JPH10256857A - Sound quality correction device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the capacity of a coefficient table. SOLUTION: A filter arithmetic section 10 obtains sets of filter coefficients in response to an input parameter and they are fed to an evaluation section 14 and a selector switch 15 via a revision section 11. The evaluation section 14 evaluates whether or not desired sound quality is obtained (proper or improper) from the filter coefficients of the set obtained through an arithmetic operation based on the input parameters stored in each evaluation item memory 12 such as a level of a center frequency, a frequency sharpness, and a cut-off frequency. When the sound quality is proper, a selector switch 15 is controlled to be closed and a sound quality correction section 16 uses the set of the filter coefficients decided tentatively as they are to correct the sound quality. When improper, the coefficient revision section 11 adjusts the filter coefficients of the set obtained by the arithmetic operation so as to obtain desired sound quality and a sound quality correction section 16 corrects the sound quality by using the set of the adjusted filter coefficients.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to, for example, a tone controller which changes the sound quality of low frequency and high frequency of audio information, and a graphic equalizer which changes the sound quality of each frequency band of audio information. More particularly, the present invention relates to a sound quality correction device in which the number of filter coefficients required for sound quality correction is reduced and the storage capacity of a memory (coefficient table) for storing the filter coefficients is reduced.

[0002]

2. Description of the Related Art As a conventional sound quality correction device, a tone controller and a graphic equalizer for controlling the level of a center frequency and a frequency sharpness (Q) using a so-called IIR filter (Infinite Impulse Response) are known.

Since the IIR filter has a feedback loop, a desired frequency characteristic can be obtained with a small amount of calculation means. However, depending on the word length of a signal component and the word length of a filter coefficient, a desired filter characteristic can be obtained. May not be obtained.

In particular, tone controllers and graphic equalizers change frequency characteristics by changing filter coefficients. However, if an optimum filter coefficient is calculated by calculation each time, the amount of calculation for this is reduced. It takes more time. For this reason, a set of filter coefficients satisfying a desired frequency characteristic is obtained in advance and stored in a coefficient table, and these are selected and used.

Specifically, a graphic equalizer is
When using an IR filter, as shown in FIG. 6, a second-order IIR filter including a delay element, a multiplier and an adder is connected in multiple stages.

As shown in FIG. 7, filter coefficients (α _n0 -β _n
The set of _n2 ) is stored in the coefficient table in advance, and the filter function is read out from this coefficient table as necessary and supplied to each multiplier, thereby changing the transfer function to obtain audio information of a desired frequency characteristic. It has become.

[0007]

However, the conventional sound quality correcting apparatus converts a set of filter coefficients as shown in FIG. 7 into each center frequency, each level, each frequency sharpness (Q) and each sampling frequency. However, since all of them are stored in the coefficient table, an enormous capacity coefficient table is required, and there is a problem that the cost increases due to the increase in the number of storage elements.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems, and can reduce the required filter coefficients, and can configure a coefficient table with a small-capacity storage element, thereby achieving low cost. It is an object of the present invention to provide a sound quality correction device capable of performing the above.

[0009]

In order to solve the above-mentioned problems, the sound quality correcting apparatus according to the present invention uses a set of filter coefficients obtained by the filter operation means as "suitable" for obtaining a desired sound quality. Evaluation means for evaluating whether the sound is appropriate or "inappropriate"; and when the evaluation is performed by this evaluation means, the filter operation means is used to obtain a desired sound quality. Filter coefficient adjustment means for adjusting each set of filter coefficients, and a set of filter coefficients determined to be "suitable" by the evaluation means, or a set of filter coefficients adjusted by the filter coefficient adjustment means, supplied from outside. Filter means for correcting the sound quality of the audio information by filtering the audio information to be output.

In such a sound quality correcting apparatus, a set of filter coefficients obtained by the filter operation means is evaluated by the evaluation means as to whether or not a desired sound quality can be obtained. Inadequately), this set of filter coefficients is adjusted by filter coefficient adjusting means so as to obtain a desired sound quality, and is used for filtering audio information supplied from the outside.

