ISO 532-3:2023

INTERNATIONAL ISO
STANDARD 532-3
First edition
2023-07
Acoustics — Methods for calculating
loudness —
Part 3:
Moore-Glasberg-Schlittenlacher
method
Reference number
ISO 532-3:2023(E)
© ISO 2023

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ISO 532-3:2023(E)
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Published in Switzerland
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ISO 532-3:2023(E)
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 General . 4
5 Input signal . 4
5.1 Single microphone . 4
5.2 Two microphones in the ear canals or microphones in a head and torso simulator . 4
5.3 Earphone presentation. 4
6 Instrumentation . 5
7 Description of the method . 5
7.1 General . 5
7.2 Transfer of sound through the outer and middle ear . 6
7.2.1 General . 6
7.2.2 Free-field transfer function . 7
7.2.3 Diffuse-field transfer function . 8
7.2.4 Signal recorded using microphones in the ear canals or using a Head and
Torso Simulator . 8
7.2.5 Earphone presentation . 8
7.3 Calculation of the running short-term spectrum . 8
7.4 Calculation of the running short-term excitation pattern . 9
7.5 Transformation of excitation into specific loudness . 10
7.5.1 General . 10
7.5.2 Reference excitation at the reference threshold of hearing . 10
7.5.3 Gain of the cochlear amplifier for inputs with low sound pressure levels . 11
7.5.4 Calculation of specific loudness from excitation when E /E ≤ E/E . 11
THRQ 0 0
7.5.5 Calculation of specific loudness from excitation when E /E > E/E .12
THRQ 0 0
10
7.5.6 Calculation of specific loudness from excitation when E/E > 10 .12
0
7.6 Calculation of short-term specific loudness . 13
7.7 Smoothing of short-term specific loudness and application of binaural inhibition .13
7.8 Calculation of short-term loudness . 15
7.9 Calculation of long-term loudness . 15
7.10 Relationship between loudness level and loudness. 15
7.11 Calculation of the reference threshold of hearing . 16
8 Uncertainty of calculated loudness sounds .17
9 Data reporting .17
Annex A (informative) Software for the calculation of loudness according to the method in
this document .19
Annex B (informative) Test signals used for verification of this document .21
Annex C (informative) Test signals used for verification of equivalence with ISO 532-2 .24
Bibliography .28
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ISO 532-3:2023(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 document 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).
ISO draws attention to the possibility that the implementation of this document may involve the use
of (a) patent(s). ISO takes no position concerning the evidence, validity or applicability of any claimed
patent rights in respect thereof. As of the date of publication of this document, ISO had/had not received
notice of (a) patent(s) which may be required to implement this document. However, implementers are
cautioned that this may not represent the latest information, which may be obtained from the patent
database available at www.iso.org/patents. ISO shall not be held responsible for identifying any or all
such patent rights.
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation of 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
www.iso.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 can be found on the ISO website.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www.iso.org/members.html.
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ISO 532-3:2023(E)
Introduction
Loudness and loudness level are two perceptual attributes of sound describing absolute and relative
sensations of sound strength perceived by a listener 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 this document is to specify a calculation procedure based on the physical properties of
sound for estimating loudness and loudness level of sound as perceived by listeners with otologically
normal hearing under specific listening conditions. This procedure seeks 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.
This document describes a method for calculating the loudness of time-varying sounds from the
input signal, which may differ for the two ears. This calculation method is based on Moore-Glasberg-
[1] to [5]
Schlittenlacher loudness calculation algorithms . The method allows calculation of two quantities:
a) The short-term loudness, which is the momentary loudness of a short segment of a sound, such as a
word in a speech sound or a single note in a piece of music.
b) The long-term loudness, which is the loudness of a longer segment of sound, such as a whole
sentence or a musical phrase.
For most everyday sounds, both the short-term loudness and the long-term loudness vary over time.
