JP2575426Y2 - Audio signal processing circuit - Google Patents

Description

[Detailed description of the invention]

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an audio signal processing circuit, and more particularly to an audio signal processing circuit for outputting a stereo audio signal.

[0002]

2. Description of the Related Art Conventionally, there has been known an audio signal processing circuit for processing an audio signal so that a so-called surround effect is imparted to the stereo audio signal to reproduce a stereo sound field having a sense of reality.

[0003] The surround effect is obtained by adding an indirect sound signal of an audio signal to an original audio signal.
As the indirect sound signal, for example, a signal (LR) of a difference between the audio signal of the left channel and the audio signal of the right channel is generated and the phase of the signal of the difference is shifted or the signal of the difference is delayed. An audio signal processing circuit that can be easily obtained by this method and obtains a sense of expanse and a sense of realism of a stereo sound field by this method is generally known as a matrix surround circuit.

The matrix surround circuit is used in many stereo reproducing devices because its circuit configuration is simple and can be formed at low cost.

Generally, in music software such as a CD (Compact Disc), a low-frequency audio signal showing almost no directional characteristics is recorded in the same phase. For this reason, when a CD or the like is reproduced by the above-described matrix surround circuit which generates a signal (LR) of the difference between the audio signals of the left and right channels as an indirect sound signal, the left and right spread feeling is obtained, but the same phase is obtained. The recorded low frequency signal component is lost from the original audio signal.

Since the reproduction of low frequency components is extremely important in reproducing music, a predetermined frequency (for example, 10
A method of adding a low-frequency boost circuit that boosts (emphasizes) low-frequency frequencies of 0 Hz or less to a matrix surround circuit to obtain a sense of realism and compensate low-frequency characteristics.

[0007]

However, according to the above-described circuit configuration, there is a problem that the sound quality is impaired due to the characteristics of a speaker to be used in order to boost and reproduce a low frequency below a predetermined frequency.

That is, generally, the dynamic characteristic of a speaker is 10
Since it is extremely complicated at a low frequency of 0 Hz or less, boosting the low frequency signal emphasizes the peculiarities and defects of the low frequency characteristics of the speaker used. As a result, low-frequency characteristics are compensated, but high-quality sound quality cannot be obtained.

Therefore, the configuration in which a low-frequency boost circuit is added to the conventional matrix surround circuit is an inexpensive product such as a radio cassette player or a television that does not require high-quality sound quality, or an excellent low-frequency characteristic. It is used only when a good quality, large and expensive speaker is used, and has a drawback that its use is limited.

In view of the above, in the present invention, an audio signal processing circuit capable of reproducing a low frequency without deteriorating sound quality and obtaining a rich sense of realism regardless of the characteristics of a speaker used. The purpose is to provide.

[0011]

The above problem can be solved by the configuration shown in FIG.

That is, the audio signal L of the first channel
Signal generating means 1 for generating a signal φ (LR) obtained by delaying a signal of a difference between the signal and the audio signal R of the second channel by a predetermined time.
1 and the delayed difference signal φ from the signal generation means 11.
The first signal K ₁ (φ) corresponding to (LR) is added to the audio signal L of the first channel and output, and the second signal K ₁ (φ) corresponding to the delayed difference signal φ (LR) is output. The signal K ₂ (φ) of the second channel is added to the audio signal R of the second channel and output means 12 is provided.
And an adder 13 for generating a sum signal (L + R) of the audio signals L and R of the second channel and the sum signal (L + R).
R) and a subharmonic generation means 14 for generating a subharmonic component Sub (L + R) of R). The output means 12 converts the output signal Sub (L + R) of the subharmonic generation means 14 into an audio signal L of the first channel. The signal is added to the first signal K ₁ (φ) corresponding to the delayed difference signal φ (LR) and output, and the output signal Sub (L + R) of the subharmonic generation means 14 is output to the second channel. The audio signal R and the delayed difference signal φ (L−
R) and a second signal K ₂ (φ) corresponding to the sum is output.

[0013]

According to the present invention having the above configuration, the signal generating means 11 is provided.
And the output means 12, the first and second indirect sound components of the audio signal L of the first channel and the audio signal R of the second channel, that is, the first and second signals corresponding to the delayed difference signal φ (LR). Signals K ₁ (φ) and K ₂ (φ) are added and output to the original sounds L and R, respectively. Further, a monaural signal (L + R) is generated by the adding means 13, and this monaural signal (L
+ R) is a subharmonic generation means 1
4 and acts so as to be further added to the original sounds L and R.

[0014]

FIG. 2 is a block diagram of a first embodiment of the present invention. In FIG. 2, a signal generating means is constituted by the subtracting amplifier 2 and the phase shifter 4, and an output means is constituted by the inverting amplifier 6 and the mixers 7a and 7b.