For this reason, for example, only a set of some basic filter coefficients can be stored in the filter coefficient storage means, and these can be adjusted and used according to the evaluation result, and stored in the filter coefficient storage means. It is possible to reduce the number of filter coefficients to be set. Therefore, it is possible to use a small-capacity filter coefficient storage means, thereby reducing the cost of the sound quality correction device.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of a sound quality correcting apparatus according to the present invention will be described below in detail with reference to the drawings.

In the sound quality correcting apparatus according to the first embodiment of the present invention, as shown in FIG. 1, an input terminal 1 to which audio data as external digital data is supplied, and a sound quality corrected to a desired sound quality. It comprises an output terminal 2 for outputting audio data, a digital signal processor 3 (DSP), and a microcomputer (microcomputer) 4.

The digital signal processor 3 is mainly composed of a sound quality correction circuit 16 for correcting the sound quality of audio data using a set of filter coefficients from the microcomputer 4.

The microcomputer 4 calculates a set of filter coefficients for performing sound quality correction in accordance with predetermined input parameters by a calculation described later, and an evaluation unit that stores input parameters input by a user. The set of filter coefficients obtained by the item memory 12 and the filter operation unit 10 is used to determine whether desired sound quality can be obtained (suitability) based on the input parameters (evaluation items) stored in each evaluation item memory 12. (Inappropriateness).

Further, when the evaluation unit 14 evaluates the inappropriateness, the microcomputer 4 adjusts the set of filter coefficients obtained by the filter operation unit 10 to a value that provides a desired sound quality. When the suitability is evaluated by the evaluation unit 11 and the evaluation unit 14, the set of filter coefficients obtained by the filter operation unit 10 is supplied to the sound quality correction circuit 16 of the DSP 3, and the evaluation is performed by the evaluation unit 14. In this case, the selection switch 15 that supplies the set of filter coefficients adjusted by the coefficient changing unit 11 to the sound quality correction circuit 16
And

The overall configuration of the DSP 3 and the microcomputer 4 is as shown in FIG. 2. The DSP 3 and the microcomputer 4 are connected by a control bus line 5 for supplying control data from the microcomputer 4 to the DSP 3. ing.

The DSP 3 comprises an input data buffer 3a, a multiplier 3b, a logical operation unit 3c, a ROM 3
d, output data buffer 3e, RAM 3f, data RA
M3g and coefficient RAM 3h are connected to each other via a data bus line 3i and a control bus line 3j, respectively.

When audio data from the outside is supplied to the input data buffer 3a via the input terminal 1, each of the sections 3a to 3h operates according to a data processing algorithm program stored in the ROM 3d or the RAM 3f. , And performs filtering processing of audio data using a set of filter coefficients from the microcomputer 4.

The microcomputer 4 includes various parts 3a to 3a of the DSP 3.
3h. Specifically, when the user operates the operation unit 6, operation data indicating the contents of the operation is supplied to the input port 4 a of the microcomputer 4. When operation data is supplied to the input port 4a, the operation processing unit 4b (CPU) is activated by the operation data. The arithmetic processing unit 4b includes an output port 4e and a control bus line 5 that execute data processing according to operation data based on a program stored in the ROM 4d or an arithmetic program stored in the RAM 4c as necessary. The control data is supplied to the DSP 3 via the DSP 3, and the filtering process performed by the DSP 3 is controlled.

Next, the ROM 4d (or R
The sound quality correcting operation of the sound quality correcting device executed based on the program stored in AM4c) will be described.

This sound quality correcting operation is executed according to the flowchart shown in FIG. That is, when the sound quality correction device is a graphic equalizer, the user operates the operation unit 6 shown in FIG. 2 to operate the operation unit 6 shown in FIG. 2 to obtain a desired frequency gain characteristic, a desired center frequency value, a desired center frequency level, The process is started by inputting a desired frequency sharpness or the like as an input parameter, and the process proceeds to step S1. Alternatively, when the sound quality correction device is a tone controller, the process is started by inputting a level of a flat portion of a desired frequency characteristic, a desired cutoff frequency, and the like as input parameters, and the process proceeds to step S1.

