JPH04124906A - Graphic equalizer - Google Patents

Abstract

PURPOSE:To easily adjust the output level of a higher harmonic wave by setting each center frequency of plural band pass filters to constitute an equalizer in regular intervals successively from frequency to be an object, in addition, setting it so that Q value is made larger in proportion as the frequency becomes higher. CONSTITUTION:A graphic equalizer is provided with plural band pass filters with frequency characteristics expressed by the center frequency and the Q value of a degree of sharpness and plural output level changing means for changing the output level of each band pass filter. Each center frequency of these plural band pass filters is set so that it becomes the integral multiple of predetermined reference frequency and the difference of the adjacent center frequencies becomes equal, and besides, each Q value is set so that it becomes larger in proportion as the frequency becomes higher. For instance, the center frequencies are set at 1kHz, 2kHz, 3kHz, 4kHz, 5kHz, 6kHz, 7kHz, and the graphic equalizer is realized by connecting seven pieces of digital filters F1 to F7 with Q values 2, 4, 6, 8, 10, 12, 14 respectively.

Description

[Detailed Description of the Invention] [Overview] In a typical graphic equalizer, the center frequency of each bandpass filter is called an octave band, and the center frequency is set to increase twice in sequence. The Q value corresponding to the half-value width for the gain at the center frequency of each bandpass filter is constant. However, when trying to adjust the output level of a specific order harmonic among harmonics of a certain frequency for purposes such as audio system analysis, as the order increases, it becomes difficult to adjust only the specific harmonic. Therefore, by setting the center frequencies of the bandpass filter at equal intervals starting from the target frequency, and setting the Q value to increase as the frequency increases, it is easy to adjust the harmonic output level. Make it.

[Industrial application field]

The present invention relates to a graphic equalizer that facilitates adjustment of the output level of harmonic components, and more particularly to a graphic equalizer used when investigating the influence of harmonics in measurements, experiments, etc.

[Conventional technology]

Audio systems use graphic equalizers that can adjust the output level of the input signal in multiple bands so that the operator can obtain the desired frequency characteristics depending on the characteristics of the audio system itself and the type of music. ing. FIG. 5 is a diagram showing an example of a graphic equalizer in an audio system. Elements that perform the same functions throughout the drawings are designated by the same reference numerals and are represented by lowercase letters of the alphabet that differ from drawing to drawing. The graphic equalizer shown in FIG. 5 is a graphic equalizer composed of digital filters, and in the case of an analog signal source IC, it graphically adjusts the frequency characteristics of the signal digitally converted by the A/D converter 3C. Use equalizer 4C. In the case of a digital signal source 2c such as a CD, use the graphic equalizer 4 as is.
It becomes the input signal of c.

Since the graphic equalizer adjusts the frequency characteristics of an input signal, it divides the frequency range of the input signal into a plurality of bands, and includes a filter whose output level corresponding to each band can be adjusted.

The input signal is output after its output level is adjusted for each band by each filter. FIG. 6 shows an example of frequency characteristics of a plurality of bandpass filters constituting a graphic equalizer. In the example shown in FIG. 6, there are seven bandpass filters, and the gain is 8 dB and -8 dB. The frequency characteristics of each bandpass filter are the center frequency indicating the center of the band, and the Q
Indicated by value.

The Q value is the reciprocal of the ratio between the frequency difference between two points and the center frequency, which results in a gain that is 3 dB smaller than the gain at the center frequency when the bandpass filter exhibits a positive gain, and the larger the Q value, the better the frequency characteristics. becomes sharp. When the gain is negative, that is, attenuated, it is zero (it can be considered as being symmetrical with respect to the IBO line).

The Q value is originally defined by a resonant circuit consisting of a capacitor, Koinope, and a resistor, but even after digital filters have come to be used as bandpass filters in recent years, it still shows the characteristics of bandpass filters. is used as a value for In Figure 6, the Q value of each band filter is
All are 2.

