Music theory is the study of how music works by examining both the notation and the "language" of music. It tries to identify different patterns and structures in the techniques of composers and across the wide range of different musical genres, styles and historical periods. Musical theory looks to simplify music down to several key elements which can then be analyzed. These elements include rhythm, melody, harmony, structure, texture and form. Music theory can also include elements of psychology and acoustics to try and explain how music is heard and perceived by the audience.
One of the key elements of a piece of music is the pitch. Pitch describes how high or low a sound is. In music the human perception of pitch is sometimes used to create auditory illusions, but in general pitch is normally only related to the frequency of the note. If the frequency of the note is too high or too low the audience will not be able to hear it due to the biological limitations of the human ear. The difference between two pitches is known as the interval.
The notes with wh ichmusic is written are an important part of musical theory. In Western music theory there are 12 notes within an octave, and these notes make up the chromatic scale. In the chromatic scale each note is separated by a semitone or half step. Two semitones make up a tone. Within the octave it is possible to use different patterns of tones and semitones to make a scale. The most common scales are the seven-toned major, the harmonic minor, the natural minor and the melodic minor. In folk music it is common to find octatonic and pentatonic scales. In non-Western music, for example Persian, Indian, Turkish or Arabic music, a quarter-tone is used, which is half a semitone, in the scales. The quarter-tone is not found in Western music. If a piece of music goes up, for example from C major to D major, then all the notes will be one tone higher. Doing this will change the feel of the piece of music as each instrument has its own pitch within which it can play and therefore changing the key will alter the relationship between the composition and the instruments in the orchestra.
In written music the key is used to work out whether the piece of music should be played in a major or minor key. If the key the music is played in is changed, the unskilled listener would be unlikely to notice the difference and it would also not interfere with the instruments, unlike a change in tone, as the instruments' pitches would not change in relation to one another.
In a good piece of music the tones of the harmonies should complement each other and if they do they will make a consonance. The opposite of this is a dissonance which is generally thought of as an unpleasant sound. A good piece of music would hope to have consonances rather than dissonances. Critics sometimes find music with just consonances to be pleasant but ultimately boring as the story the music tells is without strife and motion that a deliberate dissonance may bring to the performance.
In music theory the rhythm of the music describes how the sounds and silences of the notes are arranged. A meter is used to time out the number of beats in the bar and stresses are used in the notation to note which notes should be stressed. It is possible to have simultaneous rhythms in more than one time signature and this is known as a polymeter. The rhythm of music in recent years has become more important among music scholars including in books written by Bengt-Olov Palmqvist and Ray Jackendoff, among others.
The quality of the sound that the instrument or voice produces is known as the timbre. It is possible to change the timbre of the instrument by altering the instrument, for example by placing a bell in a trumpet, or by a singer manipulating his mouth, vocal chords or diaphragm.