We have made a precision measurement to obtain dielectric functions epsilon' and epsilon '' in the dipole glass system of deuterated rubidium ammonium dihydrogen phosphate (DRADP-x, x=0.4) in the frequency range from 10 mHz to 10 MHz. The Tikhonov regularization method was applied in the analysis of the experimental data to obtain the relaxation time distribution g(tau, T), from which we could calculate the temperature dependence of [tau], the distribution width, and the distribution asymmetry. The weighted average relaxation time [tau] was found to follow the Vogel-Fulcher law with a static freezing temperature of T-0=16.5 +/- 1.2 K for the DRADP-x (x=0.4) system.