1. A method comprising: acquiring, via a processor, voices of a plurality of unspecified speakers; acquiring, via the processor, noise in a predetermined place; adjusting, via the processor, a sound pressure of the noise based on sound pressures of the voices of the plurality of unspecified speakers; superimposing, via the processor, the noise whose sound pressure has been adjusted onto the voices of the plurality of unspecified speakers; and generating, via the processor, an unspecified speaker voice dictionary from features of the voices of the plurality of unspecified speakers onto which the noise has been superimposed, wherein the unspecified speaker voice dictionary is used in generating a personal voice dictionary for identifying a target speaker.