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Octave
A pitch interval of 2 to 1. The tone whose frequency is twice that of the given tone.

Octave Band
A division of the audible frequency range, the centre frequency of which is twice that of the preceding band centre frequency.

Omnidirectional Source
A source that radiates sound in all directions equally.

One-third Octave Band
An octave band divided into three one-third octave bands. The upper frequency limit of a one-third octave band is 2 1/3 times its lower frequency limit.

Outdoor-Indoor Transmission Class (OITC)
A classification method for rating the sound isolation performance of exterior wall constructions in accordance with ATSM E1332-90.