Hamidatul Husna Matondang
Dear Sir
My research is filtering in seismic signal. If I apply butterworth filter to my signal in SAC, I only get the result
of the filter. I want to know how much the value of pole and zero of Highpass Butterworth Filter in SAC.
Could you tell me, please.
Thank You Very Much.
Regards
Ami
-
Dear Amik Amik -
This is a strange request because a filter is not exactly the same as an instrument response, and representing one in the same way conveys little additional value to processing a signal. However, you can think of your need as similar to inverting a frequency-amplitude-phase table for an equivalent pole-zero representation. See the article in Seismological Research Letters, vol. 85, p 197ff (2014) by Anderson and Lees for some suitable approaches.
On 8 Jun 2014, at 11:14, amik Amik wrote:
Dear Sir
George Helffrich
My research is filtering in seismic signal. If I apply butterworth filter to my signal in SAC, I only get the result
of the filter. I want to know how much the value of pole and zero of Highpass Butterworth Filter in SAC.
Could you tell me, please.
Thank You Very Much.
Regards
Ami
_______________________________________________
sac-help mailing list
sac-help<at>iris.washington.edu
http://www.iris.washington.edu/mailman/listinfo/sac-help
george.helffrich<at>bris.ac.uk
-
Thank You Very Much Sir,
I've been read research paper that you recommended it
"Anderson Jake F. and Lees, J.M., (2013) Instrument Corrections by Time-Domain Deconvolution,
Seismological Research Letters. Vol. 85(1): pp. 197-201". From this paper, I found the statement :
Another common method is that of the TRANSFER
command in the widely used software package SAC(University
of California, 2012). This command uses a zero-phase highpass
or band-pass filter (through the freqlimits option) to
ensure the stability of the result. This filter is acausal and,
therefore, problematic as well.
I have some questions from statement above :
1. Is acausal filter valid only for TRANSFER command - freqlimits or almost the entire of
filter command like highpass, bandpass, or lowpass?
2. Do you know how many the values of poles of Filter in SAC? I mean If I apply the Butterworth
to my signal in SAC with "hp butter np 2 c 2" How many the value of poles in 2nd order/pole
Butterworth in SAC (Seismic Code Analysis)?
Thank You very much
Best Regards,
Ami
Pada Minggu, 8 Juni 2014 19:56, George Helffrich <George.Helffrich<at>bristol.ac.uk> menulis:
Dear Amik Amik -
This is a strange request because a filter is not exactly the same as an instrument response, and representing one in the same way conveys little additional value to processing a signal. However, you can think of your need as similar to inverting a frequency-amplitude-phase table for an equivalent pole-zero representation. See the article in Seismological Research Letters, vol. 85, p 197ff (2014) by Anderson and Lees for some suitable approaches.
On 8 Jun 2014, at 11:14, amik Amik wrote:
Dear Sir
George Helffrich
My research is filtering in seismic signal. If I apply butterworth filter to my signal in SAC, I only get the result
of the filter. I want to know how much the value of pole and zero of Highpass Butterworth Filter in SAC.
Could you tell me, please.
Thank You Very Much.
Regards
Ami
_______________________________________________
sac-help mailing list
sac-help<at>iris.washington.edu
http://www.iris.washington.edu/mailman/listinfo/sac-help
george.helffrich<at>bris.ac.uk
-
Hi Amik,
My two cents to the topic,
See below, please
HTH,
Milton
* * * * * * * * * * * * * * * * * * * * * * *
Milton P. PLASENCIA LINARES
Centro di Ricerche Sismologiche (CRS)
OGS - Istituto Nazionale di Oceanografia e di Geofisica Sperimentale
Borgo Grotta Gigante 42/C
(34010) Sgonico - Trieste - Italia
Tel: +39 040 2140 141 (Udine)
Tel: +39 040 2140 256 (Trieste)
Cel.: +39 331 6481 935
E-mail: mplasencia<at>inogs.it
ASAIN (Antarctic Seismographic Argentinean Italian Network)
*********************************
On Jun 10, 2014, at 2:54 AM, amik Amik <amik.mamat<at>yahoo.co.id> wrote:
Thank You Very Much Sir,
The command transfer performs deconvolution (using spectral division) to remove instrument response
I've been read research paper that you recommended it
"Anderson Jake F. and Lees, J.M., (2013) Instrument Corrections by Time-Domain Deconvolution,
Seismological Research Letters. Vol. 85(1): pp. 197-201". From this paper, I found the statement :
Another common method is that of the TRANSFER
command in the widely used software package SAC(University
of California, 2012). This command uses a zero-phase highpass
or band-pass filter (through the freqlimits option) to
ensure the stability of the result. This filter is acausal and,
therefore, problematic as well.
I have some questions from statement above :
1. Is acausal filter valid only for TRANSFER command - freqlimits or almost the entire of
filter command like highpass, bandpass, or lowpass?
and convolution to apply other instrument response; instead freqlimits use low pass and high pass filters
(IIR filters, zero phase and "acausal") to stabilize the result.
See the help transfer in SAC.
