An apparatus for generating ultra-high frequency sound waves with frequencies between (1 GHz-10 GHz) is proposed. The apparatus comprises a magnetic phonon-gain medium configured to generate high frequency non-equilibrium phonons by non-equilibrium magnons having the magnon velocity exceeding the sound velocity in the magnetic phonon-gain medium. The non-equilibrium magnons having the magnon velocity exceeding the sound velocity in the magnetic phonon-gain medium are generated by injected non-equilibrium electrons having spin opposite to the direction of magnetization of the magnetic phonon-gain medium. The apparatus further comprises a means for outputting the ultra-high frequency non-equilibrium phonons.