Acoustics -- Objective method for assessing the audibility of tones in noise -- Engineering method

ISO/PAS 20065:2016 describes a method for the objective determination of the audibility of tones in environmental noise. It is intended to augment the usual method for evaluation on the basis of aural impression, in particular, in cases in which there is no agreement on the degree of the audibility of tones. The method described can be used if the frequency of the tone being evaluated is equal to, or greater than, 50 Hz. In other cases, if the tone frequency is below 50 Hz, or if other types of noise (such as screeching) are to be captured, then this method cannot replace subjective evaluation. The method presented herein can be used in continuous measurement stations that work automatically.

Acoustique -- Méthode objective d'évaluation de l'audibilité des tonalités dans le bruit -- Méthode d'expertise

L'ISO/PAS 20065:2016 publiquement disponible décrit une méthode de détermination objective de l'audibilité des tonalités dans le bruit environnemental. L'ISO/PAS 20065:2016 publiquement disponible est destinée ŕ améliorer la méthode habituelle d'évaluation sur la base de l'impression auditive, en particulier en cas d'absence d'accord sur le degré d'audibilité des tonalités. La méthode décrite peut ętre utilisée lorsque la fréquence de la tonalité évaluée est égale ou supérieure ŕ 50 Hz. Dans les autres cas, si la fréquence de la tonalité est inférieure ŕ 50 Hz ou si d'autres types de bruit (par exemple un crissement) doivent ętre capturés, la présente méthode ne peut pas remplacer l'évaluation subjective. La méthode présentée ici peut ętre utilisée sur les postes de mesurage continu qui fonctionnent automatiquement.

General Information

Status
Published
Publication Date
30-Jun-2016
Current Stage
9092 - International Standard to be revised
Start Date
21-Jul-2020
Ref Project

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PUBLICLY ISO/PAS
AVAILABLE 20065
SPECIFICATION
First edition
2016-07-01
Acoustics — Objective method for
assessing the audibility of tones in
noise — Engineering method
Acoustique — Méthode objective pour évaluer l’audibilité des tons
dans le bruit — Méthode d’expertise
Reference number
ISO/PAS 20065:2016(E)
ISO 2016
---------------------- Page: 1 ----------------------
ISO/PAS 20065:2016(E)
COPYRIGHT PROTECTED DOCUMENT
© ISO 2016, Published in Switzerland

All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized otherwise in any form

or by any means, electronic or mechanical, including photocopying, or posting on the internet or an intranet, without prior

written permission. Permission can be requested from either ISO at the address below or ISO’s member body in the country of

the requester.
ISO copyright office
Ch. de Blandonnet 8 • CP 401
CH-1214 Vernier, Geneva, Switzerland
Tel. +41 22 749 01 11
Fax +41 22 749 09 47
copyright@iso.org
www.iso.org
ii © ISO 2016 – All rights reserved
---------------------- Page: 2 ----------------------
ISO/PAS 20065:2016(E)
Contents Page

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

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

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

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

4 Measurement procedure .............................................................................................................................................................................. 5

4.1 General ........................................................................................................................................................................................................... 5

4.2 Measurement instruments ........................................................................................................................................................... 5

4.3 Merging the basic spectra .............................................................................................................................................................. 5

5 Evaluation .................................................................................................................................................................................................................... 6

5.1 General information ........................................................................................................................................................................... 6

5.2 Width Δf of the critical band ..................................................................................................................................................... 7

5.3 Determination of prominent tones ........................................................................................................................................ 7

5.3.1 General information ...................................................................................................................................................... 7

5.3.2 Determination of the mean narrow-band level L of the masking noise ........................ 7

5.3.3 Determination of the tone level L of a tone in a critical band ................................................ 8

5.3.4 Distinctness of a tone ................................................................................................................................................... 9

5.3.5 Determination of the critical band level, L , of the masking noise ....................................10

5.3.6 Masking index .................................................................................................................................................................10

5.3.7 Determination of the audibility, ΔL ...............................................................................................................10

5.3.8 Determination of the decisive audibility, ΔL , of a narrow-band spectrum ................10

5.3.9 Determination of the mean audibility ΔL of a number of spectra ......................................12

6 Calculation of the uncertainty of the audibility ΔL ........................................................................................................13

7 Recommendations on the presentation of results .........................................................................................................16

7.1 Measurement .........................................................................................................................................................................................16

7.2 Acoustic environment ....................................................................................................................................................................16

7.3 Instruments for measurement, recording and evaluation .............................................................................16

7.4 Acoustic data ..........................................................................................................................................................................................16

Annex A (informative) Window effect and Picket fence effect ................................................................................................17

Annex B (informative) Resolving power of the human ear at frequencies below 1 000 Hz

and geometric position of the critical bands — corner frequencies ...........................................................20

Annex C (informative) Masking, masking threshold, masking index ..............................................................................22

Annex D (informative) Iterative method for the determination of the audibility, ∆L .....................................23

Annex E (informative) Example for the determination of the tonal audibility .....................................................27

Bibliography .............................................................................................................................................................................................................................33

© ISO 2016 – All rights reserved iii
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ISO/PAS 20065:2016(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).

Any trade name used in this document is information given for the convenience of users and does not

constitute an endorsement.

For an explanation on 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: www.iso.org/iso/foreword.html.

The committee responsible for this document is ISO/TC 43, Acoustics, Subcommittee SC 1, Noise.

iv © ISO 2016 – All rights reserved
---------------------- Page: 4 ----------------------
PUBLICLY AVAILABLE SPECIFICATION ISO/PAS 20065:2016(E)
Acoustics — Objective method for assessing the audibility
of tones in noise — Engineering method
1 Scope

This Publicly Available Specification describes a method for the objective determination of the audibility

of tones in environmental noise.

This Publicly Available Specification is intended to augment the usual method for evaluation on the

basis of aural impression, in particular, in cases in which there is no agreement on the degree of the

audibility of tones. The method described can be used if the frequency of the tone being evaluated is

equal to, or greater than, 50 Hz. In other cases, if the tone frequency is below 50 Hz, or if other types of

noise (such as screeching) are to be captured, then this method cannot replace subjective evaluation.

The method presented herein can be used in continuous measurement stations that work automatically.

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.

ISO 1996-1, Acoustics — Description, measurement and assessment of environmental noise — Part 1: Basic

quantities and assessment procedures
IEC 61672-1, Electroacoustics — Sound level meters — Part 1: Specifications
3 Terms and definitions

For the purposes of this document, the terms and definitions given in ISO 1996-1 and the following apply.

3.1
tonality

presence of a tone in a noise, the level of which is below that of the remaining noise components in the

critical band (3.5) about the tone frequency (3.2) by less than the value of the masking index (3.16), a

3.2
tone frequency

frequency of the spectral line (3.23) (or mid-band frequency of the narrow-band filter), to the level of

which the tone contributes most strongly
3.3
tone level

energy summation of the narrow-band level (3.22) with the tone frequency (3.2), f , and the lateral lines

about f , assignable to this tone

Note 1 to entry: If the critical band (3.5) for the frequency, f , under consideration contains a number of tones,

then the tone level, L , is the energy sum of these tones. This level, L , is then assigned to the frequency of the

T T
participating tone that has the maximal value of audibility (3.4), ΔL.

