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FFT

thread575-95772

FFT

FFT

(OP)
Hello All!

I am a newbie at MATLAB.

If i plot the FFT of a signal such as Asin(2pi*w1*t)+Bsin(2pi*w2*t), the magnitudes are not scaled correctly. Any idea about this?

Also, I have a PSD plot for a surface irregularity. I need to reconstruct the original time history from this plot. Can anybody help me with this?



Thanks in advance
NS

RE: FFT

1) the scaling of FFTs is an arbitrary design choice. the help will explain exactly which choices the designer has made.

2) Not possible: PSD data does not include phase, so you cannot recreate the original waveform.

Cheers

Greg Locock

RE: FFT

(OP)
is it possible to use some dummy (random) phase data then?

RE: FFT

Of course you can. In that case you just recreate the real and imaginary values using the magnitude from your PSD and the random phase, and do an inverse FFT.

I haven't done this in Matlab, so there may be detail differences, but that will be the general procedure.

You may need to scale the result - check that by going through the complete loop

data ->FFT->spectrum->IFFT->data



Cheers

Greg Locock

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