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Music theory generally attempts 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.

1 Sound

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 seriesThis article is about the harmonic series in music theory. See harmonic series (mathematics) for the related mathematical concept. Pitched musical instruments are usually based on some sort of harmonic oscillator, for example a string or a column of air,. The resonators of musical instrumentA musical instrument is a device that has been constructed or modified with the purpose of making music. In principle, anything that somehow produces sound can serve as a musical instrument, but the expression is reserved generally to items that have thats are designed to exploit these frequencies. Different instruments have different timbreIn music, timbre is the quality of a musical note which distinguishes different types of musical instrument. See also: formant of speech, singing, and musical instruments. This is why, with a little practice, you can pick out the saxophone from the trumpes because of variation in the size and shape of the instrument.

Often the fundamental aspects of sound and music are described as pitchIn music, pitch refers to the perception of the frequency of a note. For example, the A above middle C is nowadays set at (often written as "A 440 Hz", and known as concert pitch , although this has not always been the case (see #Historical pitch standard, durationA duration is an amount of time or a particular time interval. For example, an event in the common sense has a duration greater than zero (but not very long), but in certain specialised senses, a duration of zero. It is often cited as one of the fundament, intensityIn physics, intensity is a measure of the time-averaged energy flux. To find the intensity, take the energy density (that is, the energy per unit volume) and multiply it by the velocity at which the energy is moving. The resulting vector has the units of, and timbreIn music, timbre is the quality of a musical note which distinguishes different types of musical instrument. See also: formant of speech, singing, and musical instruments. This is why, with a little practice, you can pick out the saxophone from the trumpe.