A universal departure from the classical period doubling spectrum

Abstract The topology of the period doubling attractor at the onset of chaos, and its implications for the structure of the power spectrum are discussed. The presence of a seemingly anomalous peak at a non 2 n frequency is explained in terms of a topological invariant of the attractor whose systematics is shown to be universal. An experiment on an electronic circuit is performed, and its results are shown to be fully consistent with the theory.