JPH0787323B2 - Graphic equalizer - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a graphic equalizer using a digital signal processor (DSP), and more particularly to a graphic equalizer capable of changing a frequency for increasing or decreasing a strength.

[Conventional technology]

Conventionally, in order to make a reproduced sound such as music from an audio device into a sound quality desired by a listener, the audio device has a sound quality correction device called a tone control capable of adjusting the treble range and the bass range of the sound. In some cases, there is provided a sound quality correction device called a graphic equalizer, which is capable of dividing an audio frequency band into several bands and freely adding or subtracting the strength of a sound in the divided frequency bands. Of these, the graphic equalizer can freely add or subtract sound to each of the audio frequency bands divided into several parts, and thus can create a sound field that matches the taste of the listener.

[Problems to be solved by the invention]

However, the conventional graphic equalizer has a limited number of divided frequency bands, and since it is not possible to change the frequency of the divided frequency bands, it is not possible to create a sound that suits the listener's taste to some extent. Although possible, there is a problem that it is difficult to create a sound that really satisfies the listener. As a method to improve the listener's satisfaction with sound production, it is conceivable to increase the number of frequency bands to be divided. However, if the number of frequency bands to be divided is increased, the device becomes larger and the cost increases. A new problem will occur.

[Means for solving problems]

The present invention has been made to solve the problem peculiar to the conventional graphic equalizer in which the number of frequency bands to be divided is limited, and its object is to provide a finite number of divided pieces by a bandpass filter. In the graphic equalizer having a frequency band of, by changing the filter coefficient of the band pass filter, while moving each divided frequency band or bandwidth independently to the treble side or the bass range by a predetermined frequency, The purpose is to change the gain of each frequency band so that the reproduced sound can have a desired sound quality.

The graphic equalizer of the present invention to achieve the above object, A / D converter for converting an analog input signal into a digital signal, and a plurality of digital band pass filter,
A digital equalizer including a digital signal processor to which a digital signal from the A / D converter is input, and a D / A converter that converts a digital signal processed by the digital signal processor into an analog signal. An input device having a key for changing the frequency characteristic of each of the digital bandpass filters and a key for changing the gain characteristic, and changing the filter coefficient of the digital signal processor according to the data input from the input device. And a cut-off frequency of a high-cut filter and a low-cut filter constituting the band-pass filter can be changed by the control device, and the center frequency or bandwidth of each band-pass filter is changed. It is characterized by doing.

[Work]

According to the graphic equalizer of the present invention, when the characteristic change data of the band to be changed is input by the input device, the control device changes the frequency characteristic and the gain characteristic of the hand pass filter in the frequency band corresponding to the key of the input device. Therefore, it is possible to add strength to the range of the listener's liking.

〔Example〕

Embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

FIG. 1 is a block diagram showing the configuration of a graphic equalizer according to an embodiment of the present invention. The graphic equalizer 10 of this embodiment is an A / D converter for converting an analog signal into a digital signal, and a plurality of digital signals for performing processing such as sound quality correction processing such as equalizer processing and strength processing on the A / D converted data. To change the characteristics of the digital signal processor 2 (hereinafter referred to as DSP2) equipped with a band pass filter, the D / A converter 3 that converts the digital signal processed by DSP2 into an analog signal, and the equalizer processing and the dynamic processing in DSP2 Control device equipped with a microcomputer for transferring a coefficient to each digital bandpass filter of DSP2 according to data input from the input device 4 and the input device 4
5, and a display device 6 for displaying the characteristics of the digital bandpass filter of the DSP 2 changed by the control device 5. An analog signal A such as music from a sound source S such as a tape recorder or a radio is input to the A / D converter 1. The sound quality-corrected analog signal A ′ output from the D / A converter 3 is amplified by the amplifier 7 and transmitted to the speaker 8 or the like to become a sound.

