WSJT-X/lib/fil4.f90
Joe Taylor 88e47a5941 Working on implementing reference spectra.
git-svn-id: svn+ssh://svn.code.sf.net/p/wsjt/wsjt/branches/wsjtx@6600 ab8295b8-cf94-4d9e-aec4-7959e3be5d79
2016-04-08 15:23:32 +00:00

50 lines
1.7 KiB
Fortran

subroutine fil4(id1,n1,id2,n2)
! FIR lowpass filter designed using ScopeFIR
! fsample = 48000 Hz
! Ntaps = 49
! fc = 4500 Hz
! fstop = 6000 Hz
! Ripple = 1 dB
! Stop Atten = 40 dB
! fout = 12000 Hz
parameter (NTAPS=49)
parameter (NDOWN=4) !Downsample ratio
integer*2 id1(n1)
integer*2 id2(*)
real t(NTAPS)
data t/NTAPS*0.0/
! Filter coefficients:
real w(NTAPS)
data w/ &
0.000861074040, 0.010051920210, 0.010161983649, 0.011363155076, &
0.008706594219, 0.002613872664,-0.005202883094,-0.011720748164, &
-0.013752163325,-0.009431602741, 0.000539063909, 0.012636767098, &
0.021494659597, 0.021951235065, 0.011564169382,-0.007656470131, &
-0.028965787341,-0.042637874109,-0.039203309748,-0.013153301537, &
0.034320769178, 0.094717832646, 0.154224604789, 0.197758325022, &
0.213715139513, 0.197758325022, 0.154224604789, 0.094717832646, &
0.034320769178,-0.013153301537,-0.039203309748,-0.042637874109, &
-0.028965787341,-0.007656470131, 0.011564169382, 0.021951235065, &
0.021494659597, 0.012636767098, 0.000539063909,-0.009431602741, &
-0.013752163325,-0.011720748164,-0.005202883094, 0.002613872664, &
0.008706594219, 0.011363155076, 0.010161983649, 0.010051920210, &
0.000861074040/
save w,t
n2=n1/NDOWN
if(n2*NDOWN.ne.n1) stop 'Error in fil4'
k=1-NDOWN
do i=1,n2
k=k+NDOWN
t(1:NTAPS-NDOWN)=t(1+NDOWN:NTAPS) !Shift old data down in array t
t(1+NTAPS-NDOWN:NTAPS)=id1(k:k+NDOWN-1) !Insert new data at end of t
id2(i)=nint(dot_product(w,t))
enddo
return
end subroutine fil4