannot handle the recording of the audio signal on a VTR or audio tape recorder.

Therefore, an object of the present invention is to provide (3-1) an audio signal processing circuit that converts an audio signal transmitted using a 4-channel stereo system into a signal suitable for recording and playing back using the current stereo system. .

[Structure of the Invention] (Means for Solving the Problems) This invention provides a method in which a front left audio signal, a front left audio signal, a front center audio signal, and a rear audio signal are input, and the front left audio signal and the right audio signal are means for adding the front center audio signal in the same phase to each of the front left audio signals and the right audio signal, and adding the rear audio signal to the front left audio signal and the right audio signal so that they are in opposite phase to each other. It is.

(Function) When the left channel audio signal and the right channel audio signal are reproduced by the above means, the rear audio signal becomes a spacious sound image, and the front center audio signal becomes a sound image localized in the center of the left and right, so that there is no sense of discomfort. It is possible to obtain a 2-channel stereo signal.

(Example) Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows an embodiment of the present invention. The input terminal 11 has a MUSE (Multiple Sub-Ny
An FM signal of the FM signal is supplied to the tuner 2 and is guided to the tuner 2. A demodulated MUSE baseband signal is obtained from the tuner 12.

This MUSE head signal is transmitted to the video signal processing circuit 1.
3 and is also input to the audio signal demodulation circuit 14.

The video signal processing circuit 13 performs time axis conversion, scanning line number conversion, and aspect ratio conversion processing to create a video signal compatible with the current NTSC system and outputs it to the output terminal 16.

Further, the color signal is subjected to time axis expansion (TCI encoding) processing.

Audio signal demodulation circuit] 4 separates and demodulates audio signals (3-1,) and demodulates a 4-channel stereo signal.

(3-1,) Among the 4-channel stereo signals, the front left signal is output to output terminal A, the front center signal is output to output terminal B, the front center signal is output to output terminal C, and the rear signal is output to output terminal B. is output to the output terminal.

These signals are input to a mixing circuit] 5 and mixed at a predetermined ratio, and the front left audio signal output terminal A1, the front right audio signal output terminal B1, the front center audio signal are output to the output terminal C1, and the rear audio signal is output to the output terminal C1. The signal is output to the rear audio signal output terminal D].

FIG. 2 shows a specific example of the configuration of the mixing circuit 15. The front left audio signal from terminal A] is supplied to the negative input terminal of operational amplifier 21 via resistor 20 . The front center audio signal from the terminal C1 can also be input to this negative input terminal via the resistor 22 and the switch S1. Furthermore, the rear audio signal from the terminal D1 can also be input to this negative input terminal via the resistor 23 and the switch S2.

Switch S1 has input terminal X1, output terminal Y1, and Z
The output terminal Y1 is connected to the negative input terminal of the operational amplifier 21, and the output terminal Z1 is grounded. The switch S2 has an input terminal X2, an output terminal Y2, and a Z2, the output terminal Y2 is connected to the negative input terminal of the operational amplifier 21, and the output terminal Z2 is grounded.

Further, the output terminal of the operational amplifier 21 is connected to the negative input terminal via a feedback resistor 24, further connected to the input terminal X of the switch S1 via a feedback resistor 25, and further connected to the switch S1 via a feedback resistor 26. It is connected to input terminal X2 of S2.

The positive input terminal of the operational amplifier 21 is grounded, and the output is led out to the output terminal 27.

Terminal B1, where the front right audio signal appears, is connected to the negative input terminal of operational amplifier 31 via resistor 30. The negative input terminal of this operational amplifier 31 is also connected to the output terminal Y of the switch S3.
3. Output terminal Y4 of switch S4 is connected. Output terminal Z3 of switch S3, output terminal Z of switch S4
4 is grounded. and input terminal X of switch S3
3 is supplied with the front center audio signal from the terminal C1 via the resistor 32, and the output from the amplifier 45 for amplifying the rear audio signal is supplied to the input terminal of the switch S4. A feedback resistor is also connected to the operational amplifier 31, and the output terminal 3
A resistor 34 is connected between the output terminal 7 and the negative input terminal, a resistor 35 is connected between the output terminal 37 and the input terminal X3 of the switch S3, and a resistor 36 is connected between the output terminal 37 and the input terminal X4 of the switch S4.

The front center audio signal at the terminal C1 is further supplied to the negative input terminal of the operational amplifier 4 via a resistor 42. The positive input terminal of this operational amplifier 41 is grounded, and a resistor 43 is connected between the output terminal 44 and the negative input terminal.

