JP2001245399A - Ultralow frequency sound compensation system and acoustic device using it - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve the problems that a conventional ultralow frequency sound compensation system is limited in low frequency sound reproduction quality with a small-sized speaker or the like whose low cut-off frequency is high because only a gain at a low sound frequency is amplified and causes a reproduction sound apart from the substantial ultralow frequency sound when the entire low sound frequency is uniformly amplified. SOLUTION: In the ultralow frequency sound compensation system, an LPF 13 extracts a low frequency component of a sound signal received from a sound source, a harmonic tone circuit section 14 shifts the low frequency component to a frequency band being a multiple of 2n of the original frequency band and the amplitude is increased to a multiple of 2n of the original amplitude and the resulting signal is added to the original sound signal. Furthermore, the harmonic tone circuit section 14 is a series connection circuit consisting of n-sets of analog multipliers 14a.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a technique for correcting a bass reproduction defect caused by a high cut-off frequency in a low frequency range when reproducing a sound signal using a small speaker, headphones, or the like. The present invention relates to a bass correction system capable of realizing rich bass reproduction and an acoustic device using the bass compensation system.

[0002]

2. Description of the Related Art Generally, the frequency band of an audio signal input from a sound source is wider than the frequency band that can be reproduced by a speaker. Therefore, in order to faithfully reproduce the audio signal input from the sound source, it is necessary to provide a speaker having a reproducible frequency band as wide as possible. Here, the width of the reproducible frequency band of the speaker has its own range depending on the size and structure of the speaker, but generally, as the size of the speaker becomes smaller, the lower cut-off frequency becomes lower. It tends to be high, and the reproduction characteristics in the low-tone range tend to deteriorate.

[0003] However, it is used for equipment requiring portability such as a notebook personal computer and a portable audio reproducing apparatus, a compact audio system with a concept of space saving, or a car audio system installed in a limited space such as an automobile interior. Speakers or headphones are desired to be as small and lightweight as possible due to restrictions on their installation locations. For this reason, the reproduction characteristics of the low-frequency range are inevitably sacrificed, and the user cannot be dissatisfied with the inadequate reproduction of the low-frequency range.

[0004]

As means for solving the above-mentioned problems, a bass correction system for amplifying the gain of a low frequency component is conventionally provided. FIG. 6 is a graph showing an example of a frequency-gain characteristic in the conventional bass correction system. In this graph, the horizontal axis represents frequency, and the vertical axis represents gain. The solid line 1 in the figure is a frequency band in which a small speaker can reproduce (frequency f _L to frequency f _H ).
Here, 20 Hz (f _L ) to 20 kHz are shown.
A small speaker capable of reproducing the (f _H ) audio signal is taken as an example. However, the low-frequency cutoff frequency f ₀ of this small speaker is about 100 Hz, and sufficient reproduction of low-frequency components below 100 Hz cannot be performed.

A broken line 3 in the figure shows the frequency characteristic of the gain amplification amount in the conventional bass correction system.
As shown in the figure, conventionally, the gain in the entire low frequency range such as 0 Hz to 1 kHz is uniformly amplified. In addition,
The dashed line 2 in the figure indicates a flat line of 0 dB, and it is assumed that sound exists in the natural world in the entire frequency band.

Indeed, with the above-described configuration for amplifying the gain in the low frequency range, the reproduction characteristics of the low frequency range in a small speaker or the like can be covered to some extent. However, in the case of small speaker shown in this example, even raised only gain much low frequency components, since the low frequency side cutoff frequency f ₀ is 100 Hz, to play less low frequency components Has limitations. In particular, 2
Reproduction of low frequency components of 0 Hz (F _L ) or less is impossible. However, excessive gain amplification in the low frequency range causes another problem such as sound cracking and chattering of the speaker housing, and naturally limits the amount of gain amplification in the low frequency range.

Further, as described above, in the conventional bass correction system, the gain in the entire low frequency range is uniformly amplified, so that even if the amplification degree is appropriate for a certain frequency component, it is different. In many cases, the amplification is more than necessary for the frequency component. For this reason, the user feels very noisy in the sense of hearing, and the reproduced sound is far from the original rich warm deep bass.

The present invention has been made in view of the above-described problems, and when reproducing an audio signal using a small speaker, headphones, or the like, a bass reproduction defect caused by a high cut-off frequency on a low frequency side is audibly sensed. It is an object of the present invention to provide a bass correction system capable of correcting and reproducing rich bass with little distortion.