In step S1, the arithmetic processing unit 4b (CPU) shown in FIG. 2 obtains the S function of the input parameter based on the following equation 1-1 based on the program stored in the ROM 4d, thereby stabilizing the operation. The process proceeds to step S2 after obtaining the transfer function.

In step S2, the arithmetic processing unit 4b performs a bilinear S / Z conversion process on the S function to convert the S function into a Z function to make it a finite word length. Then, this value is provisionally determined as a set of filter coefficients, and the process proceeds to step S3.

Specifically, the parameters of the transfer function are arranged and the relational expression with the set of filter coefficients is shown by the following equation (1).

[0026]

(Equation 1) That is, by performing bilinear S / Z conversion processing on the S function shown in Equation 1-1 of Equation 1 using Equation 1-2, the Z function shown in Equation 1-3 is obtained, and the word length is made finite. . In addition, 1-1 formula-1
-3 filter coefficients α0, α1, α2, β1, β2
Is defined by formulas 1-4 to 1-8, respectively.

Here, the filtering operation of the shelving type graphic equalizer can be expressed by the following equation (1-9).

A 0, a 1, a 2 in the equations 1-4 to 1-8
, B0, b1, and b2 are defined by the following equations (2-1) to (2-6).

[0029]

(Equation 2) For this reason, a0 defined by the formulas 2-1 to 2-6,
By substituting a1, a2, b0, b1, and b2 into equations 1-4 to 1-8, the coefficient value of the Z function, that is, the filter coefficient of the digital filter can be obtained.

Equations 2-1 and 2-4, and equations 2-3 and 2
It is _{a 0 = b 0 = 1,} a2 = b2 -6 expression. Also,
From these, Equations 1-5 and 1-6, α ₁ = β ₁ .
Further, Ka ₁ = b ₁ is obtained from the expressions 2-2 and 2-5.

Assuming that the function for finite word length is T (x),
The filter coefficients α0, α1, α2, β1, β2 are as shown in the following equations (3-1) to (3-4).

[0032]

(Equation 3) Here, paying attention to the relationship between α ₀ and α ₂ , A _T and B _T are set as shown in the following Expression 4, and

(Equation 4) α ₀ ≒ A _T + B _T α ₂ ≒ A _T + B _T

This is because the value of the finite word length is “α ₀ −
This indicates that a desired filter characteristic cannot be obtained unless the relationship of α ₂ = 2B _T is maintained.

Therefore, if α ₀ and α ₂ are respectively set as α ₀ = A _T + B _T α ₂ = A _T -B _T , desired filter characteristics can be obtained.

The above expression 1-9 indicates the boost type, but by replacing the numerator and denominator of this expression, an attenuate type filter can be formed.

Next, considering the tone controller, in the case of the high-frequency amplification type, the following expression (5-1) is used, and in the case of the low-frequency amplification type, the expression 5-2 of the expression (5) is used. It becomes as shown in.

[0037]

(Equation 5) Note that by replacing the numerator and denominator of Equations 5-1 and 5-2, an attenuated tone controller can be realized.

Then, the expressions 5-1 and 5-2 are compared with the expression 1-1, and a ₀ , a ₁ , a ₂ , b ₀ , b ₁ , and b ₂ are obtained. By substituting into equation 8, the coefficient value of the Z function, that is, the filter coefficient of the digital filter can be obtained.

Here, in order for the DSP 3 (or the logic circuit) to be able to perform the operation of the filtering process, it is necessary to represent each filter coefficient with a certain word length. At this time, since an error occurs, it is necessary to evaluate whether or not desired characteristics (desired sound quality) can be obtained with respect to the filter coefficient represented by a fixed word length.

Therefore, in the sound quality correcting apparatus, the microcomputer 4 determines whether the desired sound quality is obtained (suitable) in step S3 based on the set of filter coefficients obtained in step S2 shown in the flowchart of FIG. Whether it is inappropriate) is evaluated, and the process proceeds to step S4.

In step S4, the microcomputer 4 determines whether or not the evaluation of "appropriateness" has been made in step S3. If Yes, the process proceeds to step S5, and if No, the process proceeds to step S6.

