Le 29/07/2018 à 13:56, Samuel Gougeon a écrit :
Hello Lester,
Le 29/07/2018 à 13:18, arctica1963 a écrit :
Hello all,
I need to increase the dimensions over which the FFT is calculated to
avoid
edge effects,
AFAIK, padding the initial signal does not avoid edge effects (i guess
one deal with edges discontinuity).
It can even be the source of discontinuity, and so yield fake high fft
amplitudes at high frequencies.
It will be the case if the original signal S has no edge
discontinuity ( S(1)~S($)) but you padd
it with zeros while its edge does not fall to zeros (=> |S($)|>>0,
S($+1)==0). Even worse,
in this case, windowing the signal will no longer be effective, since
the padding will move
the discontinuity in the body of the padded signal instead of on
signal's edge.
Padding a signal increases the lowest frequency of its numerical FT,
that is the sampling frequency
of its FFT. AFAIUnderstand, there is no edge matter there.
But this is more a signal processing topic than a Scilab one.
Le 29/07/2018 à 13:18, arctica1963 a écrit :
Hello all,
I need to increase the dimensions over which the FFT is calculated to avoid
edge effects, and following the suggestion of Samuel Gougeon back in 2016,
this was recommended:
Scilab: 6.0.1
data = [1 2 3; 4 5 6; 7 8 9]
addedRows = 3; addedCols = 3;
tmp = [data ; data($, :) .*. ones(addedRows, 1)]; // add rows to bottom
tmp = [tmp tmp(:, $) .*. ones(1,addedCols)]; // add columns to right
tmp = [repmat(tmp(1, : ), addedRows, 1) ; tmp]; // add rows to top
paddedMat = [repmat(tmp(:,1) , 1, addedCols) tmp] // add columns to left
--> paddedMat = [repmat(tmp(:,1) , 1, addedCols) tmp] // add columns to left
paddedMat =
1. 1. 1. 1. 2. 3. 3. 3. 3.
1. 1. 1. 1. 2. 3. 3. 3. 3.
1. 1. 1. 1. 2. 3. 3. 3. 3.
1. 1. 1. 1. 2. 3. 3. 3. 3.
4. 4. 4. 4. 5. 6. 6. 6. 6.
7. 7. 7. 7. 8. 9. 9. 9. 9.
7. 7. 7. 7. 8. 9. 9. 9. 9.
7. 7. 7. 7. 8. 9. 9. 9. 9.
7. 7. 7. 7. 8. 9. 9. 9. 9.
OK: here the padding is not done with zeros. Sorry for my misunderstanding.
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