O

oboe  A double-reed instrument made of wood with a nasal, "reedy" timbre. The player blows directly into a double reed (two thin strips of cane bound together), setting them in vibration.

octave  Interval between two tones seven diatonic pitches apart; the lower note vibrates half as fast as the upper and sounds an octave lower.

ode  Secular composition written for a royal occasion, especially popular in England.

offbeat  A weak beat or any pulse between the beats in a measured rhythmic pattern.

ondes Martenot  Electronic instrument that produces sounds by means of an oscillator.

open ending  The first ending in a medieval secular piece, usually cadencing on a pitch other than the final.

open form  Indeterminate contemporary music in which some details of a composition are clearly indicated, but the overall structure is left to choice or chance.

opera  Music drama that is generally sung throughout, combining the resources of vocal and instrumental music with poetry and drama, acting and pantomime, scenery and costumes.

opera buffa  Italian comic opera, sung throughout.

opéra comique  French comic opera, with some spoken dialogue.

opera seria  Tragic Italian opera.

oral tradition  Music that is transmitted by example or imitation and performed from memory.

oral transmission  Preservation of music without the aid of written notation.

oratorio  Large-scale dramatic genre originating in the Baroque, based on a text of religious or serious character, performed by solo voices, chorus and orchestra; similar to opera but without scenery, costumes or action.

orchestra  A performing group of diverse instruments; in Western art music, an ensemble of multiple string parts with various woodwind, brass and percussion instruments.

orchestral bells  See chimes.

orchestration  The technique of setting instruments in various combinations.

Ordinary  Sections of the Roman Catholic Mass that remain the same from day to day throughout the church year; as distinct from the Proper, which changes daily according to the liturgical occasion.

ordre  See suite.

organ  Wind instrument in which air is fed to the pipes by mechanical means; the pipes are controlled by two or more keyboards and a set of pedals.

organal style  Organum in which the tenor sings the melody (original chant) in very long notes while the upper voices move freely and rapidly above it.

organum  Earliest kind of polyphonic music, which developed from the custom of adding voices above a plainchant; they first ran parallel to it at the interval of a fifth or fourth and later moved more freely.

ornamentation  See embellishment.

ostinato  A short melodic, rhythmic, or harmonic pattern that is repeated throughout a work or a section of one.

overture  An introductory movement, as in an opera or oratorio, often presenting melodies from arias to come. Also an orchestral work for concert performance.