In step S6, since the evaluation made in step S3 indicates "inappropriateness", the microcomputer 4 converts each filter coefficient of the set obtained in step S2 into a signal for obtaining a desired sound quality. The value is adjusted to a value, the process returns to step S3, and the set of adjusted filter coefficients is evaluated again. Then, in step S4, the respective routines of steps S3, S4, and S6 are repeatedly executed until the determination is Yes (until it is determined that the desired sound quality is obtained).

Next, if Yes is determined in step S4, the microcomputer 4 supplies the set of filter coefficients to the DSP 3 in step S5. And
The DSP 3 uses the (tentatively determined) set of filter coefficients obtained in step S2, or
The filter processing of the audio data supplied from the input terminal 1 is performed by using the set of filter coefficients adjusted in step 6, and this is supplied to an external device such as a speaker device through the output terminal 2 to obtain the data shown in FIG. All the routines in the flowchart shown in FIG.

The specific operations of steps S3 to S6 will be described. When the sound quality correction device is a graphic equalizer, a desired frequency gain characteristic, a desired center frequency value, and a desired center frequency value input as input parameters by a user. Is stored in each evaluation item memory 12 shown in FIG. Alternatively, when the sound quality correction device is a tone controller, the level of the flat portion of the desired frequency characteristic and the desired cutoff frequency, which are input as input parameters by the user, are stored in each evaluation item memory 12.

On the other hand, when the set of filter coefficients is provisionally determined by the filter operation unit 10, the provisionally determined set of filter coefficients is supplied to the evaluation unit 14 and the selection switch 15 via the coefficient change unit 11. .

When the provisionally determined set of filter coefficients is supplied, the evaluation unit 14 receives the desired frequency gain characteristic and the desired center frequency stored in each evaluation item memory 12 via the changeover switch 13. Import the values etc. in order,
Based on these, a set of filter coefficients is evaluated, and the evaluation result is supplied to the coefficient changing unit 11 and the selection switch 15.

That is, the evaluation of the set of filter coefficients with respect to the “desired frequency gain characteristic” is performed by setting the transfer function expressed by the above-described expression (1) to Z = e ^jw (ω = 2πf). It is determined by taking the absolute value. In this calculation, since a gain characteristic may be obtained for a certain ω for each evaluation scale, evaluation can be performed with a relatively small amount of calculation.

In the case where "desired gain characteristics at desired upper frequency and / or lower frequency" are input as "desired frequency gain characteristics", ω = 0
(Lower end frequency), and gain characteristics when ω is around fs / 2 are evaluated.

In the case of a graphic equalizer, if the result falls within a certain range centered on 0 dB, the set of filter coefficients is evaluated as “appropriate”, and if the result does not fall within the certain range, it is evaluated. The set of filter coefficients is evaluated as “unsuitable”. Further, in the case of a tone controller, a set of filter coefficients is evaluated as “appropriate” if the gain is within a certain range around the desired gain, and if not within the certain range, the filter coefficient is evaluated. Evaluate the set as "Inappropriate".

As described above, the evaluation result from the evaluation unit 14 is supplied to the coefficient changing unit 11. Coefficient changing unit 11
When the evaluation result of “inappropriate” is supplied, each filter coefficient of the set is adjusted by increasing or decreasing the minimum unit of the finite word length, and is supplied to the evaluation unit 14 and the selection switch 15. The evaluation unit 14 evaluates the adjusted set of filter coefficients again. Then, “evaluation” and “adjustment” of such a set of filter coefficients are repeatedly performed until the evaluation unit 14 evaluates “suitability”.

Next, the evaluation for the "desired center frequency" of the set of filter coefficients in the case of the graphic equalizer is performed by detecting "the amount of deviation of the center frequency from the desired value".

In this method, the gain characteristics of ω at several points near fc are obtained, the magnitudes of the gain values are compared, and the center frequency is detected. If the center frequency falls within a certain range around the desired center frequency, the “appropriateness” is evaluated. If the center frequency is not within the range, the “inappropriateness” is evaluated. The above-mentioned “adjustment” is performed by increasing or decreasing the minimum unit.

