JP2004104296A - Surround reproducing circuit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To realize a surround effect by a single speaker. <P>SOLUTION: The surround reproducing circuit is provided with: an adder 5 for generating a difference signal between received L and R signals; a low pass filter 6 connected to an output of the adder 5; an operational amplifier 7 for amplifying an output signal of the low pass filter; and an adder 8 for mixing a signal outputted from the operational amplifier 7 with the L and R signals. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a surround reproduction circuit that can receive a two-channel stereo signal of an L signal (left signal) and an R signal (right signal) and realize a surround effect even with a single speaker.
[0002]
[Prior art]
Most of the audio frequency distribution that can be heard by humans is concentrated around 300 Hz to 3.5 KHz. Important for speech clarity is 1 KHz, the wavelength of which is about 30 cm. Therefore, if the voice arrives from the left lateral direction of the head, the right ear reaches the right ear in an opposite phase to the left ear because the right ear is about 15 cm away from the left ear. That is, when the same sound arrives from the left side and the right side, the listener feels that the sound image is in front.
[0003]
However, since the LR signal has a phase change and a difference in volume with respect to the R signal, a human locates the sound image of the LR signal to the left side within a range of 180 degrees to the left. That is, it feels like coming from the left side. Similarly, with respect to the RL signal, a human locates the sound image of the RL signal to the right side within a range of 180 degrees to the right, and feels as if coming from right next to the right side.
[0004]
On the other hand, when the sound comes from the front, the sound frequency band (300 Hz to 5 KHz) is emphasized by the earlobe and the ear hole, but when the sound comes from the side, the frequency characteristics are almost flat.
[0005]
Therefore, in order to make the sound of the LR signal coming from the front look like the sound coming from the left side, it is necessary to lower the level of the audio frequency band (300 Hz to 5 KHz) of the LR signal by a predetermined amount. Similarly, in order to make the sound of the RL signal coming from the front look like the sound coming from the right side, it is necessary to lower the level of the audio frequency band (300 Hz to 5 KHz) of the RL signal by a predetermined amount.
[0006]
Therefore, a conventional surround reproduction circuit in which one speaker is disposed on each of the left and right fronts, as shown in FIG. 5, uses an adder 23 to perform L-R conversion on stereo L and R signals input from input terminals 21 and 22. An L-side surround signal, which is a signal, is created, and the difference signal is input to the band elimination filter 24 having the frequency characteristics shown in FIG. 6 to lower the level of the audio frequency band (300 Hz to 5 KHz).
[0007]
Then, the gain of the L-side surround signal whose frequency characteristics have been adjusted in this way is further adjusted by an operational amplifier 25 and a variable gain amplifier including resistors R4 and R5, and the L signal line is directly added to the L signal line by an adder 26. The phase of the R signal line is inverted by an adder 27, converted into an R-side surround signal, added, and output to output terminals 28 and 29. Reference numerals 30, 31, 32, and 33 are buffers.
[0008]
In this way, the audio signal components that are easily recognized by the human ear and have a sense of direction are removed, and the reverberation and reflection sounds in the frequency band where the sense of direction is difficult to understand are enhanced to be mixed with the L signal and the R signal. The effect of the surround sound was realized by emphasizing the difference between the change in volume and the volume.
[0009]
FIG. 7 is a diagram showing another conventional surround reproduction circuit. Here, the LR signal generated by the adder 23 is input not to a band-elimination filter but to a low-pass filter 34 having a cutoff frequency of 900 Hz and a -6 dB / oct moderate attenuation characteristic as shown in FIG. ing.
[0010]
Since the LR and RL signal components do not contain much audio frequency components and mainly contain only high frequency components, the audio frequency components of the LR and RL signal components ( It is not necessary to greatly reduce the level of the vocal band (300 Hz to 3 KHz). Further, since the 3 KHz frequency component of the LR or RL signal includes a harsh signal component, The low-pass filter 34 is used because it is necessary to remove a signal near 1 KHz with a filter so as not to affect the signal. Also, as shown in FIG. 3, the low-pass filter 34 having a cutoff frequency of 900 Hz and a gradual attenuation characteristic of -6 dB / oct can be composed of one resistor and one capacitor as shown in FIG. There is an advantage that the number of capacitors is smaller than when a plurality of filters are used.
[0011]
Patent Documents 1 and 2 disclose, for example, Patent Documents 1 and 2 that realize a surround reproduction circuit using a plurality of speakers as described above.
[0012]
[Patent Document 1]
Japanese Patent Application Laid-Open No. 2000-102100 [Patent Document 2]
Japanese Patent No. 2947456 Specification
[Problems to be solved by the invention]
However, since the above method requires a plurality of speakers, it cannot be realized with a product that cannot be equipped with a plurality of speakers due to miniaturization or cost reduction.
[0014]
Also, when a stereo signal obtained by the above method is converted to a monaural signal for reproduction by one speaker, it is emphasized that a general method of adding the left and right signals by resistance division or the like is used. The components of the reverberation sound and reflected sound are offset on the left and right.
