ISO 532-2:2017
(Main)Acoustics — Methods for calculating loudness — Part 2: Moore-Glasberg method
Acoustics — Methods for calculating loudness — Part 2: Moore-Glasberg method
ISO 532-2:2017 specifies a method for estimating the loudness and loudness level of stationary sounds as perceived by otologically normal adult persons under specific listening conditions. It provides an algorithm for the calculation of monaural or binaural loudness for sounds recorded using a single microphone, using a head and torso simulator, or for sounds presented via earphones. The method is based on the Moore-Glasberg algorithm. NOTE 1 Issues of binaural calculations are discussed in Annex A. NOTE 2 Users who wish to study the details of the calculation method can review or implement the source code, which is entirely informative and provided with ISO 532-2:2017 for the convenience of the user. This method can be applied to tones, broadband noises and complex sounds with sharp line spectral components, for example transformer hum or fan noise. NOTE 3 It has been shown (see Reference [15]) 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. The evaluation of the harmful effect of sound events is outside the scope of ISO 532-2:2017.
Acoustique — Méthode de calcul d'isosonie — Partie 2: Méthode Moore-Glasberg
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Standards Content (Sample)
INTERNATIONAL ISO
STANDARD 532-2
First edition
2017-06
Acoustics — Methods for calculating
loudness —
Part 2:
Moore-Glasberg method
Acoustique — Méthode de calcul d’isosonie —
Partie 2: Méthode Moore-Glasberg
Reference number
ISO 532-2:2017(E)
©
ISO 2017
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ISO 532-2:2017(E)
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ISO 532-2:2017(E)
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 General . 5
5 Specifications of signals . 5
5.1 General . 5
5.2 Complex tone . 5
5.3 Noise consisting of bands of pink or white noise of defined width . 5
5.4 Mixture of discrete sinusoidal components and bands of pink or white noise . 6
5.5 Sound specified in terms of the sound pressure levels in 29 adjacent one-third-
octave bands . 6
6 Instrumentation . 6
7 Description of the method . 7
7.1 Introduction . 7
7.2 Determination of sound spectrum at the tympanic membrane . 7
7.2.1 General. 7
7.2.2 Free field and diffuse field transfer functions for sound picked up by a
single microphone . 8
7.2.3 Earphones . 8
7.2.4 Signal recorded at eardrum . 8
7.2.5 Head and torso simulator . 8
7.2.6 Interpolation and extrapolation . 8
7.3 Determination of sound spectrum at the oval window . 9
7.4 Transformation of sound spectrum into excitation pattern .10
7.5 Transformation of excitation pattern into specific loudness .13
7.5.1 Introduction .13
7.5.2 Reference excitation at the reference threshold of hearing . .14
7.5.3 Gain of the cochlear amplifier for inputs with low sound pressure levels .14
7.5.4 Calculation of specific loudness from excitation when E /E ≤ E/E .
THRQ 0 0 15
7.5.5 Calculation of specific loudness from excitation when E /E > E/E .
THRQ 0 0 15
10 15
7.5.6 Calculation of specific loudness from excitation when E > 10 .
8 Calculation of loudness and loudness level .16
8.1 Calculation of monaural and binaural loudness (diotic and dichotic stimuli) .16
8.2 Relationship between loudness level and loudness .17
8.3 Calculation of the reference threshold of hearing .18
9 Uncertainty of calculated loudness for stationary sounds .18
10 Data reporting .19
Annex A (informative) Comments regarding binaural loudness.20
Annex B (informative) Results for specific test signals .21
Annex C (informative) Software for the calculation of loudness .26
Bibliography .27
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ISO 532-2:2017(E)
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out
through ISO technical committees. Each member body interested in a subject for which a technical
committee has been established has the right to be represented on that committee. International
organizations, governmental and non-governmental, in liaison with ISO, also take part in the work.
ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of
electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are
described in the ISO/IEC Directives, Part 1. In particular the different approval criteria needed for the
different types of ISO documents should be noted. This document was drafted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2 (see www .iso .org/ directives).
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of
any patent rights identified during the development of the document will be in the Introduction and/or
on the ISO list of patent declarations received (see www .iso .org/ patents).
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constitute an endorsement.
For an explanation on the voluntary nature of standards, the meaning of ISO specific terms and
expressions related to conformity assessment, as well as information about ISO’s adherence to the
World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT) see the following
URL: w w w . i s o .org/ iso/ foreword .html
This document was prepared by Technical Committee ISO/TC 43, Acoustics.
A list of all parts in the ISO 532- series, published under the general title Acoustics — Methods for
calculating loudness, can be found on the ISO website.