Next, the evaluation of the set of filter coefficients for the "desired center frequency level" in the case of a graphic equalizer is performed by detecting "the amount of deviation of the level at the center frequency from a desired value". .

This is because the gain at the center frequency is
If it is within a certain range around the desired value, it is evaluated as “approved”. If not, it is evaluated as “unsuitable”, and each filter coefficient is increased or decreased by the minimum unit of finite word length. The above-mentioned “adjustment” is performed. Next, the evaluation for the "desired frequency sharpness" of the set of filter coefficients in the case of a graphic equalizer is performed by detecting "the amount of deviation of the frequency sharpness from a desired value".

In this method, the gain characteristics of ω at several points near fc are obtained, the gain value at the center frequency and ω at which the gain value is separated by a fixed value are detected, and the difference between the center frequency and this ω is determined as desired. If it is within a certain range compared to the difference, it is evaluated as “fitness”. If not, it is evaluated as “inappropriate”, and each filter coefficient is increased or decreased by the minimum unit of finite word length. The above-mentioned “adjustment” is performed.

Next, the evaluation of the set of filter coefficients for the "level of the flat portion of the desired frequency characteristic" in the case of the tone controller is based on the "deviation from the level of the flat portion of the desired frequency characteristic". Evaluate by detecting. If this deviation is within a certain range, it is evaluated as “appropriate”.
Is evaluated, and each filter coefficient is increased or decreased for each minimum unit of a finite word length, and the above-mentioned “adjustment” is performed.

Next, the evaluation of the set of filter coefficients for the "desired cutoff frequency" in the case of the tone controller is performed by detecting the "deviation from the desired cutoff frequency". If this deviation is within a certain range, it is evaluated as “appropriate”; if it is not, it is evaluated as “inappropriate”, and each filter coefficient is increased or decreased by the minimum unit of finite word length. Perform "adjustment".

Next, the evaluation section 14 performs evaluation and adjustment based on each evaluation item as described above, and when the “suitability” evaluation result is obtained without adjustment, the evaluation section 14 controls the selection switch 15 to be turned on. The set of filter coefficients from the filter operation unit 10 is supplied to the sound quality correction circuit 16 of the DSP 3 as it is.
When the set of filter coefficients is adjusted, the selection switch 15 is turned on when the evaluation of the “suitability” is obtained in the evaluation unit 14, and the set of filter coefficients adjusted by the coefficient changing unit 11 is adjusted. Is supplied to the sound quality correction circuit 16 of the DSP 3.

The sound quality correction circuit 16 has a configuration in which the secondary IIR filters as shown in FIG. 6 are connected in multiple stages. When a set of filter coefficients is supplied, the sound quality correction circuit 16 uses each filter coefficient of this set. The audio data supplied from the input terminal 1 is filtered to correct the sound quality.

At this time, when the sound quality correcting device is a graphic equalizer, the sound quality correcting circuit 16 performs a filtering process by a single precision operation when the center frequency is in a high frequency range, and performs a finite word length when the center frequency is in a low frequency range. Is performed by a double-precision operation to lengthen. Alternatively, when the sound quality correction device is a tone controller, filtering is performed by a single precision operation when the cutoff frequency is high, and filtering is performed by a double precision operation that lengthens a finite word length when the cutoff frequency is low. Perform processing.

Then, the audio data which has been subjected to the filtering processing by switching between the single precision operation and the double precision operation is
The signal is supplied to an external device such as a speaker device via the output terminal 2. As a result, it is possible to obtain a sound output or the like having a desired sound quality.

As is clear from the above description, the first
The sound quality correction apparatus according to the embodiment is a filter operation unit 1
The evaluation unit 14 evaluates whether or not a desired sound quality can be obtained. The evaluation unit 14 evaluates whether the desired sound quality can not be obtained (inappropriateness). The changing unit 11 adjusts the sound quality to obtain a desired sound quality and uses the adjusted sound quality in the filtering process of the sound quality correction circuit 16.