The loudness of sounds with durations up to 2 s or 3 s is well predicted from the maximum value of the
[4][6] to [8]
long-term loudness reached during presentation of the sound . For long-duration stationary
sounds, the long-term loudness based on the method described in this document is very close to the
[9]
loudness determined using the method described in ISO 532-2 . Deviations can occur for sounds with
strong amplitude fluctuations, such as noises with narrow bandwidth; for such sounds the calculated
loudness is more accurate for this document than for ISO 532-2.
The method of loudness calculation described in this standard can be applied to signals of any duration.
However, it does not directly give an output corresponding to the overall loudness impression of a sound
scene or soundscape over a period of minutes, hours, or days, which is called the “overall loudness” in
this standard. The output of the method of loudness calculation described in this standard can be post-
processed to estimate the overall loudness of a sound scene.
NOTE Post-processing is outside the scope of this document, but some possible methods have been
[10] to [13]
described .
This document describes the calculation procedure leading to estimation of the loudness and loudness
level of time-varying sounds and provides executable computer programs. 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 conformity with the document.
NOTE Equipment or machinery noise emissions/immissions can also be judged by other quantities defined
[14] [15] [16] [17]
in various International Standards (see e.g. ISO 1996-1 , ISO 3740 , ISO 9612 , and ISO 11200 ).
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INTERNATIONAL STANDARD ISO 532-3:2023(E)
Acoustics — Methods for calculating loudness —
Part 3:
Moore-Glasberg-Schlittenlacher method
1 Scope
This document specifies a method for estimating the loudness and loudness level of both stationary
and time-varying sounds as perceived by otologically normal adult listeners under specific listening
conditions. The sounds may be recorded using a single microphone, using a head and torso simulator,
or, for sounds presented via earphones, the electrical signal delivered to the earphones may be used.
The method is based on the Moore-Glasberg-Schlittenlacher algorithm.
NOTE 1 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 the standard for the convenience of the user.
This method can be applied to any sounds, including tones, broadband noises, complex sounds with
sharp line spectral components, musical sounds, speech, and impact sounds such as gunshots and sonic
booms.
Calculation of a single value for the overall loudness over the entire period of a time-varying signal
lasting more than 5 s is outside the scope of this document.
NOTE 2 It has been shown that, for steady tones, this method provides a good match to the contours
[18]
of equal loudness level as defined in ISO 226:2003 and the reference threshold of hearing as defined in
[19]
ISO 389-7:2019 .
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 60318-7, Electroacoustics – Simulators of human head and ear – Part 7: Head and torso simulator for
the measurement of sound sources close to the ear
IEC 61672-1, 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 terminology databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at https:// www .electropedia .org/
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ISO 532-3:2023(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 air 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 are applied, this
should be indicated by appropriate subscripts; e.g. L denotes the A-weighted sound pressure level with
p,AS
time weighting S (slow). Frequency weightings such as A-weighting should not be used when specifying sound
pressure levels for the purpose of loudness calculation using the current procedure.
[20]
Note 2 to entry: This definition is technically in accordance with ISO 80000-8:2020, 8-22 .
3.2
filter
any device or mathematical operation which, 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
3.3
band-pass filter
filter (3.2) that passes signal energy within a certain frequency band and rejects most of the signal
energy outside of this frequency band
3.4
sound spectrum
representation of the magnitudes (and sometimes of the phases) of the components of a complex sound
as a function of frequency
3.5
auditory filter
filter (3.2) within the human cochlea describing the frequency resolution of the auditory system, whose
characteristics are usually estimated from the results of masking experiments
3.6
ERB
n
equivalent rectangular bandwidth of the auditory filter for otologically normal persons
width of an idealised rectangular band-pass filter (3.3) that has the same peak transmission as the
auditory filter (3.5) at the same centre frequency and that passes the same power for a white noise input
(in Hz)
Note 1 to entry: The subscript n indicates that the value applies for listeners with otologically normal hearing.
Note 2 to entry: The unconventional use of a multiletter abbreviated term presented in italics and with a subscript
is used here in the place of a symbol to maintain the use of an established notation and to avoid confusion.