As shown in FIG. 6, each bandpass filter is set to a value called an octave band in which the center frequency sequentially increases twice so as to cover the frequency range of the input signal. In Figure 6, 125Hz, 250Hz, and 500Hz.

1 kHz, 2 kHz, 4 kHz, 8
kHz is the center frequency of each bandpass filter. The reason why the center frequency is set in this manner is that such a setting matches human auditory sense.

The larger the Q value, the sharper the frequency characteristics of the filter, which is advantageous for adjusting only the center of the band, but conversely there is the problem that sufficient adjustment becomes impossible at the periphery of the band. get up. Therefore, an appropriate value is set in consideration of the number of bandpass filters, etc., but generally each filter has the same Q value.

[Problem to be solved by the invention]

In an equalizer used to adjust the auditory sensation of music, etc., it is desirable that the center frequency of each band filter be set to an octave band as described above. However, in the development of audio systems, equalizers are sometimes used to examine the influence of specific frequencies on the sense of hearing. For example, when examining auditory sensation by emphasizing or attenuating a specific frequency portion, it is necessary to examine not only the specific frequency but also the influence of its harmonics. In other words, 3 times the 1 kHz part
This is a case where it is necessary to change the output level around 1 kHz and also change the output level around 3 kHz in order to investigate the influence of harmonics and a measure of improvement in a system that generates a large amount of kHz harmonics.

However, when the center frequency of each band filter is set to be an octave band as shown in Fig. 6, the 1 kHz adjustment can be easily made by adjusting the fourth band filter, but the 3 kHz part cannot be adjusted. Adjustment must be performed with bandpass filters with adjacent center frequencies of 2 kHz and 4 kHz.

However, this makes it impossible to adjust only the 3kHz part, and if you try to adjust the 3kHz part, the adjacent 2kHz
The output levels of the z and 4 kHz portions will also change significantly. This is true no matter how the Q value is set.

Furthermore, even if the setting of the center frequency is changed, as long as the center frequency of each bandpass filter is set to an octave band, there will always be a frequency portion of the harmonics that cannot be adjusted.

Of course, detailed adjustments can be made using an equalizer called a parametric equalizer, which allows the center frequency and Q value to be set individually, but this type of equalizer has the problem of being not only expensive but also difficult to operate. .

The present invention was made in view of the above 8 problems,
The purpose of the present invention is to provide a graphic equalizer suitable for examining the influence of frequency on auditory sensation with a simple configuration.

[Means to solve the problem]

In order to solve the above problem, in the graphic equalizer of the present invention, the center frequency of the bandpass filter is set not in an octave band, but in order from a predetermined specific frequency f, f, 2f, 3f, etc. setting and change the Q value according to the center frequency. That is, the graphic equalizer of the present invention includes a plurality of bandpass filters having frequency characteristics represented by a center frequency and a Q value, which is a sharpness, and a method for adjusting the output level of each bandpass filter for a human signal corresponding to each of the plurality of bandpass filters. This graphic equalizer is equipped with a plurality of output level variable means for changing the output level, and by operating these output level variable means, it is possible to change the frequency characteristics with respect to the human input signal. Each center frequency is set with respect to a predetermined reference frequency so that the difference between adjacent center frequencies is equal at an integer multiple of this frequency, and the Q value of each of these bandpass filters is determined by the frequency It is characterized by being set to increase in size as the size increases.

[For production]

The operation of the graphic equalizer of the present invention will be explained based on examples of frequency characteristics of bandpass filters shown in FIGS. 1A and 1B. In this example, the graphic equalizer is 7
Each bandpass filter has frequency characteristics shown in FIGS. 1A and 1B, respectively. 1st A
The figure shows a logarithmic representation of the frequency on the horizontal axis, and Figure 1B shows a linear representation of the frequency on the horizontal axis, both of which show the frequency characteristics when the gain of each band filter is 8clB and -8dB. There is. Ode the gain of each band filter
Then, the input signal becomes the output signal as it is, and if the gain is positive, the output level of that part will be increased and emphasized, and if the gain is negative, the output level will be decreased. As is clear from FIG. 1A, in this case, the output level cannot be adjusted near 100 Hz or above 10 k)Iz, but the input level of the output is maintained as it is.

