Stringed musical instrument with improved method and apparatus for tuning and signal processing

A musical instrument comprising:

• a fretboard;
• a plurality of frets aligned in a first direction on the fretboard;
• a first plurality of strings aligned in a second direction above the plurality of frets, the second direction being substantially perpendicular to the first direction;
• a first plurality of tensioning devices operable to hold the first plurality of strings in tension such that the pitches of adjacent strings of the first plurality of strings differ by one whole tone and
• a plurality of markers fixed to the fretboard, each located in proximity to an intersection of a fret of the plurality of frets and a string of the plurality of strings;
• wherein the plurality of markers distinguish notes within a particular major scale from notes outside of the major scale, and
• wherein notes outside of the major scale are grouped in clusters of two along a fret of a first set of frets and in clusters of three along a fret of a second set of frets, the frets of the first and second set of frets being interleaved.