On the Fractal Dimension of Filtered Chaotic Signals

Much progress has been done in the reconstruction of the geometry of strange attractors, from experimental single time-series, exploiting embedding techniques [l], which make possible, for instance, the estimation of fractal dimensions and metric entropies. A particularly relevant aspect of these procedures, which has not yet been pointed out, concerns the role of filtering. In fact, not only any measurement of experimental signals is to some extent filtered, due to the finite instrumental bandwidth, but often an explicit intervention of the observer is present as well, motivated by the need of “cleaning” the system’s output from the presence of noise.