# Question in GW Open Data Workshop (2023)

**URL:** <https://ask.igwn.org/t/question-in-gw-open-data-workshop-2023/753>\
**Category:** Open Data Workshop\
**Created:** [May 23, 2023, 8:53am UTC](https://ask.igwn.org/t/question-in-gw-open-data-workshop-2023/753 "2023-05-23T08:53:44Z")\
**Posts on this page:** 3\
**Page:** 1

<div class="post-metadata">

**Author:** ![duss](https://avatars.discourse-cdn.com/v4/letter/d/5e9695/32.png) [@duss](https://ask.igwn.org/u/duss)\
**Post date:** [May 23, 2023, 8:53am UTC](https://ask.igwn.org/t/question-in-gw-open-data-workshop-2023/753/1 "2023-05-23T08:53:44Z")

</div>

Hi, I’m studying the Tuto\_3.2\_Parameter\_estimation\_for\_compact\_object\_mergers.ipynb from GW Open Data Workshop 2023. I can not proceed when I reached the cell 10 in this notebook (i.e., the `psd_alpha` variable is converting the `roll_off` applied to the strain data into the fractional value used by `gwpy`). I do not understand why we should do this. Could you please provide me some brief illustrations or reference papers?

---

<div class="post-metadata">

**Author:** ![virtuoso](https://avatars.discourse-cdn.com/v4/letter/v/8baadc/32.png) [@virtuoso](https://ask.igwn.org/u/virtuoso)\
**Post date:** [May 24, 2023, 1:08pm UTC](https://ask.igwn.org/t/question-in-gw-open-data-workshop-2023/753/2 "2023-05-24T13:08:14Z")

</div>

Hi @duss  
This should be intended in the same way we obtained the asd in [odw-2023/Tuto\_1.2\_Open\_Data\_access\_with\_GWpy.ipynb at main · gw-odw/odw-2023 · GitHub](https://github.com/gw-odw/odw-2023/blob/main/Tutorials/Day_1/Tuto_1.2_Open_Data_access_with_GWpy.ipynb) , i.e. you need to window your data before calculating the psd: here in 3.2 is done in a little different way with respect to 1.2, using the Tukey window for which ‘roll\_off’ is a parameter (see [bilby.gw.detector.strain\_data.InterferometerStrainData — bilby 2.1 documentation](https://lscsoft.docs.ligo.org/bilby/api/bilby.gw.detector.strain_data.InterferometerStrainData.html))

---

<div class="post-metadata">

**Author:** ![duss](https://avatars.discourse-cdn.com/v4/letter/d/5e9695/32.png) [@duss](https://ask.igwn.org/u/duss)\
**Post date:** [May 24, 2023, 2:05pm UTC](https://ask.igwn.org/t/question-in-gw-open-data-workshop-2023/753/3 "2023-05-24T14:05:29Z")

</div>

@virtuoso  
Thank you so much for the helpful explanation! This spurs more connections for what I’ve learnt. 🥰