Note 2 to entry: The method for the determination of the tone level, L , of a tone in a critical band is described

in 5.3.3.
© ISO 2016 – All rights reserved 1
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ISO/PAS 20065:2016(E)
3.4
audibility
difference between the tone level (3.3), L , and the masking threshold (3.15), L

Note 1 to entry: The method for the determination of the decisive audibility (3.24), ΔL , of a narrow-band spectrum

(3.12) is described in 5.3.8.
3.5
critical band

frequency band with a bandwidth (3.17), ∆f , within which the auditory system integrates the sound

intensity in the formation of loudness and within which it integrates the sound intensity in the

formation of the masking threshold (3.15)

Note 1 to entry: This characteristic of a critical band (see also References [3] and [4]) holds only for a restricted

sound level range. This dependence is neglected here.
3.6
mean narrow-band level of the critical band

energy mean value of all narrow-band levels (3.22) in a critical band (3.5) that (as a rule) does not exceed

this mean value by more than 6 dB

Note 1 to entry: The method for the determination of the mean narrow-band level L of the masking noise is

described in 5.3.2 and Annex D (iterative method).
3.7
critical band level

level of noise that is assigned to the critical band (3.5) that describes the masking characteristic of the

noise for one or more tones of the noise in this critical band
Note 1 to entry: See narrow-band level (3.22) and Annex C for masking.
Note 2 to entry: For the definition formula for L , see Formula (12).
3.8
sampling frequency
number of samples taken per second

Note 1 to entry: The analogue data provided continuously are converted into samples through sampling at

discrete time intervals for digital processing.

Note 2 to entry: To ensure the reproducibility of a digitized signal, the Shannon theorem requires that the

sampling frequency, f , is at least 2 times the highest frequency of the signal components used for evaluation

in the time signal [ f ≥ 2 f , see also aliasing (3.9), antialiasing filter (3.10) and useable frequency (3.20)]. The

S N

algorithm of a Fast Fourier Transform analysis (the variant of a discrete Fourier Transform used typically and

optimized for calculation) only permits block lengths (3.11), N, that correspond to a power of two. FFT analyzers

thus need a sampling frequency that is at least 2,56 times the maximum frequency to be analysed.

3.9
aliasing

reflection in the line spectrum (3.12) of frequency components from the range above the sampling

frequency (3.8) divided by two ( f /2) in the range below f /2
S S

Note 1 to entry: Antialiasing filters (3.10) are used to avoid errors through such reflections.

Note 2 to entry: Half the sampling frequency ( f /2) is also known as the Nyquist frequency.

2 © ISO 2016 – All rights reserved
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ISO/PAS 20065:2016(E)
3.10
antialiasing filter
low-pass filter

ideal filter that allow frequencies below half the sampling frequency (3.8) to pass through completely

(without influencing the signal), but completely block all higher frequencies

Note 1 to entry: To prevent aliasing (3.9), the noise under investigation shall be filtered using an antialiasing

filter before analogue-to-digital conversion.

Note 2 to entry: Real aliasing filters have a final damping (generally 120 dB/octave) within the blocking range, i.e.

signal components in this transition range are reflected (damped). For example, in the transformation of 2 048

(2 k) data points, 1 024 frequency lines are calculated and 800 lines shown. A component in the line number

1 248 is folded back into the line number 800. With a low-pass filter of 120 dB/octave the damping of these

components is approximately 75 dB.

Note 3 to entry: The usual commercial FFT analyzers have an antialiasing filter, the limit frequency of which

can be switched automatically with the selectable sampling frequency. The reflection of simulated narrow-band

levels (3.22) is suppressed.
3.11
block length

block of sampling values that in discrete form represents a time-limited range of the time signal to be

analysed

Note 1 to entry: In contrast to frequency analysis with analogue and digital filters, the noise with the Fast Fourier

Transform is processed in data blocks. In general, these blocks embrace only a part of the noise recording. The block

length, N, expresses the number of data points processed at the same time. Due to the nature of the Fast Fourier

Transform, the value of N has the integer of power of 2. It has a value, for example, of N = 2 = 1 024 data points.

3.12
line spectrum
narrow-band spectrum
frequency spectrum

plot of the sound pressure level (narrow-band level) (3.22) as a function of the frequency in frequency

bands of constant bandwidth (3.17) (line spacing, ∆f ) (3.13)

Note 1 to entry: A-weighting of the level is assumed in this Publicly Available Specification.

Note 2 to entry: Frequency analysis delivers a line spectrum, in which each line represents the output of a filter,

the mid-frequency of which corresponds to the frequency of the spectral line (3.23).

3.13
line spacing
frequency resolution

distance between neighbouring spectral lines (3.23), where the line spacing in the FFT is given by

Δ=ff /N
where
f is the sampling frequency (3.8);
N is the block length (3.11).

Note 1 to entry: In this Publicly Available Specification, the line spacing is 1,9 Hz ≤ Δf ≤ 4,0 Hz.

© ISO 2016 – All rights reserved 3
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ISO/PAS 20065:2016(E)
3.14
time window

time data set of the signal segment (block length) (3.11) that is multiplied by a weighting function

(window function)

Note 1 to entry: In accordance with the definition of the Fourier integral, a prerequisite of the FFT analysis is that

the time data set is periodic. If this is not the case (as with stochastic signals), cut-off effects at the edges of the

time window will lead to distortion of the spectrum. These distortions are avoided through weighting functions

such as the Hanning Function.

Note 2 to entry: For more information on window and weighting functions, see, for example, Reference [5] and

Annex A.
3.15
masking threshold

audibility (3.4) threshold for a specific sound in the presence of a masking sound (masker)

Note 1 to entry: See Annex C for more information on the audibility threshold and the masking noise.

3.16
masking index

difference between the masking threshold (3.15), L , and the critical band level (3.7), L , of the

masking noise

Note 1 to entry: For frequency-dependent masking index, a , masking and masking noise, see Annex C.

3.17
bandwidth
frequency bandwidth
frequency range of a number of neighbouring spectral lines (3.23)

Note 1 to entry: If the width of a frequency band is calculated for which its beginning or end does not correspond

to the boundary between two spectral lines, then only the spectral lines that lie in their full width within the

calculated frequency range are assigned to the frequency band.
3.18
distinctness
clarity

ratio of the conspicuousness of a tone based on a bandpass noise to the conspicuousness of a sinusoidal

tone of the same tone frequency (3.2), f , and same tone level (3.3), L
T T
3.19
edge steepness

ratio of the level difference between the maximum narrow-band level (3.22) of a tone, L , and the

Tmax

narrow-band levels of the first line below/above the tone to the corresponding frequency difference

3.20
useable frequency
upper limit frequency of the signal components used for evaluation
3.21
investigation range
range within which tones are investigated in the line spectrum (3.12)
3.22
narrow-band level
averaged level within a spectral line (3.23)
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ISO/PAS 20065:2016(E)
3.23
spectral line

frequency band of bandwidth (3.17), ∆f (line spacing) (3.13), in a line spectrum (3.12)

3.24
decisive audibility
maximum audibility (3.4), ∆L, in the individual spectrum, j
4 Measurement procedure
4.1 General

The measurement procedure will depend on the aims. The requirements for the measurement and

assessment procedure in terms of the choice of measurement point, measurement time and duration of

measurement, extraneous noise, etc. shall be satisfied.

The variable for determination of audibility of prominent tones is the sound pressure p(t). For frequency

analysis, the A-weighted equivalent continuous sound pressure level, L , as given in ISO 1996-1, is to

Aeq

be established for the respective spectral lines. If the spectrum is unweighted (linear), then it shall be

corrected to A-weighting in accordance with IEC 61672-1.
4.2 Measurement instruments

Sound level meters that meet, or exceed, the requirements of Class 1 in IEC 61672-1 shall be used. These

have a frequency weighting “A”/“LIN” or “A”/“Z” with a lower limit frequency equal to, or below, 20 Hz.

Additional instruments such as recording instruments (digital or magnetic tape) may also be used. The

measured values derived through recording instruments shall lie within the tolerance range given in

IEC 61672-1.

