The choice of optimized excitation devices and strategies is now interesting recent studies about Non Destructive Eddy Current Testing (ND-ECT). Recently, the attention has been paid to the use of complex excitation signals, meant as signals different from the sinusoidal ones and with wide frequency content. In particular, some studies have highlighted their suitability, respect to the sinusoidal one, in supporting the measurement, detection and quantification stages when “difficult cases” are explored (i.e. very short or annealed cracks). Generally, two class of signal have been proposed in literature. They concern with signals that have to be analysed in the time domain and signals analysed in transformed domains. The former class is represented by signal as the pulsed or pseudo-noise, while the latter contains signal as the chirp or multi-frequency as the best candidate. The author have placed their attention to this second class of signal and in this paper they propose an experimental comparison among different realization of these excitation signals suitably designed to improve the quality of experimental data when difficult cases are experienced.