On Tuesday 08 August 2017 21:02:09 Fred van Stappen wrote:
> In your fft example:
I don't think I can explain the whole discrete-Fourier-transform (DFT) thing
because my English and my mathematical skills are limited, maybe read the
links I provided.
> A array is assigned to fftcomp:
> fftcomp.inpreal:= ar1;
The DFT transforms a series of complex values in time domain to a series of
complex values in frequency domain. The imaginary values of the input
normally are zero so "inpreal" accepts a series of real values.
> After this fftcomp.outreal produces a new array of float:
> frequdisp.traces.ydata:= fftcomp.outreal;
"outcomplex" returns the complex frequency values, "outreal" returns the
magnitude of the frequency values.
> Also fftcomp.windowfunc is defined.
> But what is the usage of windowfunc ?
The DFT "assumes" that the input sequence is repetitive -> if the input period
time is not exactly a multiple of the sample window there will be errors, see
attachment. A window function which weights samples in the middle of the
sequence more than at the ends can improve the situation.
> Here are the 3 and 4 that I am missing.
> What appends to the original ar1, what did the fftcomp to any of the data ?
> I suppose that windowfunc has to do with it, but I do not understand what
> he does.
The input data is untouched.
> On fft demo, on the right side, frequdisp, that uses
> frequdisp.traces.ydata, (the new fft array) what does it show ?
The right half of DFT frequency array is the mirror image with inverted
imaginary part of the left half so "outreal" only returns length(inpreal)/2 +
1 items. The first value is the DC-value, the last is the level of sampling
frequency / 2.
> Does fftcomp deals with channels (or must the array be split before)?
They must be split.
> By the way, one more time, I am ***very*** impressed.
> Other thing.
> I have found all the parts to make run my new toy: a RPi3B.
> Last nigth, installation offline of:
> --> micro-sd --> Rpi --> in one shot, out of the box.
> --> install.sh --> in one shot, out of the box.
> --> in one shot, out of the box.
> (Only a symlink must be added: libX11.so to libX11.so.6).
The libx11-devel package is needed.
> --> compile existing msegui projects --> ok --> run --> **OK**
And nonetheless there is no interest in Rpi community for MSEide+MSEgui.
A cross compiling and remote debugging environment for RaspberryPi with MSEide
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