Analysis of frequency components in the measurement signals is performed using a frequency

analyzer. The constant line spacing, Δf, shall lie in the range 1,9 Hz to 4 Hz (inclusive). The use of the

Hanning window is mandatory in this Publicly Available Specification. For further processing, it shall

be ensured that the digitalization of the sound pressure signal across the entire dynamic range used

has a resolution of at least 0,1 dB.

Before it is processed further, the analogue measurement signal shall be passed through a steep low-

pass filter (antialiasing filter) to avoid errors in frequency analysis. The sampling frequency (see 3.8)

shall be at least two times the maximum usable frequency present (see 3.20). The Hanning window is to

be used as time window to reduce lateral bands (see 3.14).
4.3 Merging the basic spectra

The spectra for the prominent tone assessment shall have an averaging time of approximately 3 s. Due

to the line spacing of 1,9 Hz to 4 Hz (see 4.2) and the typical frequency range, f, of a few kHz, the basic

spectra given by the frequency analyzer will have an averaging time below 1 s. To get the averaging

time of approximately 3 s, a number of basic spectra shall be merged. This shall be done line by line

with Formula (1):
© ISO 2016 – All rights reserved 5
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ISO/PAS 20065:2016(E)
 N 01,dL / B 
ij,
L = 10lg 10 dB (1)
 
j=1
 
where
L is the level of the ith spectral line for the jth spectrum;
i,j
N is the number of merged spectra.
5 Evaluation
5.1 General information

The aim of evaluation is to establish the audibility, ΔL. The procedure is the same for stationary and

non-stationary noises. For tones that can only just be perceived, a quaver (eighth note) is to be adopted

as a base time that is adequate for hearing. However, comprehensive studies have shown that the lower

limit for use of the procedure is reached at averaging times of approximately 3 s. Lower averaging times

lead to unjustified values of audibility, ΔL (too high, but also too low). Signals that have a very high

level dynamic and/or frequency dynamic that no longer correspond with a 3-second averaging can,

therefore, not be evaluated using this Publicly Available Specification. The following conditions shall be

satisfied for the measurements.

— The extended uncertainty, U, of the audibility, ΔL, with a coverage probability of 90 % in a bilateral

confidence interval (see Clause 6) shall not exceed ±1,5 dB. This is generally the case with evaluation

of at least 12 time-staggered narrow-band averaged spectra. If there are less than 12 averaged

spectra then the uncertainty shall be taken into consideration as given in Clause 6.

— Where there are alternating operating states, all of the operating states shall be covered by the

averaging spectra used (see Annex E).

Tonal components in different critical bands are evaluated separately. To arrive at a decision on whether

a tonal audibility has to be made, only the most pronounced tone is considered. If a number of tones are

present within a critical band, then an energy summation of their tone levels, L , is carried out to yield

a tone level, L (see 5.3.8).

A tonal audibility is performed for a tone only if its distinctness (see 3.18) is at least 70 %. This means

a maximal bandwidth, Δf , dependent on the tone frequency [see Formula (9)] and necessitates edge

steepness (see 3.19) of at least 24 dB/octave.
NOTE 1 For the distinctness of a tone, see 5.3.4.

NOTE 2 Harmonic multiples of a tone are evaluated, independently of that tone, similarly to all other

components of the spectrum.

A sample program to determine audibility can be downloaded from http://standards.iso.org/iso/20065

6 © ISO 2016 – All rights reserved
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ISO/PAS 20065:2016(E)
5.2 Width Δf of the critical band

The width Δf of the critical band about the tone frequency f is given by Formula (2):

c T
06, 9
 
 f /Hz
 
Δ=f 25,H07z,++50 10,,14 Hz (2)
c  
 1000 
 
 

Assuming a geometric position of the corner frequencies of the critical band (see Annex B), these corner

frequencies, f and f , are derived as follows:
1 2
ff=× f (3)
T 12
Δff+4
−Δf
f = + (4)
2 2
ff=+Δf (5)
21 c
5.3 Determination of prominent tones
5.3.1 General information

The audibility of a tone is determined using the tone level, L , and the critical band level, L , of the

T G

masking noise in the critical band about the tone frequency, f . The frequency of all maxima of the

spectrum is considered as the tone frequency.

The use of the Hanning window is recommended in Annex A. With window functions (except for

rectangular windows), the effective analysis bandwidth, Δf , is greater than the bandwidth, Δf, of an

ideal filter (see 3.13), i.e. the individual bands are thus superimposed. In the summation process, the

energy components are counted a number of times (see Annex A for more information).

In a frequency analyzer, this influence of summation (number of lines >1) is taken into consideration

through a correction value; if the level addition is simulated by the analyzer program, then this

correction value has to be considered in the computing program, both in the formation of the tone level

[see Formula (8)] and in the calculation of the masking noise [see Formula (12)].

5.3.2 Determination of the mean narrow-band level L of the masking noise

The mean narrow-band level, L , [see Formula (6)] is derived in an iterative procedure from the lines

of the critical band about the line under investigation. The procedure commences with the energy

averaging of all lines of the critical band with the exception of the line under investigation itself. In the

subsequent steps, the levels of the lines of the critical band under consideration are no longer taken

into consideration in the averaging procedure if their level exceeds the energy mean value determined

beforehand by more than 6 dB. The iterative procedure is discontinued, if in an iteration step, the new

energy mean value is equal within a tolerance of ±0,005 dB to that of the previous iteration step or if

the number of lines contributing to the mean narrow-band level to the right or left of the line under

investigation falls below a value of 5. In this case, the energy mean value from the last iteration step, at

which the number of energy averaged levels on both sides of the line under investigation in each case

was still at least 5 is used to form the mean narrow-band level.

For determination of the mean narrow-band level, the entire critical band about the line under

investigation is used. Consequently, the range under investigation (see 3.21) is limited relative to the

useable frequency f such that the upper limit of the uppermost critical band being considered does not

exceed the useable frequency f . A corresponding condition also applies in principle for the lower limit

of the lowest critical band considered. Since the use of this Publicly Available Specification is restricted

© ISO 2016 – All rights reserved 7
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ISO/PAS 20065:2016(E)

to tone frequencies greater than or equal to 50 Hz and the usual analyzers generate line spectra starting

at 0 Hz, it is not generally necessary to take any special precautions.
The mean narrow-band level L is given by Formula (6):
 
 
 
1 M Δf
01,dL / B
 
L = 10lg 10 +10lg  ddB (6)
 
i=1
 
M Δf
 
 
 
 
where
L is the narrow-band level of the ith spectral line, in decibels (dB);
M is the number of spectral lines to be averaged in the critical band;
Δf is the line spacing, in Hertz (Hz) (see 3.13);

Δf is the effective bandwidth in Hz; if a Hanning window is used then the effective bandwidth, Δf ,

e e
is 1,5 times the frequency resolution (line spacing), Δf (see Annex A).

If the spectrum is unweighted (linear), then it shall be A-weighted in accordance within IEC 61672-1.

NOTE 1 If the iteration is discontinued, because the remaining number of spectral lines to be averaged on one

or both sides falls below 5, then the audibility may be somewhat greater than the audibility calculated with this

mean narrow-band level.
NOTE 2 The iteration procedure is described in Annex D.

NOTE 3 Using a digital calculation program, the equal condition in the iteration procedure is typically given

by the resolution of the number format (high resolution should be used).
5.3.3 Determination of the tone level L of a tone in a critical band

The tone level L is determined from the individual levels of the spectral lines in the critical band about

f that contain energy to be assigned to the tone. In principle, a tone may only be present if the level of

the spectral line considered is at least 6 dB greater than the corresponding mean narrow-band level L .