That is, since a set of filter coefficients is obtained by calculation, it is possible to use a small-capacity coefficient table as a coefficient table, thereby reducing the cost of the sound quality correction apparatus. Can be.

The filtering process requiring real-time processing is executed by the DSP 3 (or logic circuit), and the determination of the set of filter coefficients depending on the user's instruction is executed by the microcomputer 4. Since the necessary set of work is shared by the DSP 3 and the microcomputer 4, the hardware processing and the software processing can be selectively used, the hardware cost can be reduced, and the sound quality correction device can be reduced in cost. it can.

Further, in the sound quality correction circuit 16 of the DSP 3, the filtering process is performed by switching between the single precision operation and the double precision operation in accordance with the center frequency and the cutoff frequency. This can further reduce the cost of the sound quality correction device.

In the above description of the first embodiment, the DSP 3 and the microcomputer 4 are provided separately. However, since the DSP 3 and the microcomputer 4 are both arithmetic circuits under program control, they are both provided. You may make it comprise integrally.

Next, a sound quality correcting apparatus according to a second embodiment of the present invention will be described.

In the description of the sound quality correcting apparatus according to the second embodiment, the same reference numerals are given to the parts which exhibit the same operations as those of the sound quality correcting apparatus according to the first embodiment.
Duplicate explanations will be avoided.

That is, the sound quality correcting device according to the second embodiment is supplied through an input terminal 1 in addition to the configuration of the sound quality correcting device according to the first embodiment as shown in FIG. A one-sampling-period detection unit 20 that detects one sampling period of the extracted audio data, and a buffer circuit 21 (buffer) that stores a set of filter coefficients.

Such a sound quality correction device is provided by the evaluation unit 14
However, the selection switch 15 is turned on so that the set of filter coefficients provisionally determined by the filter operation unit 10 is supplied to the buffer 21 as it is, and the set of filter coefficients temporarily determined is adjusted by the coefficient change unit 11. In this case, the selection switch 15 is turned on so that a set of filter coefficients is supplied to the buffer 21 for each adjustment.

On the other hand, one sampling period detecting section 20
One sampling period of the audio data supplied via the input terminal 1 is detected, and this detection output is supplied to the buffer 21.

The buffer 21 first stores the tentatively determined set of filter coefficients. When the tentatively determined set of filter coefficients is adjusted by the coefficient changing unit 11, the one sampling period detecting unit 20 , The currently stored tentatively determined set of filter coefficients is simultaneously re-stored (updated) within one sampling period with the new set of adjusted filter coefficients.

The buffer 21 performs such an updating operation until a final set of filter coefficients is formed by the above-described adjustment, and stores the finally adjusted set of filter coefficients. Based on the detection output from the one sampling period detection unit 20, the signal is supplied to the sound quality correction circuit 16 of the DSP 3 every one sampling period.

As a result, it is possible to change (adjust) the set of filter coefficients in real time.
The same effects as those of the sound quality correction device according to the first embodiment can be obtained.

Next, a sound quality correcting device according to a third embodiment of the present invention will be described.

In the description of the sound quality correcting apparatus according to the third embodiment, the same reference numerals are given to the parts which exhibit the same operations as those of the sound quality correcting apparatus according to the second embodiment.
Duplicate explanations will be avoided.

That is, the sound quality correcting device according to the third embodiment is supplied through an input terminal 1 in addition to the configuration of the sound quality correcting device according to the second embodiment as shown in FIG. It has a zero-crossing determination unit 22 that detects a timing (zero-crossing point) at which the obtained audio data becomes a zero level and supplies the detection output to the buffer 21.

In such a sound quality correcting device, as described above, the set of filter coefficients stored in the buffer 21 is simultaneously changed within one sampling period, and the finally adjusted set of filter coefficients is stored. The buffer 21 supplies the set of filter coefficients to the sound quality correction circuit 16 of the DSP 3 at the timing when the input audio data crosses zero based on the detection output from the zero cross determination unit 22.

As a result, it is possible to reduce the change in the output audio data due to the change in the filter coefficient in the sound quality correction circuit 16, to enable a more natural and favorable filtering process, and to perform the above-described first and second filtering processes. The same effect as that of the sound quality correction device according to the second embodiment can be obtained.

