Double stopping is a technique achieved on bowed string instruments by bowing across more than one string at the same time, thus producing more than one note. Sounding two strings together is double stopping, sounding three is triple stopping, and four is quadruple stopping. This allows for one instrument to play complex sounds and even, in the hands of a skilled composer, to sound like two or more independent voices.
Multiple stopping was developed in the mid-1500s and has remained a popular technique. Bach was one of the most skillful and well-known proponents of multiple stopping, particularly in his cello suites. Double stopping has also been adopted as a drone tech in folk music.