  The measurements of very low level signals at low frequency is a very
difficult problem, because environmental noise increases in this frequency
domain and it is very difficult to filter it efficiently. In order to
counteract these major problems, we propose a simple and generic denoising
technique, which mixes several features of traditional feedback techniques and
those of noise estimators. As an example of application, large band
measurements of the thermal fluctuations of a mechanical oscillator are
presented. These measurements show that the proposed denoising technique is
easy to implement and gives good results.