In general, a number of spectral lines have to be taken into consideration, since, for instance, because

of the Picket fence ef
...

PUBLICLY ISO/PAS
AVAILABLE 20065
SPECIFICATION
First edition
Acoustics — Objective method for
assessing the audibility of tones in
noise — Engineering method
Acoustique — Méthode objective pour évaluer l’audibilité des tons
dans le bruit — Méthode d’expertise
PROOF/ÉPREUVE
Reference number
ISO/PAS 20065:2016(E)
ISO 2016
---------------------- Page: 1 ----------------------
ISO/PAS 20065:2016(E)
COPYRIGHT PROTECTED DOCUMENT
© ISO 2016, Published in Switzerland

All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized otherwise in any form

or by any means, electronic or mechanical, including photocopying, or posting on the internet or an intranet, without prior

written permission. Permission can be requested from either ISO at the address below or ISO’s member body in the country of

the requester.
ISO copyright office
Ch. de Blandonnet 8 • CP 401
CH-1214 Vernier, Geneva, Switzerland
Tel. +41 22 749 01 11
Fax +41 22 749 09 47
copyright@iso.org
www.iso.org
ii © ISO 2016 – All rights reserved
---------------------- Page: 2 ----------------------
ISO/PAS 20065:2016(E)
Contents Page

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

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

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

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

4 Measurement procedure .............................................................................................................................................................................. 5

4.1 General ........................................................................................................................................................................................................... 5

4.2 Measurement instruments ........................................................................................................................................................... 5

4.3 Merging the basic spectra .............................................................................................................................................................. 5

5 Evaluation .................................................................................................................................................................................................................... 6

5.1 General information ........................................................................................................................................................................... 6

5.2 Width Δf of the critical band ..................................................................................................................................................... 6

5.3 Determination of prominent tones ........................................................................................................................................ 7

5.3.1 General information ...................................................................................................................................................... 7

5.3.2 Determination of the mean narrow-band level L of the masking noise ........................ 7

5.3.3 Determination of the tone level L of a tone in a critical band ................................................ 8

5.3.4 Distinctness of a tone ................................................................................................................................................... 9

5.3.5 Determination of the critical band level, L , of the masking noise ....................................10

5.3.6 Masking index .................................................................................................................................................................10

5.3.7 Determination of the audibility, ΔL ...............................................................................................................10

5.3.8 Determination of the decisive audibility, ΔL , of a narrow-band spectrum ................10

5.3.9 Determination of the mean audibility ΔL of a number of spectra ......................................12

6 Calculation of the uncertainty of the audibility ΔL ........................................................................................................13

7 Recommendations on the presentation of results .........................................................................................................15

7.1 Measurement .........................................................................................................................................................................................15

7.2 Acoustic environment ....................................................................................................................................................................15

7.3 Instruments for measurement, recording and evaluation .............................................................................16

7.4 Acoustic data ..........................................................................................................................................................................................16

Annex A (informative) Window effect and Picket fence effect ................................................................................................17

Annex B (informative) Resolving power of the human ear at frequencies below 1 000 Hz

and geometric position of the critical bands — corner frequencies ...........................................................21

Annex C (informative) Masking, masking threshold, masking index ..............................................................................23

Annex D (informative) Iterative method for the determination of the audibility, ∆L .....................................24

Annex E (informative) Example for the determination of the tonal audibility .....................................................28

Annex F (informative) Sample program to determine the audibility ..............................................................................34

Bibliography .............................................................................................................................................................................................................................53

© ISO 2016 – All rights reserved PROOF/ÉPREUVE iii
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ISO/PAS 20065:2016(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).

Any trade name used in this document is information given for the convenience of users and does not

constitute an endorsement.

For an explanation on 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: www.iso.org/iso/foreword.html.

The committee responsible for this document is ISO/TC 43, Acoustics, Subcommittee SC 1, Noise.

iv PROOF/ÉPREUVE © ISO 2016 – All rights reserved
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PUBLICLY AVAILABLE SPECIFICATION ISO/PAS 20065:2016(E)
Acoustics — Objective method for assessing the audibility
of tones in noise — Engineering method
1 Scope

This Publicly Available Specification describes a method for the objective determination of the audibility

of tones in environmental noise.

This Publicly Available Specification is intended to augment the usual method for evaluation on the

basis of aural impression, in particular, in cases in which there is no agreement on the degree of the

audibility of tones. The method described can be used if the frequency of the tone being evaluated is

equal to, or greater than, 50 Hz. In other cases, if the tone frequency is below 50 Hz, or if other types of

noise (such as screeching) are to be captured, then this method cannot replace subjective evaluation.

The method presented herein can be used in continuous measurement stations that work automatically.

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.

ISO 1996-1, Acoustics — Description, measurement and assessment of environmental noise — Part 1: Basic

quantities and assessment procedures
IEC 61672-1, Electroacoustics — Sound level meters — Part 1: Specifications
3 Terms and definitions

For the purposes of this document, the terms and definitions given in ISO 1996-1 and the following apply.

3.1
tonality

presence of a tone in a noise, the level of which is below that of the remaining noise components in the

critical band (3.5) about the tone frequency (3.2) by less than the value of the masking index (3.16), a

3.2
tone frequency

frequency of the spectral line (3.23) (or mid-band frequency of the narrow-band filter), to the level of

which the tone contributes most strongly
3.3
tone level

energy summation of the narrow-band level (3.22) with the tone frequency (3.2), f , and the lateral lines

about f , assignable to this tone

Note 1 to entry: If the critical band (3.5) for the frequency, f , under consideration contains a number of tones,

then the tone level, L , is the energy sum of these tones. This level, L , is then assigned to the frequency of the

T T
participating tone that has the maximal value of audibility (3.4), ΔL.

Note 2 to entry: The method for the determination of the tone level, L , of a tone in a critical band is described

in 5.3.3.
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ISO/PAS 20065:2016(E)
3.4
audibility
difference between the tone level (3.3), L , and the masking threshold (3.15), L

Note 1 to entry: The method for the determination of the decisive audibility (3.24), ΔL , of a narrow-band spectrum

(3.12) is described in 5.3.8.
3.5
critical band

frequency band with a bandwidth (3.17), ∆f , within which the auditory system integrates the sound

intensity in the formation of loudness and within which it integrates the sound intensity in the

formation of the masking threshold (3.15)

Note 1 to entry: This characteristic of a critical band (see also References [3] and [4]) holds only for a restricted

sound level range. This dependence is neglected here.
3.6
mean narrow-band level of the critical band

energy mean value of all narrow-band levels (3.22) in a critical band (3.5) that (as a rule) does not exceed

this mean value by more than 6 dB

Note 1 to entry: The method for the determination of the mean narrow-band level L of the masking noise is

described in 5.3.2 and Annex D (iterative method).
3.7
critical band level

level of noise that is assigned to the critical band (3.5) that describes the masking characteristic of the

noise for one or more tones of the noise in this critical band
Note 1 to entry: See narrow-band level (3.22) and Annex C for masking.
Note 2 to entry: For the definition formula for L , see Formula (12).
3.8
sampling frequency
number of samples taken per second

Note 1 to entry: The analogue data provided continuously are converted into samples through sampling at

discrete time intervals for digital processing.

Note 2 to entry: To ensure the reproducibility of a digitized signal, the Shannon theorem requires that the

sampling frequency, f , is at least 2 times the highest frequency of the signal components used for evaluation

in the time signal [ f ≥ 2 f , see also aliasing (3.9), antialiasing filter (3.10) and useable frequency (3.20)]. The

S N

algorithm of a Fast Fourier Transform analysis (the variant of a discrete Fourier Transform used typically and

optimized for calculation) only permits block lengths (3.11), N, that correspond to a power of two. FFT analyzers

thus need a sampling frequency that is at least 2,56 times the maximum frequency to be analysed.

