| |
 |
|
| Computers Forum Index » Computer - DSP » Band Pass & Stop Band Filter Coef Transform from Low... |
|
Page 1 of 1 |
|
| Author |
Message |
| pdvmipv... |
 Posted: Tue Oct 27, 2009 8:08 pm |
|
|
|
Guest
|
Hello,
as I am not an expert I am asking help to transform the IIR Coefficients
of a Low Pass Butterworth 6 poles filter to Band Pass and Stop.
I coded my application in C and after performing the computation of the
normalized coefficient with normalized frequency of 1 Hz, I performed the
low pass to low pass transform and the low pass to high pass transform
obtaining the new coefficients. (To that I used a commercial library but in
it I am not able to find the others transform). Then I performed the
filtering of data with success. After I need to transform the normalized
coefficients to band pass and band stop but I have no idea of how to do
it.
Does anybody can help me with C code, examples, everything can help me, to
transform the low pass normalized coefficients to band pass and stop ?
Thanks in advance |
|
|
| Back to top |
|
|
|
| Rune Allnor... |
| Posted: Tue Oct 27, 2009 8:08 pm |
|
|
|
Guest
|
On 27 Okt, 20:12, "pdvmipv" <luigino.pagan... at (no spam) agustawestland.com>
wrote:
Quote: On 27 Okt, 17:08, "pdvmipv" <luigino.pagan... at (no spam) agustawestland.com
wrote:
Hello,
as I am not an expert I am asking help to transform the IIR
Coefficients
of a Low Pass Butterworth 6 poles filter to Band Pass and Stop.
I coded my application in C and after performing the computation of
the
normalized coefficient with normalized frequency of 1 Hz, I performed
the
low pass to low pass transform and the low pass to high pass transform
obtaining the new coefficients. (To that I used a commercial library
but in
it I am not able to find the others transform). Then I performed the
filtering of data with success. After I need to transform the
normalized
coefficients to band pass and band stop but I have no idea of how to
do
it.
Does anybody can help me with C code, examples, everything can help me,
to
transform the low pass normalized coefficients to band pass and stop ?
Thanks in advance
The book by Proakis and Manolakis has the transforms, but be
warned that the editions up to and including the 3rd contain
typos. The typos were corrected for the 4th edition.
Rune
If anybody have already performed such a transformation and have a C code
or in other language please send it to me. I have already took a look at
the first book but as I am not an expert I do not understand how to
implement the transfomation with a programming language.
The trick is to keep the filter on a biquad representation
(as a set of fractions of 2nd order polynomials) and not
multiply out the whole expressions. If you do that, the
transforms are trivial - albeit tedious.
Rune |
|
|
| Back to top |
|
|
|
| Rune Allnor... |
| Posted: Tue Oct 27, 2009 8:08 pm |
|
|
|
Guest
|
On 27 Okt, 17:08, "pdvmipv" <luigino.pagan... at (no spam) agustawestland.com>
wrote:
Quote: Hello,
as I am not an expert I am asking help to transform the IIR Coefficients
of a Low Pass Butterworth 6 poles filter to Band Pass and Stop.
I coded my application in C and after performing the computation of the
normalized coefficient with normalized frequency of 1 Hz, I performed the
low pass to low pass transform and the low pass to high pass transform
obtaining the new coefficients. (To that I used a commercial library but in
it I am not able to find the others transform). Then I performed the
filtering of data with success. After I need to transform the normalized
coefficients to band pass and band stop but I have no idea of how to do
it.
Does anybody can help me with C code, examples, everything can help me, to
transform the low pass normalized coefficients to band pass and stop ?
Thanks in advance
The book by Proakis and Manolakis has the transforms, but be
warned that the editions up to and including the 3rd contain
typos. The typos were corrected for the 4th edition.
Rune |
|
|
| Back to top |
|
|
|
| Clay... |
| Posted: Tue Oct 27, 2009 8:08 pm |
|
|
|
Guest
|
On Oct 27, 12:08 pm, "pdvmipv" <luigino.pagan... at (no spam) agustawestland.com>
wrote:
Quote: Hello,
as I am not an expert I am asking help to transform the IIR Coefficients
of a Low Pass Butterworth 6 poles filter to Band Pass and Stop.
I coded my application in C and after performing the computation of the
normalized coefficient with normalized frequency of 1 Hz, I performed the
low pass to low pass transform and the low pass to high pass transform
obtaining the new coefficients. (To that I used a commercial library but in
it I am not able to find the others transform). Then I performed the
filtering of data with success. After I need to transform the normalized
coefficients to band pass and band stop but I have no idea of how to do
it.
Does anybody can help me with C code, examples, everything can help me, to
transform the low pass normalized coefficients to band pass and stop ?
Thanks in advance
The book "Discrete-Time Signal Processing" by Oppenheim and Schafer
has the transformation equations for converting lowpass to bandpass
and highpass and bandstop filters. I have the 1989 version and the
details you want start on page 430.
IHTH,
Clay |
|
|
| Back to top |
|
|
|
| pdvmipv... |
| Posted: Tue Oct 27, 2009 11:12 pm |
|
|
|
Guest
|
Quote: On 27 Okt, 17:08, "pdvmipv" <luigino.pagan... at (no spam) agustawestland.com
wrote:
Hello,
as I am not an expert I am asking help to transform the IIR
Coefficients
of a Low Pass Butterworth 6 poles filter to Band Pass and Stop.
