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Discussion Starter · #1 ·
Consider these 2 views of the same measurement

This one uses the default settings (100ms rise, 500ms window)

Text Plot Colorfulness


This one simply reduces the rise time to 10ms

Text Plot Colorfulness Screenshot


I understand this is an IR window question so I'm curious to know why this happens. Can anyone shed light on this?
 

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Hi all,

I checked the help, manual etc. But can you tell me what the "Rise Time" exactly is doing ? Because concerning windows for IR measurement/analysis I never came across the term "Rise Time" (might be because I'm german )
But also googleing was not satisfying.

Is it sth like Tukey, and Rise Time=0ms --> Rectangle ? and Rise Time = quite long --> similar ro Hann Window?




(Rise Time normally seems to be used for the time the Step Response Signal needs to rise from 10% to 90% )

Thanks and Regards
 

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Ok, but I did this already and it only says:
"The Rise Time control sets the width of the Left Hand window. Shorter settings give greater time resolution but make the frequency variation less easy to see." ...

"It refers to the duration of the left hand window"

What kind of window shape does the left window have? Rectangle?
And is the "Rise Time" exactly the length of the window?
 

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Discussion Starter · #7 ·
Ok, but I did this already and it only says:
"The Rise Time control sets the width of the Left Hand window. Shorter settings give greater time resolution but make the frequency variation less easy to see." ...

"It refers to the duration of the left hand window"

What kind of window shape does the left window have? Rectangle?
And is the "Rise Time" exactly the length of the window?
If you click the IR Windows button then you'll see the various options (hann, rectangular, blackman-harris et al). You can see this visually by going to the Impulse Graph, zooming out and checking the box (in the legend) to show the window.
 

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Ok, but I did this already and it only says:
"The Rise Time control sets the width of the Left Hand window. Shorter settings give greater time resolution but make the frequency variation less easy to see." ...

"It refers to the duration of the left hand window"

What kind of window shape does the left window have? Rectangle?
And is the "Rise Time" exactly the length of the window?
Well it says a bit more than that, in fact most of the section about how waterfalls are generated is about the effect of the left hand window and there are 4 images to illustrate the effect it has. There doesn't really seem much point in me simply reproducing the whole lot here in a forum post. The window types for spectral decay and waterfall plots are selected on the Analysis preferences tab, Spectral Decay Left and Spectral decay Right.
 

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I'm sorry, because I basically know what waterfalls and window functions are and how they are generated, I totally overread this "(the window types are selected via the Spectral Decay entries in the Analysis Preferences)."

So I was always searching (and asking) for the window type, because tried to change the Window (left and right side) in "Impulse" "IR Windows" - but this (of course) had no effect on the waterfalls.

So now I know:

Rise Time ist the time from the Start of the left window to the Peak of the IR (or maybee the time in ms that the the left window takes between 10% and 90% of the IR peak)
and that I have to change the window curve in the preferences.
 

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The 'rise time' terminology dates back to the late 80s and MLSSA. In MLSSA it referred to the 10% to 90% rise time of a left hand window formed by convolving a window function with a unit step (in essence, the step response of the chosen window function). The actual width of the window was much greater, depending on the window type - about twice the rise time for a Hann window, for example, or about 3 times the rise time for Blackmann-Harris. In REW the term is used to refer to the overall width of the left hand window, somewhat misusing it in the interest of retaining terminology that is in common use for CSD plots whilst adopting a definition that provides a clearer indication of what parts of the response lie inside and outside the chosen window settings. To obtain similar results to the MLSSA-style definition use an REW setting that is twice as long.
 
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