3.9
aliasing

reflection in the line spectrum (3.12) of frequency components from the range above the sampling

frequency (3.8) divided by two ( f /2) in the range below f /2
S S

Note 1 to entry: Antialiasing filters (3.10) are used to avoid errors through such reflections.

Note 2 to entry: Half the sampling frequency ( f /2) is also known as the Nyquist frequency.

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ISO/PAS 20065:2016(E)
3.10
antialiasing filter
low-pass filter

ideal filter that allow frequencies below half the sampling frequency (3.8) to pass through completely

(without influencing the signal), but completely block all higher frequencies

Note 1 to entry: To prevent aliasing (3.9), the noise under investigation shall be filtered using an antialiasing

filter before analogue-to-digital conversion.

Note 2 to entry: Real aliasing filters have a final damping (generally 120 dB/octave) within the blocking range, i.e.

signal components in this transition range are reflected (damped). For example, in the transformation of 2 048

(2 k) data points, 1 024 frequency lines are calculated and 800 lines shown. A component in the line number

1 248 is folded back into the line number 800. With a low-pass filter of 120 dB/octave the damping of these

components is approximately 75 dB.

Note 3 to entry: The usual commercial FFT analyzers have an antialiasing filter, the limit frequency of which

can be switched automatically with the selectable sampling frequency. The reflection of simulated narrow-band

levels (3.22) is suppressed.
3.11
block length

block of sampling values that in discrete form represents a time-limited range of the time signal to be

analysed

Note 1 to entry: In contrast to frequency analysis with analogue and digital filters, the noise with the Fast Fourier

Transform is processed in data blocks. In general, these blocks embrace only a part of the noise recording. The block

length, N, expresses the number of data points processed at the same time. Due to the nature of the Fast Fourier

Transform, the value of N has the integer of power of 2. It has a value, for example, of N = 2 = 1 024 data points.

3.12
line spectrum
narrow-band spectrum
frequency spectrum

plot of the sound pressure level (narrow-band level) (3.22) as a function of the frequency in frequency

bands of constant bandwidth (3.17) (line spacing, ∆f ) (3.13)

Note 1 to entry: A-weighting of the level is assumed in this Publicly Available Specification.

Note 2 to entry: Frequency analysis delivers a line spectrum, in which each line represents the output of a filter,

the mid-frequency of which corresponds to the frequency of the spectral line (3.23).

3.13
line spacing
frequency resolution

distance between neighbouring spectral lines (3.23), where the line spacing in the FFT is given by

Δ=ff /N
where
f is the sampling frequency (3.8);
N is the block length (3.11).

Note 1 to entry: In this Publicly Available Specification, the line spacing is 1,9 Hz ≤ Δf ≤ 4,0 Hz.

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ISO/PAS 20065:2016(E)
3.14
time window

time data set of the signal segment (block length) (3.11) that is multiplied by a weighting function

(window function)

Note 1 to entry: In accordance with the definition of the Fourier integral, a prerequisite of the FFT analysis is that

the time data set is periodic. If this is not the case (as with stochastic signals), cut-off effects at the edges of the

time window will lead to distortion of the spectrum. These distortions are avoided through weighting functions

such as the Hanning Function.

Note 2 to entry: For more information on window and weighting functions, see, for example, Reference [5] and

Annex A.
3.15
masking threshold

audibility (3.4) threshold for a specific sound in the presence of a masking sound (masker)

Note 1 to entry: See Annex C for more information on the audibility threshold and the masking noise.

3.16
masking index

difference between the masking threshold (3.15), L , and the critical band level (3.7), L , of the

masking noise

Note 1 to entry: For frequency-dependent masking index, a , masking and masking noise, see Annex C.

3.17
bandwidth
frequency bandwidth
frequency range of a number of neighbouring spectral lines (3.23)

Note 1 to entry: If the width of a frequency band is calculated for which its beginning or end does not correspond

to the boundary between two spectral lines, then only the spectral lines that lie in their full width within the

calculated frequency range are assigned to the frequency band.
3.18
distinctness
clarity

ratio of the conspicuousness of a tone based on a bandpass noise to the conspicuousness of a sinusoidal

tone of the same tone frequency (3.2), f , and same tone level (3.3), L
T T
3.19
edge steepness

ratio of the level difference between the maximum narrow-band level (3.22) of a tone, L , and the

Tmax

narrow-band levels of the first line below/above the tone to the corresponding frequency difference

3.20
useable frequency
upper limit frequency of the signal components used for evaluation
3.21
investigation range
range within which tones are investigated in the line spectrum (3.12)
3.22
narrow-band level
averaged level within a spectral line (3.23)
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ISO/PAS 20065:2016(E)
3.23
spectral line

frequency band of bandwidth (3.17), ∆f (line spacing) (3.13), in a line spectrum (3.12)

3.24
decisive audibility
maximum audibility (3.4), ∆L, in the individual spectrum, j
4 Measurement procedure
4.1 General

The measurement procedure will depend on the aims. The requirements for the measurement and

assessment procedure in terms of the choice of measurement point, measurement time and duration of

measurement, extraneous noise, etc. shall be satisfied.

The variable for determination of audibility of prominent tones is the sound pressure p(t). For frequency

analysis, the A-weighted equivalent continuous sound pressure level, L , as given in ISO 1996-1, is to

Aeq

be established for the respective spectral lines. If the spectrum is unweighted (linear), then it shall be

corrected to A-weighting in accordance with IEC 61672-1.
4.2 Measurement instruments

Sound level meters that meet, or exceed, the requirements of Class 1 in IEC 61672-1 shall be used. These

have a frequency weighting “A”/“LIN” or “A”/“Z” with a lower limit frequency equal to, or below, 20 Hz.

Additional instruments such as recording instruments (digital or magnetic tape) may also be used. The

measured values derived through recording instruments shall lie within the tolerance range given in

IEC 61672-1.

Analysis of frequency components in the measurement signals is performed using a frequency

analyzer. The constant line spacing, Δf, shall lie in the range 1,9 Hz to 4 Hz (inclusive). The use of the

Hanning window is mandatory in this Publicly Available Specification. For further processing, it shall

be ensured that the digitalization of the sound pressure signal across the entire dynamic range used

has a resolution of at least 0,1 dB.

Before it is processed further, the analogue measurement signal shall be passed through a steep low-

pass filter (antialiasing filter) to avoid errors in frequency analysis. The sampling frequency (see 3.8)

shall be at least two times the maximum usable frequency present (see 3.20). The Hanning window is to

be used as time window to reduce lateral bands (see 3.14).
4.3 Merging the basic spectra

The spectra for the prominent tone assessment shall have an averaging time of approximately 3 s. Due

to the line spacing of 1,9 Hz to 4 Hz (see 4.2) and the typical frequency range, f, of a few kHz, the basic

spectra given by the frequency analyzer will have an averaging time below 1 s. To get the averaging

time of approximately 3 s, a number of basic spectra shall be merged. This shall be done line by line

with Formula (1):
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ISO/PAS 20065:2016(E)
 N 01,dL / B 
ji,
L = 10lg 10 dB (1)
 
i=1
 
where
L is the level of the spectrum, j, and the spectral line, i;
j,i
N is the number of merged spectra.
5 Evaluation
5.1 General information

The aim of evaluation is to establish the audibility, ΔL. The procedure is the same for stationary and

non-stationary noises. For tones that can only just be perceived, a quaver (eighth note) is to be adopted

as a base time that is adequate for hearing. However, comprehensive studies have shown that the lower

limit for use of the procedure is reached at averaging times of approximately 3 s. Lower averaging times

lead to unjustified values of audibility, ΔL (too high, but also too low). Signals that have a very high

level dynamic and/or frequency dynamic that no longer correspond with a 3-second averaging can,

therefore, not be evaluated using this Publicly Available Specification. The following conditions shall be

satisfied for the measurements.