The rear audio signal at terminal D1 is connected to the negative input terminal of operational amplifier 45 via resistor 46, and the positive input terminal of operational amplifier 45 is grounded. A resistor 47 is connected between the output terminal 44 and the negative input terminal.

In the mixing circuit 15 described above, (3-1) the 4-channel stereo signal is directly output to the terminal 27.37.44.4.
8, switch S1, S2, S3, S
4 are switched to the output terminals Z1, Z2, Z3, and Z4, respectively. As a result, the front left audio signal, front right audio signal, front center audio signal, and rear audio signal are outputted to the output terminals 27, 37, and 4 through operational amplifier circuits with similar gains, respectively.
4.48. The operational amplifiers 41.45 are for performing phase matching with the signal output from the operational amplifier 21.3.

Next, when converting to a conventional stereo signal, switches S1, S2, S3, and S4 are output terminals Y1 and Y, respectively.
It can be switched to the 2, Y3, and Y4 sides.

Feedback resistors 25, 26, 35, 35 are switches S1 to S4
It is set so that the voltage at the audio output terminal does not change even if the audio output terminal is switched.

Then, the front left audio signal, the front center audio signal, and the rear audio signal (in positive phase) are input to the operational amplifier 21. Further, the operational amplifier 31 receives a front left audio signal, a front center audio signal, and a rear audio signal (reverse phase).

Regarding the phase of the rear audio signals appearing at the output terminals 27 and 37, the rear audio signal from the terminal D] is input to the operational amplifier 21, and the rear audio signal from the operational amplifier 45 is input to the operational amplifier 3. ing. Therefore, the output terminal 27
The rear audio signals appearing at and 37 are in opposite phase to each other.

Now, the amplitude of the front left audio signal of terminal A1 is L, the amplitude of the front right audio signal of terminal B is R, the amplitude of the front center audio signal of terminal C is C, and the amplitude of the rear audio signal of terminal D1 is S.

Then, the signal L'R' appearing at terminals 27 and 37 is L'-k. (k+ ・L+k 2 ・C+ 3 ・S)R'-k. (k+ ・2 for R+
・ C- becomes 3 ・ S). ko Sk+ k
2, k3 are operational amplifiers 21.31.41.4, respectively
This is a constant determined by the input combined resistance of 4 and the feedback resistance.

As can be seen from the above equation, the center audio signal C is in the same phase as the combined left and right signals L'R', and the rear audio signals are combined in opposite phase and reproduced by the front speakers. become.

Therefore, the sound image of the central audio signal C is localized at the front center.

Further, the rear audio signal S is localized with a left and right spread.

In general, since the rear audio signal is mainly a surround component consisting of reverberation components, the reproduced sound will be more natural if left and right spread. Either the phase of the entire audio signal is inverted by the mixing circuit 15, or the absolute phase of the sound pressure is not detected by the human ear. If the relative phase relationship of each audio signal is maintained, there will be no particular problem in reproduction.

The invention is not limited to the above embodiments.

FIG. 3 shows another embodiment of the invention.

The same parts as in FIG. 1 are given the same reference numerals. The front left audio signal, front right audio signal, front center audio signal, and rear audio signal output from the audio signal demodulation circuit 14 are respectively led out to output terminals A3, B3, C3, and D3, and are input to the mixing circuit 50. be done. (3-1) When using 4-channel stereo signals, terminals A3, B3, and C
3, the signal D3 is used.

When used as a normal stereo signal, the audio signals at the output terminals 51 and 52 of the mixing circuit 50 are used. The mixing circuit 50 converts a (3i, .) 4-channel stereo signal into a normal 2-channel stereo signal, and is specifically constructed as shown in FIG. 4.

A front left audio signal is supplied to input terminal A53, a front right audio signal is supplied to input terminal 85B, a front center audio signal is supplied to input terminal C53, and a rear audio signal is supplied to input terminal D53.

Input terminal A53 is grounded via resistor R1 and connected to the base of transistor Q1. The collector of the transistor Q1 is connected to the positive power supply line +Vcc, and the emitter is connected to the negative power supply line -VEH via a resistor R2. Further, this emitter is connected to the base of a transistor Q5 via a capacitor C1 and a resistor R3.

Input terminal 85B is grounded via resistor RIO and connected to the base of transistor Q2. The collector of this transistor Q2 is connected to a positive power supply line, and the emitter is connected to a negative power supply line via a resistor R11. Further, this emitter is connected to the base of a transistor Q6 via a capacitor C2 and a resistor R12.