As is clear from FIG. 1B, the center frequencies of the bandpass filters are set at constant intervals from l kHz, such as l kHz, 2 kHz, -, 7 kHz.

This is because the target reference frequency is set to 1k)lz, and if the target reference frequency is changed, the result will naturally be different. Q value is 2.4, 6, 8, 10.12 in order.
- It is set to increase proportionally as the center frequency increases, such as 14.

As a result, as shown in FIG. 1B, when the frequency on the horizontal axis is linear, the frequency characteristics of each filter have the same half-width and are similar.

The target standard frequency is 1 kHz, and the first thing to do is to be able to individually adjust the output levels of its harmonics, 2 kHz, 3 kHz, ...
This is clear from Figure B. If the center frequency is equidistant from 1 kHz and the Q value of each filter is all 2, as the center frequency increases, the overlap with adjacent filters will increase, as shown in Figure 1C. It can be seen that it becomes impossible to adjust the output level of only a particular frequency section without affecting the adjacent sections.

As described above, according to the graphic equalizer of the present invention, a specific frequency portion and its harmonics can be individually adjusted without affecting others.

〔Example〕

Although the graphic equalizer based on the present invention can be implemented with an analog filter, it is suitable to implement it with a digital filter using a digital signal processor (DSP). FIG. 2 shows the configuration of an audio system having an equalizer using DSP. D
The SP 8a is an IC equipped with a large number of multipliers, adders, and delay memories, and forms a digital filter by setting the coefficients of each part using the microcomputer 9a. Microcomputer 9a
reads the set value of an output level changing means (not shown) operated by the user, and changes the coefficient of the DSP ga so that an output level corresponding to the read value is obtained.

In the audio system shown in FIG. 2, in the case of an analog signal source 1a, the signal is digitally converted by an A/D converter 3a and then input to a DSP 3a. In the case of the digital signal source 2a, the signal is directly input to the DSP 8a. DSP
The coefficients etc. of ga are set to form a desired digital filter, and the input signal is converted into an analog signal by the D/A converter 5a after the output level is adjusted for each band, and then converted to an analog signal by the amplifier 6a. After being amplified, it becomes an acoustic signal by the speaker 7a.

In this embodiment, each digital filter is a bandpass filter, and an example of the configuration of the digital filter in this case is shown in FIG. In FIG. 3, amplifiers 13b to 18b have coefficients ao to a5, respectively. 17b to 2
0b is a delay memory that delays the signal by one sampling time. 21b is an adder.

As mentioned above, the frequency characteristics of each bandpass filter are expressed by the center frequency and the Q value indicating the sharpness.
The relationship between the coefficient of , the center frequency, and the Q value is shown by equations (1) to (8).

ao"1...(1)
a+=O...(2) a2=1...(3)a
3 ” (2+2-wa”)/p ”' (
4) a4= (I Gm-wa/Q + Wo”
)/P...(5) aS = ((Gp-Gm)-W
a/Q)/P ・ (6) P = 1+Gm-Wo/
Q + Wo' - (7) f o = Wo /
2π (8) In equations (1) to (8), fo is the center frequency, Wo is the resonance angular frequency, and cp and Gm are constants determined by the amplification degree, that is, the output level.

As is clear from equations (1) to (8), the center frequency,
Once the Q value and output level are determined, the digital filter Fb
aS is determined from each coefficient a0 of the multipliers 11b to 16b. Conversely, by determining the coefficients a0 to a5, the center frequency, Q value, and output level are determined.

In this example, the center frequencies are 1 kHz and 2 kHz.
z, 3 kHz.

