Fretography: The Tetrachord Structure of Keys

This diagram shows the tetrachord structure of keys in the Circle of 5ths.

Since each key comprises two identical tetrachords with a whole-step between them, the second tetrachord of each key becomes the first tetrachord of the next key, which is then followed by a whole-step and another identical tetrachord, and so on.

This diagram shows the tetrachord structure of each mode in any key:

About Fretography

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The Fretography® method is a unique system for mapping and diagramming the fretboard based on the standard diatonic system of music.

Areas of the fretboard are defined in terms of their relationship to the diatonic system. A basic understanding of conventional music theory is necessary in making use of the Fretography®method.

Fretography® is a registered trademark belonging to Mark Newstetter. All contents of this blog are copyright Mark Newstetter and may not be reproduced without permission.

Fretography Glossary

The meaning of terms used in Fretography;

(*Terms marked with an asterisk are standard music theory - otherwise the Fretography terms are based on standard theory vocabulary adapted to the Fretography method.)

Aeolian Axis - The fret axis at which the lowest (6th string) and highest (1st string) tone represent the final of the Aeolian mode in a given key - i.e., the 5th and 17th fret position in the key of C.

Aeolian Zone - The span of frets beginning at the Aeolian Axis (5th fret in the key of C) and ending with the Dorian Axis (10th fret- key of C). This and other Zones repeat in the equivalent position in successive octaves.

Axis - A fret position at which there is a tone of a given key on each string. There are three axis positions, each named after the diatonic mode for which the final tone is found on the 1st and 6th string; The Phrygian (3rd mode), the Aeolian (6th mode) and the Dorian (2nd mode) Axes.

The Aeolian Axis in the key of C is at the 5th fret where A, the 6th tone of C and the final of the Aeolian mode is found on the 1st and 6th string. Hence, the Phrygian Axis of C is at the open strings and the 12th fret, the Dorian Axis in C is at the 10th fret.

These three axes appear in every key in the same positions on the fretboard, relative to that key.

Complementary Keys - Keys which are halfway around the circle of 5ths from each other - e.g., the keys of A major and Eb Major are complementary keys. C Major and Gb Major are complementary keys.

Dorian Axis - The fret axis at which the lowest (6th string) and highest (1st string) tone represent the final of the Dorian mode in a given key - i.e., the 10th fret position in the key of C.

Dorian Zone - The span of frets beginning at the Dorian Axis (10th fret in the key of C) and ending with the Phrygian Axis (12th fret- key of C). Also known as the Void Zone. This and other Zones repeat in the equivalent position in successive octaves.

Enharmonic (*) - A tonal synonym. A single tone with more than one name - i.e., F# is the enharmonic of Gb.

Fret Space - The area between the frets on the fretboard where a finger is placed to produce a note of a particular pitch, as distinguished from the actual metal fret.

Fret Span - The total number of fret spaces included when considering two particular fret positions - i.e, if one note is on the 1st fret, and another note is on the 5th fret, the Fret Span is 5 frets.

Half-step Cluster - Where the 3rd & 4th and the 7th & 1st scale degrees coincide on adjacent strings on the fretboard.

Lower String Group - The three lowest pitched strings on the guitar.

Mode (*) - Essentially a scale or group of tones belonging to a particular key which span an octave - i.e., C D E F G A B C is generally called 'the C major scale' when played in sequence, but it is also known as the Ionian Mode. D E F G A B C D is the second mode of the key of C, known as the Dorian Mode. It contains only notes belonging to the key of C, but begins and ends on D. The note which begins and ends a mode is called the 'final'. For more information, see the blog entry about modes.

Mirror Modes - Pairs of diatonic modes which are intervalic opposites - i.e., the Ionian mode interval pattern is WWHWWWH, while the Phrygian mode interval pattern is HWWWHWW, thus the Ionian and Phrygian are Mirror Modes. The other mirror modes are; Aeolian - Mixolydian, and Lydian - Locrian. The remaining mode, the Dorian, has no mirror as it has its own internal symmetry.

Phrygian Axis - The fret axis at which the lowest (6th string) and highest (1st string) tone represent the final of the Phrygian mode in a given key - i.e., the open strings and the 12th fret position in the key of C.

Perfect 4th (*) - An interval spanning 4 tones comprising two whole-steps and one half-step. The interval between the 1st and 2nd string, and between the 3rd & 4th, 4th & 5th, 5th & 6th strings.

Phrygian Zone - The span of frets beginning at the Phrygian Axis (Open position in the key of C) and ending with the Aeolian Axis (5th fret - key of C). This and other Zones repeat in the equivalent position in successive octaves.

Primary Key - The key which is the primary subject of discussion or the focus of a diagram.

Secondary Aeolian Axis - The fret axis at which the lowest (6th string) and highest (1st string) tone represent the final of the Aeolian mode of in a key which is halfway round the circle of 5ths from the primary key. Also called the Void Axis.

Spiral Galaxy Pattern - A rotationally symmetrical pattern in the Upper String Group formed by connecting the note positions around the Center Half-step Cluster. The resulting string of connected notes resembles the shape of a spiral galaxy consisting of the center cluster and two curving arms. Each arm is named after the Zone in which it is found (the Phrygian Arm is in the Phrygian Zone, the Aeolian Arm is in the Aeolian Zone).

String Group - A selected set of strings, usually adjacent. In Fretography, the four top (highest pitch) strings on the guitar (1,2,3,4) are referred to as the Upper String Group. The three bottom (low pitch) strings (4,5,6) are the Lower String Group.

Tonal Landmark - A particular grouping of tones at an area of the fretboard, which has theoretical significance and helps to connect a music theory concept with the geometric arrangement of tones. Half-step Clusters are tonal landmarks.

Upper String Group - The four highest pitched strings on the guitar.

Void Axis, Void Position - The fret position in a given key at which there are no tones belonging to that key. The Void Axis in the key of C Major is at the 11th fret, where all the tones are flats/sharps. This position is also called the Secondary Aeolian Axis.

Void Zone - Also known as the Dorian Zone, The span of frets beginning at the Dorian Axis (10th fret in the key of C) and ending with the Phrygian Axis (12th fret- key of C). This Zone spans only three frets, the middle being the Void Axis which consists entirely of tones not belonging to the primary key.

Zone - A range of fret spaces bordered by some significant set of tonal landmarks, usually named for the landmark at the lowest fret position - i.e., the the Phrygian Zone is the range of fret positions from the Phrygian Axis to the Aeolian Axis. The Aeolian Zone is the range from the Aeolian Axis to the Dorian Axis.

The Tetrachord Structure of Keys

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