Octave bands are defined as:

• A. A single frequency band
• B. A range of frequencies from one frequency to exactly double that frequency
• C. A range of frequencies from one frequency to half that frequency
• D. A range of frequencies covering all audible frequencies

Answer: (B)

Octave bands group frequencies so that the upper limit is double the lower limit. In other words, a band runs from a starting frequency f up to 2f. This 2:1 range is the defining feature of an octave band, which is why the example from 125 Hz to 250 Hz (or 1 kHz to 2 kHz, etc.) fits. This approach matches how sound energy is often analyzed across the spectrum because human hearing and musical pitch relate to logarithmic spacing, so each octave represents a doubling of frequency. So the correct description is a range from a frequency to exactly twice that frequency. A single frequency isn’t a band, and ranges that don’t follow the 2:1 ratio (like from f to 0.5f or encompassing all audible frequencies) don’t define an octave band.