FIG. 2 shows an example of the key configuration of the input device 4, and in this example, there are five audio frequency bands.
It is divided into F1 to F5, and four keys Fna, Fnb, Fnc, and Fnd (n is a frequency band number, n = 1 to 5 in this embodiment) are provided for each of the five frequency bands. ing. The center frequencies of these five frequency bands are preset when the graphic equalizer is manufactured. For example, F1: 100H
z, F2: 330Hz, F3: 1kHz, F4: 3.3kHz, F5: 10kHz. And the keys Fna, Fnb, Fnc, Fnd of each frequency band are Fna
Is a key that moves the frequency to the higher side, Fnb is a key that moves the frequency to the lower side, Fnc is the key to increase the gain, and Fnd is the key to decrease the gain.

FIG. 3 shows an example of the configuration of the display device 6. The display device 6 is provided with two display windows 6a and 6b for each of the above-mentioned frequency bands F1 to F5. For example, the center frequency of each frequency band is displayed on the display window 6a and the center frequency of each frequency band is displayed on the display window 6b. Gain characteristics are displayed. That is,
By operating the key F1a of the input device 4, the display window 6 of the frequency band F1
The frequency in a becomes high, and if the key F2b is operated, the frequency in the display window 6a of the frequency band 2 becomes low, and the key of the input device 4 becomes
When F3c is operated, the gain value in the frequency band F3 display window 6b is increased, and when key F4d is operated, the frequency band F4 display window 6b is displayed.
The gain in b becomes smaller.

FIG. 4 shows the characteristic of the digital bandpass filter BPFn (n is a natural number) provided in DSP2 of the graphic equalizer of the present invention in which the audio frequency band is divided into n, and FIG. 5 shows this digital band. Pass filter BP
Fn shows the individual configuration. The digital bandpass filter BPF1 is composed of four delay elements Z ₁₁ , Z ₁₂ , Z ₁₃ and Z ₁₄ and six coefficient multipliers K ₁₀ , K ₁₁ , K ₁₂ , K ₁₃ , K ₁₄ and K _15. Therefore, the other digital bandpass filters BPFn also have exactly the same number of delay elements Z _n1 , Z _n2 , Z _n3 , Z _n4 and coefficient multipliers K _n0 , K _n1 , K.
_{It has n2} , K _n3 , K _n4 and K _n5 . 9 is an adder.

In the aforementioned digital bandpass filter BPFn, the coefficient multipliers K _n0 , K _n1 , K _n2 , K _n3 and K _n4 are involved in the band characteristic of the digital band pass filter BPFn, and the coefficient multiplier K _n5 is a digital band pass filter. It is involved in the gain of the filter BPFn. That is, the coefficient multipliers K _N0 , K _n1 , K _n2 , K _n3 , K _n4
By changing N1, KN2, KN3, and KN4, the band characteristic of the digital bandpass filter BPFn shown in FIG. 4 (center frequency f _n0 )
Is changed, and the gain of the digital bandpass filter BPFn is changed by changing the coefficient K N5 of the coefficient multiplier K _n5 .

Next, the operation of the graphic equalizer of the present invention configured as above will be described with reference to the flowchart of FIG. Step 601 in this flowchart
~ Step 617 also shows the operation when any one of the keys F1a, F1b, F1c, F1d is operated in order to change the characteristic of the digital band pass filter BPF1. The same operation is performed when the key is operated, and thus the description thereof will be omitted.

Steps 601 to 604 are for detecting which one of the keys F1a, F1b, F1c, F1d of the digital bandpass filter BPF1 has been operated, and the keys F1a, F1b, F1c of the digital bandpass filter BPF1, If F1d is not operated, all steps are NO, and the process proceeds to step 620 for detecting which of the keys of the digital bandpass filter BPF2 has been operated. Here, each case will be described assuming that only one key of the digital bandpass filter BPF1 is operated (the characteristic changing key may be operated in two or more frequency bands at the same time).

(A) When the key F1a is operated (frequency increasing operation): YES is determined in step 601 and the process proceeds to step 605, where it is determined whether the center frequency f ₁₀ of the digital bandpass filter BPF1 exceeds the maximum center frequency F1H. To be judged. If the center frequency f ₁₀ of the digital band-pass filter BPF1 does not exceed the maximum center frequency F1H proceeds to (NO), step 606, and the center frequency f ₁₀ is applied a predetermined frequency ArufaHz, higher frequency the center frequency f ₁₀ Towards αHz. Then, in step 610, the coefficients K10, K11, K12, K13, K14 are calculated.

