# Power spectral density PDFs

**URL:** https://discourse.obspy.org/t/power-spectral-density-pdfs/619
**Category:** Users Mailing List Archive
**Tags:** archive
**Created:** [March 13, 2017, 3:54pm UTC](https://discourse.obspy.org/t/power-spectral-density-pdfs/619 "2017-03-13T15:54:27Z")
**Posts on this page:** 4
**Page:** 1

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### Author: ![Hicks\_S.P](https://discourse.obspy.org/letter_avatar_proxy/v4/letter/h/e9c0ed/32.png) [@Hicks\_S.P](https://discourse.obspy.org/u/Hicks_S.P)
#### Post date: [March 13, 2017, 3:54pm UTC](https://discourse.obspy.org/t/power-spectral-density-pdfs/619/1 "2017-03-13T15:54:27Z")

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I’d like to calculate PSD PDFs using PPSD in ObsPy.

I have already done some processing of the data and the instrument response is removed.

Is it possible for PPSD to ‘know’ that an instrument response is already removed and the trace units are in velocity (as opposed to counts) to ensure that instrument response is not removed twice?

Or do I somehow have to somehow restore the instrument response before using PPSD?

Thanks,  
Steve

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### Author: ![megies](https://discourse.obspy.org/user_avatar/discourse.obspy.org/megies/32/9_2.png) [@megies](https://discourse.obspy.org/u/megies)
#### Post date: [March 13, 2017, 7:23pm UTC](https://discourse.obspy.org/t/power-spectral-density-pdfs/619/2 "2017-03-13T19:23:49Z")

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Short answer: You should use the raw data and station metadata whenever  
possible.

Long answer:  
In principle you might be able to misuse the PPSD(...,  
special\_handling='ringlaser') setting and using a dictionary with  
'sensitivity': 1 as `metadata`. But you're on your own with this special  
tinkering. I'd really recommend you use raw data and station metadata.

cheers,  
T

P.S.: How do you expect PPSD to know what units the data is you feed it?  
There is no way for PPSD to know this, in general it is assumed that all  
data that enter it are raw digitized data (i.e. the data described by  
station metadata in SEED or StationXML)

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### Author: ![Christian\_Weidle1](https://discourse.obspy.org/letter_avatar_proxy/v4/letter/c/aeb1de/32.png) [@Christian\_Weidle1](https://discourse.obspy.org/u/Christian_Weidle1)
#### Post date: [March 13, 2017, 7:24pm UTC](https://discourse.obspy.org/t/power-spectral-density-pdfs/619/3 "2017-03-13T19:24:48Z")

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You can supply a dummy paz with sensitivity 1 to already corrected data.

paz = {‘gain’: 1.,  
‘poles’: ,  
‘zeros’: ,  
‘sensitivity’: 1.}

Cheers  
Christian

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### Author: ![Christian\_Weidle1](https://discourse.obspy.org/letter_avatar_proxy/v4/letter/c/aeb1de/32.png) [@Christian\_Weidle1](https://discourse.obspy.org/u/Christian_Weidle1)
#### Post date: [March 13, 2017, 7:29pm UTC](https://discourse.obspy.org/t/power-spectral-density-pdfs/619/4 "2017-03-13T19:29:50Z")

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You can supply a dummy paz with sensitivity 1 to already corrected data.

paz = {‘gain’: 1.,  
‘poles’: ,  
‘zeros’: ,  
‘sensitivity’: 1.}

Cheers  
Christian