An octave band is defined as:

• A. A range of frequencies extending from one frequency to exactly double that frequency
• B. A range of frequencies extending from one frequency to half that frequency
• C. A single frequency
• D. The entire audible spectrum

Answer: (A)

An octave band is defined by a doubling relationship: the upper frequency is twice the lower frequency. So the band runs from a base frequency f up to 2f. For example, starting at 125 Hz gives an octave band from 125 Hz to 250 Hz. This convention lets us compare spectral content consistently across the spectrum. The other options don’t fit because halving the frequency would not produce an octave band, a single frequency has no bandwidth, and the entire audible spectrum covers many octaves rather than a single octave.