— The extended uncertainty, U, of the audibility, ΔL, with a coverage probability of 90 % in a bilateral

confidence interval (see Clause 6) shall not exceed ±1,5 dB. This is generally the case with evaluation

of at least 12 time-staggered narrow-band averaged spectra. If there are less than 12 averaged

spectra then the uncertainty shall be taken into consideration as given in Clause 6.

— Where there are alternating operating states, all of the operating states shall be covered by the

averaging spectra used (see Annex E).

Tonal components in different critical bands are evaluated separately. To arrive at a decision on whether

a tonal audibility has to be made, only the most pronounced tone is considered. If a number of tones are

present within a critical band, then an energy summation of their tone levels, L , is carried out to yield

a tone level, L (see 5.3.8).

A tonal audibility is performed for a tone only if its distinctness (see 3.18) is at least 70 %. This means

a maximal bandwidth, Δf , dependent on the tone frequency [see Formula (9)] and necessitates edge

steepness (see 3.19) of at least 24 dB/octave.
NOTE 1 For the distinctness of a tone, see 5.3.4.

NOTE 2 Harmonic multiples of a tone are evaluated, independently of that tone, similarly to all other

components of the spectrum.
5.2 Width Δf of the critical band

The width Δf of the critical band about the tone frequency f is given by Formula (2):

c T
06, 9
 
 f /Hz
 
Δ=f 25,H07z,++50 10,,14 Hz (2)
 
1000
 
 
 

Assuming a geometric position of the corner frequencies of the critical band (see Annex B), these corner

frequencies, f and f , are derived as follows:
1 2
ff=× f (3)
T 12
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ISO/PAS 20065:2016(E)
Δff+4
−Δf
f = + (4)
2 2
ff=+Δf (5)
21 c
5.3 Determination of prominent tones
5.3.1 General information

The audibility of a tone is determined using the tone level, L , and the critical band level, L , of the

T G

masking noise in the critical band about the tone frequency, f . The frequency of all maxima of the

spectrum is considered as the tone frequency.

The use of the Hanning window is recommended in Annex A. With window functions (except for

rectangular windows), the effective analysis bandwidth, Δf , is greater than the bandwidth, Δf, of an

ideal filter (see 3.13), i.e. the individual bands are thus superimposed. In the summation process, the

energy components are counted a number of times (see Annex A for more information).

In a frequency analyzer, this influence of summation (number of lines >1) is taken into consideration

through a correction value; if the level addition is simulated by the analyzer program, then this

correction value has to be considered in the computing program, both in the formation of the tone level

[see Formula (8)] and in the calculation of the masking noise [see Formula (12)].

5.3.2 Determination of the mean narrow-band level L of the masking noise

The mean narrow-band level, L , [see Formula (6)] is derived in an iterative procedure from the lines

of the critical band about the line under investigation. The procedure commences with the energy

averaging of all lines of the critical band with the exception of the line under investigation itself. In the

subsequent steps, the levels of the lines of the critical band under consideration are no longer taken

into consideration in the averaging procedure if their level exceeds the energy mean value determined

beforehand by more than 6 dB. The iterative procedure is discontinued, if in an iteration step, the new

energy mean value is equal within a tolerance of ±0,005 dB to that of the previous iteration step or if

the number of lines contributing to the mean narrow-band level to the right or left of the line under

investigation falls below a value of 5. In this case, the energy mean value from the last iteration step, at

which the number of energy averaged levels on both sides of the line under investigation in each case

was still at least 5 is used to form the mean narrow-band level.

For determination of the mean narrow-band level, the entire critical band about the line under

investigation is used. Consequently, the range under investigation (see 3.21) is limited relative to the

useable frequency f such that the upper limit of the uppermost critical band being considered does not

exceed the useable frequency f . A corresponding condition also applies in principle for the lower limit

of the lowest critical band considered. Since the use of this Publicly Available Specification is restricted

to tone frequencies greater than or equal to 50 Hz and the usual analyzers generate line spectra starting

at 0 Hz, it is not generally necessary to take any special precautions.
The mean narrow-band level L is given by Formula (6):
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ISO/PAS 20065:2016(E)
 
 
 M 
1 01,dL / B Δf
  
L = 10lg 10 +10lg ddB (6)
 
i=1  
 M Δf 
 
 e 
 
where
L is the narrow-band level of the ith spectral line, in decibels (dB);
M is the number of spectral lines to be averaged in the critical band;
Δf is the line spacing, in Hertz (Hz) (see 3.13);

Δf is the effective bandwidth in Hz; if a Hanning window is used then the effective bandwidth, Δf ,

e e
is 1,5 times the frequency resolution (line spacing), Δf (see Annex A).

If the spectrum is unweighted (linear), then it shall be A-weighted in accordance within IEC 61672-1.

NOTE 1 If the iteration is discontinued, because the remaining number of spectral lines to be averaged on one

or both sides falls below 5, then the audibility may be somewhat greater than the audibility calculated with this

mean narrow-band level.
NOTE 2 The iteration procedure is described in Annex D.

NOTE 3 Using a digital calculation program, the equal condition in the iteration procedure is typically given

by the resolution of the number format (high resolution should be used).
5.3.3 Determination of the tone level L of a tone in a critical band

The tone level L is determined from the individual levels of the spectral lines in the critical band about

f that contain energy to be assigned to the tone. In principle, a tone may only be present if the level of

the spectral line considered is at least 6 dB greater than the corres
...

SPÉCIFICATION ISO
PUBLIQUEMENT 20065
DISPONIBLE
Première édition
2016-07-01
Acoustique — Méthode objective
d’évaluation de l’audibilité des
tonalités dans le bruit — Méthode
d’expertise
Acoustics — Objective method for assessing the audibility of tones in
noise — Engineering method
Numéro de référence
ISO/PAS 20065:2016(F)
ISO 2016
---------------------- Page: 1 ----------------------
ISO/PAS 20065:2016(F)
DOCUMENT PROTÉGÉ PAR COPYRIGHT
© ISO 2016, Publié en Suisse

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l’adresse ci-après ou au comité membre de l’ISO dans le pays du demandeur.
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ii © ISO 2016 – Tous droits réservés
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ISO/PAS 20065:2016(F)
Sommaire Page

Avant-propos ..............................................................................................................................................................................................................................iv

1 Domaine d’application ................................................................................................................................................................................... 1

2 Références normatives ................................................................................................................................................................................... 1

3 Termes et définition .......................................................................................................................................................................................... 1

4 Mode opératoire de mesurage ............................................................................................................................................................... 5

4.1 Généralités .................................................................................................................................................................................................. 5

4.2 Instruments de mesurage .............................................................................................................................................................. 5

4.3 Moyennage des spectres de base ............................................................................................................................................ 6

5 Évaluation .................................................................................................................................................................................................................... 6

5.1 Informations générales .................................................................................................................................................................... 6

5.2 Largeur Δf de la bande critique .............................................................................................................................................. 7

5.3 Détermination des tonalités marquées.............................................................................................................................. 7

5.3.1 Informations générales .............................................................................................................................................. 7

