subroutine filbig(id,nmax,f0,newdat,c4a,c4b,n4) C Filter and downsample complex data for X and Y polarizations, C stored in array id(4,nmax). Output is downsampled from 96000 Hz C to 1500 Hz, and the low-pass filter has f_cutoff = 375 Hz and C f_stop = 750 Hz. parameter (NFFT1=5376000,NFFT2=77175) integer*2 id(4,nmax) !Input data complex c4a(NFFT2),c4b(NFFT2) !Output data complex ca(NFFT1),cb(NFFT1) !FFTs of input real*8 df real halfpulse(8) !Impulse response of filter (one side) complex cfilt(NFFT2) !Filter (complex; imag = 0) real rfilt(NFFT2) !Filter (real) integer*8 plan1,plan2,plan3,plan4,plan5 logical first include 'fftw3.f' equivalence (rfilt,cfilt) data first/.true./ data halfpulse/114.97547150,36.57879257,-20.93789101, + 5.89886379,1.59355187,-2.49138308,0.60910773,-0.04248129/ save if(first) then npatience=FFTW_ESTIMATE ! npatience=FFTW_MEASURE C Plan the FFTs just once call sfftw_plan_dft_1d_(plan1,NFFT1,ca,ca, + FFTW_BACKWARD,npatience) call sfftw_plan_dft_1d_(plan2,NFFT1,cb,cb, + FFTW_BACKWARD,npatience) call sfftw_plan_dft_1d_(plan3,NFFT2,c4a,c4a, + FFTW_FORWARD,npatience) call sfftw_plan_dft_1d_(plan4,NFFT2,c4b,c4b, + FFTW_FORWARD,npatience) call sfftw_plan_dft_1d_(plan5,NFFT2,cfilt,cfilt, + FFTW_BACKWARD,npatience) C Convert impulse response to filter function do i=1,NFFT2 cfilt(i)=0. enddo fac=0.00625/NFFT1 cfilt(1)=fac*halfpulse(1) do i=2,8 cfilt(i)=fac*halfpulse(i) cfilt(NFFT2+2-i)=fac*halfpulse(i) enddo call sfftw_execute_(plan5) base=cfilt(NFFT2/2+1) do i=1,NFFT2 rfilt(i)=real(cfilt(i))-base enddo df=96000.d0/NFFT1 first=.false. endif C When new data comes along, we need to compute a new "big FFT" C If we just have a new f0, continue with the existing ca and cb. if(newdat.ne.0) then nz=min(nmax,NFFT1) do i=1,nz ca(i)=cmplx(float(id(1,i)),float(id(2,i))) cb(i)=cmplx(float(id(3,i)),float(id(4,i))) enddo if(nmax.lt.NFFT1) then do i=nmax+1,NFFT1 ca(i)=0. cb(i)=0. enddo endif call sfftw_execute_(plan1) call sfftw_execute_(plan2) newdat=0 endif C NB: f0 is the frequency at which we want our filter centered. C i0 is the bin number in ca and cb closest to f0. i0=nint(f0/df) + 1 nh=NFFT2/2 do i=1,nh !Copy data into c4a and c4b, j=i0+i-1 !and apply the filter function c4a(i)=rfilt(i)*ca(j) c4b(i)=rfilt(i)*cb(j) enddo do i=nh+1,NFFT2 j=i0+i-1-NFFT2 if(j.lt.1) j=j+NFFT2 c4a(i)=rfilt(i)*ca(j) c4b(i)=rfilt(i)*cb(j) enddo C Do the short reverse transform, to go back to time domain. call sfftw_execute_(plan3) call sfftw_execute_(plan4) n4=min(nmax/64,NFFT2) return end