We present a new method to analyse data obtained by Brillouin scattering. Using two scattering geometries simultaneously and measuring separately the refractive index n(T) we can determine the logarithmic derivative partial derivative dlgM’(omega, T)/partial derivative lg omega = Q(M) and thus are able to characterize unambiguously the dominant fast processes by high precision frequency shift measurements. For a sufficient narrow relaxation time distribution the imaginary part M"(omega, T) of the complex modulus M(omega, T) = M’(omega, T) + iM"(omega, T) can be derived. Analysing data of poly(propylene glycol) with M(w) = 1000 (PPG 1000) we find the fastest process to show Arrhenius behaviour. Using published data from impulsive surface scattering we can finally deconvolute a set of three different processes : two exhibiting Arrhenius behaviour and one showing Vogel-Fulcher-Tammann behaviour. These three processes describe the data to a high accuracy and are tentatively assigned to molecular motions. At high frequencies the relaxation time distribution observed narrows to a single relaxation time. In the light of these results it seems questionable to use linewidth data from Brillouin scattering experiments to determine the width of the relaxation process. From the present work we believe the experiments with surface acoustic waves to be the most effective since they can be coupled with Brillouin scattering experiments.