JPH0828645B2 - Equalizer - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Outline] The present invention divides adjacent frequency bands into a plurality of groups so as to be separated from each other, and a plurality of specific band level adjusting means for connecting these groups in parallel, and each of the plurality of specific band level adjusting means. A plurality of adders for synthesizing the output signal of the specific band level adjusting means together with its input signal, and the output terminal of the adder is an equalizer sequentially connected in series to the specific band level adjusting means of the plurality of groups and attenuated. Even if the ratio is increased, distortion does not occur, and the number of steps in the program can be reduced to reduce the load on the DSP.

[Industrial applications]

The present invention relates to an equalizer for correcting frequency characteristics of audio signals.

For example, the above equalizer is required to obtain a desired sound from an audio signal obtained by reproducing a source of an audio device.

[Conventional technology]

FIG. 4 is a block diagram showing a conventional audio system for correcting frequency characteristics. The configuration of this figure is shown below. In addition, the same reference numerals or symbols are used to represent the same components throughout the drawings. Audio system
30 is an analog source 31, an analog-digital converter A / D32 connected to the analog source 31, an equalizer 4 connected to the A / D32 and the digital source 33, and a digital-analog converter connected to the equalizer 4. D /
A34, a power amplifier 35 connected to the D / A34, and a speaker 36 connected to the power amplifier 35.

Next, the necessity of the equalizer 4 will be described. Generally, when reproducing a source such as an analog source 31 and a digital source 33 such as a compact disc (hereinafter abbreviated as CD), the reproduction frequency characteristic changes depending on the size and material of the room. Therefore, the frequency characteristics of the audio signal Si may change and the desired sound may not be obtained.
As a countermeasure against this, conventionally, as a frequency characteristic correction means, for example, an audio signal is output by a graphic equalizer 4.
Correction signal by correcting the frequency characteristics of Si in a specific frequency band
A desired sound was transmitted from the speaker 36 after outputting So and amplifying this correction signal So by the amplifier 35.

Here, the equalizer 4 is a DSP (Digital Signal Proc
essor) composed of a digital filter. FIG. 5 is a block diagram of a digital filter for frequency characteristic correction. In FIG. 5, the frequency characteristic correcting digital filter 1 includes multipliers 13a to 13e, 18j, delay memories 13f to 13i for delaying a signal by one sampling time, and an adder 13j,
It is composed of 18k. Here, various parameters of the filter, for example, filter coefficients a0, a1, a2, b1, b2 and k0 of the multipliers 13a to 13e, 18j are k0 = {(Gp-Gm) .W0 / Q} / P a0 = 1 a1 = 0 a2 = -1 b1 = − (− 2 + 2 · W0 ² ) / P b2 = − (1-Gm · W0 / Q−W0 ² ) / P, and the setting of these filter coefficients is DSP It is performed by the program in. However, it is _{P = 1 + G M · W} 0 / Q + W 0 2. Where W ₀ is the resonance angular frequency, Q is the sharpness and
G _P and G _M are constants determined by the amplification factor and Indicates the center frequency of the frequency band to be corrected. The level of a specific frequency band is adjusted by adjusting various parameters of the digital filter.

FIG. 6 is a diagram showing frequency characteristics of the digital filter shown in FIG. In this figure, the horizontal axis is frequency (Hz) and the vertical axis is gain (dB) for amplification and attenuation, and the individual frequency characteristics of the nine types of digital filters (F ₀₁ , F ₀₂ , ... F ₀₉ ) are displayed. . The portion of the digital filter 1 in FIG. 5 is designated as F _n, and the entire portion of FIG. 5 is designated as F _0n (where n is 1, 2, 3, ...).
For example, the gain of each digital filter is +12 dB and −
The resonance frequency f ₀ is 62.5Hz (F ₀₁ ), 125Hz (F ₀₂ ), 250Hz
(F ₀₃ ), 500Hz (F ₀₄ ), 1000Hz (F ₀₅ ), 2000Hz (F ₀₆ ), 4
000Hz (F _07), was set to 8000Hz (F ₀₈₎ and 16000Hz (F _09). The gain can be freely adjusted by arbitrarily changing the filter coefficient of each digital filter.

FIG. 7 is a diagram showing a series connection of digital filters having the characteristics shown in FIG. This diagram is an example of the configuration of the equalizer 4 of FIG. 4, and the digital filters F ₀₁ , F ₀₂ , F ₀₃ , ... F ₀₉ described above are connected in series. Regarding the operation of the equalizer 4, when an input signal Si of a certain frequency is input to the equalizer 4, it is amplified or attenuated by the digital filter of the corresponding frequency band according to its gain, and is passed by the digital filter of another frequency band. Output signal S ₀ .

