ISO/DIS 532-1

Acoustics -- Method for calculating loudness

Acoustique -- Méthode de calcul du niveau d'isosonie

Standards Content (sample)

DRAFT INTERNATIONAL STANDARD ISO/DIS 532-1
ISO/TC 43 Secretariat: DS
Voting begins on Voting terminates on
2011-07-19 2011-12-19

INTERNATIONAL ORGANIZATION FOR STANDARDIZATION • МЕЖДУНАРОДНАЯ ОРГАНИЗАЦИЯ ПО СТАНДАРТИЗАЦИИ • ORGANISATION INTERNATIONALE DE NORMALISATION

Acoustics — Method for calculating loudness —
Part 1:
Stationary sounds
Acoustique — Méthode de calcul du niveau d'isosonie —
Partie 1: Bruits stationnaires
[Revision of first edition (ISO 532:1975)]
ICS 17.140.01

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© International Organization for Standardization, 2011
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ISO/DIS 532-1
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ISO/DIS 532-1
Contents Page

Foreword ............................................................................................................................................................iv

Introduction.........................................................................................................................................................v

1 Scope......................................................................................................................................................1

2 Normative references............................................................................................................................1

3 Terms and definitions ...........................................................................................................................1

4 General...................................................................................................................................................5

5 Input of signals......................................................................................................................................5

5.1 Specifications ........................................................................................................................................5

5.2 Instrumentation .....................................................................................................................................6

6 Description of the method....................................................................................................................6

6.1 Introduction............................................................................................................................................6

6.2 Determination of sound spectrum at the tympanic membrane........................................................7

6.3 Determination of sound spectrum at the oval window......................................................................8

6.4 Transformation of sound spectrum into excitation pattern............................................................10

6.5 Transformation of excitation pattern into specific loudness .........................................................11

7 Calculation of loudness and loudness level ....................................................................................16

7.1 Calculation of monaural and binaural loudness (diotic and dichotic stimuli)..............................16

7.2 Relationship between loudness level and loudness .......................................................................17

7.3 Calculation of the reference threshold of hearing...........................................................................18

8 Uncertainty of steady loudness .........................................................................................................18

Annex A (informative) Comments regarding binaural loudness..................................................................20

Annex B (informative) Results for selected test signals...............................................................................21

Annex C (informative) Software for calculation of loudness according to the method in this

document .............................................................................................................................................26

Bibliography......................................................................................................................................................27

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ISO/DIS 532-1
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.

International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2.

The main task of technical committees is to prepare International Standards. Draft International Standards

adopted by the technical committees are circulated to the member bodies for voting. Publication as an

International Standard requires approval by at least 75 % of the member bodies casting a vote.

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.

ISO 532-1 was prepared by Technical Committee ISO/TC 43, Acoustics.

ISO 532-1 is the first part of a new standards series ISO 532-x, which replaces ISO 532:1975, Acoustics –

Method for calculating loudness level. ISO 532-x consists of the following parts, under the general title

Acoustics — Methods for calculating loudness:
⎯ Part 1: Stationary sounds
⎯ Part 2: Time-varying sounds
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ISO/DIS 532-1
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 standard is to specify calculation procedures based on 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 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

This part of ISO 532 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-

Glasberg loudness calculation algorithms [11, 15, 17]. Part 2 of ISO 532 covers the procedures for

calculation of loudness and loudness level of arbitrary non-stationary (time-varying) sounds including

stationary sounds as a special case.

The standard describes the calculation procedures leading to estimation of loudness and loudness level and

provides an executable computer program. The software provided with this International Standard is entirely

informative and provided for the convenience of the user. Use of the provided software is not required for

conformance with the International Standard.

The method in the current standard differs from the methods included the previous ISO 532:1975 [3]. The

former ISO 532:1975, A method (Stevens loudness [18]), was removed as this method was not often used

and its predictions were not accurate for sounds with strong tonal components. The former ISO 532:1975, B

method (Zwicker loudness), was removed as this method, and the revised version of that method in the

German standard DIN 45631:1991 [12], both predict equal-loudness level contours that are not in accordance

with those in ISO 226:2003 [1]. The method described in the current standard also improves precision of

calculated loudness at low frequency range and allows for calculation of loudness under conditions where the

sound differs at the two ears.

