MODULATION

in electronics, technique for impressing information (voice, music, picture, or data) on a radio-frequency carrier wave by varying one or more characteristics of the wave in accordance with the intelligence signal. There are various forms of modulation, each designed to alter a particular characteristic of the carrier wave. The most commonly altered characteristics include amplitude, frequency, phase, pulse sequence, and pulse duration. in music, most commonly the transition from one key (set of interrelated notes and chords) to another. The Latin word modulare was originally used with reference to melody. Thus, medieval theorists frequently defined music as ars bene moduland (the art of modulating well). More recently, modifications in vocal and instrumental tone production have been labeled modulation. Still, modulation retains its primary significance, both expressive and structural, in the realm of harmony. There are three principal methods of modulation in classical harmony: diatonic, in which a pivot chord is common to both keys; chromatic, in which the notes of the pivot chord are altered by a semitone (i.e., by the addition of a sharp, flat, or natural sign); and enharmonic, in which the notes of the pivot chord, while retaining their original tones, simply assume different names (e.g., the chord ceg becomes dfa). Modulation may be transitory, as in the course of thematic development, or structural, contributing to the harmonic definition of form.