It is well known that in normal technical condition of the objects of control and diagnostics for noisy signal which are received from corresponding sensors classical conditions such as normal distribution law, stationarity and etc. take place. Also it is well known that during exploitation of the control objects because of different defects like wear, microcracks, corrosion, deformation and etc. the hidden period of failure origin take place. In this period noise which have correlation with the useful signal appears. That is why determination of spectral and correlation characteristics of the noisy signal using traditional algorithms and technologies in the hidden stage of failures origin in the control objects take place with some errors. In this case the indication of the hidden stage of defects origin which lead to failures in the objects in some cases is belated. In the article algorithms and technologies of the substitution of unmeasurement readings of the noise for their approximate values are offered. Also the possibility of the use of the given readings for both determination the values of spectral and correlation characteristics of the noise and for providing the robustness of the results of correlation and spectral analysis in the hidden period of failures on the control objects is shown.