NOTE Equipment or machinery noise emissions/immissions may also be judged by other quantities defined in

various International Standards (see e.g. ISO 1996-1 [4], ISO 3740ff [5], and ISO 9612 [6]).

Under preparation
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DRAFT INTERNATIONAL STANDARD ISO/DIS 532-1
Acoustics — Method for calculating loudness —
Part 1:
Stationary sounds
1 Scope

This part of ISO 532 specifies a method for estimating the loudness and loudness level of stationary sounds

as perceived by otologically normal adult listeners under specific listening conditions. The document 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.

NOTE 1 Problems of binaural calculations are discussed in Annex A.

The method is based on the Moore-Glasberg algorithm and 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.

NOTE 2 Users who do not wish to understand the details of the calculation method can still apply the standard by using

an executable computer program which is entirely informative and provided with the standard for the convenience of the

user.

This method can be applied to tones, broadband noises, and to complex sounds with sharp line spectral

components, e.g., transformer hum or fan noise. It has been shown that this method provides a good match to

the contours of equal loudness level as defined in ISO 226:2003 [1] and the reference threshold of hearing as

defined in ISO 389-7 [2].
2 Normative references

The following documents, in whole or in part, are normatively referenced in this document and are

indispensable for its application. For dated references, only the edition cited applies. For undated references,

the latest edition of the referenced document (including any amendments) applies.

IEC 61260:1995, Electroacoustics — Octave-band and fractional-octave-band filters

IEC 61672-1:2002, Electroacoustics — Sound level meters — Part 1: Specifications

IEC/TR 60959, Provisional head and torso simulator for acoustic measurements on air conduction hearing

aids

ISO/IEC Guide 98-3, Uncertainty of measurement — Part 3: Guide to the expression of uncertainty in

measurement (GUM:1995)
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
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ISO/DIS 532-1
3.1
sound pressure level

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
L = 10lg dB (1)
where the reference value, p , in gases is 20 μPa

NOTE 1 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 time weighting S (slow). Frequency weightings

p,AS

such as A-weighting should not be used when specifying sound pressure levels for the propose of loudness calculation

using the current procedure.

NOTE 2 This definition is technically in accordance with ISO 80000-8:2007, 8-22 [8].

3.2
frequency band
continuous set of frequencies lying between two specified limiting frequencies

NOTE 1 A frequency band is characterized by two values which define its position in the frequency spectrum, for

instance its lower and upper cut-off frequencies.
NOTE 2 Frequency is expressed in Hz.
[IEV 702:1995, 702-01-02 [13]]
3.3
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
3.4
cut-off frequency

the lowest (f) or the highest (f ) frequency beyond which the response of the device specified by the given

l h

bandwidth does not exceed -3 dB relative to the response measured at the centre frequency (f )

3.5
band-pass filter

filter that passes signal energy within a certain frequency band and rejects most of the signal energy outside

of this frequency band
3.6
filter bandwidth
for a band-pass filter the difference between f and f
h l
3.7
one-third-octave band

the frequency band with the width of one-third of an octave as specified in IEC 61260

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ISO/DIS 532-1
3.8
band-reject filter

filter that rejects signal energy within a certain frequency band and passes most of the signal energy outside

of this frequency band
NOTE A narrow band-reject filter is also called a notch filter.
3.9
band level

sound pressure level of sound contained within a restricted frequency band (b), expressed in decibels

3.10
one-third-octave-band level

sound pressure level of sound contained within a frequency band with the width of one-third of an octave,

expressed in decibels
3.11
sound spectrum
distribution of sound energy of a particular sound as a function of frequency
3.12
spectrum density level; spectrum level

level of the limit, as the width of the frequency band 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 The words "spectrum level" should be preceded by a descriptive modifier describing the measured quantity.

