double stop explained
The technique of playing two notes simultaneously on a bowed string instrument
In Depth
Double stopping requires the player to press two strings simultaneously and draw the bow across both, producing a two-note chord. The technique is demanding because both notes must be perfectly in tune and the bow must distribute pressure evenly. Triple and quadruple stops are also possible, though on bowed instruments the outer notes must be rolled slightly. Paganini's caprices contain some of the most demanding double-stop writing in the violin literature, requiring extraordinary left-hand strength and accuracy.
Paganini's ability to play double stops in tune at extreme speed led some contemporaries to seriously believe he had made a pact with the devil.