An input terminal 1a receives a left channel audio signal L, which is an audio signal of a first channel, and is supplied to the subtraction amplifier 2 and the mixer 7a. Also, the input terminal 1b
Receives the right channel audio signal R, which is the audio signal of the second channel, and is supplied to the subtraction amplifier 2 and the mixer 7b.

The subtracting amplifier 2 subtracts and amplifies the audio signals L and R of both channels, and supplies the result to the phase shifter 4 as (LR). The phase shifter 4 shifts the phase of the input signal by a predetermined time and delays the input signal by φ (LR), and supplies it to the inverting amplifier 6 and the mixer 7a. The inverting amplifier 6 inverts and amplifies this to make φ (RL) and supplies it to the mixer 7b. The above is
This is a general configuration of a conventionally known matrix surround circuit.

Further, each of the audio signals L and R of both channels is inputted to an addition amplifier 3 which is an addition means, and is added and amplified, and is converted into a monaural signal (L + R) to a subharmonic generator 5 which is a subharmonic generation means. Supplied.

By the way, voices generated in the natural world generally consist of a fundamental tone and a plurality of harmonics, which are harmonic components thereof, regardless of whether it is a musical instrument or a human voice. That is, when the sound of A (the sound of "la") with the fundamental frequency f = 55 Hz is played, the fundamental tone of the frequency f is generated, and at the same time, the frequencies 2f, 3f, 4f, 5f, 6f, ... nf (n is an integer)
Generates overtones.

The subharmonic generator 5, which is a subharmonic generating means, comprises:
For example, 2f = 110 Hz out of 55 Hz harmonics (harmonics) are detected from the frequency components of the original sound, and the fundamental tone f = 55 Hz is generated, and the low frequency components of the original sound are selectively emphasized. Output.

As described above, the monaural signal (L + R) input to the subharmonic generator 5 is converted into a signal Sub (L + R) in which the low frequency component is selectively enhanced, and the mixers 7a, 7
b. Therefore, this signal Sub (L + R)
Is a subharmonic signal in which the low frequency component of the signal included in the monaural signal (L + R) that has been added and amplified is detected, emphasized, and output.

The mixer 7a mixes the left channel audio signal L, the phase-shifted difference signal φ (LR) and the subharmonic signal Sub (L + R) at a predetermined mixing ratio given by the following equation: An output signal L _OUT is output to the left channel output terminal 8a. That is, L _OUT = L + K ₁ φ (LR) + K ₃ Sub (L + R) (1) Also, the mixer 7b outputs the signal φ (RL) obtained by inverting the right channel audio signal R and the signal of the phase-shifted difference. ) and and the subharmonic signal Sub (L + R) were mixed at a predetermined mixing ratio shown in the following equation, and outputs as an output signal R _OUT to the right channel output terminal 8b. That is, R _OUT = R + K ₂ φ (RL) + K ₄ Sub (L + R) (2) where the mixing ratio K ₁ to the original voice signal L of the left channel
K ₃ is configured to be arbitrarily set by the variable resistors R _{1 and} R ₃ provided in the mixer 7a. On the other hand, the mixing ratio K _{2 and} K ₄ for the right channel original voice signal R is determined by the mixer 7b.
And it is configured so as to be arbitrarily set by the variable resistor R _2, R ₄ provided.

In each of the above equations, the third term K ₃ Sub (L +
R) and K ₄ Sub (L + R) are monaural signals (L + R)
, The output signal L of each channel
_{OUT and} R _OUT have widened low frequency characteristics.

Also, the second term K ₁ φ (LR) (ie, the first signal corresponding to the delayed difference signal) and K ₁ φ (LR)
_{2 φ} (R-L) (i.e., a second signal corresponding to the signal of the delayed difference) is a well-known indirect sound components.

By driving these speakers by amplifying these output signals, a realistic sound field can be obtained without impairing the low-frequency characteristics. In addition, the variable resistors R1 _, R
_2, the R _3, R _4, indirect sound component φ (L-R), φ (R-
L) and the subharmonic signal Sub (L + R) can be mixed with the original sound signals L and R of both channels at an appropriate ratio, so that it is possible to make fine sound of the surround system,
It can be widely used regardless of the grade of the stereo playback device.

FIGS. 3 and 4 are characteristic diagrams showing the characteristics of the first embodiment of the present invention, respectively, in comparison with the characteristics of a conventional audio signal processing circuit. FIG. 3 shows the frequency response, where Ia is the case of the first embodiment, IIa is the case of through, and IIIa is the case of only the conventional matrix surround circuit. FIG. 4 shows a frequency analysis of the sound of a specific musical instrument (in this example, a fundamental frequency of 55 Hz). Ib is the case of the first embodiment, IIb is the case of through, and IIIb is the case of only the conventional matrix surround circuit.