Input terminal C53 is grounded via resistor R18 and connected to the base of transistor Q3. The collector of transistor Q3 is connected to the positive power supply line and to the negative power supply line via resistor R19. . Further, this emitter is connected to the base of a transistor Q5 via a capacitor C3 and then a resistor R4, and to the base of a transistor Q6 via a resistor R13.

Input terminal D53 is grounded via resistor R20 and connected to the base of transistor Q4. The collector of this transistor Q4 is connected to the positive power supply line via a resistor R21, and the collector is connected to the negative power supply line via a resistor R22.

In addition, the collector of transistor Q4 is connected to capacitor C4.
, is connected to the base of transistor Q6 via resistor R14, and its emitter is connected to the base of transistor Q5 via resistor R5.

Looking at the base input of transistor Q5, the front left audio signal, front center audio signal, and rear signal are input, and looking at the base input of transistor Q6, the front left audio signal, front center audio signal, and rear signal are input. An audio signal will be input. However, for the rear audio signal, the transistors Q5 and Q6 have opposite phases.

The base of the transistor Q5 is grounded through a resistor R6, the collector is connected to a positive power supply line, and the emitter is connected to a negative power supply line through a resistor R7. Further, this emitter is connected to the output terminal 51 through a capacitor C5 and then to ground through a resistor R8. The base of the transistor Q6 is grounded through a resistor R15, the collector is connected to a positive power supply line, and the emitter is connected to a negative power supply line through a resistor R16. Further, this emitter is connected to the output terminal 52 through a capacitor C6 and then to ground through a resistor R17.

The above mixing circuit 50 is also the previous mixing circuit 15 or the switch S1.
The same operation as when ~S4 is switched to terminals Y1, Y2, Y3, and Y4 can be obtained.

For example, the signals L'R' at the output terminals 51 and 52 are expressed as follows.

L゛-(1/2.4)(L+0.7C+0.758)R
゛-(1/2.4)(R+0.7C-0,75S) When this signal is recorded and played back with a video signal on a VTR, for example, and the sum and difference of the left and right audio signals are taken, L"+R"- (1/2.4) (L+R+1.4C)L
゛-R''-(1/2.4)(L-R+1.4S).

Therefore, by recording the converted audio signal as described above on a VTR,
By reproducing and taking the sum and difference, the front central audio signal can be extracted by addition, and the rear audio signal can be extracted from the incomplete rear audio signal by subtraction. Of course, if LR- is used as it is, it can be used as a front left audio signal or a front right audio signal. In addition, when obtaining a front center audio signal and a rear audio signal, addition and subtraction processing can be performed to extract the center audio signal and rear audio signal.

As explained above, (,3-1) Of the 4-channel stereo signal, the front center audio signal is added to the left and right audio signals in the same phase, and the rear audio signal is added to the left and right audio signals in reverse phase. It is possible to obtain a converted signal that is the same as a two-channel stereo signal and has no information loss. In addition, the sound reproduced by this means that the sound image is in the same position and there is no sense of discomfort.

Furthermore, when the above two-channel stereo signal is recorded and played back on a VTR, if a signal is created by adding and subtracting the left and right signals, the front center audio signal and the rear audio signal can be separated and reproduced. (31) It also has the advantage of being able to restore a signal close to a 4-channel stereo signal.

[Effects of the Invention] As described above, according to the present invention, an audio signal transmitted in the (3-1,) 4-channel stereo system can be converted into a signal suitable for recording and reproducing in the current stereo system. I can do it.

[Brief explanation of drawings]

FIG. 1 is a configuration explanatory diagram showing one embodiment of this invention, FIG. 2 is a circuit diagram showing a specific example of the mixing circuit of FIG. 1, and FIG. 3 is a configuration explanatory diagram showing another embodiment of this invention. , FIG. 4 is a circuit diagram showing a specific example of the mixing circuit of FIG. 3. ] 2... Tuner, 13... Video signal processing circuit, 1
4... Audio signal demodulation circuit, 15.50... Mixing circuit. Applicant's agent Patent attorney Takehiko Suzue

Claims (2)

[Claims] (1) A front left audio signal, a front right audio signal, a front center audio signal, and a rear audio signal are input, and the front center audio signal is added in phase to the front left audio signal and the right audio signal, respectively; Further, the present invention is characterized by comprising means for adding the rear audio signal to the front left audio signal and the right audio signal respectively so as to have opposite phases to each other to obtain a left channel audio signal and a right channel audio signal. audio signal processing circuit. (2) The audio signal processing circuit according to claim 1, further comprising means for obtaining an addition output and a subtraction output of the left channel audio signal and the right channel audio signal.