WSJT-X/lib/wav11.f90

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subroutine wav11(d2,npts,dd)
! Convert i*2 data sampled at 12000 Hz to r*4 sampled at 11025 Hz.
parameter (NZ11=60*11025,NZ12=60*12000)
parameter (NFFT1=64*12000,NFFT2=64*11025)
integer*2 d2(NZ12)
real*4 dd(NZ11)
real x(NFFT2)
complex cx(0:NFFT1/2)
equivalence (x,cx)
save x,cx
jz=min(NZ12,npts)
x(1:jz)=d2(1:jz)
x(jz+1:)=0.0
call four2a(x,nfft1,1,-1,0) !Forwarxd FFT, r2c
df=12000.0/NFFT1
ia=5000.0/df
cx(ia:)=0.0
call four2a(cx,nfft2,1,1,-1) !Inverse FFT, c2r
npts=jz*11025.0/12000.0
fac=1.e-6
dd(1:npts)=fac*x(1:npts)
if(npts.lt.NZ11) dd(npts+1:NZ11)=0.0
return
end subroutine wav11