Graphic equalizers

• US 7,676,048 B2
• Filed: 05/11/2005
• Issued: 03/09/2010
• Est. Priority Date: 05/14/2004
• Status: Active Grant

• Current Assignee: Texas Instruments, Inc.
• Original Assignee: Texas Instruments, Inc.
• Inventors: Tsutsui, Ryo
• Primary Examiner(s): Mei; Xu
• Assistant Examiner(s): Paul; Disler
• Application Number:
  US11/128,064
• Publication Number:
  US 20050254564A1
• Time in Patent Office: 1,763 Days
• Field of Search: 381/103, 381 98- 99, 381/94.3, 381/101, 333/28.R, 333/28.T
• US Class Current: 381/103
• CPC Class Codes: H03G 5/025 Equalizers; Volume or gain control in limited frequency bands

Abstract

Graphic equalizer as a cascade of equalization filters with the gain of each individual filter compensated for the gain leakage from other filters. A linear approximation allows individual filter gains to be set to give desired frequency responses.

Claims

1. A digital graphic equalizer, comprising:

(a) a cascade of peak/notch filters F⁽¹⁾, F⁽²⁾, . . . , F^(N) where N is an integer greater than 1, and each of said filters has a transfer function which is a bilinear transform of an analog transfer function of the form

(s²+2K^1/2α

ω

₀s+ω

₀²s²)/(s²+2K<sup>−

1/2</sup>α

ω

₀s+ω

₀²s²)

with K a gain, α

a positive constant, and ω

₀ an analog center frequency;

(b) wherein said center frequency corresponding to F^(j) is equal to a band-edge frequency corresponding to F^(j+1) and/or F<sup>(j−

1)</sup> for j=1, 2, . . . N, and wherein α

is the same for all of said filters.

2. The equalizer of claim 1, further comprising:

(a) a low frequency shelf filter F_l coupled to said cascade, wherein F_l has a transfer function which is a bilinear transform of an analog transfer function of the form

(s+K^1/2ω

₀)/(s+K<sup>−

1/2</sup>ω

₀)

with K a gain and ω

₀ an analog band-edge frequency; and

(b) a high frequency shelf filter F_h coupled to said cascade, wherein said F_h has a transfer function which is a bilinear transform of an analog transfer function of the form

(K^1/2s+ω

₀)/(K<sup>−

1/2</sup>s+ω

₀)

with K a gain and ω

₀ an analog band-edge frequency;

(c) wherein for F_l the band-edge frequency equals the center frequency for F⁽¹⁾ and for F_h the band-edge frequency equals the center frequency for F^(N).

3. The equalizer of claim 1, further comprising:

(a) a controller coupled to said cascade, said controller operable to compute center frequency filter gains for said peak/notch filters with leak gain compensation from input desired center frequency filter gains for said peak/notch filters.

4. The equalizer of claim 3, wherein:

(a) said leak gain compensation uses a linear approximation.

5. The equalizer of claim 3, wherein:

(a) said leak gain compensation uses an iterated linear approximation.

6. A method of digital signal processor for graphic equalizer control, comprising:

(a) receiving a plurality of desired center frequency filter gains for a cascade of equalization filters, each of said filters has a transfer function which is a bilinear transform of an analog transfer function of the form

(s²+2K^1/2α

ω

₀s+ω

₀²s²)/(s²+2K<sup>−

1/2</sup>α

ω

₀s+ω

₀²s²)

with K a gain, α

a positive constant, and ω

₀ an analog center frequency, wherein said center frequency corresponding to the cascade of equalization filters is equal to a band-edge frequency corresponding to F^(j+1) and/or F<sup>(j−

1)</sup> for j=1, 2, . . . N, and wherein α

is the same for all of said filters;

(b) converting said desired center frequency filter gains into compensated center frequency filter gains for said cascade, wherein said converting compensates for leak gains.

7. The method of claim 6, wherein:

(a) said leak gains includes leak gains from low frequency and high frequency shelf filters having desired low frequency and high frequency gains.

8. The method of claim 6, wherein:

(a) said converting uses a linear approximation.