  AIMS: We have found that the interferometric visibilities of VLTI-AMBER
observations, extracted via the standard reduction package, are significantly
biased when faint targets are concerned. The visibility biases derive from a
time variable fringing effect (correlated noise) appearing on the detector.
METHODS: We have developed a method to correct this bias that consists in a
subtraction of the extra power due to such correlated noise, so that the real
power spectrum at the spatial frequencies of the fringing artifact can be
restored. RESULTS: This pre-processing procedure is implemented in a software,
called AMDC and available to the community, to be run before the standard
reduction package. Results obtained on simulated and real observations are
presented and discussed.