In FIG. 4, when the output level of 55 Hz is compared, the output level of IIIb is lower than that of IIb which is the original sound, but 2f = 110 Hz is detected for Ib, and the original tone of 55 Hz which is the fundamental sound is detected. The output level is more emphasized and compensated. Further, as a feature of the first embodiment of the present invention, it is possible to generate a deep bass even for a source in which the low frequency component is insufficient or missing in the original sound, thereby enabling powerful stereo reproduction.

In this embodiment, the monaural signal (L +
R), a subharmonic signal Sub (L + R) is generated and mixed with the original sound signal of each channel. However, since a low-frequency audio signal of 100 Hz or less hardly shows a directional characteristic, there is no problem in hearing. No. With this configuration, the low frequency band of both channels can be compensated by one subharmonic generator and one adder amplifier, and a circuit can be constructed at low cost because two subharmonic generators are not required.

FIG. 5 is a block diagram of a second embodiment of the present invention. In the first embodiment, the subharmonic signal is generated and mixed with the monaural signal (L + R) generated from the original sound signals L and R of both channels. However, in the present embodiment, the signal {L +
K ₁ φ (LR)} and {R + K ₂ φ (RL)}
Mixers 7c and 7d to generate subharmonic signals for
Are connected in series with the subharmonic generators 5a and 5b, and the subharmonic signal K ₃ Sub ｛L + K ₁ φ (L−
R) {, K ₄ Sub {R + K ₂ φ (RL)}
At e and 7f, the original sound signals L and R and the indirect sound component K ₁ φ, respectively.
(LR) and K ₂ φ (RL).

That is, in FIG. 5, the output signal of each channel is L _OUT = K ₃ Sub ｛L + K ₁ φ (LR)｝ + L + K ₁ φ (LR) (3) R _OUT = K ₄ Sub ｛R + K ₂ φ (RL)｝ + R + K ₂ φ (RL) (4) The same effects as in the first embodiment can be obtained.

According to each of the above-described embodiments, the lack of low-frequency range, which is a fundamental drawback of the matrix surround circuit, is eliminated by the subharmonic generator, and high-quality low-frequency reproduction without using the conventional low-frequency boost method. Becomes possible. Thereby, natural and rich music can be reproduced in a well-balanced manner over the entire frequency range from the deep bass range to the treble range which is extremely important for stereo sound reproduction, and the surround effect can be further enhanced.

Further, since the low frequency range of the original sound signal is expanded in a natural manner, the characteristics of the low frequency range of the speaker to be used are not selected, so that the above effect can be obtained without using an expensive speaker. Can be Therefore, since it can be used from a small speaker to a large speaker, there is a feature that it can be used not only for a television, a radio cassette player, and a car stereo but also for a wide range of uses such as a high-end audio product.

In the above embodiment, the variable resistors R _1, R
_2, R _{3 and} R ₄ are provided to vary the mixing ratio of the indirect sound component and the subharmonic component to the original sound. However, even if these mixing ratios are fixed to the optimal values set for the sound field, I do not care.

[0033]

According to the present invention, as described above, since the indirect sound component and the low harmonic component are mixed and output to the audio signals of the first and second channels, the sound quality in the low frequency range is impaired. Low-frequency characteristics can be compensated for, and high-quality stereo reproduction with rich presence over a wide band can be performed.

[Brief description of the drawings]

FIG. 1 is a block diagram of the principle of the present invention.

FIG. 2 is a block diagram of a first embodiment of the present invention.

FIG. 3 is a characteristic diagram showing the frequency response of the conventional audio signal processing circuit and the first embodiment of the present invention.

FIG. 4 is a characteristic diagram of a conventional audio signal processing circuit and a frequency analysis of a reproduced signal of the first embodiment of the present invention.

FIG. 5 is a block diagram of a second embodiment of the present invention.

[Explanation of symbols]

2 subtraction amplifier (signal generation means) 3 addition amplifier (addition means) 4 phase shifter (signal generation means) 5, 5a, 5b low harmonic generator (low harmonic generation means) 6 inverting amplifier (output means) 7a, 7b, 7c, 7d, 7e, 7f Mixer (output means) 11 Signal generation means 12 Output means 13 Addition means 14 Subharmonic generation means

Claims (1)

(57) [Scope of request for utility model registration] 1. A signal generating means for generating a signal obtained by delaying a signal of a difference between an audio signal of a first channel and an audio signal of a second channel by a predetermined time, and a signal having a delayed difference from the signal generating means. The first according to the signal
Output means for adding and outputting the signal of the first channel and the audio signal of the first channel, and adding and outputting a second signal corresponding to the delayed difference signal with the audio signal of the second channel. An audio signal processing circuit comprising: an adding unit that generates a sum signal of the audio signals of the first and second channels; and a subharmonic generation unit that generates a subharmonic component of the sum signal. The output unit adds the output signal of the subharmonic generation unit to a first signal corresponding to the audio signal of the first channel and the delayed difference signal, and outputs the sum. An audio signal processing circuit configured to add and output an output signal of a generation unit with an audio signal of the second channel and a second signal corresponding to the delayed difference signal.