I'm doing some sims in LTspice, that take a long time, 30+ minutes...so if I just sample say 20mS, using the Mr Blackman's window, at what LF should I ignore the results?
Truthiness makes me want to think that it is 100Hz, but the plots are deceiving me
Martin
Bum.... you only have to do that windowing stuff if you don't pick a start and end point on the waveform that does not make it wrap around and agree with itself coming up the other side afterwards.
Go look at when you want it to start and when you want it to end and then tell the FFT what those are without the windowing.
DNA
didnt understand a word of that :-(
Martin
symmetry of the waveform?
Martin,
Are you familiar with what windowing does? Remember, the FFT takes your data set and treats it as if it were a continuous signal. That is, if your data set is 20ms long then it will (effectively) repeat that set over and over again and look at the frequenc content of this (continuous) signal. If, when the pattern repeats (at 20.00x ms) there is now a large discontinuity, then this will created bogus high frequency components that really aren't in your original signal. Windowing is an attempt to "soften" those discontinuities and reduce these high frequency artifacts.
In terms of the low frequency stuff, if you truncate your signal then you might lose some of the low frequency information, but I don't think it could add any low frequency artifacts (but I'd have to really think about that to be sure).
Bob
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