A drone is a harmonic or monophonic effect or accompaniment where a note or a chord is continuously sounded throughout most or all of a piece. A drone effect can be achieved through a sustained sound or through repetition of a note. It most often establishes a tonality upon which the rest of the piece is built.
With a fiddle, a drone is an adjacent open string that is bowed at the same time the melody string is bowed. The open string harmonizes (creating a 2 note chord) with the fingered or open note being played on the melody string. Drones are one of the distinctive features found in Old Time Fiddle style music.
Drones to Help You Stay in Tune
Drones can also be used for ear training and pitch awareness and help the fiddler stay in tune. Playing with a drone background will actually help the beginner fiddler notice more quickly when he is drifting out of tune.
The basic process for drone tuning is listening to a drone, then playing along with a drone and adjusting the finger position until the note is in tune.
Drone Tone Tool
At Drone Tone each key is a natural cello reference tone.
Real Fiddle Drones
A good source for real fiddle drones is a CD or mp3 download called Chromatic Violin from Apprentice Music. It contains 5-minute single note drones of all 12 chromatic notes played on the violin in mid range. Each violin drone is calibrated to a 440 A and played on a violin without vibrato. cdBaby has both the CD and the mp3 download.
This Fiddlehed video shows how to play in tune with drone notes.
Fiddlehed has another video talking about how practicing with a drone can make practice more fun and productive when practicing scales, tunes, variations on tunes, and improvising.