FFT

[neutralsteer]

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

 

[GregLocock]

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

 

[neutralsteer]

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

 

[GregLocock]

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