ISO 532-1:2017

INTERNATIONAL ISO
STANDARD 532-1
First edition
2017-06
Corrected version
2017-11
Acoustics — Methods for calculating
loudness —
Part 1:
Zwicker method
Acoustique — Méthode de calcul du niveau d'isosonie —
Partie 1: Méthode de Zwicker
Reference number
©
ISO 2017
© ISO 2017, Published in Switzerland
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ii © ISO 2017 – All rights reserved

Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Specification of input signal and instrumentation . 4
5 Method for stationary sounds . 5
5.1 General . 5
5.2 Description of the method . 6
5.3 Calculation of loudness and loudness level . 9
6 Method for time-varying sounds .12
6.1 General .12
6.2 Description of the method .13
6.3 Calculation algorithm .14
6.4 Guidance for determining the loudness of time-varying sounds .15
7 Reporting data .16
Annex A (normative) Numerical details and program code for the calculation of loudness of
stationary and time-varying sounds (test implementation) .17
Annex B (normative) Test signals for the validation of implementation .45
Annex C (informative) Graphical user interface for the calculation of loudness of stationary
and time-varying sounds .48
Annex D (informative) Guidance for determining the loudness when using head and torso
simulator microphones .53
Annex E (informative) Uncertainty considerations .54
Bibliography .57
Foreword
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URL: www.iso.org/iso/foreword.html
This document was prepared by Technical Committee ISO/TC 43, Acoustics.
This first edition cancels and replaces ISO 532:1975, which has been technically revised.
A list of all parts in the ISO 532 series can be found on the ISO website.
This corrected version of ISO 532-1:2017 incorporates the following correction:
— Table A.9 has been corrected.
iv © ISO 2017 – All rights reserved

Introduction
Loudness and loudness level are two perceptual attributes of sound, describing absolute and relative
sensations of sound strength perceived by a person under specific listening conditions. Due to inherent
individual differences among people, both loudness and loudness level have the nature of statistical
estimators characterized by their respective measures of central tendency and dispersion determined
for a specific sample of the general population.
The object of the ISO 532 series is to specify calculation procedures based on physical properties of
sound for estimating loudness and loudness level of sound as perceived by persons with otologically
normal hearing under specific listening conditions. Each procedure provides single numbers that can be
used in many scientific and technical applications to estimate the perceived loudness and loudness level
of sound, without conducting separate human observer studies for each application. Because loudness
is a perceived quantity, the perception of which may vary among people, any calculated loudness
value represents only an estimate of the average loudness as perceived by a group of individuals with
otologically normal hearing.
ISO 532-1 and ISO 532-2 specify two different methods for calculating loudness which may yield
different results for given sounds. Since no general preference for one or the other method can
presently be stated, it is up to the user to select the method which appears most appropriate for the
given situation. Some major features of each of the methods are described below to facilitate the choice.
The first method of this document describes the calculation of loudness and loudness level of stationary
sounds and is based on DIN 45631:1991. The second method of this document covers the procedures for
calculation of loudness and loudness level of arbitrary non-stationary (time-varying) sounds, including
stationary sounds as a special case, and is based on DIN 45631/A1:2010.
This document also includes a program code for both methods leading to estimates of loudness and
loudness level for stationary and time-varying sounds. An executable computer program is also
provided for both methods. The applied software is normative for calculating loudness values, against
which other implementations can be checked subject to stated tolerances, and provides additional
functionality for the convenience of the user.
The method for stationary sounds in this document differs slightly from the methods included in the
previous ISO 532:1975, method B, by specifying corrections for low frequencies and by restricting the
description of the approach to numerical instructions only, thus allowing a unique software description.
For reasons of continuity, the method given in this document is in accordance with ISO 226:1987 instead
of the later revised version, ISO 226:2003.
Based on the general concept of the method for stationary sounds, the method for time-varying sounds
incorporates a generalization of the Zwicker approach to arbitrary, non-stationary sounds. Of course,
this generalization is compatible with the method for stationary sounds in that it gives the same
loudness values as the method for stationary sounds if applied to stationary sounds.
The Moore-Glasberg method as implemented in ISO 532-2 is limited to stationary sounds and can be
applied to tones, broadband noises and complex sounds with sharp line spectral components. The
method in ISO 532-2 differs from those in ISO 532:1975. ISO 532:1975, method A (Stevens loudness),
was removed as this method was not often used and its predictions were not accurate for sounds with
strong tonal components. The method described in ISO 532-2 also improves the precision of calculated
loudness in the low frequency range and allows for calculation of loudness under conditions where the
sound differs at the two ears. It has been shown that this method provides a good match to the contours
of equal loudness level as defined in ISO 226:2003 and the reference threshold of hearing as defined in
ISO 389-7:2005.
NOTE Equipment or machinery noise emissions/immissions can also be judged by other quantities defined
in various International Standards (see e.g. ISO 1996-1, ISO 3740, ISO 9612 and ISO 11200).
INTERNATIONAL STANDARD ISO 532-1:2017(E)
Acoustics — Methods for calculating loudness —
Part 1:
Zwicker method
1 Scope
This document specifies two methods for estimating the loudness and loudness level of sounds as
perceived by otologically normal persons under specific listening conditions. The first method is
intended for stationary sounds and the second method for arbitrary non-stationary (time-varying)
sounds, including stationary sounds as a special case.
The methods can be applied to any sound recorded as single-channel measurements using a microphone,
or as multi-channel measurements, for example by means of a head and torso simulator (see Annex D).
Since most important technical sounds are time-varying, a model of time-varying loudness is preferable.
[14]
The methods are based on the Zwicker algorithm. The method for stationary sounds is provided for
reasons of continuity and also offers the use of measured one-third-octave-band levels as input. The
more general method for arbitrary sounds calculates the specific loudness pattern based on measured
time signals by applying a signal processing model that is directly related to physiological and
psychological characteristics of the human hearing system. Loudness is calculated from the specific
loudness pattern. It has been shown that this method provides a good match to the results of many
loudness experiments using synthetic and technical sounds.
No prior knowledge about the properties of the sound (e.g. broadband or narrowband noise, tonal
content) and no user interactions are required for the fully automated application of the method.
The evaluation of the harmful effect of sound events is outside the scope of this document.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements of this document. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any amendments) applies.
IEC 61260-1:2014, Electroacoustics — Octave-band and fractional-octave-band filters — Part 1:
Specifications
IEC 61672-1:2013, Electroacoustics — Sound level meters — Part 1: Specifications
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— ISO Online browsi
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