[0009]

In order to achieve the above object, in a bass correction system according to the present invention, an extraction means for extracting a low frequency component of an audio signal input from a sound source, Means for shifting the low-frequency component extracted by the means to a frequency band of 2 ⁿ times the original, and increasing the amplitude to the original 2 ⁿ power; An adding unit for adding an output signal of the circuit unit to the audio signal.

Also, a mixing means for mixing the L channel component and the R channel component of the audio signal which is divided into two systems from the sound source and an extraction for extracting a low frequency component from the output signal of the mixing means. Means, and extracting the low-frequency component extracted by the extraction means to the original 2 ⁿ
A harmonic circuit portion composed of n analog multipliers for shifting the frequency to a frequency band of 2 times and increasing the amplitude to the original 2 ⁿ power, and outputting the output signal of the harmonic circuit portion to the L channel component and the R channel It may be configured to have an adding means for adding to the components.

In the bass correction system having the above-described configuration, a high-pass filter for removing the low frequency component from the audio signal is provided, and an output signal of the overtone circuit is added to an output signal of the high-pass filter. It is good to have composition. Further, a low-pass filter for removing unnecessary high frequency components may be provided between the overtone circuit section and the adding means.

Further, in the acoustic device according to the present invention,
The present invention is characterized in that the above-described bass correction system is used for a drive system such as a small speaker or a headphone.

[0013]

FIG. 1 is a graph showing an example of frequency-gain characteristics in a bass correction system according to the present invention. In this graph, the horizontal axis represents frequency, and the vertical axis represents gain. A solid line 1 in the figure indicates a reproducible frequency band (frequency f _L to frequency f _H ) of the small speaker, and here, 20 Hz (f _L ) to 20 kHz (f _H ).
A small speaker capable of reproducing the audio signal of FIG. However, the low-frequency cutoff frequency f ₀ of this small speaker is about 100 Hz, and sufficient reproduction of low-frequency components below 100 Hz cannot be performed. The dashed line 2 in the figure indicates a flat line of 0 dB, and it is assumed that sound exists in the natural world in the entire frequency band.

Here, in the bass correction system according to the present invention, unlike the conventional configuration in which only the gain in the low frequency range is uniformly amplified, the low frequency components of the input audio signal (A in the figure) (Region shown in FIG. 3B) is shifted to a frequency band 2 ⁿ times as large as the original, and the amplitude thereof is raised to the power of 2 ⁿ and output (region shown by B in the figure).

First, a first embodiment of the bass correction system according to the present invention will be described. FIG. 2 is a block diagram illustrating a schematic configuration of the bass correction system according to the first embodiment. Here, the case where the audio signal input from the sound source is a stereo signal having an L channel component and an R channel component will be described as an example.

As shown in FIG.
Are connected to the input terminal of the mixer 12 and the input terminal of the first adder 15 via the. The terminal b is connected to the input terminal of the mixer 12 and the input terminal of the second adder 16 via the buffer 11. An output terminal of the mixer 12 is connected to an input terminal of a low-pass filter 13 (hereinafter, referred to as an LPF 13). An output terminal of the LPF 13 has an overtone circuit section 14 composed of n (n ≧ 1) analog multipliers 14a. Is connected to the input terminal of Further, the output terminal of the overtone circuit unit 14 is connected to each input terminal of the first adder 15 and the second adder 16. The output terminal of the first adder 15 is connected to a terminal c via a buffer 17, and the output terminal of the second adder 16 is connected to a terminal d via a buffer 18. The terminals c and d are connected to a speaker (not shown).

Next, the flow of signal processing in the bass correction system having the above configuration will be described. L channel component L of the audio signal input to terminal a from the sound source
_IN is connected to the mixer 12 and the first adder 1 via the buffer 10.
5, respectively. The R channel component R _IN of the audio signal input from the sound source to the terminal b is input to the mixer 12 and the second adder 16 via the buffer 11.

The mixer 12 adds the input L-channel component L _IN and R-channel component R _IN and sends the result to the LPF 13. The LPF 13 has a predetermined cut-off frequency (here, 10 to match the low-frequency cutoff frequency f ₀ of the speaker).
0 Hz), and has a characteristic of passing only a frequency component lower than the cutoff frequency. Therefore, L
The signal output from the PF 13 to the overtone circuit section 14 is a signal obtained by extracting only the low-frequency component from the output signal of the mixer 12 (ie, the addition signal of the L channel component L _IN and the R channel component R _IN ). Becomes

The overtone circuit section 14 performs a process of shifting the output signal of the LPF 13 to a frequency band of 2 ⁿ times the original, that is, 2 ⁿ overtone conversion (also referred to as 2 ⁿ octave conversion), and also converts the amplitude to the original 2 ⁿ octave. ^The output is raised to the ^nth power. The configuration and operation of the overtone circuit section 14 will be described later in detail. The output signal of the overtone circuit section 14 is added to the original L channel component L _IN and R channel component R _IN by the first adder 15 and the second adder 16. Thereafter, the output signal of the first adder 15 is output from the terminal c to the speaker as an L channel component L _OUT ,
The output signal of the second adder 16 is output from the terminal d to the speaker as an R channel component R _OUT .

