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.

Impulsive Sound Exposure Statistics (ISO 13474) is for the source whose level at the receiver is not one number: a blast or a shot kilometres away, heard ten decibels louder or quieter as the weather between them changes. From the level and probability of each replica atmosphere it builds the statistical distribution of the single-event sound exposure level, spreads it for turbulence, and reads off the long-term level, the rating level with the impulsive adjustment K, and the level exceeded by any percentage of the events.

Soundscape Analysis (ISO/TS 12913) turns the question round: not how much sound arrives, but how the people there hear it. Its input is a questionnaire rather than a signal: the scale values and site medians of the ISO/TS 12913-2 questionnaire, the pleasantness and eventfulness of each site on the two-dimensional model of ISO/TS 12913-3, the correlations that link the answers to the measured levels, and the binaural analysis of the same place at both ears.

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. The exposure statistics page stands beside them for firing ranges, quarries and demolition, where the weather decides the level, and the soundscape page for a study that asks the people who live with the sound.

• 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.
• Impulsive Sound Exposure Statistics (ISO 13474): the long-term and rating levels of a blast from its replica atmospheres, the ordered classes and their densities, the spread for turbulence and the exceedance levels.
• 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.
• Soundscape Analysis (ISO/TS 12913): the questionnaire and its scale values, the pleasantness and eventfulness of Figure A.1, the Spearman and Pearson correlations, the Method B statistics, the binaural metrics of Table D.1 and the reporting record.

• 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.