This paper reports an experimental comparison of two types of multi-frequency excitation for the detection of cracks in non-ferromagnetic conductive plates using eddy current testing. The first multifrequency excitation is based on a typical multi-frequency signal with a large bandwidth of frequencies using 64 tones, between 100Hz and 6.4 kHz. The second multi-frequency excitation is based on a multi-frequency signal that uses 16 sinusoidal tones, between 100 Hz and 1.6 kHz, combined with a sinusoidal signal at 6.4 kHz. Experimental tests were performed in a 4 mm thick aluminum plate containing 12 cracks with different depths and lengths. The 12 cracks were inspected in the surface and sub-surface locations. The advantage and disadvantage of the two types of multi-frequency excitations are discussed.