[0015]
SUMMARY OF THE INVENTION It is an object of the present invention to provide a surround reproduction circuit that can obtain a good surround effect even with a single speaker and that requires only a simple filter.
[0016]
[Means for Solving the Problems]
The invention according to claim 1 is a first adder that generates a difference signal between an input L signal and an R signal, a low-pass filter connected to an output side of the first adder, and an output of the low-pass filter. A surround reproduction circuit includes a second adder that mixes the signal as a surround signal with the L signal and the R signal.
[0017]
According to a second aspect of the present invention, there is provided a first adder for generating a difference signal between an input L signal and an R signal, a low-pass filter connected to an output side of the first adder, and an output of the low-pass filter. Second and third adders for mixing the L signal and the R signal in a phase relationship opposite to each other as a surround signal, and one of the input L signal and the R signal and the second and the third signals. And a fourth adder for mixing the input L signal and the output signal of the adder corresponding to the other of the R signals among the three adders. And
[0018]
According to a third aspect of the present invention, in the surround reproduction circuit according to any one of the first to second aspects, the low-pass filter has a cutoff frequency of 700 Hz to 2 kHz and an attenuation characteristic of -6 dB / oct. Surround reproduction circuit characterized by the following.
[0019]
According to a fourth aspect of the present invention, in the surround reproduction circuit according to any one of the first to third aspects, a variable gain amplifier is inserted on an output side of the low-pass filter, and an output signal of the variable gain amplifier is supplied to the second signal. A surround reproduction circuit characterized in that the signal is input to an adder of 2.
[0020]
According to a fifth aspect of the present invention, in the surround reproduction circuit according to any one of the second to third aspects, a variable gain amplifier is inserted on an output side of the low-pass filter, and an output signal of the variable gain amplifier is output to the second signal. A surround reproduction circuit characterized in that the signals are input to the second and third adders.
[0021]
BEST MODE FOR CARRYING OUT THE INVENTION
As a result of repeating the experiment of the surround effect using various music sources, the inventor has found that the signal included in the difference component between the L signal (left signal) and the R signal (right signal) of the stereo signal has a slightly high vocal. It has been confirmed that the frequency is mainly composed of the component of "scissors" and the reverberation of about 5 KHz or less.
[0022]
Generally, when a stereo signal is converted into a monaural signal for reproduction by one speaker, the L and R signal components or the RL signal component are canceled because the L signal and the R signal are mixed by resistance voltage division or the like. Is not output. In other words, the sound is perceived as having no reverberation component and having no depth.
[0023]
Therefore, an attempt was made to amplify an LR signal or an RL signal containing a large amount of reverberation components and mix it with an L + R signal to obtain an output signal containing a large amount of reverberation. In addition, in order to make the reverberation component audible from the lateral direction, the LR signal or the RL signal is input to a band elimination filter having the frequency characteristic of FIG. I tried to attenuate it by a predetermined amount.
[0024]
However, the high frequency component of about 3 KHz or more of the LR signal component or the RL signal component was perceived as harsh. In addition, since the high-frequency component has strong directivity, the sound image of the reverberation sound is localized at the center of the speaker, and the spread is not felt.
[0025]
Therefore, by inputting the LR signal or the RL signal into a low-pass filter having a cut-off frequency of 900 Hz and a gradual attenuation characteristic of -6 dB / oct as shown in FIG. Removed, so that the reverberation sound image is not localized at the center of the speaker.
[0026]
[First Embodiment]
FIG. 1 is a diagram showing a surround reproduction circuit according to a first embodiment of the present invention configured in consideration of the above points. 1 is an L signal input terminal, 2 is an R signal input terminal, 3 and 4 are buffers, 5 is an adder for generating an LR signal, 6 is a cutoff frequency of 900 Hz and a -6 dB / oct gradual attenuation characteristic. A low-pass filter, 7 is an operational amplifier constituting a variable gain amplifier together with the resistors R1 and R2, 8 is an adder, 9 is a buffer, and 10 is a signal output terminal.
[0027]
The adder 5 performs a subtraction process of the L signal and the R signal to remove a signal component for localizing the sound image at the center and extract a surround voice component. The LR signal component obtained therefrom has a frequency of 300 Hz or less. There are few low frequency components, and the main components are "scissesseso" components and reverberations at high frequencies with slight vocals.
[0028]
This signal component is input to the low-pass filter 6, and a high-frequency component exceeding 900 Hz is removed. Of the LR signal components, frequency components of 3 KHz or more include annoying signal components, which are removed by the low-pass filter 6. As shown in FIG. 2, the low-pass filter 6 has a -6 dB / oct gradual attenuation characteristic at a cut-off frequency of 900 Hz, so that a signal near 1 KHz, which is a vocal band, is not significantly affected.
[0029]
The variable gain amplifier including the operational amplifier 7 and the resistors R1 and R2 adjusts the gain of the LR signal component output from the low-pass filter 6. At this time, by changing one or both of the values of the resistors R1 and R2, the amount of addition when the LR signal component is added to the L signal and the R signal as a surround signal can be adjusted.
