[Help-gsl] Reg :: Passing File name as argument and normalization of fft function.

[Sumit Adhikari]

Hello All,
  I wrote a wrapper over gsl_fft_complex_forward and I am using it 
successfully with very high reliability.
I have two questions. as follows :

1. How do I pass file-name (whatever I am dumping) as parameter ?
2. How do I normalize FFT outputs (Some how like PSD output)?

The class is as follows :

// File fft.h
# include <iostream>
using namespace std ;

# include <gsl/gsl_errno.h>
# include <gsl/gsl_fft_complex.h>

# ifndef FFT_H
# define FFT_H

# define REAL(z,i) ((z) [2*(i)])
# define IMAG(z,i) ((z) [2*(i) + 1])

namespace tools {
class fft {
   public :
     fft();
     ~fft();
     void read(double data[],const int Npoints,double Fs,int DATA_DSMPLE);
};
}

# endif


// File fft.cpp
# include "fft.h"

namespace tools {
fft::fft(){}
fft::~fft(){}

void fft::read(double data[],const int Npoints,double Fs,int DATA_DSMPLE){

   double *fft_data_buff ;
   fft_data_buff = (double *) malloc (2*Npoints * sizeof(double));
   fft_data_buff = new double [2*Npoints] ;



   for (int i = 0 ; i < Npoints ;i++){
      REAL(fft_data_buff,i) = data[i] ;
      IMAG(fft_data_buff,i) = 0.0 ;
   }


   delete [] data ;

   gsl_fft_complex_wavetable* wavetable ;
   gsl_fft_complex_workspace* workspace ;

   wavetable = gsl_fft_complex_wavetable_alloc(Npoints);
   workspace = gsl_fft_complex_workspace_alloc(Npoints);

   int status = 
gsl_fft_complex_forward(fft_data_buff,1,Npoints,wavetable,workspace);

   double *fft_out ;
   fft_out = (double *) malloc (2*Npoints * sizeof(double));
   fft_out = new double [2*Npoints] ;

   FILE* fp_fft_data ;
   fp_fft_data = fopen("./fft.dat","w");

   for (int i = 0 ; i < Npoints ;i++){
      fft_out[i] = 
20*log10(sqrt(REAL(fft_data_buff,i)*REAL(fft_data_buff,i) + 
IMAG(fft_data_buff,i)*IMAG(fft_data_buff,i))) ;
   }

   delete [] fft_data_buff ;
   gsl_fft_complex_wavetable_free(wavetable);
   gsl_fft_complex_workspace_free(workspace);

   double *f ;
   f = (double *) malloc (Npoints >> 1 * sizeof(double));
   f = new double [Npoints >> 1] ;

   for(int i = 0 ; i < (Npoints >> 1) /DATA_DSMPLE; i++){
     f[i] = (Fs*i)/(Npoints );
     fprintf(fp_fft_data,"%0f %0f\n",f[i],fft_out[i]);
   }

    fclose(fp_fft_data);

}

}


Best Regards,

--

--------------------------------------------
Sumit Adhikari
System Design Engineer
austriamicrosystems AG
Business Unit : Automotive
Mob : 00-91-9885271710/00-91-9000161710