I coded my application in C and after performing the computation of
the
normalized coefficient with normalized frequency of 1 Hz, I performed
the
low pass to low pass transform and the low pass to high pass transform
obtaining the new coefficients. (To that I used a commercial library
but in
it I am not able to find the others transform). Then I performed the
filtering of data with success. After I need to transform the
normalized
coefficients to band pass and band stop but I have no idea of how to
do
it.
Does anybody can help me with C code, examples, everything can help me,
to
transform the low pass normalized coefficients to band pass and stop ?
Thanks in advance
The book by Proakis and Manolakis has the transforms, but be
warned that the editions up to and including the 3rd contain
typos. The typos were corrected for the 4th edition.
Rune
If anybody have already performed such a transformation and have a C code
or in other language please send it to me. I have already took a look at
the first book but as I am not an expert I do not understand how to
implement the transfomation with a programming language. Thanks in advance |
|
|
| Back to top |
|
|
|
| Rune Allnor... |
| Posted: Wed Oct 28, 2009 9:08 am |
|
|
|
Guest
|
On 28 Okt, 09:15, "pdvmipv" <luigino.pagan... at (no spam) agustawestland.com>
wrote:
Quote: Starting from the array of the above normalized coefficients what are the
steps to perform the transformation of the coefficient in order to filter,
- Find the transforms in a textbook.
- Analytically derive the transformed biquads.
- Implement the derived formulas in a programming
language of your choise.
- Apply the functions to your prototype filter.
- Use the resulting coefficients when filtering
your data.
Rune |
|
|
| Back to top |
|
|
|
| pdvmipv... |
| Posted: Wed Oct 28, 2009 12:15 pm |
|
|
|
Guest
|
Quote: On 27 Okt, 20:12, "pdvmipv" <luigino.pagan... at (no spam) agustawestland.com
wrote:
On 27 Okt, 17:08, "pdvmipv" <luigino.pagan... at (no spam) agustawestland.com
wrote:
Hello,
as I am not an expert I am asking help to transform the IIR
Coefficients
of a Low Pass Butterworth 6 poles filter to Band Pass and Stop.
I coded my application in C and after performing the computation of
the
normalized coefficient with normalized frequency of 1 Hz, I
performed
the
low pass to low pass transform and the low pass to high pass
transform
obtaining the new coefficients. (To that I used a commercial
library
but in
it I am not able to find the others transform). Then I performed
the
filtering of data with success. After I need to transform the
normalized
coefficients to band pass and band stop but I have no idea of how
to
do
it.
Does anybody can help me with C code, examples, everything can help
me,
to
transform the low pass normalized coefficients to band pass and stop
?
Thanks in advance
The book by Proakis and Manolakis has the transforms, but be
warned that the editions up to and including the 3rd contain
typos. The typos were corrected for the 4th edition.
Rune
If anybody have already performed such a transformation and have a C
code
or in other language please send it to me. I have already took a look
at
the first book but as I am not an expert I do not understand how to
implement the transfomation with a programming language.
The trick is to keep the filter on a biquad representation
(as a set of fractions of 2nd order polynomials) and not
multiply out the whole expressions. If you do that, the
transforms are trivial - albeit tedious.
Rune
In fact it is what I do.
I Comupute the normalized IIR Coefficient for a 6 order butterworth filter
(Sample Rate 1Hz and Cutoff 1/2 pi=0.15915 Hz) giving the following biquad
filter coefficients (b0,b1,b2,a1,a2):
"1.267923e-01, 2.535845e-01, 1.267923e-01, -5.960975e-01, 1.032665e-01"
"1.441050e-01, 2.882099e-01, 1.441050e-01, -6.774909e-01, 2.539108e-01"
"1.887428e-01, 3.774856e-01, 1.887428e-01, -8.873498e-01, 6.423210e-01"
"5.619045e-309, 5.271038e-309, 0.000000e+00, 2.529616e-321,
-1.555730e+00"
"-1.567740e+00, 3.667700e-01, 6.191000e-01, 9.555300e-01, -3.902100e-01"
"8.353800e-01, -1.138500e-01, -7.781000e-02, -1.499000e-01, 9.041000e-02"
Then I have two functions to transform from low pass to low pass and low
pass to high pass. I do not have the source code of such a functions. But
what I am not able to do are the others trasnformations: band pass and stop
band.
Starting from the array of the above normalized coefficients what are the
steps to perform the transformation of the coefficient in order to filter,
for example, a signal sampled at 512 sample per seconds with band stop
cutoff freqs of fc1 40 Hz, fc2 80 Hz and similary a band pass filter with
the same low and high cutoff frequencies ?
Thanks |
|
|
| Back to top |
|
|
|
| Al Clark... |
| Posted: Wed Oct 28, 2009 5:38 pm |
|
|
|
Guest
|
Rune Allnor <allnor at (no spam) tele.ntnu.no> wrote in news:813a6fda-6508-4557-9999-
b92243778e1f at (no spam) z2g2000yqm.googlegroups.com:
Quote: On 28 Okt, 09:15, "pdvmipv" <luigino.pagan... at (no spam) agustawestland.com
wrote:
Starting from the array of the above normalized coefficients what are the
steps to perform the transformation of the coefficient in order to filter,
- Find the transforms in a textbook.
- Analytically derive the transformed biquads.
- Implement the derived formulas in a programming
language of your choise.
- Apply the functions to your prototype filter.
- Use the resulting coefficients when filtering
your data.
Rune
Or buy a filter program that does everything for you. I ise QEDesign from
Momentum Data Systems (www.mds.com)
Al Clark
www.danvillesignal.com |
|
|
| Back to top |
|
|
|
|
|
All times are GMT
The time now is Mon Nov 23, 2009 11:01 pm
|
|