Digital band pass filter BPFn is high pass filter HP
Since it is composed of Fn and low-pass filter LPFn, A,
With B, C, D, E, and F as constants, the coefficients Ki0, Ki1, Ki2, Ki3, Ki4 of the i-th digital bandpass filter BPFi are LPFH (z) = (A + BZ- ¹ ) / (1-CZ ^-1 ), HPFH (z) = (D + EZ ^-1 ) / (1-FZ ^-1 ), From the above, a transfer function of Ki0 = A × D, Ki1 = B + E, Ki2 = B × E, Ki3 = C + F, Ki4 = C × F is obtained with T as the sampling frequency. The upper and lower ends and the cutoff frequency of the digital bandpass filter BPFi moved from this are obtained, and the coefficients Ki0 to Ki4 (i
Is calculated from 1 to N).

The coefficients K10 to K14 of the digital bandpass filter BPF1 are calculated in step 610 by the above equations, and these coefficients are transferred to the DSP2 in step 617. By the above operation, the center frequency f ₁₀ of the digital bandpass filter BPF ₁ is moved to the high frequency side by the frequency αHz, that is, the frequency band αHz.

If key F1a is operated as it is, step 6
01 → the procedure of Step 605 → Step 606 → Step 610 → Step 617 is repeated, the center frequency f ₁₀ of the digital band-pass filter BPF1 continues to move by frequency αHz to a higher frequency side. However, the digital bandpass filter BPF1
The center frequency f _{10 of} is not infinitely movable to the high frequency side, and is set so as not to overlap the area of the adjacent digital band pass filter BPF2 in this embodiment.

Therefore, when it is determined in step 605 that the center frequency f ₁₀ exceeds the maximum center frequency F1H of the digital bandpass filter BPF1, the process proceeds to step 607, and the center frequency f ₁₀ of the digital bandpass filter BPF1 is set to the maximum center frequency F1H. After replacement, the process proceeds from step 610 to step 617, that is, the center frequency f ₁₀ is guarded by the maximum center frequency F1H.

In this way, the center frequency f ₁₀ of the digital bandpass filter BPF1 can be moved to the maximum center frequency F1H by operating the key F1a.

(B) When the key F1b is operated (frequency reduction operation) After NO in step 601 and YES in step 602, the process proceeds to step 608, where the center frequency f ₁₀ of the digital bandpass filter BPF1 is the minimum. It is determined whether or not the frequency is below the center frequency F1L. Digital bandpass filter
If the center frequency f _{10 of} BPF1 is not lower than the minimum center frequency F1L (NO), the process proceeds to step 609, where the predetermined frequency αHz is subtracted from the center frequency f ₁₀ to reduce the center frequency f ₁₀ to αHz to the lower frequency side. Moving. Then, the process proceeds to step 610, and the coefficients K10, K11, K12, K13, K14 are calculated by the above equation. Then, this coefficient is transferred to the DSP 2 in step 617. By the above operation, the center frequency f ₁₀ of the digital bandpass filter BPF1 is moved to the low frequency side by the frequency αHz, that is, the frequency band αHz.

If key F1b is operated as it is, step 6
01 → the procedure of Step 602 → Step 608 → Step 609 → Step 610 → Step 617 is repeated, the center frequency f ₁₀ of the digital band-pass filter BPF1 continues to move by frequency αHz the low frequency side.

However, similar to the above, the digital bandpass filter BPF1
Center frequency f ₁₀ of the even is set lower limit in this embodiment, therefore, if the center frequency f ₁₀ is determined to have less than the minimum center frequency F1L of digital band-pass filter BPF1 In step 608, the process proceeds to step 611 , The center frequency f ₁₀ of the digital bandpass filter BPF1 is replaced by the minimum center frequency F1L, and the process proceeds from step 610 to step 617, that is, the center frequency f ₁₀ is guarded by the minimum center frequency FIL.

In this way, the center frequency f ₁₀ of the digital bandpass filter BPF1 can be moved to the minimum center frequency F1L by operating the key F1b.

