I'm using LTspiceXVII ( I run a simulation and make an FFT plot. Then I change a parameter and the time waveform updates, but the FFT plot doesn't update. I have only been able to see the updated results by creating a new FFT plot. How do I get the existing FFT plot to update?

9/27/22 Follow up edit: After making updates to the FFT window, I saved the settings in a .plt file with these contents:

[FFT of time domain data]
  Npanes: 1
     traces: 1 {524290,0,"V(out)"}
     X: ('M',0,10000,4.999e+006,5e+007)
     Y[0]: (' ',0,1e-008,20,1)
     Y[1]: ('K',0,-30000,30000,300000)
     Log: 1 2 0
     GridStyle: 1
     PltMag: 1

I pulled up a new FFT window on a new set of data and tried to apply these settings to the new FFT window by clicking the space bar. I got this error:

this error

How do I apply the saved FFT settings to a new FFT plot?

  • 6
    \$\begingroup\$ That’s just how it works. \$\endgroup\$
    – GodJihyo
    Sep 26, 2022 at 22:23

1 Answer 1


Since you had to manually perform an FFT after the simulation, it follows that you have to repeat the process everytime you need an FFT. There is no automatic process. If you're worried that you may lose the FFT plots, don't close the windows. If you need different FFT plots in the same window then you have two choices:

  1. use a .STEP, if your circuit allows, or
  2. export the data then collate the results.
  • \$\begingroup\$ I updated my original question with a followup. I was able to save the FFT settings in a file, but I can't figure out how to apply the settings to a new FFT plot. \$\endgroup\$
    – Sanjo
    Sep 27, 2022 at 14:56
  • \$\begingroup\$ Your edit has changed the OP. Since it looks like you're new to the site, don't do that -- it renders all the answers invalid, and makes it look like the people have wasted spending their free time to help you. I'm not saying htis is what you were after, just that this is likely that will be understood. As for your new edit, the message clearly states what's wrong: you don't have plot settings for FFT plots. \$\endgroup\$ Sep 27, 2022 at 17:55
  • \$\begingroup\$ Should I delete my new comments of the original post and post a new question? \$\endgroup\$
    – Sanjo
    Sep 28, 2022 at 18:18
  • \$\begingroup\$ Once, it happens, you can leave it now but, if you feel like you want two questions, go ahead. It's a Q&A site, after all. \$\endgroup\$ Sep 28, 2022 at 18:29
  • \$\begingroup\$ Okay. The reason I edited the original one is because the follow up question needed formatting, and the formatting doesn’t work out in this reply section. \$\endgroup\$
    – Sanjo
    Sep 28, 2022 at 18:33

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