Frequency float method and system for realizing a signal filter
View Patent ↗A method for realizing a digital filter in an electronic system. The method includes first determining the specific number of coefficients to be calculated for a design filter and calculating the value of some of the coefficients for the design filter, typically all but one. Next, a reference filter is selected having the same number of coefficients as the design filter and each coefficient of the reference filter is calculated. With the reference filter's coefficients, the method concludes by determining the value of the remaining coefficients of the design filter that were previously not calculated. The determination is based upon an arithmetic comparison to the coefficients of the reference filter. The system and method improve second-order filter response for certain filters implemented with a direct-form topology.
1. A method for realizing a filter, the method comprising:
receiving a signal at a digital filtering block of an electronic system;
determining a specific number of coefficients to be calculated for the filter;
calculating the value of some of the coefficients for the filter;
selecting a reference filter having coefficients;
calculating the value of at least some of the coefficients of the reference filter;
determining the value of the remaining uncalculated coefficients of the filter based upon an arithmetic comparison to the coefficients of the reference filter
generating a digital block in a digital filtering block of a electronic system for filtering a signal representing information with the filter such that the information represented changes.
2. The method of claim 1 , further comprising quantizing the calculated coefficients prior to determining the value of the remaining uncalculated coefficients.
3. The method of claim 1 , further comprising selecting filter parameters including a center frequency, Q, and gain for the filter.
4. The method of claim 3 , further comprising determining whether or not to calculate any coefficients of the filter based on an assessment of the filter parameters desired for the filter.
5. The method of claim 3 further comprising calculating coefficients based upon the determined center frequency, Q, and gain.
6. The method of claim 5 wherein the selection of parameters corresponds to a bell filter and the coefficients are calculated based upon:
a
0
=
g
sin
(
θ
o
)
+
2
Q
sin
(
θ
o
)
+
2
Q
,
a
1
=
-
4
Q
cos
(
θ
o
)
sin
(
θ
o
)
+
2
Q
,
a
2
=
2
Q
-
g
sin
(
θ
o
)
sin
(
θ
o
)
+
2
Q
;
a
1
=
A
o
+
A
1
+
A
2
-
a
0
-
a
2
;
and
b
1
=
-
a
1
b
2
=
1
-
a
0
-
a
2
.
7. The method of claim 5 wherein the selection of parameters corresponds to a band-pass filter and the coefficients are calculated based upon:
a
0
=
sin
(
θ
o
)
sin
(
θ
o
)
+
2
Q
,
b
1
=
4
Q
cos
(
θ
o
)
sin
(
θ
o
)
+
2
Q
;
b
1
=
B
1
+
2
A
0
-
2
a
0
;
and
a
2
=
-
a
0
a
1
=
0
b
2
=
2
a
0
-
1.
8. The method of claim 5 wherein the selection of parameters corresponds to a high-pass filter and the coefficients are calculated based upon:
a
0
=
Q
+
Q
cos
(
θ
o
)
sin
(
θ
o
)
+
2
Q
,
b
1
=
4
Q
cos
(
θ
o
)
sin
(
θ
o
)
+
2
Q
;
b
1
=
B
1
-
2
A
0
+
2
a
0
;
and
a
2
=
a
0
a
1
=
-
2
a
0
b
2
=
b
1
-
4
a
0
+
1.
9. The method of claim 5 wherein the selection of parameters corresponds to a low-pass filter and the coefficients are calculated based upon:
a
0
=
Q
-
Q
cos
(
θ
o
)
sin
(
θ
o
)
+
2
Q
,
b
1
=
4
Q
cos
(
θ
o
)
sin
(
θ
o
)
+
2
Q
;
and
a
2
=
a
0
a
1
=
2
a
0
b
2
=
1
-
4
a
0
-
b
1
.
10. The method of claim 1 , further comprising implementing receiving a first user input corresponding to the filter and receiving a second user input corresponding to adjusting the coefficients of the filter.
11. A system for realizing a filter, the system comprising:
an input for a digital signal;
an equalization component coupled to the input having at least one user-configurable filter, the equalization component including a filter realization component operable to:
determine a specific type of filter to be realized, the filter having a defined number of coefficients that correspond to filter elements;
calculate the value of some of the coefficients for the filter;
select a reference filter having coefficients;
calculate the value of the coefficients of the reference filter; and
determine the value of the remaining coefficients of the filter based upon an arithmetic comparison to the coefficients of the reference filter; and
an output for a filtered digital signal coupled to the equalization component.
12. The system of claim 11 , further comprising a user interface embodied in a computer platform and having software-enabled control features such that a user is operable to control the equalization component via the software executing on the computer platform.
13. The system of claim 11 , further comprising an analog-to-digital converter for converting an audio signal from analog to digital prior to the input and a digital-to-analog converter for converting the audio signal from digital to analog after the output.
14. The system of claim 11 wherein the filter comprises a filter from the group comprising a peaking filter, a bell-filter, a parametric filter, a band-pass filter, a band-cut filter, a low-pass filter, a high-pass filter, a low-cut filter, a high-cut filter, a high-shelf filter, a low-shelf filter, and a unity filter.
15. The system of claim 11 embodied within a rack-mountable standalone outboard device.