[0030]
As shown in FIG. 3, the low-pass filter 6 can be composed of one resistor R3 and one capacitor C1. As described above, although it can be constituted by one capacitor, its capacitance value becomes large. Therefore, when the whole is made into an IC, it is externally attached to the IC. In this case, the number of IC pins is increased by one. The low-pass filter 6 can be formed by using a low-capacity capacitor using a gm amplifier having a large output impedance. However, forming a low-pass filter by forming a capacitor inside an IC causes deterioration of S / N. The external attachment as described above is preferable because there is a possibility of the above.
[0031]
In this embodiment, as the characteristics of the low-pass filter 6, the cut-off frequency is 900 Hz and the mode has a gentle attenuation characteristic of −6 dB / oct. However, if the cut-off frequency is in the range of 700 Hz to 2 KHz, A desired surround effect can be obtained. Further, the LR signal is extracted by the adder 5, but the RL signal may be extracted.
[0032]
[Second Embodiment] The inventor of the present invention pays attention to the block configuration of another conventional surround reproduction circuit shown in FIG. 7 and compares the L-side output signal and the R-side input signal or the R-side output signal of FIG. It has been confirmed that the same function as that of the first embodiment can be obtained by adding an adder for mixing the L-side input signal.
[0033]
FIG. 4 is a diagram showing a surround reproduction circuit according to a second embodiment of the present invention configured in consideration of the above points. The same components as those of the surround reproduction circuit shown in FIG. 1 are denoted by the same reference numerals. 11, 12, and 13 are adders, and 14, 15, and 16 are buffers.
[0034]
In the present embodiment, the LR signal component output from the variable gain amplifier including the operational amplifier 7 and the resistors R1 and R2 is added to the original L signal as an L-side surround signal, and the LR signal is added to the original R signal. The signal components are inverted and added as an R-side surround signal. Further, the L-side output signal and the R-side input signal are mixed by the adder 13 and output to the signal output terminal 10.
[0035]
That is, since the L + R signal and the LR surround signal are mixed as a result, the signal output to the signal output terminal 10 in FIG. 4 is equivalent to the signal output to the signal output terminal 10 in FIG. Thus, the same surround effect as in the first embodiment can be obtained.
[0036]
Further, in this embodiment, when a conventional surround reproduction circuit using two speakers and a surround reproduction circuit using one speaker according to the present invention are constructed in one system, most of the circuits can be shared. Therefore, the circuit scale can be reduced.
[0037]
【The invention's effect】
As described above, according to the present invention, the conventional surround reproduction circuit requires a plurality of speakers in order to obtain the surround effect. However, the L + R signal and the LR signal attenuated from the middle band to the high band by the low-pass filter are required. Is added, a surround effect with a natural depth can be obtained even with one speaker.
[0038]
Further, by adding one adder to a conventional surround reproduction circuit using a plurality of speakers, it is possible to construct a system in which a good surround effect can be obtained even with one speaker.
[Brief description of the drawings]
FIG. 1 is a circuit diagram of a surround reproduction circuit according to a first embodiment.
FIG. 2 is a frequency characteristic diagram of a low-pass filter.
FIG. 3 is a circuit diagram of a low-pass filter.
FIG. 4 is a circuit diagram of a surround reproduction circuit according to a second embodiment.
FIG. 5 is a circuit diagram of a conventional surround reproduction circuit.
FIG. 6 is a frequency characteristic diagram of the band elimination filter.
FIG. 7 is a circuit diagram of another conventional surround reproduction circuit.
[Explanation of symbols]
1: L signal input terminal, 2: R signal input terminal, 3: 4: buffer, 5: adder, 6: low-pass filter, 7: operational amplifier, 8: adder, 9: buffer, 10: output terminal, 11 , 12, 13: adder, 14, 15, 16: buffer, 17: L signal output terminal, 18: R signal output terminal.

Claims (5)

A first adder for generating a difference signal between an input L signal and an R signal, a low-pass filter connected to an output side of the first adder, and an output signal of the low-pass filter as a surround signal; And a second adder for mixing with the R signal. A first adder for generating a difference signal between the input L signal and R signal, a low-pass filter connected to the output side of the first adder, and a phase-reversed output signal of the low-pass filter as a surround signal Second and third adders for mixing the L signal and the R signal in relation to each other; one of the input L signal and the R signal and the second and third adders; A surround reproduction circuit comprising: a fourth adder for mixing an input L signal and an output signal of an adder on a side corresponding to the other of the R signals. The surround reproduction circuit according to claim 1, wherein
A surround reproduction circuit, wherein the low-pass filter has a cutoff frequency of 700 Hz to 2 KHz and an attenuation characteristic of -6 dB / oct. The surround reproduction circuit according to claim 1, wherein
A surround reproduction circuit, wherein a variable gain amplifier is inserted on an output side of the low-pass filter, and an output signal of the variable gain amplifier is input to the second adder. The surround reproduction circuit according to claim 2, wherein
A surround reproduction circuit, wherein a variable gain amplifier is inserted on an output side of the low-pass filter, and an output signal of the variable gain amplifier is input to the second and third adders.

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