5.3.2 Détermination du niveau moyen en bande fine L du bruit de masquage ..................... 7

5.3.3 Détermination du niveau de la tonalité L d’une tonalité dans une

bande critique .................................................................................................................................................................... 8

5.3.4 Distinction d’une tonalité ......................................................................................................................................... 9

5.3.5 Détermination du niveau de bande critique L du bruit de masquage .........................10

5.3.6 Indice de masquage ....................................................................................................................................................10

5.3.7 Détermination de l’audibilité ΔL ..................................................................................................................... 10

5.3.8 Détermination de l’audibilité décisive ΔL d’un spectre en bande fine ..........................11

5.3.9 Détermination de l’audibilité moyenne ΔL d’un nombre de spectres ............................12

6 Calcul de l’incertitude de l’audibilité ΔL ...................................................................................................................................13

7 Recommandations pour la présentation des résultats .............................................................................................16

7.1 Mesurage ...................................................................................................................................................................................................16

7.2 Environnement acoustique .......................................................................................................................................................16

7.3 Instruments de mesurage, d’enregistrement et d’évaluation......................................................................16

7.4 Données acoustiques ......................................................................................................................................................................16

Annexe A (informative) Effet de fenêtre et effet de palissade .................................................................................................17

Annexe B (informative) Pouvoir de résolution de l’oreille humaine à des fréquences

inférieures à 1 000 Hz et positions géométriques des bandes critiques —

fréquences de coupure ................................................................................................................................................................................20

Annexe C (informative) Masquage, seuil de masquage, indice de masquage ..........................................................22

Annexe D (informative) Méthode itérative de détermination de l’audibilité ∆L .................................................23

Annexe E (informative) Exemple de détermination de l’audibilité tonale.................................................................27

Bibliographie ...........................................................................................................................................................................................................................33

© ISO 2016 – Tous droits réservés iii
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ISO/PAS 20065:2016(F)
Avant-propos

L’ISO (Organisation internationale de normalisation) est une fédération mondiale d’organismes

nationaux de normalisation (comités membres de l’ISO). L’élaboration des Normes internationales est

en général confiée aux comités techniques de l’ISO. Chaque comité membre intéressé par une étude

a le droit de faire partie du comité technique créé à cet effet. Les organisations internationales,

gouvernementales et non gouvernementales, en liaison avec l’ISO participent également aux travaux.

L’ISO collabore étroitement avec la Commission électrotechnique internationale (IEC) en ce qui

concerne la normalisation électrotechnique.

Les procédures utilisées pour élaborer le présent document et celles destinées à sa mise à jour sont

décrites dans les Directives ISO/IEC, Partie 1. Il convient, en particulier de prendre note des différents

critères d’approbation requis pour les différents types de documents ISO. Le présent document a été

rédigé conformément aux règles de rédaction données dans les Directives ISO/IEC, Partie 2 (voir www.

iso.org/directives).

L’attention est appelée sur le fait que certains des éléments du présent document peuvent faire l’objet de

droits de propriété intellectuelle ou de droits analogues. L’ISO ne saurait être tenue pour responsable

de ne pas avoir identifié de tels droits de propriété et averti de leur existence. Les détails concernant

les références aux droits de propriété intellectuelle ou autres droits analogues identifiés lors de

l’élaboration du document sont indiqués dans l’Introduction et/ou dans la liste des déclarations de

brevets reçues par l’ISO (voir www.iso.org/brevets).

Les appellations commerciales éventuellement mentionnées dans le présent document sont données

pour information, par souci de commodité, à l’intention des utilisateurs et ne sauraient constituer un

engagement.

Pour une explication de la signification des termes et expressions spécifiques de l’ISO liés à

l’évaluation de la conformité, ou pour toute information au sujet de l’adhésion de l’ISO aux principes

de l’OMC concernant les obstacles techniques au commerce (OTC), voir le lien suivant: Avant-propos —

Informations supplémentaires.

Le comité chargé de l’élaboration du présent document est l’ISO/TC 43, Acoustique sous-comité SC 1, Bruit.

iv © ISO 2016 – Tous droits réservés
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SPÉCIFICATION PUBLIQUEMENT DISPONIBLE ISO/PAS 20065:2016(F)
Acoustique — Méthode objective d’évaluation de
l’audibilité des tonalités dans le bruit — Méthode
d’expertise
1 Domaine d’application

La présente Spécification publiquement disponible décrit une méthode de détermination objective de

l’audibilité des tonalités dans le bruit environnemental.

La présente Spécification publiquement disponible est destinée à améliorer la méthode habituelle

d’évaluation sur la base de l’impression auditive, en particulier en cas d’absence d’accord sur le degré

d’audibilité des tonalités. La méthode décrite peut être utilisée lorsque la fréquence de la tonalité

évaluée est égale ou supérieure à 50 Hz. Dans les autres cas, si la fréquence de la tonalité est inférieure

à 50 Hz ou si d’autres types de bruit (par exemple un crissement) doivent être capturés, la présente

méthode ne peut pas remplacer l’évaluation subjective.

La méthode présentée ici peut être utilisée sur les postes de mesurage continu qui fonctionnent

automatiquement.
2 Références normatives

Les documents ci-après, dans leur intégralité ou non, sont des références normatives indispensables à

l’application du présent document. Pour les références datées, seule l’édition citée s’applique. Pour les

références non datées, la dernière édition du document de référence s’applique (y compris les éventuels

amendements).

ISO 1996-1, Acoustique — Description, mesurage et évaluation du bruit de l’environnement — Partie 1:

Grandeurs fondamentales et méthodes d’évaluation.
IEC 61672-1, Électroacoustique — Sonomètres — Partie 1: spécifications.
3 Termes et définition

Pour les besoins de la présente Norme internationale, les termes et définitions donnés dans l’ISO 1996-1

ainsi que les suivants s’appliquent.
3.1
tonalité

présence d’une tonalité dans un bruit, dont le niveau est inférieur à celui des autres composantes de

bruit dans la bande critique (3.5) autour de la fréquence de la tonalité (3.2) de moins de la valeur de

l’indice de masquage (3.16), a
3.2
fréquence de la tonalité

fréquence de la raie spectrale (3.23) (ou de la fréquence à mi-bande du filtre en bande fine), au niveau de

laquelle la tonalité contribue le plus fortement
© ISO 2016 – Tous droits réservés 1
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ISO/PAS 20065:2016(F)
3.3
niveau de la tonalité

sommation d’énergie du niveau en bande fine (3.22) contenant la fréquence de la tonalité (3.2), f , et de

ceux des raies latérales autour de f pouvant être assignées à cette tonalité

Note 1 à l’article: Si la bande critique (3.5) pour la fréquence f considérée contient un certain nombre de tonalités,

alors le niveau de la tonalité L est la somme de l’énergie de ces tonalités. Ce niveau L est ensuite assigné à la

T T

fréquence de la tonalité participante qui présente la valeur maximale d’audibilité (3.4) ΔL.

