Octave Band Analysis
Definition
Octave Band Analysis
Octave band analysis groups audio frequencies into standardized bands defined by IEC 61260-1:2014, where each band spans a 2:1 frequency ratio (one octave). The standard defines center frequencies at 31.5, 63, 125, 250, 500, 1000, 2000, 4000, 8000, and 16000 Hz. Sub-octave analysis (1/3 octave) provides finer resolution with three bands per octave. SonaVyx performs octave band analysis in real time.
Upper band edge = fc × 2^(1/2), Lower band edge = fc / 2^(1/2), where fc = center frequency
How Octave Band Is Measured
Octave band levels are computed by summing the energy of all FFT bins that fall within each band boundary. SonaVyx performs this calculation in its Rust WASM DSP engine, computing the squared magnitudes of all FFT bins within each band and converting to decibels. The result is displayed as a bar chart with one bar per octave or third-octave band.
Practical Example
An HVAC noise assessment requires octave band levels for NC curve comparison. SonaVyx measures the background noise spectrum and displays octave band levels: 63 Hz at 52 dB, 125 Hz at 48 dB, 250 Hz at 42 dB, 500 Hz at 38 dB, 1 kHz at 35 dB, 2 kHz at 30 dB, 4 kHz at 28 dB, 8 kHz at 25 dB. The highest tangent NC curve is NC-40, exceeding the NC-35 target for open offices.
Full Octave vs Third-Octave
Full octave (1/1) analysis uses 10 bands covering 31.5 Hz to 16 kHz, providing a quick overview suitable for noise criteria assessment and broadband characterization. Third-octave (1/3) analysis uses 31 bands from 20 Hz to 20 kHz, offering resolution that approximates human auditory critical bands. Third-octave is preferred for room acoustics, speaker measurement, and detailed noise analysis because it reveals spectral features that full-octave analysis would average out.
NC and NR Curves
Noise Criteria (NC) and Noise Rating (NR) curves are standardized octave-band spectral shapes used to rate background noise in occupied spaces. The NC rating equals the lowest NC curve that is not exceeded by any measured octave band level. NC-25 is appropriate for concert halls, NC-30 for private offices, NC-35 for open offices, and NC-40 for retail spaces. SonaVyx automatically calculates NC ratings by comparing measured octave band levels against the reference curves.
RT60 per Octave Band
Reverberation time varies with frequency, so ISO 3382-1 requires RT60 measurement in individual octave bands from 125 Hz to 4 kHz. Low-frequency RT60 is typically longer due to reduced absorption by common materials. Octave band RT60 data guides acoustic treatment decisions — if RT60 is excessive only at 125 Hz, bass traps are needed rather than broadband absorbers.
Sound Insulation
Sound insulation performance is measured in 1/3 octave bands from 100 Hz to 3150 Hz per ISO 717-1. The measured transmission loss curve is compared against a reference curve to derive the single-number Rw rating. Octave band analysis is fundamental to building acoustics because different wall constructions have different frequency-dependent weaknesses.
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