For a chromatogram of intensities—I(n)—where n is a RT position from 1 to N (which does not take into account time spacing), the application calculates a noise value for each point (from n=2 to n=N–1) as follows:
noise(n) = abs[I(n – 1) - 2 * I(n) + I(n + 1)]
This is a triangular method in which the noise for every point is estimated by using its direct neighbors. It assumes that direct neighbors must have a very similar intensity. If the three points have equal intensity, the estimated noise will be zero. If two of the points have equal or very similar intensity and the other point has an intensity difference of ∆I, the estimated noise will be approximately ∆I.
The noise for the chromatogram is then the average of all noise(n), such as: