Unidad de intervalo de frecuencia que corresponde a un aumento en la frecuencia multiplicada por dos, p. ej., de 1000 Hz a 2000 Hz es una octava.  En un teclado de piano estándar existen ocho octavas.
   <(A.): Oktave: ist das Intervall zwischen zwei Tönen, deren höchste Grundfrequenz doppelt so hoch ist wie die niedrigste. Aufgeteilt in mehrere Teilintervalle erlaubt es, Skalen zu definieren.
   <(F.): Octave: est l’intervalle séparant deux sons dont la fréquence fondamentale du plus aigu est le double de celle du plus grave. Divisée en plusieurs sous-intervalles, elle permet de définir les gammes.
   <(In.): Octave band spectrum: a description of a sound spectrum based upon the Sound Pressure Level (SPL) in a series of octave bands. Other band spectra (half-octave, third octave, etc.) are also used. If a given octave band spectrum is converted to half-octave then, since the power in each band is halved, while the reference power defined for the bands will (in general) remain the same, there will be an apparent "drop" of 3db in the overall spectrum (4.75 db for 1/3 octave). If the level is defined per unit bandwidth (hz) rather than some form of octave basis, the apparent drop in any given unit bandwidth will be that much greater, and in general there will be an increasing drop of 3 db/octave at increasing frequencies. Of course, if, instead of merely converting, the measurements were retaken using narrower band analysis, the overall shape of the spectrum would very likely be considerably modified since there is no reason, in general, why the power in a given frequency band should be uniformly distributed throughout the band. The so-called spectrum level correction is based on the assumption of uniform distribution of acoustic energy.