FIG. 8 is a diagram showing a synthetic frequency characteristic of the digital filter of FIG. This figure shows each digital filter F ₀₁ , F
The parameter coefficient of ₀₂ , F ₀₃ , ... F ₀₉ is gain 12dB, 6dB, −6d
It is a composite frequency characteristic when each digital filter is connected in series as shown in FIG. The composite frequency characteristics are symmetrical in terms of amplification and attenuation, and the respective peak values are affected by the shape of the tail of the waveform of the frequency characteristics of each digital filter, and rise slightly. Thus, the audio signal is corrected to the desired signal by such a composite frequency characteristic.

FIG. 9A is a diagram showing parallel connection of digital filters having the characteristics shown in FIG. This figure shows the equalizer 4 in Figure 4.
Is another example of the configuration of the digital filters F ₁ , F ₂ , F ₃ , ... F ₉ and the digital filters F ₁ , F ₂ , F ₃ ,
... An adder 3 for synthesizing the output signal of F ₉ and the input signal (Si). Regarding the operation of this equalizer 4,
When an input signal Si of a certain frequency is input to the equalizer 4, it passes through the digital filter of the corresponding frequency band and is amplified or attenuated according to its gain, while it cannot pass through the digital filter of another frequency band.
The passed signal is added to the input signal Si by the adder 3 and becomes the output signal S ₀ .

Further, the inventor of the present application has improved the parallel connection in Japanese Patent Application No. 63-192830 "Frequency characteristic correction device" in order to reduce the number of DSP program steps. Figure 9B shows
FIG. 9B shows an improvement of the parallel connection of FIG. 9A. As shown in FIG. 9B, in the parallel connection, the multipliers 13a and 13b and the delay units 13e and 13f are shared, so that the number of steps of the program can be reduced as compared with the series connection.

[Problems to be Solved by the Invention]

However, as shown in FIG. 7, the digital filter F
_The equalizer 4 in which ₀₁ , F ₀₂ , ... F ₀₉ are connected in series has good frequency characteristics synthesized as shown in FIG. 8, but the digital filters F ₁ , F ₂ , ... F ₉ shown in FIG. There is the first problem that the DSP program steps cannot be saved as compared with the equalizer 4 connected in parallel, and thus the scale of the DSP becomes large.

On the other hand, in the equalizer 4 in which the digital filters are connected in parallel, when the adjacent digital filters have a large attenuation gain, on the other hand, in the equalizer 4 in which the digital filters are connected in parallel, the input signal Si is attenuated by the digital filter. A signal obtained by inverting the input signal and adjusting the amplitude according to the attenuation rate is added to the input signal Si by the adder 3. FIG. 10 is a diagram showing a combined frequency characteristic of the digital filters of FIGS. 9A and 9B. In this figure, when the gain is 12 dB, 6 dB, and -6 dB, the composite frequency characteristics are almost the same as in the case of the series connection shown in Fig. 8, but when the gain is -12 dB, it is significantly different and the attenuation is not performed normally. , A second problem of causing significant distortion. The reason is that the attenuation characteristics overlap in a digital filter with adjacent frequency bands, so when both gains are large due to attenuation, the inversion signal generated from both becomes too large and not only the input signal Si is attenuated. This is because it is inverted and amplified.

Therefore, in view of the above problems, it is an object of the present invention to provide an equalizer that has no distortion and can reduce the number of DSP program steps.

[Means for solving the problem]

FIG. 1 is a diagram showing the principle configuration of the present invention. The present invention has a plurality of specific band level adjusting means 2-1, 2-2, ..., 2-K and a plurality of adders 3-1, 3-2 ,. The plurality of specific band level adjusting means 2-1, 2-2, ..., 2-K are divided into a plurality of groups so as to isolate adjacent frequency bands, and are connected in parallel within each group. Each of the adders 3-1, 3-2, ..., 3-K synthesizes the output signal of each of the plurality of specific band level adjusting means 2-1, 2-2 ,. To do. Further, the adder 3-1,3-
Output terminals of 2, ..., 3-K-1 are sequentially connected in series to the specific band level adjusting means 2-2, 2-3 ,.

[Work]

In FIG. 1, an input signal Si having a constant frequency is amplified and attenuated as desired by any of the specific band adjusting means 2-1, 2-2, ..., 2-K, and the specific band adjusting means 2-1. , 2-2, ...,
At 2-K, it is added to the input signal Si and becomes the output signal S ₀ . In this case, since the frequency characteristics of the specific band adjusting means do not substantially overlap with each other in the same group, the distortion due to the overlap in the adjacent frequency band is eliminated unlike the conventional case. Moreover, since the specific band adjusting means are connected in parallel within the same group, it is possible to reduce the number of DSP program steps.