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ISO 532-2:2017(E)
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 seeks 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.
This document is limited to calculation of loudness and loudness level of stationary sounds and the
calculations are based on the spectral properties of a sound. This calculation method is based on Moore-
[14-17]
Glasberg loudness calculation algorithms . It starts by converting a specified signal spectrum
into a series of sinusoidal components representing that spectrum. This series is then transformed
into a specific loudness pattern by applying four consecutive transformations, each of which is directly
related to physiological and psychological characteristics of the human hearing system. Loudness is
calculated from the specific loudness pattern.
This document describes the calculation procedures leading to estimation of loudness and loudness
level and provides an executable computer program and code. The software provided with this
document is entirely informative and provided for the convenience of the user. Use of the provided
software is not required for conformance with this document.
The Moore-Glasberg method is limited to stationary sounds and can be applied to tones, broadband
noises and complex sounds with sharp line spectral components. The method in this document
[18]
differs from those in ISO 532:1975. Method A of ISO 532:1975 (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 this document 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.
The Zwicker method in ISO 532-1 can be applied for stationary and arbitrary non-stationary sounds.
The method for stationary sounds in ISO 532-1 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 ISO 532-1 is in accordance with ISO 226:1987 instead of
the later revised version, ISO 226:2003.
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).
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INTERNATIONAL STANDARD ISO 532-2:2017(E)
Acoustics — Methods for calculating loudness —
Part 2:
Moore-Glasberg method
1 Scope
This document specifies a method for estimating the loudness and loudness level of stationary sounds
as perceived by otologically normal adult persons under specific listening conditions. It provides an
algorithm for the calculation of monaural or binaural loudness for sounds recorded using a single
microphone, using a head and torso simulator, or for sounds presented via earphones. The method is
based on the Moore-Glasberg algorithm.
NOTE 1 Issues of binaural calculations are discussed in Annex A.
NOTE 2 Users who wish to study the details of the calculation method can review or implement the source
code, which is entirely informative and provided with this document for the convenience of the user.
This method can be applied to tones, broadband noises and complex sounds with sharp line spectral
components, for example transformer hum or fan noise.
NOTE 3 It has been shown (see Reference [15]) 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.
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
IEC/TS 60318-7, Electroacoustics — Simulators of human head and ear — Part 7: Head and torso simulator
for the measurement of hearing aids
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 browsing platform: available at http:// www .iso .org/ obp
— IEC Electropedia: available at http:// www .electropedia .org/
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ISO 532-2:2017(E)
3.1
sound pressure level
L
p
ten times the logarithm to the base 10 of the ratio of the square of the sound pressure, p, to the square
of a reference value, p , expressed in decibels
0
2
p
L =10lg dB
p
2
p
0
where the reference value, p , in gases is 20 μPa
0
2
Note 1 to entry: Because of practical limitations of the measuring instruments, p is always understood to
denote the square of a frequency-weighted, frequency-band-limited or time-weighted sound pressure. If specific
frequency and time weightings as specified in IEC 61672–1 and/or specific frequency bands (3.2) are applied, this
should be indicated by appropriate subscripts, for example L denotes the A-weighted sound pressure level
p,AS
with time weighting S (slow). Frequency weightings such as A-weighting should not be used when specifying
sound pressure levels for the purpose of loudness (3.17) calculation using the current procedure.
Note 2 to entry: This definition is technically in accordance with ISO 80000-8:2007, 8.
3.2
frequency band
continuous set of frequencies lying between two specified limiting frequencies
Note 1 to entry: A frequency band is characterized by two values that define its position in the frequency
spectrum, for instance its lower and upper cut-off frequencies.
Note 2 to entry: Frequency is expressed in Hz.
[SOURCE: IEC 60050-702:1992, 702-01-02]
3.3
filter
device or mathematical operation that, when applied to a complex signal, passes energy of signal
components of certain frequencies while substantially attenuating energy of signal components of all
other frequencies
3.4
cut-off frequency
lowest ( f ) or highest ( f ) frequency beyond which the response of the filter (3.3) to a sinusoidal signal
l h
does not exceed −3 dB relative to the maximum response measured between ( f ) and ( f )
l h
3.5
one-third-octave band
frequency band (3.2) with the centre frequency f and the width of one-third of an octave
T
Note 1 to entry: The subscript T instead of c is used to specify the centre frequency in the special case of a one-
third-octave band.
Note 2 to entry: Width of one-third of an octave as specified in IEC 61260-1.