The above embodiments are merely examples of the present invention, and various changes can be made according to the design and the like within a range not departing from the technical idea of the present invention. Of course.

[0081]

The sound quality correcting apparatus according to the present invention can reduce the filter coefficients stored in the filter coefficient storage means. For this reason, it is possible to use a small-capacity filter coefficient storage means, thereby reducing the cost of the sound quality correction device.

[Brief description of the drawings]

FIG. 1 is a block diagram of a main part of a sound quality correction device according to a first embodiment of the present invention.

FIG. 2 is a block diagram of a sound quality correction device according to the first embodiment.

FIG. 3 is a flowchart for explaining a sound quality correction operation of the sound quality correction device according to the first embodiment.

FIG. 4 is a block diagram of a main part of a second embodiment of the sound quality correction apparatus according to the present invention.

FIG. 5 is a block diagram of a main part of a third embodiment of the sound quality correction apparatus according to the present invention.

FIG. 6 is a block diagram showing a graphic equalizer formed by connecting secondary IIR filters in multiple stages.

FIG. 7 is a signal flowchart showing an algorithm of signal processing of the graphic equalizer.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Input terminal, 2 ... Output terminal, 3 ... DSP (digital signal processor) 4 ... Microcomputer (microcomputer), 10 ... Filter operation part 11 ... Coefficient change part, 12 ... Evaluation item memory, 13 ... Changeover switch 14 ... Evaluation Unit, 15 selection switch, 16 sound quality correction circuit 20 sampling period detection unit, 21 buffer, 2
2… Zero cross judgment section

Claims (7)

[Claims] 1. A filter calculating means for calculating a set of filter coefficients used for filtering audio information in accordance with a predetermined input parameter, and a set of filter coefficients obtained by the filter calculating means is set to the predetermined value. Evaluation means for evaluating whether the sound quality is appropriate or unsuitable for obtaining the sound quality according to the input parameter of the input parameter, when the evaluation of the inappropriateness is performed by the evaluation means, the predetermined input parameter In order to obtain the appropriate sound quality,
A filter coefficient adjusting unit that adjusts each filter coefficient of the set obtained by the filter operation unit; and if the evaluation unit evaluates aptitude, the filter coefficient set obtained by the filter operation unit is used. The audio information supplied from outside is filtered and output, and when the inappropriateness is evaluated by the evaluation means, the audio information is supplied from outside using the set of filter coefficients adjusted by the filter coefficient adjustment means. Filter means for filtering and outputting the processed audio information. 2. The sound quality correcting device according to claim 1, wherein said filter means is a graphic equalizer. 3. The predetermined input parameter may include a desired frequency gain characteristic and / or a desired center frequency value,
And / or the level of the desired center frequency, and / or
A desired frequency sharpness, and the evaluation means includes a deviation amount of the desired frequency gain characteristic and / or a deviation amount from a desired center frequency value,
And / or the amount of deviation from the desired center frequency level,
3. The sound quality correction device according to claim 2, wherein a set of filter coefficients obtained by said filter calculation means is evaluated based on a deviation amount from a desired frequency sharpness. 4. The sound quality correction device according to claim 1, wherein said filter means is a tone controller. 5. The predetermined input parameter is a level of a flat part of a desired frequency characteristic and / or a desired cutoff frequency, and the evaluation unit determines a level of the flat part of the desired frequency characteristic from the level of the flat part of the desired frequency characteristic. 5. The sound quality correction apparatus according to claim 4, wherein a set of filter coefficients obtained by said filter calculation means is evaluated based on a shift amount of the filter coefficient and / or a shift amount from a desired cutoff frequency. 6. The sound quality correcting apparatus according to claim 1, wherein said filter coefficient adjusting means adjusts each filter coefficient within one sampling period of said audio information. . 7. The filter coefficient adjustment unit according to claim 1, wherein the filter coefficient adjustment unit adjusts each filter coefficient at a timing when a level of audio information supplied from the outside crosses zero. The sound quality correction device as described.