Here is a look at what octaves are and how this measurement is used in audio recording and post-production.
The audio spectrum itself is difficult to understand in a practical sense. This audio spectrum is really a series of pitches with differences between them, which is much easier to dictate in terms of music instead of technical audio terms. Within this audio spectrum the intervals are referred to as octaves, which is identified by the interval between two pitches. An octave exists as a measurement between two pitches of either double or half the frequency of the other, which dictates how the range of sound range between each identifiable pitch.
In the audio spectrum there are ten octaves that are identified. These ten octaves make up the entire range of human hearing with a range that goes from twenty hertz to twenty kilohertz. The octave range is one that represents aesthetics as taken by the listener a little more than a technical measurement that is useful scientifically. The octaves themselves do correspond to frequencies, though it is somewhat generally associated to those frequencies and not incredibly specific. These ten octaves range from around 31.5 HZ and running then through 63 Hz, 125 Hz, 250 Hz, 500 Hz, 1 kHz, 2 kHz, 4 kHz, and ending on 8 kHz. It is in this set up that you can see the double forward, half backward, relationship between octaves in terms of Hz. Like all sound measurement, there is also an aesthetic and subject correlation between the octaves. For example, the octaves early on at 63 Hz and 125 Hz will be much more in line with sounds like deep hum tones and low voices. The last octaves at around 4 kHz and 8 kHz will be closer to sounds like high range static sounds and high voice peaks. The lowest and highest octaves are usually the first cut from audio effects like gating and different pass filters. The sources themselves add the characteristics that separate different sounds that share the same octaves. This is where things like timbre are used to describe the different sounds that are not separated because of just octaves.
Equalizers can often show up graphic representations for these octaves, usually displayed in fractions of octaves. A 1/3 of an octave is often the marking point and will make up a 27 band equalizer. A ten band equalizer simply lists these different octaves as singles instead of as a fraction. The understanding of the octave itself is essential during the equalization process and taking a clear look at this can help to identify noises, add audio effects, and make other audio post-production decisions. Octaves are best associated with music as notation tends to follow this measurement clearly. This may be why measuring and understanding octaves is still essential for digital audio post-production for musical tracks.