bi-tone

The 3rd bridge is an extended playing technique used on the electric guitar and other string instruments that allows a musician to produce distinctive timbres and overtones that are unavailable on a conventional string instrument with two bridges (a nut and a bridge). The timbre created with this technique is close to that of gamelan instruments like the bonang and similar Indonesian types of pitched gongs.

A third bridge can be devised by inserting a rigid preparation object between the strings and the body or neck of the instrument, effectively diving the string into distinct vibrating segments.
Third bridge instruments can be custom-made by experimental luthiers (as with guitars designed and played by Hans Reichel); modified from a non-third bridge instrument (as with conventional guitars modified with a pencil or screwdriver under the strings); or may take advantage of design quirks of factory-built instruments (as with the Fender Jazzmaster, which has strings that continue from the "standard" bridge to the vibrato mechanism).
Perhaps the best-known examples of this technique come from No Wave artists like Glenn Branca and Sonic Youth. The 3rd bridge technique has a physical connection with Pythagoras' monochord, because both function with the scale of harmonics. Many non-Western musical scales and musical instruments share these consonant just pitch relations.

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