(C) When the key F1c is operated (gain increase operation): YES in step 603 after NO in steps 601 and 602
Then, the process proceeds to step 612, where it is determined whether the gain n1 of the digital bandpass filter BPF1 exceeds the maximum value max. If the gain n1 of the digital band pass filter BPF1 does not exceed the maximum value max. (NO), step
Proceeding to 613, a predetermined gain βdB is added to the current gain n1. Then, the coefficient K15 of the coefficient multiplier K ₁₅ has the formula, obtained by K15 = 10 ^{n1 / 20} proceeds to step 616. And
This coefficient K15 is transferred to DSP2 in step 617. With the above operation, the gain of the digital band pass filter BPF1
n1 is increased.

If key F1c is operated as it is, step 6
The procedure of 01 → step 602 → step 603 → step 612 → step 613 → step 616 → step 617 is repeated, and the gain n1 of the digital bandpass filter BPF1 continues to increase. However, when it is determined in step 612 that the gain n1 has reached the maximum value max., Step 613
Return without proceeding to. In this way, the gain n1 of the digital bandpass filter BPF1 can be increased to the maximum value max.

(D) When the key F1d is operated (gain reduction operation) After NO in steps 601, 602, and 603, in step 604
If YES, the process proceeds to step 614, where it is determined whether or not the gain n1 of the digital bandpass filter BPF1 is below the maximum value min. If the gain n1 of the digital bandpass filter BPF1 is not less than the maximum value min. (NO), proceed to step 615, and set the gain β1 from the current gain n1 to the predetermined gain βdB.
Is subtracted. Then, the coefficient K15 of the coefficient multiplier K ₁₅ has the formula, obtained by K15 = 10 ^{n1 / 20} proceeds to step 616.
Then, this coefficient K15 is transferred to the DSP 2 in step 617. With the above operation, the digital bandpass filter BPF1
The gain n1 of is reduced.

If key F1d is operated as it is, step 6
The procedure of 01 → step 602 → step 603 → step 604 → step 614 → step 615 → step 616 → step 617 is repeated, and the gain n1 of the digital bandpass filter BPF1 continues to decrease. However, when it is determined in step 614 that the gain n1 has reached the minimum value min., The process returns without proceeding to step 615. In this way, the gain n1 of the digital bandpass filter BPF1 is the minimum value min.
Can be reduced to.

As described above, in the graphic equalizer of the present invention, the center frequency of the finite number of digital bandpass filters BPFn divided by the key operation of the input device 4 can be independently increased and decreased, and the gain of each digital bandpass filter BPFn is also increased. Can be changed.

FIG. 7 shows a changeover switch 41 showing a part of the configuration of another embodiment of the present invention, which is provided separately from the key group shown in FIG. 2 of the input device 4. Changeover switch 41
Is the frequency UP key Fna and frequency DOWN key Fnb of the keys in Fig. 2.
To change the function of the three positions L, C, R
have. As shown in FIG. 7, when the changeover switch 41 is in the position C, the keys of the input device 4 operate in the same manner as in the above-mentioned embodiment, and by operating the keys Fna and Fna, the respective digital bandpass signals are operated. The center frequency of the filter BPFn can be changed independently.

On the other hand, when the changeover switch 41 is set to the position L or the position R, the bandwidth of each digital bandpass filter BPFn can be independently changed by operating the keys Fna and Fnb. That is, when the keys Fna and Fnb are operated with the changeover switch 41 in the position L, the cutoff frequency on the low frequency side of the nth bandpass filter BPFn.
FnCL can be changed, and conversely, when the keys Fna and Fnb are operated with the changeover switch 41 in the position R, the cutoff frequency FnCH on the high frequency side of the nth bandpass filter BPFn is changed. be able to.

In this embodiment, the change range of the cutoff frequencies FnCL and FnCH on the low frequency side and high frequency side of each bandpass filter BPFn is limited, and for example, as shown in FIG. The minimum frequency that the cutoff frequency F1CL on the side can take is LMIN and the maximum frequency is LMAX, and the minimum frequency that the cutoff frequency F1CH on the high frequency side can take is HMIN and the maximum frequency is HMAX.

Next, the operation of the graphic equalizer of this embodiment capable of changing the bandwidth of each bandpass filter BPFn as described above will be described with reference to the flowchart of FIG.
In this flowchart, the characteristics of the bandpass filter BPF1 are changed as in the above embodiment, and the keys F1a, F1b,
This figure shows the operation when either F1c or F1d is operated. When the key operation of the other band pass filters BPFn is performed, the same operation as this is performed, and thus the description thereof will be omitted.