Here, the configuration and operation of the overtone circuit section 14 will be described. The overtone circuit section 14 provided in the present embodiment is a circuit in which n analog multipliers 14a are connected in series, so that an output signal of the previous-stage analog multiplier 14a becomes an input signal of the next-stage analog multiplier 14a. Make up. Note that each analog multiplier 14a does not have a special circuit configuration, and has two input signals X,
This is a very general method of outputting the product signal XY for Y. Now, for the analog multiplier 14a, exactly the same input signal X, as shown in the following equation (1),
Consider the case where Y is input. It is assumed that the input signals X and Y in the equation (1) are functions of the time t, and are sine waves oscillating at the amplitude A and the frequency f.

(Equation 1)

When such identical input signals X and Y are input to the analog multiplier 14a, the output signal XY can be expressed by the following formula (2) from the trigonometric function conversion formula.

(Equation 2)

As is apparent from the above equation (2), after dividing the input signal to the analog multiplier 14a into the same two signals X and Y, and taking the product XY of those signals, the output signal XY Is 2f, which is a value obtained by doubling the frequency f of the input signal. The amplitude of the output signal XY is a value obtained by squaring the amplitude A of the A ^2, whereby the input signal. As described above, after the input signal having a certain frequency component is divided into the same two signals, the product of those signals is obtained by the analog multiplier 14a, thereby shifting the input signal to twice the original frequency band. At the same time, it is possible to output the signal with its amplitude squared.

Therefore, the amplitude A and the frequency f are applied to the overtone circuit section 14 in which n analog multipliers 14a are connected in series.
If the input signal oscillating at is divided into two identical signals and input, the frequency of the output signal is 2 ⁿ
The value is multiplied. The amplitude of the output signal is a value obtained by raising the amplitude A of the input signal to the power of 2 ⁿ . As described above, by dividing an input signal having a certain frequency component into the same two signals and then inputting the same to the overtone circuit section 14, the input signal is shifted to the original 2 ⁿ times frequency band and the amplitude thereof is increased. Can be output as the original 2 ⁿ power.

Here, in this embodiment, the LPF 13
Is divided into the same two signals and input to the overtone circuit section 14. Therefore, the low frequency component (0 to 100 Hz) extracted by the LPF 13 is output to the overtone circuit 1
4 by 2 ⁿ times the original frequency band (0 to 100 × 2 ⁿ H
z) is ^2n- harmonic. With this, even in the case of the speaker having low bass reproduction capability, the low frequency component is shifted to a reproducible frequency band, so that the low frequency component can be reproduced with high audibility. It becomes possible.

In particular, if the number n of analog multipliers 14a constituting the overtone circuit section 14 is increased, it is possible to reproduce an extremely low frequency component exceeding the human audible limit.
Also, as can be seen from the above equation (2), if the input signal is not distorted, the output signal XY is not distorted. Therefore, by applying the overtone circuit section 14 to the bass correction system, very high quality can be obtained. It is possible to perform heavy bass correction.

Next, the gain amplification operation of the overtone circuit section 14 will be described. FIG. 3 is a graph showing input / output characteristics of the overtone circuit section 14. The horizontal axis of this graph indicates the amplitude of the input signal to the overtone circuit section 14, and the vertical axis indicates the amplitude of the output signal of the overtone circuit section 14. Here, the solid line 4 in the figure indicates the input / output characteristics of the overtone circuit section 14, and the broken line 5 indicates the input / output characteristics when the input signal is directly used as the output signal.

As described above, after dividing the input signal to the overtone circuit section 14 into the same two signals X and Y, and taking the product XY of those signals, the value obtained by raising the amplitude of the original input signal to the power of 2 ^{n is} obtained. Has the characteristic that the amplitude of the input signal is equal to the amplitude of the output signal. Therefore, a signal in which the amplitude of the input signal is greater than 1 is amplified by the overtone circuit unit 14, and conversely, a signal smaller than 1 is reduced. Therefore, by applying the overtone circuit section 14 to the bass correction system, a very sharp and sharp output signal can be obtained.

