Assessment and regulation

Propagation says what arrives at the receiver. Assessment says what it counts as, which is a separate question with its own standards. It is a chain with three links: an indicator averages the sound over a defined period; adjustments add decibels for character the average does not capture, tone by tone and impulse by impulse; and a limit, always national, decides. ISO 1996 supplies the first two links, and a national regulation supplies the third together with its own version of the second.

Environmental Levels (ISO 1996-1/-2) is the indicator and adjustment layer, and the page most readers of this subsection want. Lden weights the evening by +5 dB and the night by +10 dB over default 12/4/8 h periods, adjustable because Member States define them differently; Ldn is the day-night variant; and the composite rating level of clause 6.5 generalises both to arbitrary periods with source and character adjustments, from +5 dB for regularly impulsive sound to +12 dB for highly impulsive sound. The ISO 1996-2 half of the page determines rather than defines: the Annex C tonal adjustment, the clause 10.4 correction for residual noise, and the Annex F uncertainty budget that says how much the rating level is worth. It starts from period levels you already have; producing those is Integrated and Statistical Levels.

Impulsive-sound prominence (NT ACOU 112) is the adjustment for sound whose impulses make it more annoying than its LAeq suggests, in both the Nordtest closed form and the ISO/PAS 1996-3 measurement chain: from the onset rate and level difference of each impulse it predicts a prominence and converts it into the graduated adjustment KI added to the measured LAeq. It is the measurement that replaces an assessor’s judgement in the character-adjustment slot of the chain above, and it ends in a .report() assessment fiche.

Spanish Noise Regulation (RD 1367/2007) is what the whole chain looks like once a state has legislated it: the corrected level LKeq with its tonal, low-frequency and impulsive corrections Kt, Kf and Ki, evaluation periods split into noise phases, and the limit tables an activity is judged against by land use. Read it as the worked example of a national layer even if you do not work in Spain — it shows which parts of ISO 1996 a regulation typically restates, and which it replaces. Kf, the correction driven by the difference between the C-weighted and the A-weighted level, has no counterpart in ISO 1996 at all.

Read Environmental Levels first, then the impulsive-sound page as the adjustment that feeds it, then the Spanish regulation as the national assembly of both.

Pages in this section

• Environmental Levels (ISO 1996-1/-2): Lden, Ldn and the composite rating level of clause 6.5, the Annex C tonal adjustment, the clause 10.4 residual-noise correction and the Annex F uncertainty budget.
• Impulsive-sound prominence (NT ACOU 112): the predicted prominence of impulsive sounds, the graduated LAeq adjustment KI, the ISO/PAS 1996-3 measurement chain and the assessment fiche.
• Spanish Noise Regulation (RD 1367/2007): the corrected level LKeq, the Kt/Kf/Ki corrections, the evaluation periods and noise phases, and the immission limit tables.

See also

Pages elsewhere on the site that this section leans on:

• Integrated and Statistical Levels: the LAeq, percentile and event levels of each reference period, which every indicator here starts from.
• Objective audibility of tones in noise: the ISO/PAS 20065 engineering method whose mean audibility the ISO 1996-2 tonal adjustment maps into decibels.
• Outdoor Sound Propagation: the path that delivered the sound to the receiver being assessed.

What this section does not cover

• The library starts where the sound level meter stops. ISO 1996-2 fixes the receiver positions and the façade corrections that turn a raw measurement into the level these functions expect, and those position and correction procedures are not implemented — only the arithmetic that follows once you have applied them. The same is true nationally: the Annex IV measurement procedures of RD 1367/2007 (microphone positions, series duration, number of measurements) are not implemented either, and the acoustic zoning, noise maps and action plans of Ley 37/2003 are planning instruments rather than calculations. Two published alternatives are deliberately absent: only the graduated KI of NT ACOU 112 Formula 2 is implemented, not the flat 5 dB fallback of its Note 4, and the ISO 1996-1 Table A.1 category adjustments appear only as the assessor’s-judgement baseline the measurement replaces. Finally, no limit table other than the Spanish one is built in: a limit is national, and the library gives you the rating level to compare against whichever one applies.