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ISO 532-3:2023(E)
3.7
ERB -number scale
n
equivalent rectangular bandwidth number scale
transformation of the frequency scale constructed such that an increase in frequency equal to one ERB
n
(Hz) (3.6) leads to an increase of one unit on the ERB -number scale
n
Note 1 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
3.8
loudness level
sound pressure level 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.
3.9
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 listeners
Note 1 to entry: Loudness is expressed in sones.
Note 2 to entry: Loudness depends primarily upon the sound pressure 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 whose loudness level is 40 phon.
Note 4 to entry: A sound that is twice as loud as another sound is characterized by doubling the number of sones.
3.10
short-term loudness
loudness of an individual brief segment of sound, such as a syllable in speech, a single musical note, or a
short burst of a sound, typically lasting up to 500 ms
3.11
long-term loudness
loudness of a long sound, such as a whole sentence, a musical phrase, or a continuous noise, typically
lasting up to 5 s
Note 1 to entry: The overall loudness of a sound or soundscape lasting longer than 5 s can be estimated by post-
processing of the long-term loudness as a function of time. Such post-processing is outside the scope of this
standard, but some possible methods are described in References [10] to [13].
3.12
excitation
E
output of an auditory filter (3.5) 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 of 0 dB presented in a free field with frontal incidence.
3.13
excitation level
L
E
ten times the logarithm to the base 10 of the ratio of the excitation (3.12) at the output of an auditory
filter (3.5) centred at the frequency of interest to the reference excitation (3.12), E
0
E
L =10lg dB
E
E
0
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ISO 532-3:2023(E)
where the reference excitation E is the excitation produced by a 1 000 Hz tone with a sound pressure
0
level of 0 dB presented in a free field with frontal incidence
3.14
specific loudness
N'
calculated loudness evoked over a frequency band with a bandwidth of 1 ERB centred on the frequency
n
of interest
4 General
The method described in this document specifies a method for calculating loudness and loudness level
of any sound based on the Moore-Glasberg-Schlittenlacher procedure.
The method 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 one of the computer programs
(see Annex A) 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 A 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
published earlier elsewhere in References [1] to [5].
NOTE 2 Uncertainties are addressed in Clause 8.
5 Input signal
The signal that is used as input to the algorithm is the waveform for each ear (left and right), sampled
1)
using a 32 kHz sampling rate. If the Matlab® code described in Annex C is used, higher sampling rates
for the signal are allowed. These are automatically converted by the Matlab® software to a 32 kHz
sampling rate. The signal can be obtained in three ways.
5.1 Single microphone
The sound can be recorded using a single microphone placed at the centre of the position of the listener’s
head, after the listener has been removed from the sound field. In this case, the sound would be diotic
(the same at the two ears) and the single recorded signal would be presented to both input channels of
the algorithm.
5.2 Two microphones in the ear canals or microphones in a head and torso simulator
The sound can be recorded using two small probe microphones with the tips placed close to each ear
drum (left and right) or using the two ear simulators (left and right) in a head and torso simulator.
5.3 Earphone presentation
If the sound is delivered via earphones, the input signals for the algorithm correspond to the electrical
signals delivered to the earphones, but with allowance for the transfer function from each earphone to
the eardrum; see 7.2.4.
1) Matlab® is a trademark of MathWorks. This information is given for the convenience of users of this document
and does not constitute an endorsement by ISO of the product named. Equivalent products may be used if they can
be shown to lead to the same results
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ISO 532-3:2023(E)
6 Instrumentation
Measuring instrumentation used to acquire a signal to be used as an input for method 5.1 and 5.2
shall conform to IEC 61672-1. The microphone(s) used for method 5.1 shall have an omnidirectional
characteristic or a free-field characteristic. If a head and torso simulator is used it shall conform to
IEC 60318-7. For signals acquired using a head and torso simulator, the transfer function of the simulator
as supplied by the equipment manufacturer or acquisition software shall be allowed for.
7 Description of the method
7.1 General
The procedure involves a sequence of processing operations, as illustrated in Figure 1.
