IEC 61260-1: Scope — Octave and Fractional-Octave Band Analysis
TL;DR
IEC 61260-1:2014 specifies the performance requirements for analog and digital octave-band and fractional-octave-band filters used in acoustic measurements. It defines 1/1 octave and 1/3 octave filters as the primary types, with provisions for finer resolutions (1/6, 1/12, 1/24 octave). Three performance classes are defined: Class 0 (laboratory reference), Class 1 (precision), and Class 2 (field measurements). The standard covers centre frequencies, bandwidths, attenuation limits, and filter response shapes. It is essential for SPL meter octave analysis, building acoustics, and environmental noise monitoring.
What IEC 61260-1 Covers
IEC 61260-1 "Electroacoustics — Octave-band and fractional-octave-band filters — Part 1: Specifications" defines the filtering stage used when sound level meters and analyzers break the audio spectrum into octave bands or narrower fractional-octave bands. This spectral analysis is fundamental to almost every acoustic measurement standard.
Filter Types
The standard defines filters by their bandwidth fraction b:
| Fraction (b) | Common name | Bands per octave | Typical application |
|---|---|---|---|
| 1/1 | Octave | 1 | NC/NR curves, broad spectral overview |
| 1/3 | Third-octave | 3 | Building acoustics, noise surveys, SPL analysis |
| 1/6 | Sixth-octave | 6 | Detailed spectral analysis |
| 1/12 | Twelfth-octave | 12 | Speaker measurement, room EQ |
| 1/24 | Twenty-fourth-octave | 24 | High-resolution analysis |
Performance Classes
IEC 61260-1 defines three classes with progressively tighter tolerances:
- Class 0: Laboratory reference — tightest tolerances, used for calibrating other analyzers
- Class 1: Precision — required for standards-compliant measurements (ISO 3382, ISO 16283)
- Class 2: Field measurements — acceptable for general-purpose surveys
The class system parallels IEC 61672-1 and ANSI S1.4 classifications.
Applications
Octave-band analysis is required by numerous standards:
- ISO 3382-1: RT60 per octave band from 125 Hz to 4 kHz
- IEC 60268-16: STI computed in 7 octave bands
- ISO 717-1: Sound insulation Rw with 1/3 octave data
- ISO 1996: Environmental noise assessment
Relationship to IEC 61672-1
A sound level meter with octave-band analysis capability must conform to both IEC 61672-1 (for the broadband measurement) and IEC 61260-1 (for the filter bank). See the integration section for how they work together.
SonaVyx RTA
The SonaVyx Real-Time Analyzer implements 1/1 and 1/3 octave analysis using FFT-based power spectrum method with IEC 61260-1 compliant centre frequencies and bandwidth specifications.
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Last updated: March 19, 2026