〔Example〕

Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 2 is a view showing an equalizer which is an embodiment according to the present invention. In this figure, the configuration different from that of FIG. 7 and FIG. 9A is the arrangement of digital filters F ₁ , F ₂ , ..., F ₉ for adjusting the level of a specific band of frequency. Equalizer 4
Are connected in parallel so as to isolate adjacent frequency bands, and a first group of digital filters 2-1 consisting of digital filters F ₁ , F ₄ and F ₇ to which an input signal Si is applied are connected in parallel. Digital filter
A _second group of digital filters 2-2 consisting of F ₂ , F ₅ and F _8, digital filters F ₃ and F connected in parallel
Digital filter 2-3 of the third group consisting of ₆ and F ₉ , Digital filter 2-1 of the first group
Output signals of the first group adder 3-1 and the second group digital filter 2-2 for adding the output signal and the input signal Si of the second group and outputting the result to the second group digital filter 2-2. And the second adder 3-2 and the third group digital filter 2-3, which add the output signals of the first adder 3-1 and output the result to the digital filter 2-3 of the third group. Output signal of the second adder 3-2 and the third adder 3-2 for adding the result to the next stage, for example, the signal S ₀ to be output to the D / A 34. The present invention divides the nine types of digital filters and these into three groups for the sake of clarity, but the present invention is not limited to these.
Next, the frequency characteristics of the equalizer according to the embodiment of the present invention will be described. FIG. 3 is a diagram showing a synthetic frequency characteristic of the digital filter of FIG. In this figure, there is no distortion of the characteristic at a gain of -12 dB as shown in FIG. 10, and the same frequency characteristic as in the case of series connection in FIG. 8 can be obtained. The reason for this is, for example, the first group of digital filters F ₁ , F ₄ and F.
_In FIG. ₇ , the overlapping portion is very small from FIG. 6 and is almost the same for the second and third groups. Therefore, the influence of the adjacent digital filter of the present invention is as good as the series connection of FIG. Moreover, in the first group, the second group, and the third group of this embodiment, the number of steps of the DSP program can be reduced by the improvement by the parallel connection shown in FIG. 9B.

〔The invention's effect〕

As described above, according to the present invention, the plurality of specific band level adjusting means are divided into a plurality of groups so as to isolate the adjacent frequency bands and are connected in parallel,
In the plurality of adders, the output signals of the plurality of specific band level adjusting means are combined with their input signals, and the output terminals of the adders are sequentially connected in series to the plurality of groups of specific band level adjusting means. Therefore, even if the attenuation rate is increased, there is no distortion as in the past, and DS
The number of steps in the program can be reduced to reduce the burden on P.

[Brief description of drawings]

FIG. 1 is a diagram showing a principle configuration of the present invention, FIG. 2 is a diagram showing an equalizer which is an embodiment according to the present invention, FIG. 3 is a diagram showing a synthesized frequency characteristic of the digital filter of FIG. 2, and FIG. FIG. 7 is a block diagram showing an audio system for correcting the conventional frequency characteristic, FIG. 5 is a block diagram of a digital filter for frequency characteristic correction, FIG. 6 is a diagram showing the frequency characteristic of the digital filter in FIG. 5, and FIG. The figure shows a series connection of digital filters having the characteristics shown in FIG. 6, FIG. 8 shows the combined frequency characteristics of the digital filters shown in FIG. 7, and FIG. 9A shows the digital filter having the characteristics shown in FIG. FIG. 9 is a diagram showing a parallel connection, FIG. 9B is a diagram showing an improvement of the parallel connection of FIG. 9A, and FIG. 10 is a diagram showing a joint frequency characteristic of the digital filters of FIGS. 9A and 9B. In the figure, 1 ... Specific band level adjusting means F ₁ , F ₂ , ..., F _n , F ₀₁ , F ₀₂ ,,
... F _0n , 2-1, 2-2, ..., 2-K ...... Specific band level adjusting means for a plurality of groups, 3-1, 3-2, ..., 3-K ...... adder, Si ...... input Signal, S ₀ ... Output signal.

Claims (1)

[Claims] 1. An equalizer (4) comprising a plurality of specific band level adjusting means (1) for outputting an audio signal (So) in which the frequency characteristic of an audio signal (Si) is corrected, and adjacent frequency bands are sufficiently separated from each other. A plurality of specific band level adjusting means (2-1, 2-2, ... 2-K) for dividing the plurality of specific band level adjusting means (1) into a plurality of groups and connecting them in parallel, Each of the plurality of specific band level adjusting means (2-1, 2-2, ... 2)
-K) and a plurality of adders (3-1, 3-2, ... 3-K) for synthesizing the output signal with the input signal, and the adders (3-1, 3-2, ... 3- The output end of K-1) is the specific band level adjusting means (2-2, 2-3, ... 2-) of the plurality of groups.
An equalizer characterized by being connected in series to K).