NOTE 2 For illustration, the sound pressure spectrum level L at the midband frequency is obtained practically by

2 2
L = 10lg[]()p /Δf /(p /Δ f) dB (2)
pbs b 0 0

where p is the time-mean-square sound pressure measured through a filter system, p the reference sound pressure, Δf

b 0

the bandwidth of the filter system, and Δ f the reference bandwidth of 1 Hz. For computational purposes, with L for the

0 b

band sound pressure level observed through the filter, the above relation becomes

L = L − 10lg[Δf /Δ f] dB (3)
pbs pb 0
3.13
auditory filter

a filter within the human cochlea describing the frequency resolution of the auditory system, whose

characteristics are usually estimated from the results of masking experiments
3.14
auditory filter bandwidth
bandwidth of an auditory filter
3.15

equivalent rectangular bandwidth of the auditory filter for otologically normal persons

ERB

auditory filter bandwidth determined by measuring tone detection thresholds in wideband noise passed

through band-reject (notch) filters of various bandwidths.

NOTE The subscript N indicates that the value applies for listeners with otologically normal hearing.

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ISO/DIS 532-1
3.16
loudness level

sound level of a given sound that is judged by otologically normal persons as loud as the sound pressure level

of a reference sound being a frontally incident, sinusoidal plane progressive wave, presented binaurally at a

frequency of 1 000 Hz
NOTE 1 Loudness level is expressed in phons.
3.17
calculated loudness level

loudness level calculated according to the procedure specified in this International Standard.

3.18
loudness

perceived magnitude of a sound, which depends on the acoustic properties of the sound and its manner of

presentation to the listener, as estimated by otologically normal listeners
NOTE 1 Loudness is expressed in sones.

NOTE 2 Loudness depends primarily upon the sound pressure although it also depends upon the frequency,

waveform, bandwidth, and duration of the sound.
NOTE 3 One sone is the loudness of a sound whose loudness level is 40 phon.

NOTE 4 A sound that is twice as loud as another sound is characterized by double the number of sones.

3.19
calculated loudness

loudness calculated according to the procedure specified in this International Standard

3.20
excitation

the output of an auditory filter centred at a given frequency, specified in units that are linearly related to power

NOTE 1 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.

NOTE 2 Since excitation E is specified relative to the reference value specified in NOTE 1, it is a dimensionless

quantity.
3.21
excitation level

ten times the logarithm to the base 10 of the ratio of the excitation at the output of an auditory filter centred at

the frequency of interest to the reference excitation E
L = 10lg dB (4)

where the reference excitation, E is the excitation produced by a 1 000 Hz tone with a sound pressure level

of 0 dB presented in a free field with frontal incidence
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3.22
specific loudness

the loudness evoked over a frequency band that is one-ERB wide and centred on the frequency of interest

NOTE Specific loudness is expressed in sones per ERB .
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 and the executable software

implementing the procedure is included (see Annex C). The description of the procedure is provided so that

the user can understand how the procedure works. 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.

NOTE 1 The computational procedure described in this document is an updated version of procedures published

earlier elsewhere [11, 14, 16, 17].
NOTE 2 Uncertainties are addressed in Clause 8.
5 Input of signals
5.1 Specifications
5.1.1 General

The spectrum of the signal whose loudness is to be determined shall be specified at each ear in order to

calculate loudness. The signal spectrum can be specified in several ways as described below. The spectrum

can be specified exactly (methods of 5.1.2 to 5.1.4), or approximately using one-third-octave-band levels

(method of 5.1.5). The first three methods may be of interest for synthetic signals or signals analysed by Fast

Fourier Transformation. 5.1.5 will be the method usually used for practical purposes. 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.
5.1.2 Complex tone

This is a sound whose spectrum 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.
5.1.3 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 white

noise (with a constant spectrum level within the passband) or pink noise (whose spectrum level within the

passband 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 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

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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 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.

NOTE The spacing of the components (10 Hz or 1 Hz) is not a property of the input signal. The spacing is chosen to

approximate the spectrum of the signal with sufficient accuracy for the purpose of the computation of loudness.

5.1.4 Mixture of discrete sinusoidal components and bands of pink or white noise
5.1.2 specifies the former and 5.1.3 specifies the latter.

