The principle of operation of an experimental setup for studying the velocity and absorption of hypersound in liquids based on a two-pass Fabry-Perot interferometer is described in detail, the displacements and widths of the MandelstamBrillouin components in aniline-cyclohexane solution in the vicinity of the critical point are measured, and a slow increase is observed when approaching tk from the side of the homogeneous phase the displacement of the Mandelstam-Brillouin components, and when approaching ∆t from the side of the single-phase state, a slow increase in the widths of the Mandelstam-Brillouin components is observed, according to the results obtained, it was assumed that relaxation processes exist at hypersonic frequencies in the vicinity of the critical point.