Next, a second embodiment of the bass correction system according to the present invention will be described. FIG. 4 is a block diagram illustrating a schematic configuration of the bass correction system according to the second embodiment. This embodiment is a further development of the above-described first embodiment, and includes a first adder 15 and a second adder 16.
The high-pass filters 19 and 20 (hereinafter, referred to as “below”) for removing low frequency components from the L channel component R _IN and the R channel component R _{IN of the} original audio signal input to the
HPFs 19 and 20). And HP
The output signals of F19 and F20 and the output signal of the overtone circuit section 14 are added and output to the speaker.

Each of the HPFs 19 and 20 is a mixer 1
The LPF 13 is connected in parallel to a series circuit including the LPF 13 and the overtone circuit unit 14. The input terminal of the HPF 19 is connected to the buffer 10, and the output terminal of the HPF 19 is connected to the first adder 15. On the other hand, the input terminal of the HPF 20 is connected to the buffer 11.
And the output terminal is connected to the second adder 16. Here HPF19,20 the predetermined cutoff frequency (in this case, the 100Hz in accordance with the low cut-off frequency f ₀ of the speaker) has, to pass only frequency components higher than this cutoff frequency characteristic There is. Therefore, the signals output from the HPFs 19 and 20 to the first adder 15 and the second adder 16 are converted from the original L channel component L _IN and R channel component R _IN into the overtone circuit section 14.
Is a signal from which low frequency components are removed.

With such a configuration, in the bass correction system of the present embodiment, the low frequency components originally included in the L channel component L _IN and the R channel component R _IN input from the sound source are removed. The output signal of the overtone circuit section 14 is replaced, and the resulting audio signals are output from the terminals c and d as the L channel component L _OUT and the R channel component R _OUT . Thus, the low frequency components based on the L channel component L _IN and R channel component R _IN had, since there is no such thing as a low frequency component which receives the correction by the harmonic circuit portion 14 from interfering with each other Very high quality bass reproduction can be realized.

Next, a third embodiment of the bass correction system according to the present invention will be described. FIG. 5 is a block diagram showing a schematic configuration of the bass correction system according to the third embodiment. This embodiment corresponds to the first embodiment or the second embodiment.
The overtone circuit unit 1 is a further development of the embodiment.
4, a low-pass filter 21 (hereinafter referred to as LPF 21) is provided between the first adder 15 and the second adder 16, and an input terminal of the LPF 21 is connected to the overtone circuit section 14,
The output terminal is connected to the first adder 15 and the second adder 16.

Here, the LPF 21 has a predetermined cutoff frequency (here, 200 Hz), and has a characteristic of passing only a frequency component lower than the cutoff frequency. Therefore, the first adder 15 and the second adder 15
The signal output to the adder 16 is output to the overtone circuit section 14.
Is a signal obtained by removing unnecessary frequency components higher than 200 Hz from the output signal of FIG. In this way, by removing unnecessary frequency components generated on the high frequency side by the bass correction in the overtone circuit section 14, the reproduced sound from the speaker becomes clearer, and extremely high-fidelity reproduction is performed. It is possible to do. In particular, such a configuration is effective when the number n of analog multipliers 14 constituting the overtone circuit section 14 is set to be large.

The LPF 13, HPF 19, and HPF 2 provided in the bass correction system of the embodiment described above.
0, each cut-off frequency of the LPF 21, and the overtone circuit section 14.
It is necessary to make different adjustments for each characteristic value, such as the output gain, depending on the input sound source, the frequency characteristics of small speakers and headphones, the use environment, and the like. In addition, if these characteristic values are set excessively, there is a possibility that the hearing perception of the original sound source may be impaired. For this reason, when setting the characteristic value, it is desirable to try several types of audibility and make adjustments so as to obtain a well-balanced reproduction result for all audibility.

[0034]

In the bass correction system according to the present invention, a low-frequency component of an audio signal input from a sound source is extracted, and the low-frequency component is shifted to a frequency band 2 ⁿ times the original frequency. , The amplitude of which is raised to the power of 2 ⁿ and then added to the audio signal. When the audio signal is a stereo signal having an L channel component and an R channel component, the L channel component and the R channel component of the audio signal are mixed, and a low frequency component extracted from the mixed signal is used as an original. The frequency band may be shifted to 2 ⁿ times of the frequency band, and the amplitude may be raised to the original 2 ⁿ power and added to the L channel component and the R channel component, respectively.

