thirdoctaveband

A third-octave band is a frequency interval used in acoustics and audio engineering. Each band is one third of an octave wide, and the center frequencies form a geometric progression with a constant ratio of 2^(1/3). This arrangement produces a fine, but standardized, spectral decomposition of a sound signal, typically spanning from about 20 Hz to 20 kHz in practical measurements.

Third-octave bands are defined and standardized by international bodies for consistency in measurement and reporting. In practice, devices and software implement a bank of narrow filters or a corresponding digital processing algorithm to isolate energy within each band. The result is a spectrum composed of the energy levels for all bands, which can be aggregated into one-third octave levels or used for more detailed spectral analysis.

The concept is widely used in environmental and occupational noise assessment, audio equipment testing, room acoustics, and sound system design. It provides a balance between spectral resolution and data tractability, allowing engineers to identify dominant frequency regions, compare performances, and comply with regulatory limits. Third-octave analysis is commonly contrasted with octave-band analysis, which uses wider bands, and with higher-resolution Fourier methods, which can provide more detailed spectral information but at greater computational cost.

Overall, third-octave bands are a standard tool for evaluating and communicating the spectral content of sounds in many scientific, regulatory, and industry contexts.