5.1.5 Sound specified in terms of the sound pressure levels in 29 adjacent one-third-octave bands

The nominal centre frequencies of the 29 adjacent one-third-octave bands are as defined by IEC 61260 within

the range 25 Hz to 16 000 Hz. Within each band, the spectrum is assumed to be flat, and, as described for

noise bands in 5.1.3 above, the spectrum is approximated as a series of sinusoidal components spaced at

10 Hz intervals or (for centre frequencies of 125 Hz and below) at 1 Hz intervals. The level of each component

is calculated as follows. Let the width of a one-third-octave band at a given centre frequency be W (e.g.

230 Hz for a centre frequency of 1 000 Hz). The sound pressure level in that band, L , is converted to the

spectrum level in that band as: L − 10lg(W/1 Hz) dB. The level of each component in the approximation is

then set 10 dB above the spectrum level, i.e., to L − 10lg(W/1 Hz) dB + 10 dB.

EXAMPLE Consider the one-third-octave band centred at 1 000 Hz, and assume that the band sound pressure level is

63 dB. The spectrum level is then 63 dB – 10lg(230) dB = 39,4 dB. The spectrum of that one-third-octave band would thus

be approximated by components at 890 Hz, 900 Hz, 910 Hz, 920 Hz …. 1 080 Hz, 1 090 Hz, 1 100 Hz, 1 110 Hz, each

with a sound pressure level of 49,4 dB.
5.2 Instrumentation

If the one-third-octave-band sound pressure levels as described in 5.1.5 are determined in a sound field this

shall be done through the use of a sound acquisition system that conforms to IEC 61672-1 in conjunction with

one-third-octave filters that conform to IEC 61260. Equipment used to present the one-third-octave spectrum

in real time has to meet the requirements of IEC 61672-1:2002, class 1, or IEC 61260:1995, class 1. The

microphone(s) shall have an omnidirectional characteristic or a free-field characteristic. If a head and torso

simulator is used it shall conform to IEC/TR 60959. However, the procedure described in this part of ISO 532

applies to the sound that has been already acquired.
6 Description of the method
6.1 Introduction
The method of calculating loudness consists of the following discrete steps:

(1) transformation of the recorded sound spectrum into the sound spectrum at the tympanic membrane for

each ear;

(2) transformation of the sound spectrum at the tympanic membrane into the sound spectrum at the oval

window;

(3) transformation of the sound spectrum at the oval window into an excitation pattern on the basilar

membrane;
(4) transformation of the excitation pattern into a specific loudness pattern;
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ISO/DIS 532-1

(5) calculation of monaural and binaural loudness using the concept of binaural inhibition.

These steps are illustrated in the flow chart in Figure 1 and will be described sequentially in 6.2 to 6.5.

Figure 1 — Flow chart illustrating the sequence of the method
6.2 Determination of sound spectrum at the tympanic membrane
6.2.1 General

The spectrum specified in Clause 5 is transformed to the spectrum of sound reaching the tympanic

membrane. This is done by applying one of the transfer functions specified in 6.2. Several different listening

situations are possible and the transfer function chosen depends on the situation. The methods listed are not

mutually exclusive.
6.2.2 Free field and diffuse field

These transfer functions are applicable when the sound is picked up via a microphone placed at the centre of

the position where the listener’s head would be. The acoustical effects of the head/torso and outer ear on

transmission of sound to the tympanic membrane are represented by two standard transfer functions. The

first, applicable to free field listening with frontal incidence of the sound source, is specified in column 2 of

Table 1. The second, applicable to listening in a diffuse field, is specified in column 3 of Table 1. The transfer

functions represent the mean for adult humans [19, 20, 21].

The diffuse field transfer function can also be used for sounds presented via earphones that are designed to

have a diffuse field response (see 6.2.3).
6.2.3 Earphones

It is possible to calculate loudness for sounds transmitted via earphones. Note that the sensitivity level of the

earphones (the sound pressure level produced for a given applied voltage) shall be taken into account when

determining the spectra at the tympanic membrane. The transfer function of the earphones to the tympanic

membrane shall be specified. This is done by specifying the deviations from a flat response at several

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frequencies. A file containing these deviations is called an “earphone correction file”. The transfer function of

the earphone can be measured using a microphone close to the tympanic membrane or using the method

described in ISO 11904-1 [7].
6.2.4 Signal recorded at eardrum
Spectra at the tympanic membrane can be recorded using a pr
...