For each ear, the processing operations are:
a) a filter to allow for the effects of transfer of sound through the outer and middle ear;
b) a short-term spectral analysis of the sound spectrum with greater frequency resolution at low than
at high frequencies;
c) calculation of an excitation pattern, representing the magnitudes of the outputs of the auditory
filters as a function of centre frequency;
d) application of a compressive nonlinearity to the output of each auditory filter to transform
excitation to specific loudness;
e) smoothing over time of the resulting instantaneous specific loudness pattern using an averaging
process resembling an automatic gain control (AGC) to give short-term specific loudness.
Subsequent stages are:
f) the short-term specific loudness patterns for each ear are used to calculate broadly-tuned binaural
inhibition functions, the amount of inhibition depending on the relative short-term specific
loudness at the two ears;
g) the inhibited specific loudness patterns are summed across frequency to give an estimate of the
short-term loudness for each ear;
h) the binaural short-term loudness is calculated as the sum of the short-term loudness values for the
two ears;
i) the long-term loudness for each ear is calculated by smoothing the short-term loudness for that ear,
again by a process resembling AGC;
j) the binaural long-term loudness is obtained by summing the long-term loudness across ears.
These steps are described sequentially in 7.2 to 7.9.
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ISO 532-3:2023(E)
Figure 1 — Flow chart illustrating the sequence of processing operations in the method
7.2 Transfer of sound through the outer and middle ear
7.2.1 General
The transfer of sound through the outer and middle ear is modelled using one of three finite impulse
response (FIR) filters with 4 097 coefficients. Different filters are used depending on the method by
which the sound was picked up and the method by which the sound was delivered to the listeners. Each
filter represents the combined effect of the outer ear and the middle ear. The transfer function for the
[9]
middle ear is the same as for ISO 532-2:2017 , 7.3 and is specified in column 4 of Table 1. This transfer
function is referred to as “middle ear only”.
Table 1 — Transfer functions
Frequency Difference between the sound Difference between the sound Scaled transfer
pressure level at the tympan- pressure level at the tympan- function value for
ic membrane and the sound ic membrane and the sound the middle ear
pressure level measured in the pressure level measured in
free field (in the absence of a the diffuse field (in the ab-
listener) sence of a listener)
Hz dB dB dB
20 0,0 0,0 −39,6
25 0,0 0,0 −32,0
31,5 0,0 0,0 −25,85
40 0,0 0,0 −21,4
50 0,0 0,0 −18,5
63 0,0 0,0 −15,9
a
Values are in a range that has not been validated.
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ISO 532-3:2023(E)
TTabablele 1 1 ((ccoonnttiinnueuedd))
Frequency Difference between the sound Difference between the sound Scaled transfer
pressure level at the tympan- pressure level at the tympan- function value for
ic membrane and the sound ic membrane and the sound the middle ear
pressure level measured in the pressure level measured in
free field (in the absence of a the diffuse field (in the ab-
listener) sence of a listener)
Hz dB dB dB
80 0,0 0,0 −14,1
100 0,0 0,0 −12,4
125 0,1 0,1 −11,0
160 0,3 0,3 −9,6
200 0,5 0,4 −8,3
250 0,9 0,5 −7,4
315 1,4 1,0 −6,2
400 1,6 1,6 −4,8
500 1,7 1,7 −3,8
630 2,5 2,2 −3,3
750 2,7 2,7 −2,9
800 2,6 2,9 −2,6
1 000 2,6 3,8 −2,6
1 250 3,2 5,3 −4,5
1 500 5,2 6,8 −5,4
1 600 6,6 7,2 −6,1
2 000 12,0 10,2 −8,5
2 500 16,8 14,9 −10,4
3 000 15,3 14,5 −7,3
3 150 15,2 14,4 −7,0
4 000 14,2 12,7 −6,6
5 000 10,7 10,8 −7,0
6 000 7,1 8,9 −9,2
6 300 6,4 8,7 −10,2
8 000 1,8 8,5 −12,2
9 000 -0,9 6,2 −10,8
10 000 -1,6 5,0 −10,1
11 200 1,9 4,5 −12,7
12 500 4,9 4,0 −15,0
a
14 000 2,0 3,3 −18,2
a
15 000 -2,0 2,6 −23
...