One of the most common instruments used to accompany vocal performances is the guitar. It has a three-octave tone range and is primarily used for harmonic accompaniment or lead. When playing a song on the guitar, especially when trying to match a vocalist, the songwriter may need to transpose the guitar notation into a different key. A key in music refers to the scale on which the song is built, and all chords and notes fall within that scale. To correctly transpose guitar chords, the songwriter must be familiar with the fretboard as well as the relationships between musical notes and keys.
There are seven degrees, or intervals, in each of the twelve major musical scales, plus the octave of the root note. For example, the C major scale is made up of seven whole notes in ascending order from C to B, plus the octave of C. Meanwhile, G, A, B, C, D, E, F#, and the octave of G make up the G scale. Guitarists transpose music calculating the corresponding scale intervals and transposing the notes and chords according to their root intervals. A dissonant song results from a lack of proper transposition.
The A major scale is made up of the notes A, B, C#, D, E, F#, G#, and A in a song written in the key of A. Because A, D, and E are the first, fourth, and fifth intervals of this scale, a I-IV-V chord progression in the key of A would include A, D, and E chords. In the key of D, on the other hand, the chords D, G, and A — the same intervals as the D major scale — would be included in the same progression. Learning all of the scale intervals allows the guitarist to transpose guitar songs between any two keys; once the notes have been transposed, the guitar must be physically retuned to the correct key.
A capo is the most commonly used tool to quick-tune strings upward when a guitarist needs to play songs in a transposed key. The capo is worn over the strings at the desired fret and keeps them in tune. The tone is determined the fret, and the open tone is determined the capo. Setting a capo at the seventh fret of a guitar and playing an E chord, for example, changes the chord’s tone seven half-steps, transforming it into a B chord.