3.6
band-reject filter
filter (3.3) that rejects signal energy within a certain frequency band (3.2) and passes most of the signal
energy outside of this frequency band
Note 1 to entry: A narrow band-reject filter is also called a notch filter.
3.7
band level
L
pb
sound pressure level (3.1) of sound contained within a restricted frequency band (b)
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ISO 532-2:2017(E)
3.8
one-third-octave-band level
L
T
sound pressure level (3.1) of sound contained within a frequency band (3.2) with the width of one-third
of an octave
3.9
sound spectrum
representation of the magnitudes (and sometimes of the phases) of the components of a complex sound
as a function of frequency
3.10
spectrum density level
spectrum level
level of the limit, as the width of the frequency band (3.2) approaches zero, of the quotient of a specified
quantity distributed within a frequency band, by the width of the band, expressed in decibels
Note 1 to entry: The words “spectrum level” should be preceded by a descriptive modifier describing the
measured quantity.
Note 2 to entry: For illustration, the sound pressure spectrum level L at the midband frequency is obtained
ps
practically by
22
Lp=Δ10lg //fp /Δ f dB
pbs ()b0()0
2
where p is the time-mean-square sound pressure measured through a filter (3.3) system, p the reference
b 0
sound pressure, Δf the bandwidth of the filter system, and Δ f the reference bandwidth of 1 Hz. For computational
0
purposes, with L for the band sound pressure level (3.1) observed through the filter, the above relation becomes
pb
LL=− 10lgΔΔff/ dB
ppbs b 0
3.11
auditory filter
filter (3.3) within the human cochlea describing the frequency resolution of the auditory system, with
characteristics that are usually estimated from the results of masking experiments
3.12
otologically normal person
person in a normal state of health who is free from all signs or symptoms of ear disease and from
obstructing wax in the ear canals, and who has no history of undue exposure to noise, exposure to
potentially ototoxic drugs or familial hearing loss
[SOURCE: ISO 226:2003, 3.1]
3.13
equivalent rectangular bandwidth of the auditory filter for otologically normal persons
ERB
n
auditory filter (3.11) bandwidth determined by measuring tone detection thresholds in wideband noise
passed through band-reject (notch) filters of various bandwidths
Note 1 to entry: The subscript n indicates that the value applies for persons with otologically normal hearing.
Note 2 to entry: The multi-letter abbreviated term presented in italics and with a subscript is used here instead
of a symbol to maintain an established notation and to avoid confusion.
Note 3 to entry: Bandwidth is measured in Hertz (Hz).
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ISO 532-2:2017(E)
3.14
equivalent rectangular bandwidth number scale
ERB -number scale
n
transformation of the frequency scale constructed so that an increase in frequency equal to one ERB
n
leads to an increase of one unit on the ERB -number scale
n
Note 1 to entry: ERB is measured in Hertz (Hz).
n
Note 2 to entry: The unit of the ERB -number scale is the Cam. For example, the value of ERB for a centre
n n
frequency of 1 000 Hz is approximately 132 Hz, so an increase in frequency from 934 Hz to 1 066 Hz corresponds
to a step of one Cam. The equation relating ERB -number to frequency is given in 7.4.
n
3.15
loudness level
sound pressure level (3.1) of a frontally incident, sinusoidal plane progressive wave, presented binaurally
at a frequency of 1 000 Hz that is judged by otologically normal persons as being as loud as the given sound
Note 1 to entry: Loudness level is expressed in phons.
3.16
calculated loudness level
L
N
loudness level (3.15) calculated following the procedure of a predictive model
3.17
loudness
perceived magnitude of a sound, which depends on the acoustic properties of the sound and the specific
listening conditions, as estimated by otologically normal persons
Note 1 to entry: Loudness is expressed in sones.
Note 2 to entry: Loudness depends primarily upon the sound pressure level (3.1) although it also depends upon
the frequency, waveform, bandwidth, and duration of the sound.
Note 3 to entry: One sone is the loudness of a sound with a loudness level (3.15) of 40 phon.
Note 4 to entry: A sound that is twice as loud as another sound is characterized by doubling the number of sones.
3.18
calculated loudness
N
loudness (3.17) calculated following the procedure of a predictive model
3.19
excitation
E
output of an auditory filter (3.11) centred at a given frequency, specified in units that are linearly related
to power
Note 1 to entry: An excitation of 1 unit is produced at the output of an auditory filter centred at 1 000 Hz by a
tone with a frequency of 1 000 Hz with a sound pressure level (3.1) of 0 dB presented in a free field with frontal
incidence.
