Modulation is the process of varying a signal to encode information. In communication systems, it allows data to be transmitted over various media, such as radio waves or telephone lines. By changing characteristics like amplitude, frequency, or phase of a carrier wave, information can be effectively sent and received. In music, modulation refers to changing the key of a piece. This shift can create contrast and maintain listener interest. Composers often use modulation to transition between different sections, enhancing the emotional impact of the music while keeping it engaging for the audience.