# Different Time Series Plots and SNR when using pycbc and gwpy

**URL:** https://ask.igwn.org/t/different-time-series-plots-and-snr-when-using-pycbc-and-gwpy/339
**Category:** Open Data Workshop
**Tags:** odw-2022
**Created:** [May 31, 2022, 12:38pm UTC](https://ask.igwn.org/t/different-time-series-plots-and-snr-when-using-pycbc-and-gwpy/339 "2022-05-31T12:38:27Z")
**Posts on this page:** 2
**Page:** 1

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### Author: ![aravbj](https://avatars.discourse-cdn.com/v4/letter/a/ecc23a/32.png) [@aravbj](https://ask.igwn.org/u/aravbj)
#### Post date: [May 31, 2022, 12:38pm UTC](https://ask.igwn.org/t/different-time-series-plots-and-snr-when-using-pycbc-and-gwpy/339/1 "2022-05-31T12:38:27Z")

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I have been attempting the data challenge and while working on the second one I noticed that using gwpy to read the “.gwf” file gives a duration of data different from that given when reading using pycbc.

Since I needed to find the q\_transform as well I used the gwpy method first to load the data and then used the .to\_pycbc() method to calculate the SNR time series. The answer I got here for the SNR peak differed from what I got when reading directly using pycbc and proceeding as usual.

I am not sure how to proceed.

Edit: I am able to get a much better q transform plot when using the pycbc approach. I still do not understand why the duration of the data is different.  
 ![image](https://canada1.discourse-cdn.com/flex031/uploads/gwosc/original/1X/1a41593f34d9692ace2a472b1ea2c4b14ebc99e1.png)

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### Author: ![jonah](https://yyz1.discourse-cdn.com/flex031/user_avatar/ask.igwn.org/jonah/32/10_2.png) [@jonah](https://ask.igwn.org/u/jonah)
#### Post date: [June 1, 2022, 8:51pm UTC](https://ask.igwn.org/t/different-time-series-plots-and-snr-when-using-pycbc-and-gwpy/339/2 "2022-06-01T20:51:10Z")

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@aravbj Thank you for spotting this!

Some of the data files (file 1 and 2, I think) include some negative time values. Apparently, `gwpy` expects all time values to be positive, and seems to only read in the positive time values. I’ll try to fix this for next year.