Hi, I hope this is not off topic! I'm trying to make use of the FFTW library (V3.01) but I have some difficulties working out the data types which comes with the library - and possibly the coding too! Below I have pasted in my current source code which should calculate the FFT of real input data. The input is a sinusoid signal and I'm looking for non-zero data in the output vector but all I get is zeros. I'm fairly green in terms of c++ programming so there might be some really basic problems with my code. Furthermore, I'm not really sure how to extract data from the output vector (a vector of the fftw_complex) Does anyone know how to do this? Cheers Thomas // FFT specific int N = 256; // Input test signal double input[256]; char txt[256]; for(int indx=0; indx<256; indx++) { input[indx]=cos(2.f*22.f/7.f*1000.f*(indx/20000.f)); sprintf(txt,"sample[%d]= %f",indx,input[indx]); OutputDebugString(txt); } double *in; fftw_complex *out; fftw_plan p; in = (double *)fftw_malloc(sizeof(double) * N); out = (fftw_complex *)fftw_malloc(sizeof(fftw_complex) * N); p = fftw_plan_dft_r2c_1d(N, in, out, FFTW_MEASURE); fftw_execute(p); /* repeat as needed */ fftw_destroy_plan(p); in = input; fftw_free(in); fftw_free(out); for(int indx=0; indx<256; indx++) { sprintf(txt,"re[%d]=%f,& im[%d]=%f", indx, &out[indx][0], indx, &out[indx][1]); OutputDebugString(txt); sprintf(txt,"re[%d]=%f,& im[%d]=%f", indx, out[indx][0], indx, out[indx][1]); OutputDebugString(txt); }

# FFTW 3.01 and C++

Started by ●December 25, 2005

Reply by ●December 25, 20052005-12-25

Hi , I found a bug so here is the sourcecode that still isn't working! :) // FFT specific int N = 256; // Input test signal double input[256]; char txt[256]; for(int indx=0; indx<256; indx++) { input[indx]=cos(2.f*22.f/7.f*1000.f*(indx/20000.f)); sprintf(txt,"sample[%d]= %f",indx,input[indx]); OutputDebugString(txt); } double *in; fftw_complex *out; fftw_plan p; in = (double *)fftw_malloc(sizeof(double) * N); out = (fftw_complex *)fftw_malloc(sizeof(fftw_complex) * N); in = input; p = fftw_plan_dft_r2c_1d(N, in, out, FFTW_MEASURE); fftw_execute(p); /* repeat as needed */ for(int indx=0; indx<256; indx++) { sprintf(txt,"re[%d]=%f,& im[%d]=%f", indx, &out[indx][0], indx, &out[indx][1]); OutputDebugString(txt); } fftw_destroy_plan(p); fftw_free(in); fftw_free(out);

Reply by ●December 26, 20052005-12-26

I've not uaed the latest version of fftw, but it appears that you are missing several steps.. You create your raw data in the array input, but I never see you copy that to the array "in" that you are using for the fftw routines. I never see you use the "out" array before you free it up again. (actually you use the array immediately after you free it, so I'm surprised that you don't get some sort of exception.)

Reply by ●December 26, 20052005-12-26

Why do people use the fftw library routines on a dsp? I would assume that using DSP optimized libraries would get faster results, and be more optimized for memory access as well. I use fftw on the PC, for general purpose FFT calculations, but in that case, having source code that compiles cross platform is helpful. Also, I have not found better optimized distributable C/C++ FFT routines.

Reply by ●December 26, 20052005-12-26

"William C Bonner" <wbonner@wimsworld.com> wrote in message news:1135608574.878347.126730@g44g2000cwa.googlegroups.com...> Why do people use the fftw library routines on a dsp? > > I would assume that using DSP optimized libraries would get faster > results, and be more optimized for memory access as well. > > I use fftw on the PC, for general purpose FFT calculations, but in that > case, having source code that compiles cross platform is helpful. Also, > I have not found better optimized distributable C/C++ FFT routines. >Hi, Thanks for your reply. The transform is now working correctly. I found the bug this morning :) Cheers Thomas

Reply by ●December 27, 20052005-12-27

Heureka wrote:> in = (double *)fftw_malloc(sizeof(double) * N); > > out = (fftw_complex *)fftw_malloc(sizeof(fftw_complex) * N);Idk if it's the same with fftw_malloc as with the regular malloc, but you should not cast the result of a malloc(). you have to include stdlib.h (if i remember good) btw, you say it's C++, but you can call that C, cuz all you type here was in C

Reply by ●December 29, 20052005-12-29

Michel Rouzic wrote:> Idk if it's the same with fftw_malloc as with the regular malloc, but > you should not cast the result of a malloc(). you have to include > stdlib.h (if i remember good)You have to cast the result of malloc (or fftw_malloc, which has the same prototype) if you want it to work with a C++ compiler.