Device for correcting frequency characteristic of sound field

• US 5,541,866 A
• Filed: 04/14/1995
• Issued: 07/30/1996
• Est. Priority Date: 11/28/1991
• Status: Expired due to Term

• Current Assignee: JVC Kenwood Corporation
• Original Assignee: Kabushiki Kaisha Kenwood
• Inventors: Sato, Makoto, Nagashima, Norio
• Primary Examiner(s): Ramirez, Ellis B.
• Assistant Examiner(s): PEESO, THOMAS R
• Application Number:
  US08/422,764
• Time in Patent Office: 473 Days
• Field of Search: 381/103, 381/122, 381/108, 330/304, 330/306, 330/291, 364/724.2, 364/572
• US Class Current: 708/323
• CPC Class Codes: H03G 5/005 of digital signals
• CPC Class Codes: H03G 5/025 Equalizers; Volume or gain control in limited frequency bands
• CPC Class Codes: H03G 5/04 in untuned amplifiers
• CPC Class Codes: H03H 17/0294 Variable filters; Programmable filters
• CPC Class Codes: H03H 2017/0297 Coefficients derived from input parameters

Abstract

A transmission frequency characteristic compensating apparatus capable of obtaining a combination of parameter values allowing a synthetic characteristic not to exceed a predetermined level. The transmission frequency characteristic compensating apparatus has a plurality of filters whose filter coefficients and characteristic are determined in accordance with parameter values corresponding to the center frequency, peak factor, and gain. The apparatus is provided with an input unit 1 for setting parameter values of each filter, an optimum parameter value calculating unit 2 for calculating optimum parameters of a designated filter so as to set the synthetic characteristic of a filter group obtained from the parameter values of the designated filter, within the range of the predetermined level, and a control unit 5 for displaying the frequency characteristic of the designated filter and filter group in accordance with the calculated optimum parameter values.

Claims

1. Sound field frequency characteristic compensation apparatus comprising an input unit (1) for entering object data of gain values respectively at a plurality of predetermined frequency points in a sound field frequency band, the gain values specifying an object frequency characteristics for compensation, a processing unit (2) for determining parameters which define filters to be set according to the object data of gain values entered by said input unit, and a variable filter unit (4) for setting filters on the basis of the determined parameters to approximate the object frequency characteristics with synthesized frequency characteristics of the set filters, wherein

(1) said processing unit determines a first filter of peaking type or notch type which has a center frequency equal to the frequency point associated with the maximum or minimum gain value in the object data, and gain and peak factor estimated according to the object date of gain values,

(2) said processing unit obtains error values between the frequency characteristics of the determined first filter and the object frequency characteristics at the frequency points in each of sub-bands which are assigned by dividing the sound field frequency band and determines one sub-band having the maximum total error which is the total of error values in that sub-band,

(3) said processing unit determines a second filter which has a center frequency equal to the frequency point associated to the maximum or minimum error value in said determined one sub-band, and gain and peak factor estimated according to the error values, and

(4) said processing unit obtains error values between the synthesized frequency characteristics of the determined first and second filters and the object frequency characteristics at the frequency points in the sound field frequency band, determines one sub-band having the maximum total error except for a case where the obtained error value for every frequency point is within a predetermined tolerance, and repeats the above steps (3) and (4) to sequentially determine parameters for a third, a forth . . . filters.

2. Sound field frequency characteristic compensation apparatus of claim 1, wherein said variable filter unit has a function capable of setting n filters as the maximum number, and when there remain the error between the synthesized frequency characteristics of all the n set filters and the object frequency characteristics at any frequency point over the predetermined tolerance, the center frequency of the first filter is shifted by an estimated amount with respect to the frequency point associated with the maximum remaining error value and then the steps (1)-(4) is performed by said processing unit.

3. Sound field frequency characteristic compensation apparatus of claim 1, wherein the peak factor of the peaking filter or notch filter to be set is estimated from the difference in frequency (e.g., provisional band width) between the frequency points associated with the maximum and minimum gain values or error values.

4. Sound field frequency characteristic compensation apparatus of claim 1, the peak factor of the peaking filter or notch filter to be set is estimated as a constant value when the difference in gain between the maximum and minimum gain values or error values is smaller than a predetermined gain value.

5. Sound field frequency characteristic compensation apparatus of claim 1, wherein the peak factor of the peaking filter or notch filter is estimated from the difference in gain between the gain value at the filter center frequency and the gain value at the frequency point neighboring to the filter center frequency and the difference in frequency between the filter center frequency and the frequency point neighboring to the filter center frequency.

6. Sound field frequency characteristic compensation apparatus of claim 1, wherein after obtaining the error in the synthesized frequency characteristics of the first and second filters, the processing unit determines an alternative first filter the center frequency of which is shifted from that of the first filter by an amount estimated from the obtained error, obtains the error in the synthesized frequency characteristics of the alternative first filter and second filter, and determines which one of the errors before the center frequency shifting and after the center frequency shifting is smaller, and adopts either one of the originally determined first filter and the alternative first filter which has the smaller error.

7. Sound field frequency characteristic compensation apparatus of claim 1, wherein the estimation of the peak factor is performed by fuzzy estimation rules.

8. Sound field frequency characteristic compensation apparatus of claim 1, wherein said variable filter unit comprises a plurality of Bell-type bandpass digital filters and said processing unit determines the characteristic coefficients for the digital filters.