2. Do you know how many the values of poles of Filter in SAC? I mean If I apply the Butterworth
It is most complicated answer, but i think the most important here is:
to my signal in SAC with "hp butter np 2 c 2" How many the value of poles in 2nd order/pole
Butterworth in SAC (Seismic Code Analysis)?
When you use the filters is necessary to know that more poles we get, the sharper the cut-off,
but it can generate problems (acausal) to the filtered signal, so use the number of poles with attention.
Max poles number in SAC is 10. i always use 2 (4 maximum).
Other important aspect in SAC filtering to avoid the acausal effect of IIR filters is the npasses option,
use 2. the default in SAC lowpass command is 1.
I think that to obtain the values of poles you must use other software, eg. DSP package of MatLab.
Thank You very much
Best Regards,
Ami
Pada Minggu, 8 Juni 2014 19:56, George Helffrich <George.Helffrich<at>bristol.ac.uk> menulis:
Dear Amik Amik -
This is a strange request because a filter is not exactly the same as an instrument response, and representing one in the same way conveys little additional value to processing a signal. However, you can think of your need as similar to inverting a frequency-amplitude-phase table for an equivalent pole-zero representation. See the article in Seismological Research Letters, vol. 85, p 197ff (2014) by Anderson and Lees for some suitable approaches.
On 8 Jun 2014, at 11:14, amik Amik wrote:
Dear Sir
George Helffrich
My research is filtering in seismic signal. If I apply butterworth filter to my signal in SAC, I only get the result
of the filter. I want to know how much the value of pole and zero of Highpass Butterworth Filter in SAC.
Could you tell me, please.
Thank You Very Much.
Regards
Ami
_______________________________________________
sac-help mailing list
sac-help<at>iris.washington.edu
http://www.iris.washington.edu/mailman/listinfo/sac-help
george.helffrich<at>bris.ac.uk
_______________________________________________
sac-help mailing list
sac-help<at>iris.washington.edu
http://www.iris.washington.edu/mailman/listinfo/sac-help
-
Dear Amik Amik -
1. The filtering done in the TRANSFER function is not guaranteed causal. The other SAC filters are causal if they are one pass.
2. The number of filter poles is given by the NPOLES parameter in any of the filter commands (2 <= N <= 10). If you want to know their values, refer to any books/papers on filter design -- the pole positions on the unit circle are standard.
On 10 Jun 2014, at 01:54, amik Amik wrote:
Thank You Very Much Sir,
George Helffrich
I've been read research paper that you recommended it
"Anderson Jake F. and Lees, J.M., (2013) Instrument Corrections by Time-Domain Deconvolution,
Seismological Research Letters. Vol. 85(1): pp. 197-201". From this paper, I found the statement :
Another common method is that of the TRANSFER
command in the widely used software package SAC(University
of California, 2012). This command uses a zero-phase highpass
or band-pass filter (through the freqlimits option) to
ensure the stability of the result. This filter is acausal and,
therefore, problematic as well.
I have some questions from statement above :
1. Is acausal filter valid only for TRANSFER command - freqlimits or almost the entire of
filter command like highpass, bandpass, or lowpass?
2. Do you know how many the values of poles of Filter in SAC? I mean If I apply the Butterworth
to my signal in SAC with "hp butter np 2 c 2" How many the value of poles in 2nd order/pole
Butterworth in SAC (Seismic Code Analysis)?
Thank You very much
Best Regards,
Ami
Pada Minggu, 8 Juni 2014 19:56, George Helffrich <George.Helffrich<at>bristol.ac.uk> menulis:
Dear Amik Amik -
This is a strange request because a filter is not exactly the same as an instrument response, and representing one in the same way conveys little additional value to processing a signal. However, you can think of your need as similar to inverting a frequency-amplitude-phase table for an equivalent pole-zero representation. See the article in Seismological Research Letters, vol. 85, p 197ff (2014) by Anderson and Lees for some suitable approaches.
On 8 Jun 2014, at 11:14, amik Amik wrote:
Dear Sir
George Helffrich
My research is filtering in seismic signal. If I apply butterworth filter to my signal in SAC, I only get the result
of the filter. I want to know how much the value of pole and zero of Highpass Butterworth Filter in SAC.
Could you tell me, please.
Thank You Very Much.
Regards
Ami
_______________________________________________
sac-help mailing list
sac-help<at>iris.washington.edu
http://www.iris.washington.edu/mailman/listinfo/sac-help
george.helffrich<at>bris.ac.uk
george.helffrich<at>bris.ac.uk
-
If the intent is to use a Butterworth filter, it is best to use the SAC commands LP, BP, or HP. As George writes, one can make the filters causal or acausal.
The SAC versions of Butterworth filters is not a simple pole-zero filter, which is what one does with analog filtering. As it says in the BANDPASS help file: " These analog prototype filters are mapped to digital filters via the bilinear transformation, a transformation which preserves the stability of the analog prototypes." This trasform maps the Nyquist into infinity, so the lowpass filter drops of more rapidly than a pole-zero analog filter would do.
http://www.iris.edu/files/sac-manual/commands/bandpass.html
There is no reason to use TRANSFER unless one wants to do a truly pole-zero version of the filter.
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George Helffrich
Milton Plasencia
Arthur Snoke
