      SUBROUTINE NOISE(NPT,Y,SIG)
C
C  ADDS NOISE AT THE 'SIG' STANDARD DEVIATION LEVEL
C
      DIMENSION Y(8001)
	INTEGER*4 MN
C      X=RAN(0)
	MN=2**16+1
      DO 200 I=1,NPT
      X=RAN(MN)
      IF(Y(I).LT.0.0)GO TO 150
      Y(I)=Y(I)+SIG*SQRT(Y(I))*(0.5-X)
      GO TO 200
150   Y(I)=Y(I)-SIG*SQRT(-Y(I))*(0.5-X)
200   CONTINUE
      RETURN
      END