With such a configuration, even if the speaker has low bass reproduction capability, the low frequency component is shifted to a reproducible frequency band. Can be reproduced fairly faithfully. Further, in the bass correction system according to the present invention, since the low frequency component is corrected by the overtone circuit unit composed of n analog multipliers, if the input audio signal is not distorted, the output signal is also distorted. However, it is possible to obtain a very pure output signal. By increasing the number n of the analog multipliers, it is possible to reproduce an extremely low frequency component exceeding the human audible limit.

Also, since the overtone circuit has a characteristic that the value obtained by multiplying the amplitude of the original input signal to the power of 2 ⁿ is the amplitude of the output signal, a signal having an amplitude greater than 1 is amplified, and a signal having an amplitude smaller than 1 is amplified. Is reduced. Therefore, the bass correction system according to the present invention can perform very sharp bass correction with a sharp feeling. The middle and high frequency components other than the low frequency components are output without any correction, so that the original audibility of the middle and high frequency components is not impaired.

Further, in addition to the above configuration, a high-pass filter for removing the low frequency component from the original audio signal input from the sound source is provided, and an output signal of the overtone circuit is output from the high-pass filter. It is preferable to add a configuration to the signal. With such a configuration, the bass correction system replaces the low frequency components originally contained in the audio signal with the output signal of the overtone circuit section. Therefore, since the low frequency components of the original audio signal and the low frequency components corrected by the overtone circuit unit do not interfere with each other, very high quality bass reproduction is realized. it can.

Further, a low-pass filter for removing unnecessary high frequency components from the output signal of the overtone circuit may be provided. With such a configuration, the reproduced sound from the speaker becomes clearer, and extremely high-fidelity reproduction can be performed. In particular, such a configuration is effective when the number n of the analog multipliers constituting the overtone circuit section is set large.

As described above, by using the bass correction system according to the present invention for a drive system such as a small speaker or a headphone in an audio device, even a small speaker having low bass reproduction ability has a fairly high audibility. Since low-frequency sound reproduction can be performed, it is not necessary to increase the size of the speaker unnecessarily in order to obtain low-frequency sound reproduction capability as in the related art. Therefore, miniaturization of the acoustic device,
It is possible to contribute to weight reduction, weight reduction, and low cost.

[Brief description of the drawings]

FIG. 1 is a graph showing an example of a frequency-gain characteristic in a bass correction system according to the present invention.

FIG. 2 is a block diagram illustrating a schematic configuration of a bass correction system according to the first embodiment.

3 is a graph showing input / output characteristics of the overtone circuit section 14. FIG.

FIG. 4 is a block diagram illustrating a schematic configuration of a bass correction system according to a second embodiment.

FIG. 5 is a block diagram illustrating a schematic configuration of a bass correction system according to a third embodiment.

FIG. 6 is a graph showing an example of a frequency-gain characteristic in a conventional bass correction system.

[Explanation of symbols]

 Reference Signs List 12 mixer 13 low-pass filter 14 harmonic circuit part 14a analog multiplier 15 first adder 16 second adder

Claims (5)

[Claims] 1. An extracting means for extracting a low frequency component of an audio signal input from a sound source, and shifting the low frequency component extracted by the extracting means to a frequency band 2 ⁿ times as large as the original. A harmonic circuit comprising n analog multipliers for raising the amplitude to the original 2 ⁿ power and outputting the result; and adding means for adding an output signal of the harmonic circuit to the audio signal. Heavy bass correction system. 2. A mixing means for mixing an L channel component and an R channel component of an audio signal which is divided into two systems from a sound source, and an extraction for extracting a low frequency component from an output signal of the mixing means. means and, together to the low-frequency shift of the frequency components to the original 2 ⁿ times the frequency bands extracted by said extraction means, 2 ⁿ of the basis of the amplitude
A harmonic circuit comprising n analog multipliers for raising and outputting powers, and an adding means for adding an output signal of the harmonic circuit to the L channel component and the R channel component. Bass correction system. 3. A high-pass filter for removing the low-frequency component from the audio signal, wherein an output signal of the overtone circuit is added to an output signal of the high-pass filter. The bass correction system according to claim 1 or 2. 4. The apparatus according to claim 1, wherein said harmonic circuit section and said adding means are provided between:
4. The bass correction system according to claim 1, further comprising a low-pass filter for removing unnecessary high frequency components. 5. An acoustic device, wherein the bass correction system according to claim 1 is used for a drive system such as a small speaker or a headphone.