Music theory is a set of systems for analyzing, classifying, and composing music and the elements of music. Narrowly it may be defined as the description in words of elements of music, and the interrelationship between the notation of music and performance practice. Broadly, theory may be considered any statement, belief, or conception of music (Boretz, 1995). The academic study of music is called musicology.
Music theory generally follows the pattern of attempting to reduce the practice of composing and playing into rules and ideas. Generally, music theory works are both descriptive and prescriptive, that is they both attempt to define practice and to influence later practice. Thus, music theory generally lags behind practice in important ways, but also points towards future exploration and performance. Musicians study music theory in order to be able to understand the relationships that a composer or songwriter expects to be understood in the notation, and composers study music theory in order to be able to understand how to produce effects and to structure their own works. Composers may study music theory in order to guide their precompositional and compositional decisions. Broadly speaking music theory in the Western tradition focuses on harmony and counterpoint, and then uses these to explain large scale structure and the creation of melody.
Music theory describes how sounds, which travel in waves, are notated, and the relationship between what is sounded, or played, is perceived by listeners. The study of how humans interpret sound is called psychoacoustics. In music these waves are not usually measured by length (or wavelength) or period, but by frequency.
Every object has a resonant frequency which is determined by the object's composition. The different frequencies at which the sound producers of most instruments vibrate are given by the harmonic series. The resonators of musical instruments are designed to exploit these frequencies. Different instruments have different timbres because of variation in the size and shape of the instrument.
Rhythm is the arrangement of sounds in time. Metre divides time into regular intervals, called measures (or bars in British English). The time signature specifies how many beatss are in a measure, and which kind of note lasts for one beat. Syncopated rhythms are rhythms in which normally unaccented beats are accented. Playing simultaneous rhythms in more than one time signature is called polyrhythm.
Melody combines notes pitches with rhythm. In a piece of music, the melody is the most identifiable theme. Melodies will often imply certain scales. Counterpoint is the study of combining and layering more or less independent melodies.
Harmony happens when two or more notes sound at the same time, although an unaccompanied melody can still imply harmony. Melodies are often structured around sequences of chordss, called chord progressions.
Music notation is the graphical representation of music. Notes and rhythms are represented as symbols on the musical staff, along with directions indicating the key, tempo, dynamics, etc.
The AB guides, written by Eric Taylor, are published by the Associated Board of the Royal Schools of Music, famous for their graded music examinations.
The AB Guide to Music Theory, Part I; ISBN 1854724460
The AB Guide to Music Theory, Part II; ISBN 1854724479
Music Theory Spectrum Official print journal of the Society for Music Theory. Features articles and book reviews on a range of topics in music theory and analysis, including aesthetics, the history of theory, linear analysis, post-tonal theory, and narratology. http://www.ucpress.edu/journals/mts/
Music Theory Online The online journal of the Society for Music Theory. http://www.societymusictheory.org/mto/
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