Drone

 It is a harmonic or monophonic effect used for accompaniment where a note or chord is continuously sounded throughout most or all of a piece. The main differences between a drone and a pedal point is that the first is sustained from much longer periods of time, it does not have to resolve. Similarly, to pedal point, it can be achieved through a sustained sound or through the repetition of a note and it can be placed in different registers – in the bass, middle or high register. Normally, it establishes a tonality upon which the rest of the piece is built. The drone is most often placed upon the tonic or dominant.