Computation of loudness (Zwicker model) according to ISO 532B / DIN 45631 norms.
This model is valid for steady sounds.
Code based on BASIC program published in the following article:
Program for calculating loudness according to DIN 45 631 (ISO 532B)",
E.Zwicker and H.Fastl, J.A.S.J (E) 12, 1 ...
