diff --git a/lib/degrade_snr.f90 b/lib/degrade_snr.f90
new file mode 100644
index 000000000..8e6efb35a
--- /dev/null
+++ b/lib/degrade_snr.f90
@@ -0,0 +1,20 @@
+subroutine degrade_snr(d2,npts,db)
+
+  integer*2 d2(npts)
+  real dat(60*12000)
+
+  dat(1:npts)=d2
+  p0=dot_product(dat(1:npts),dat(1:npts))/npts
+  s=sqrt(p0*(10.0**(0.1*db) - 1.0))
+  do i=1,npts
+     d2(i)=nint(dat(i) + s*gran())
+  enddo
+  
+!  dat(1:npts)=d2
+!  p1=dot_product(dat(1:npts),dat(1:npts))/npts
+!  print*,db,p0,s,10.0*log10(p1/p0)
+
+  return
+end subroutine degrade_snr
+
+