Hello GNURadio Community,
Please ignore the above problem, I figured it out.
George
On Sun, Apr 17, 2022 at 5:16 PM George Edwards <gedwards....@gmail.com>
wrote:
> Dear Gnuradio Community,
>
> I am writing an OOT signal processing algorithm in C++ that requires both
> fft and ifft. I use the Gnuradio C++ library to get the fft and ifft
> functions. To confirm understanding of setting up these functions, I wrote
> C++ OOT blocks for both fft and ifft blocks. I ran a complex sinusoid into
> the fft block and fed its output to the ifft block to reverse the process.
> In the GRC flowgraph, the time and frequency plots seem correct (the output
> of the ifft shows the sinusoidal frequency it recovers is right on mark).
>
> For further validation, I decided to compare Gnuradio C++ fft computation
> to that of Matlab. I created a Python QA file to Debug the fft block and
> examine the fft computation. For the experiment, I fed 8 complex data
> samples into the fft block to see how its fft computation compares to that
> of Matlab. The OOT fft computation was not correct! Here is a snippet of my
> C++ OOT code written to test the fft computation (below "in and out" points
> to the addresses of Gnuradio input/out data variables).
>
> memcpy(d_fft.get_inputbuf(), in, sizerof(gr_complex)*d_fft_size);
> d_fft.execute();
> memcpy(out, d_fft.get_output(), sizerof(gr_complex)*d_fft_size);
> gr_complex c_data[8];
> for(int i = 0; i < 8; i++) {
> c_data[i] = out[i];
> }
> As can be seen in my code, I wrote the fft output into the array variable
> c_data. c_data has 1+1j in c_data[0] and all the other elements of the
> array have values 0+0j. The values are all wrong (not the same as Matlab).
> So I am at a loss!
>
> I appreciate any suggestions?
>
> Thank you!
> George
>