Also, steps 601 to 6 in the flowchart of FIG.
Reference numeral 17 is for changing the center frequency and the gain of the bandpass filter BPF1, and since these operations have already been described in the flowchart of FIG. 6, these steps have the same step numbers as those in FIG. Is attached and its description is omitted. Then, here, only the operation of changing the bandwidth of the bandpass filter BPF1 will be described, and the time when the changeover switch 41 is in the position L and the position R will be described separately.

(A) When the changeover switch 41 is in the position L: If the key F1a is operated, YES is determined in step 601 and the process proceeds to step 901, and NO is determined in step 901 in which it is determined whether or not the center frequency is changed this time. Determined to be step 9
Go to 02. Step 902 is the cutoff frequency f1C on the low frequency side.
It is determined whether or not L is changed. Here, YES is determined and the process proceeds to step 903. Step 903 determines whether or not the cutoff frequency f1CL on the low frequency side exceeds the maximum frequency LMAX, and if f1CL ≤ LMAX (NO), step 90
Proceeding to 4, the predetermined frequency αHz is added to the cutoff frequency f1CL on the low frequency side, the cutoff frequency f1CL on the low frequency side is moved toward the higher frequency by αHz, and the bandwidth of the bandpass filter BPF1 is narrowed. On the other hand, if f1Cl> LMAX (YES), the process proceeds to step 905, the cutoff frequency f1CL on the low speed side is replaced with the maximum frequency LMAX, and the process proceeds to step 610.

Thus, when the key F1a is operated while the changeover switch 41 is in the position L, the bandwidth of the bandpass filter BPF1 is narrowed.

When key F1b is operated, NO in step 601 and step
If YES in step 602, the flow proceeds to step 909. If it is determined in step 909 whether this time is a change in center frequency, NO is determined and the flow proceeds to step 910. In step 910, it is determined whether or not the cutoff frequency f1CL on the low frequency side is changed. Here, the determination is YES, and the process proceeds to step 911. Step 911 is to determine whether or not the cutoff frequency f1CL on the low frequency side is lower than the minimum frequency LMIN, and if f1CL ≧ LMAX (N
O) proceeds to step 912 and cutoff frequency f1 on the low frequency side
The predetermined frequency αHz is reduced from CL, the cutoff frequency f1CL on the low frequency side is moved toward the lower frequency side by αHz, and the bandwidth of the bandpass filter BPF1 is widened. On the other hand, if f1CL <LMAX (YES), the process proceeds to step 913, where the cutoff frequency f1CL on the low frequency side is replaced with the minimum frequency LMIN, and step 61
Go to 0.

Thus, when the key F1b is operated while the changeover switch 41 is in the position L, the bandwidth of the bandpass filter BPF1 is expanded.

(B) When the changeover switch 41 is in the position H: If the key F1a is operated, YES is obtained in the step 601 and the process proceeds to the step 901, and it is determined whether or not the center frequency is changed this time. Determined to be step 9
Go to 02. Step 902 is the cutoff frequency f1C on the low frequency side.
It is determined whether or not L is changed. Since this time is the change of the cutoff frequency f1CH on the high frequency side, NO is determined and the process proceeds to step 906. Step 906 is to determine whether or not the cutoff frequency f1CH on the high frequency side exceeds the maximum frequency HMAX. If f1CL ≤ HMAX (NO), proceed to step 907 to set the cutoff frequency f1CH on the high frequency side. When the predetermined frequency αHz is added, the cutoff frequency f1CH on the high frequency side is moved toward the higher frequency by αHz, and the bandwidth of the bandpass filter BPF1 is widened. On the other hand, if f1CH> HMAX (YES), step 908
And the cutoff frequency f1CH on the high frequency side is the maximum frequency HM.
Replaced by AX and proceed to step 610.

Thus, when the key F1a is operated while the changeover switch 41 is in the position H, the bandwidth of the bandpass filter BPF1 is widened.

