Levels and weighting

A sound level meter does three things to a calibrated signal, in order: it weights it in frequency to mimic the ear’s sensitivity, it smooths it in time with a standardised ballistic, and it integrates it into a level. The three pages of this section implement exactly that chain, one page per stage, following IEC 61672-1:2013 closely enough that the weightings are verified against the standard’s own tolerance tables in CI.

Frequency Weighting (A, C, G, Z) covers the first stage. The A-curve tracks hearing sensitivity at moderate levels and dominates regulation; C is nearly flat and serves peaks and low-frequency checks; Z is unweighted by definition; and the G-curve of ISO 7196 extends the idea into infrasound, where conventional weightings are blind.

Time Weighting covers the second stage: the exponential Fast (125 ms), Slow (1 s) and Impulse ballistics that decide how quickly a displayed level follows the sound. phonometry implements the exact time constants, verified against the toneburst responses of the standard.

Integrated and Statistical Levels is the payoff: the equivalent continuous level Leq and its A-weighted LAeq, the percentile levels L10/L50/L90 that describe fluctuating noise, LCpeak and SEL, the noise dose of IEC 61252, the day-evening-night level Lden and the rating levels of ISO 1996-1 with their adjustments, plus the octave spectrogram for visualising level against time and band at once. This is the page where most practical measurements end, and where the environmental and occupational sections pick up.

Pages in this section

• Frequency Weighting (A, C, G, Z): the IEC 61672-1 A/C/Z curves and the ISO 7196 infrasound G-weighting.
• Time Weighting: Fast, Slow and Impulse exponential ballistics.
• Integrated and Statistical Levels: Leq and LAeq, percentile levels, LCpeak/SEL, noise dose, Lden and rating levels, and octave spectrograms.