acoustic-decibels

The decibel arithmetic you always end up re-deriving when working with sound levels. Pure ESM, zero dependencies.

• SPL ⇄ sound pressure (reference: 20 µPa)
• combine incoherent sources on an energy basis
• back out one level from a measured total (background subtraction)
• point-source inverse-square distance attenuation
• IEC 61672 A-weighting

Why decibels are annoying

They add logarithmically. Two identical machines are not "twice as loud" — they are +3 dB. Ten of them are +10 dB. This library does that bookkeeping so you do not have to keep 10^(L/10) in your head.

import { combineLevels, attenuateDistance, applyAWeighting } from 'acoustic-decibels';

combineLevels(80, 80);          // 83.01 dB
combineLevels(...Array(10).fill(70)); // 80 dB

// a 100 dB point source, heard at 4 m instead of 1 m
attenuateDistance(100, 1, 4);   // ~88 dB

// weight an 90 dB tone at 1 kHz for perceived loudness
applyAWeighting(90, 1000);      // ~90 dBA

Pressure conversions

import { splFromPressure, pressureFromSpl } from 'acoustic-decibels';

splFromPressure(1);       // 93.98 dB SPL (1 Pa)
pressureFromSpl(94);      // ~1.0 Pa

A-weighting

aWeighting(f) returns the correction (dB) for a band at frequency f, normalised to 0 dB at 1 kHz per the standard A-curve. Roughly -19 dB at 100 Hz, +1.2 dB around 2.5 kHz, rolling back off in the treble.

License

Apache-2.0