What is an octave defined as?

An octave is defined as a doubling of frequency. This concept is integral to understanding sound and music theory. When you move up an octave, you reach a pitch that has a frequency twice that of the original pitch. For example, if you start with a note that has a frequency of 440 Hz (the pitch of the A above middle C), the note one octave higher would have a frequency of 880 Hz.

This definition of octave connects with how we perceive musical notes and scales, as each successive octave contributes to the harmonic structure of music. It explains why scales are structured the way they are, with each step on the scale representing a consistent multiplicative change in frequency, thereby creating a naturally pleasing sound progression.

The other options relate to different aspects of sound perception, such as intensity, loudness, and sound pressure, but they do not accurately describe the specific concept of an octave within the realm of acoustics and music theory. Doubling intensity, for example, does not equate to an octave, as intensity is measured in a different manner than frequency and affects the overall perceived loudness of a sound rather than its pitch.