Chords and music theory

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As soon as you want to do a bit more with music than just playing, it is very useful to know a bit about music theory. The following section tries to provide as much information that terms such as key, tonality, minor, major, chords, chord progressions, intervals, circle of fifths, will get a bit more meaningful. Clearly written sheet music (with chord symbols and accompaniment parts generated therefrom) as provided using music notation program MusiCAD, greatly helps in the understanding of music theory in practice.

Note distances

Every two tones have a relationship that corrsponds with the ratio of their pitches. In most (Western) music, the most important relationship is the octave. The octave is a ratio at which the frequency of the one note is exactly two times as high as the other. On stringed instruments this is illustrated by looking at what happens when a string is divided into two equal parts with the fingers. The note-distance between the string when sounding in full length and the string divided by a finger into two equal parts is exactly one octave. Similarly, when the half-length string again be divided in two, the quarter-length-string sound one octave higher again. The sound of a whole-length-string and that of a quarter-length-string have a relationship of two-octaves (a double octave).

Musical distances in octaves sound 'easy' to our ears. In fact it is sometimes difficult to hear if two tones are just of equal height (or unison), or are an octave apart.


Over the centuries a musical scale has been developed which divides the octave into 12 equal parts, called semitones.

For historical reasons some other tone distances were given their own names. The naming can be found on the piano, start at middle C and going all the way up using the white keys to the right: prime, second, third, fourth, fith, sixth, seventh and octave. A series of tones that always a semitone apart is called a chromatic series (white and black on piano), in contrast to a diatonic series as the white keys on the piano.