Sympathetic strings or
resonance strings are auxiliary strings found on many
Indian musical instruments, as well as some Western
Baroque instruments and a variety of folk instruments. They are typically not played directly by the performer (except occasionally as an effect), only indirectly through the tones that are played on the main strings, based on the principle of
sympathetic resonance. The resonance is most often heard when the
fundamental frequency of the string is in unison or an
octave lower or higher than the catalyst note, although it can occur for other
intervals, such as a
fifth, with less effect.