4 kHz, 5 kHz, 6 k)! z,
7 kHz, respectively 2.4. -6.8.1
It has a Q value of 0.12.14.

A graphic equalizer is realized by connecting the seven digital filters determined as described above in series as shown in FIG. The frequency characteristics of the graphic equalizer obtained in this way are shown in Figures 1A and 1.
As shown in Figure B, the characteristics are suitable for adjusting a specific frequency and its harmonic components, as explained above.

The graphic equalizer of the present invention is intended to adjust the output level of a specific frequency and its harmonics, and has a problem in that it is difficult to adjust the output level of other frequencies. For example, as is clear from FIG. 1A, the frequencies include a region of 500 tlz or less, a region of 8 kHz or more, and a frequency portion intermediate the center frequency of each band filter, such as 1.5 kHz or 2.5 kHz. However, since the purpose of the graphic equalizer of the present invention is to adjust the output level of a specific frequency and its harmonics, if the target frequency and the specific frequency of the graphic equalizer of the present invention match, , there is no problem.

Further, in the case of a digital filter using a DSP, the input signal is sampled at a high frequency of about gQkHz and processed. Therefore, the target frequency is 1
When changing from kl(z to 500Hz, it is possible to change the target frequency without changing the coefficients of the digital filter at all by thinning the signal input to the digital filter in half and giving it. Almost all frequencies can be targeted in this way.

However, when there are multiple target frequencies and it is necessary to adjust each harmonic, or when it is necessary to adjust the output level of the target frequency and its harmonics while also adjusting other bands. This can be achieved by combining a plurality of graphic equalizers according to the present invention, or by adding a graphic equalizer according to the present invention to a conventional graphic equalizer.

〔Effect of the invention〕

According to the present invention, it is possible to realize an equalizer capable of adjusting only a specific frequency and its harmonics, which is suitable for examining the influence of a specific frequency and its harmonics on the auditory sensation in an audio system.

[Brief explanation of drawings]

FIG. 1A and FIG. 1B are diagrams showing examples of frequency characteristics of each bandpass filter of a graphic equalizer based on the present invention. FIG. 1C is a diagram showing the frequency characteristics of each bandpass filter when the center frequency is the same as in FIGS. 1A and 1B and the Q value is constant. FIG. 2 is a diagram showing the configuration of an audio system having an equalizer using DSP. FIG. 3 is a diagram showing an example in which a bandpass filter is configured with a digital filter. FIG. 4 is a diagram showing a configuration example of a graphic equalizer in which seven digital filters of FIG. 3 are connected in series. FIG. 5 is a diagram showing a configuration example of an audio system having a graphic equalizer. FIG. 6 is a diagram showing an example of frequency characteristics of each bandpass filter of a conventional graphic equalizer. In the figure, 1a... Analog signal source, 2a... Digital signal source, 3a... A/D converter, 4C... Graphic equalizer, 5a... D/A converter, 6a... Amplifier, 7a-
x peaker, 8a=DSP. 9a...Microcomputer, Fb...Digital filter, 11b-16b...Amplifier, 17b-20b...Delay memory, 21b...Adder. Example and system configuration hole 2 Diagram Digital filter 1 Structure of each Obitsuka filter 3i
4 C Diagram 5th Crystal

Claims (1)

[Claims] A plurality of bandpass filters having frequency characteristics represented by a center frequency and a Q value that is sharpness, and corresponding to each of the plurality of bandpass filters, changing the output level of each bandpass filter with respect to an input signal. In a graphic equalizer that is equipped with a plurality of output level changing means and capable of changing the frequency characteristics of an input signal, the center frequency of each of the plurality of bandpass filters is set to a predetermined reference frequency. The difference between adjacent center frequencies is set to be equal at frequencies that are integral multiples of the reference frequency, and the Q value of each of the plurality of bandpass filters is set to increase as the frequency increases. A graphic equalizer characterized by: