Merjenje glasnosti po ISO 532

Calculation of loudness index according to ISO 532

Program izračuna indeks glasnosti za podano vrednost v decibilih po standardu ISO 532. Vrednosti so v standardu podane tabelarično, program pa vmesno vrednost izračuna s pomočjo linearne interpolacije.

Pogosto je zaželeno, da iščemo le eno vrednost glasnosti ali stopnje glasnosti določenega zvoka. Takšno vrednost lahko izračunamo, če imamo na voljo analizo spektra zvoka, ki smo jo dobili s fizičnimi meritvami. Razumeti moramo, da je izračunana vrednost statistična, kar pomeni, da ponuja manj informacij kot njena meritev spektra, iz katere izhaja.
Takšne analize pogosto izvedemo v smislu oktavske lestvice ali tretjinske oktavske lestvice. Spekter zvoka, ki nima prekinitev v obliki frekvence, lahko predstavimo kot oktavske lestvice, zvok, ki pa ima takšne prekinitve lahko zahteva tretjinske analize oktavske lestvice, če ga hočemo ustrezno opisati.
ISO 532 določa dve metodi za računanje glasnosti ali stopnje glasnosti sestavljenega zvoka, ki se razlikujeta ne le v metodi analize zvoka, ampak tudi v principu ocenitve. Prva, metoda A, izkorišča fizične meritve iz analize spektra v smislu oktavske lestvice. Druga, metoda B, izkorišča analize spektra v smislu tretjinske oktavske lestvice.
Razen različne širine lestvice pri fizičnem merjenju, se te dve metodi razlikujeta v drugih pogledih in razultati se zato vedno ne ujemajo. Metoda B da ponavadi malenkost višje rezultate kot metoda A, razlika pa je po vsej verjetnosti 5 fonov, vendar je bolje upoštevati tiste variacije v spektru zvoka, ki se pojavijo v ožjem frekvenčnem območju.
Vrednosti izračunane po katerikoli metodi morajo biti označene s sklicevanjem na eno ali drugo metodo, z uporabo sistema simbolov in kratic podanih v tabeli 1.

This program displays calculated loudness index for given band pressure level (dB) in accordance with ISO 532. Values in ISO 532 are given in tabular form. Program calculates intermediate value by linear interpolation.

It is often desirable to seek a single number that corresponds to the loudness or to the loudness level of a given sound. Such a number can be calculated if there is available a spectrum analysis of the sound obtained by physical measurement. It has to be understood that the calculated number is a statistic, i.e. it conveys less information than the spectrum measurements from which it is derived.
Such analysis is often accomplished in terms of either octave bands or one-third octave bands. Sounds in which the spectra do not have discontinuities as a function of frequency can be represented adequately in terms of octave bands, but sounds which contain such discontinuities may require one-third octave band analysis if they are to be described adequately.
ISO 532 specifies two methods for calculating the loudness or loudness level of a complex sound, which differ not only in the method of analysis of the sound, but also in the principles of computation. The first, method A, utilizes physical measurements obtained from spectrum analysis in terms of octave bands. The second, method B, utilizes spectrum analysis in terms of one-third octave bands.
In addition to the different band widths involved in the basic physical measurements, the two methods differ in other respects, and the results obtained do not always agree. Method B generally gives slightly higher results than those obtained for the same sounds by method A, the difference being possibly as much as 5 phons, but it would seem to take better into account those variations in sound spectra that occur within narrow ranges of frequency.
The quantities calculated by either method should be designated with specific reference to one or other method using the system of symbols and abbrevations given in table 1.