Banjo timbre from string stretching and frequency modulation

Abstract

The geometry of a floating bridge on a drumhead soundboard produces string stretching that is first order in the amplitude of the bridge motion. This stretching modulates the string tension and consequently modulates string frequencies at acoustic frequencies. Early work in electronic sound synthesis identified such modulation as a source of bell-like and metallic timbre. And increasing string stretching by adjusting banjo string-tailpiece-head geometry is known to enhance characteristic banjo tone. Hence, this mechanism is likely a significant source of the ring, ping, clang, and plunk common to the family of instruments that share floating- bridge/drumhead construction. Incorporating this mechanism into a full, realistic model calculation remains an open challenge.

12 pages, 3 figures; this revision includes 1 new figure to accompany a more detailed geometry of stretch; also added minor comments on other possible sources of distinct banjo sound