3.20
excitation level
L
E
ten times the logarithm to the base 10 of the ratio of the excitation (3.19) at the output of an auditory
filter (3.11) centred at the frequency of interest to the reference excitation E
0
E
L =10lg dB
E
E
0
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ISO 532-2:2017(E)
where the reference excitation, E , is the excitation produced by a 1 000 Hz tone with a sound pressure
0
level (3.1) of 0 dB presented in a free field with frontal incidence
3.21
specific loudness
N ‘
calculated loudness (3.18) evoked over a frequency band (3.2) with a bandwidth of one ERB (3.13)
n
centred on the frequency of interest
Note 1 to entry: Specific loudness is expressed in sones/Cam.
Note 2 to entry: The definition together with the stated unit are different from those in ISO 532-1.
4 General
The method described in the main part of this document specifies a method for calculating loudness
and loudness level based on the Moore-Glasberg procedure.
The procedure involves a sequence of stages. Each stage is described below. However, it is envisaged
that those wishing to calculate loudness using this procedure will use the computer program (see
Annex C) provided with this document that implements the described procedure. It is not expected
that the procedure will be implemented by hand. Such computations would be very time consuming.
The source code provided in Annex C gives an example of the implementation of the method. Other
implementations using different software are possible.
NOTE 1 The computational procedure described in this document is an updated version of procedures
[14-17]
published earlier elsewhere .
NOTE 2 Uncertainties are addressed in Clause 9.
5 Specifications of signals
5.1 General
The spectrum of the signal whose loudness is to be determined shall be specified at each ear. The
spectrum can be specified exactly using the methods described in 5.2, 5.3 and 5.4 for the case of a
complex tone, noise consisting of bands of pink or white noise of defined width, or sounds having a
mixture of discrete sinusoidal components or bands of pink or white noise. The sound spectrum can
be specified approximately using one-third-octave-band levels specified in the method described
in 5.5. For this, one-third-octave bands according to IEC 61260-1:2014 should be used. The methods
described in 5.2 to 5.4 may be of interest for synthetic signals or signals analysed by discrete Fourier
transform techniques. The method described in 5.5 will be usually used for practical signals. If the
spectrum is specified exactly, the predicted loudness will be more accurate than when the spectrum is
approximated using one-third-octave-band levels.
5.2 Complex tone
This is a sound with a spectrum that consists of discrete sinusoidal components. The spectrum can be
specified in terms of frequency components that are either harmonically or non-harmonically spaced.
The frequency and sound pressure level of each component shall be specified.
5.3 Noise consisting of bands of pink or white noise of defined width
The number of noise bands and their widths shall be specified. Each band can be composed of either
filtered white noise (with a constant spectrum level within the passband) or filtered pink noise (with
a spectrum level within the passband that decreases with increasing centre frequency at a rate of
3 dB/octave). For each band, the following shall be specified: the lower cut-off frequency, the upper
cut-off frequency and the spectrum level. In the case of pink noise, the frequency at which the spectrum
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ISO 532-2:2017(E)
level is determined shall also be specified. Within the procedure, the spectra of bands of noise are
approximated by a series of discrete sinusoidal components. When the bandwidth of the noise exceeds
30 Hz, the components are spaced at 10 Hz intervals, and the level of each component is set 10 dB higher
than the spectrum level at the corresponding frequency. When the bandwidth of the noise is less than
30 Hz, the components are spaced at 1 Hz intervals, and the level of each component is set equal to the
spectrum level at the corresponding frequency.
EXAMPLE 1 A band of white noise extending from 200 Hz to 500 Hz with a spectrum level of 50 dB would be
approximated by sinusoidal components with frequencies 205 Hz, 215 Hz, 225 Hz, 235 Hz …. 475 Hz, 485 Hz,
495 Hz, each component having a sound pressure level of 60 dB.
EXAMPLE 2 A band of pink noise having lower and upper cut-off frequencies of 100 Hz and 115 Hz, respectively,
with a spectrum level of 65 dB would be approximated by sinusoidal components with frequencies 101 Hz,
102 Hz, 103 Hz, 104 Hz …. 113 Hz, 114 Hz, 115 Hz, with the components having sound pressure levels increasing
progressively from 64,7 dB at 101 Hz to 65,3 dB at 115 Hz.
NOTE The spacing of the components (10 Hz as in Example 1 or 1 Hz as in Example 2) is not a property of
the input signal. The 1 Hz spacing is used to ensure sufficient accuracy in the computation of loudness when the
bandwidth of the spectrum of the signal is narrow, i.e. less than 30 Hz. For signals with wider bandwidth, i.e.
30 Hz or greater, then a 10 Hz spacing will result in sufficient accuracy for the purpose of the com
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