WSJT-X/fil658.f

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subroutine fil658(c1,n1,c2,n2)
C FIR lowpass filter designed using ScopeFIR
C Pass #1 Pass #2 Pass #3
C-----------------------------------------------
C fsample (Hz) 96000.0 24000 6000 Input sample rate
C Ntaps 47 47 47 Number of filter taps
C fc (Hz) 6000 1500 375 Cutoff frequency (-3 dB)
C fstop (Hz) 11025.0 2756.25 689.0625 Lower limit of stopband
C Ripple (dB) 0.06 0.06 0.06 Ripple in passband
C Stop Atten (dB) 41 41 41 Stopband attenuation
C fout (Hz) 24000.0 6000 1500 Output sample rate
parameter (NTAPS=47)
parameter (NH=NTAPS/2)
parameter (NDOWN=4) !Downsample ratio = 1/4
complex c1(n1)
complex c2(n1/NDOWN)
C Filter coefficients:
real a(-NH:NH)
data a/
+ 0.004066057444,-0.000483030239,-0.002085155775,-0.004036668720,
+ -0.005338083014,-0.004952374329,-0.002267639582, 0.002499787691,
+ 0.008113543743, 0.012522509052, 0.013441779030, 0.009233544068,
+ -0.000256999594,-0.013156485907,-0.025660797518,-0.032755808092,
+ -0.029602578877,-0.013013352845, 0.017249853203, 0.057885304099,
+ 0.102497204557, 0.142897857652, 0.171067807479, 0.181167084990,
+ 0.171067807479, 0.142897857652, 0.102497204557, 0.057885304099,
+ 0.017249853203,-0.013013352845,-0.029602578877,-0.032755808092,
+ -0.025660797518,-0.013156485907,-0.000256999594, 0.009233544068,
+ 0.013441779030, 0.012522509052, 0.008113543743, 0.002499787691,
+ -0.002267639582,-0.004952374329,-0.005338083014,-0.004036668720,
+ -0.002085155775,-0.000483030239, 0.004066057444/
n2=(n1-NTAPS+NDOWN)/NDOWN
k0=NH-NDOWN+1
C Loop over all output samples
do i=1,n2
c2(i)=0.
k=k0 + NDOWN*i
do j=-NH,NH
c2(i)=c2(i) + c1(j+k)*a(j)
enddo
enddo
return
end