Using a field cycling technique, the Larmor frequency (νL) dependence of the proton Zeeman spin-lattice relaxation time T1 has been measured in the smectic A, smectic C, smectic B and smectic VII phases of terephtal-bis-butylaniline (TBBA) between νL = 90 MHz and νL = 0.14 MHz and a significant dispersion has been found. The observed ω1/2L dispersion law in the smectic A phase and the deviations from it at low frequencies can be explained by nematic director fluctuations in the smectic A phase and the coupling between nematic and smectic order