If the key F1b is operated, NO is determined in step 601 and YES is determined in step 602, and the process proceeds to step 909. If it is determined whether or not the center frequency is changed this time, it is determined to be NO and the process proceeds to step 910. . In step 910, it is determined whether or not the cut-off frequency f1CL on the low frequency side is changed. Since this time, the cut-off frequency f1CH on the high frequency side is changed, the result is NO and the process proceeds to step 914. Step 914 is to determine whether or not the cutoff frequency f1CH on the high frequency side is below the minimum frequency HMIN, and when f1CL ≧ HMIN (NO)
Goes to step 915 and cutoff frequency f1CH on the high frequency side
Then, the predetermined frequency αHz is reduced, and the cutoff frequency f1CH on the high frequency side is moved to the lower frequency side by αHz to narrow the bandwidth of the bandpass filter BPF1. On the other hand, if f1CH <HMAX (YES), the process proceeds to step 916, where the cutoff frequency f1CH on the high frequency side is replaced with the minimum frequency HMIN, and step 61
Go to 0.

As described above, when the key F1a is operated while the changeover switch 41 is in the position H, the bandwidth of the bandpass filter BPF1 is narrowed.

In addition, in the above-described configuration in which the bandwidths of the high band side and the low band side of the band filter are changed, a plurality of issuing diodes (LEDs) are lit one at a predetermined frequency on each of the high band side and the low band side. ) Can be provided side by side. As a result, the frequency band from the center frequency is displayed, so that the listener can know the current frequency band and can easily adjust to the desired sound quality.

As described above, in the graphic equalizer of this embodiment, by changing the changeover switch 41, the center frequency of the bandpass filter BPFn, the bandwidth, and the gain characteristic can be changed, and the sound quality can be made finer. It can be adjusted.

〔The invention's effect〕

As described above, the graphic equalizer of the present invention independently moves each frequency band divided into a plurality of frequencies by operating a key of the input device to a high frequency side or a low frequency side by a predetermined frequency, or The width can be changed and the gain can also be changed individually, so that the listener can adjust the range of his / her preference to create a sound that satisfies the listener. There is an effect.

[Brief description of drawings]

FIG. 1 is a block diagram showing the configuration of an embodiment of the graphic equalizer of the present invention, FIG. 2 is a diagram showing the key configuration of the input device of FIG. 1, and FIG. 3 is a configuration of the display device of FIG. FIG. 4 shows an example, FIG. 4 is a characteristic diagram showing characteristics of individual digital bandpass filters of the graphic equalizer of the present invention, FIG. 5 is a circuit configuration diagram of the digital bandpass filter of the present invention, and FIG. FIG. 7 is a flow chart showing a control procedure of an embodiment of the graphic equalizer of FIG. 7, FIG. 7 is a view showing a part of a configuration of another embodiment of the present invention, and FIG. 8 is a view of a graphic equalizer of the other embodiment of the present invention. FIG. 9 is a diagram showing the bandwidth changing characteristic of each digital bandpass filter, and FIG. 9 is a flow chart showing the control procedure of another embodiment of the present invention. 1 ... A / D converter, 2 ... Digital signal processor (DSP), 3 ... D / A converter, 4 ... Input device, 5 ... Control device, 6 ... Display device, 9 ... Adder, 41 ... Changeover switch.

Claims (3)

[Claims] 1. An A / D converter for converting an analog input signal into a digital signal, and a plurality of digital bandpass filters,
A digital equalizer including a digital signal processor to which a digital signal from a converter is input, and a D / A converter that converts a digital signal processed by the digital signal processor to an analog signal, wherein the digital band An input device having a key for changing the frequency characteristic of each pass filter and a key for changing the gain characteristic; and a control device for changing the filter coefficient of the digital signal processor according to the data input from the input device. The cutoff frequency of the high-cut filter and the low-cut filter constituting the bandpass filter can be changed by the control device, and operates so as to change the center frequency or the bandwidth of each bandpass filter. And a graphic equalizer. 2. The high-frequency side and low-frequency side cutoff frequencies of each of the bandpass filters are set so as not to exceed a predetermined frequency range, respectively. Graphic equalizer. 3. The display device according to claim 1, further comprising display means for displaying the center frequency or bandwidth of each of the digital band pass filters.
The graphic equalizer according to item.