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The lattice dynamics in BiTe and SbTe were investigated both microscopically and macroscopically using Sb and Te nuclear inelastic scattering, x-ray diffraction, and heat capacity measurements. In combination with earlier inelastic neutron scattering data, the element-specific density of phonon states was obtained for both compounds and phonon polarization analysis was carried out for BiTe. A prominent peak in the Te specific density of phonon states at , that involves mainly in-plane vibrations, is mostly unaffected upon substitution of Sb with Bi revealing vibrations with essentially Te character. A significant softening is observed for the density of vibrational states of Bi with respect to Sb, consistently with the mass homology relation in the long-wavelength limit. In order to explain the energy mismatch in the optical phonon region, a force constant softening of the Sb-Te bond with respect to the Bi-Te bond is required. The reduced average speed of sound at in BiTe …