Note 2 à l’article: Le procédé de détermination du niveau de la tonalité L d’une tonalité dans une bande critique

est décrit en 5.3.3.
3.4
audibilité

différence entre le niveau de la tonalité (3.3), L et le seuil de masquage (3.15), L′

Note 1 à l’article: Le procédé de détermination de l’audibilité décisive (3.24), ΔL d’un spectre à bande fine (3.12) est

décrit en 5.3.8.
3.5
bande critique

bande de fréquence d’une largeur de bande (3.17) ∆f dans laquelle le système auditif intègre l’intensité

acoustique dans la formation de la sonie et dans laquelle il intègre l’intensité acoustique dans la

formation du seuil de masquage (3.15)

Note 1 à l’article: Cette caractéristique d’une bande critique (voir également les Références [3] et [4]) ne vaut que

pour une gamme de niveau sonore limitée. Cette dépendance est ici négligée.
3.6
niveau moyen de la bande critique en bande fine

valeur énergétique moyenne de tous les niveaux à bande fine (3.22) dans une bande critique (3.5) qui (en

règle générale) ne dépasse pas cette valeur moyenne de plus de 6 dB

Note 1 à l’article: Le procédé de détermination du niveau moyen à bande fine L du bruit de masquage est décrit

en 5.3.2 et à l’Annexe D (méthode itérative).
3.7
niveau de bande critique

niveau de bruit qui est assigné à la bande critique (3.5) qui décrit la caractéristique de masquage du

bruit pour une ou plusieurs tonalités du bruit dans cette bande critique

Note 1 à l’article: Voir niveau à bande fine (3.22) et Annexe C pour le masquage.

Note 2 à l’article: Pour la formule de définition de L , voir la Formule (12).
3.8
fréquence d’échantillonnage
nombre d’échantillons pris par seconde

Note 1 à l’article: Les données analogiques fournies en continu sont converties en échantillons par échantillonnage

à des intervalles de temps discrets pour le traitement numérique.
2 © ISO 2016 – Tous droits réservés
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ISO/PAS 20065:2016(F)

Note 2 à l’article: Pour garantir la reproductibilité d’un signal numérisé, le théorème de Shannon exige que la

fréquence d’échantillonnage f soit au moins 2 fois supérieure à la fréquence la plus élevée des composantes

de signaux utilisés pour l’évaluation du signal temporel [ f ≥ 2 f , voir également repliement (3.9), filtre anti-

S N

repliement (3.10) et fréquence utile (3.20)]. L’algorithme d’analyse de transformée de Fourier rapide (la variante

d’une transformation de Fourier discrète généralement utilisée pour le calcul optimisé) ne permet que des

longueurs de bloc (3.11), N qui correspondent à une puissance de deux. Les analyseurs FFT exigent donc une

fréquence d’échantillonnage qui est au moins égale à 2,56 fois la fréquence maximale à analyser.

3.9
repliement

réflexion dans le spectre de raies (3.12) des composantes de fréquence de la gamme supérieure à la

fréquence d’échantillonnage (3.8) divisée par deux ( f /2) vers la gamme inférieure à f /2

S S

Note 1 à l’article: Les filtres anti-repliement (3.10) sont utilisés pour éviter les erreurs dues à ces réflexions.

Note 2 à l’article: La moitié de la fréquence d’échantillonnage ( f /2) est également connue comme la fréquence de

Nyquist.
3.10
filtre anti-repliement
filtre passe-bas

filtre idéal qui permet aux fréquences inférieures à la moitié de la fréquence d’échantillonnage (3.8) de

traverser complètement (sans influencer le signal), mais bloque complètement toutes les fréquences

plus élevées

Note 1 à l’article: Pour éviter le repliement (3.9), le bruit étudié doit être filtré en utilisant un filtre anti-repliement

avant la conversion analogique-numérique.

Note 2 à l’article: Les filtres anti-repliement réels ont un amortissement final (généralement 120 dB/octave) dans

la plage de blocage, c’est à dire que les composantes du signal dans cette gamme de transition sont réfléchies

(amorties). Par exemple, dans la transformation de 2 048 (2 k) points de données, 1 024 lignes de fréquence sont

calculées et 800 lignes sont affichées. Une composante de la ligne numéro 1 248 est repliée dans le numéro de

ligne 800. Avec un filtre passe-bas de 120 dB/octave, l’amortissement de ces composantes est d’environ 75 dB.

Note 3 à l’article: Les analyseurs FFT commerciaux habituels possèdent un filtre anti-repliement dont la fréquence

limite peut être commutée automatiquement avec la fréquence d’échantillonnage sélectionnable. La réflexion des

niveaux à bande fine simulés (3.22) est supprimée.
3.11
longueur de bloc

bloc de valeurs d’échantillonnage qui sous une forme discrète, représente un intervalle de temps limité

du signal temporel à analyser

Note 1 à l’article: Contrairement à l’analyse de fréquence avec les filtres analogiques et numériques, le bruit avec

la transformée de Fourier rapide est traité dans des blocs de données. En général, ces blocs englobent seulement

une partie de l’enregistrement sonore. La longueur du bloc N indique le nombre de points de données traités en

même temps. En raison de la nature de la transformée de Fourier, la valeur de N a une valeur entière de puissance

de 2. La valeur est par exemple de N = 2 = 1 024 points de données.
3.12
spectre de raies
spectre en bande fine
spectre de fréquence

tracé du niveau de pression sonore (niveau en bande fine) (3.22) en fonction de la fréquence dans des

bandes de fréquences de largeur de bande constante (3.17) (espacement des raies, ∆f ) (3.13)

Note 1 à l’article: Une pondération A du niveau est supposée dans la présente Spécification publiquement

disponible.

Note 2 à l’article: L’analyse de fréquence délivre un spectre de raies, dans lequel chaque raie représente la sortie

d’un filtre dont la fréquence moyenne correspond à la fréquence de la raie spectrale (3.23).

© ISO 2016 – Tous droits réservés 3
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ISO/PAS 20065:2016(F)
3.13
espacement des raies
résolution en fréquence

distance entre des raies spectrales voisines (3.23), où l’espacement des raies dans la FFT est donné par

Δ=ff /N
f est la fréquence d’échantillonnage (3.8);
N est la longueur de bloc (3.11)

Note 1 à l’article: Dans la présente Spécification publiquement disponible, l’espacement des raies est dans

l’intervalle 1,9 Hz ≤ Δf ≤ 4,0 Hz.
3.14
fenêtre temporelle

ensemble de données temporelles du segment de signal (longueur de bloc) (3.11) qui est multiplié par

une fonction de pondération (fenêtrage)

Note 1 à l’article: Conformément à la définition de l’intégrale de Fourier, un prérequis de l’analyse FFT est que

l’ensemble des données temporelles est périodique. Si ce n’est pas le cas (comme avec les signaux stochastiques),

alors les effets de coupure sur les bords de la fenêtre temporelle entraînent une distorsion du spectre. Ces

distorsions sont évitées grâce à des fonctions de pondération telles que la fonction de Hanning.

Note 2 à l’article: Pour plus d’informations sur la fonction de fenêtrage et la fonction de pondération, voir par

exemple la Référence [5] et l’Annexe A.
3.15
seuil de masquage

seuil d’audibilité (3.4) pour un son spécifique en présence d’un son de masquage (masqueur)

Note 1 à l’article: Voir l’Annexe C pour plus d’informations sur le seuil d’audibilité et le bruit de masquage.

3.16
indice de masquage

différence entre le seuil de masquage (3.15), L , et le niveau de bande critique (3.7) L du bruit de

masquage

Note 1 à l’article: Pour un indice de masquage dépendant de la fréquence a , masquage et bruit de masquage, voir

l’Annexe C.
3.17
largeur de bande
largeur de bande de fréquences
gamme de fréquences d’un certain nombre de raies spectrales voisines (3.23)

Note 1 à l’article: Si la largeur d’une bande de fréquence est calculée pour que son début ou sa fin ne corresponde

pas à la limite entre deux raies spectrales, alors seules les raies spectrales qui se trouvent dans toute leur largeur

dans la plage de fréquences calculée sont affectées à la bande de fréquences.
3.18
distinction
clarté

rapport de la netteté d’une tonalité sur la base d’un bruit passe-bande sur la netteté d’un signal

sinusoïdal de même fréquence de tonalité (3.2) f et de même niveau de tonalité (3.3) L

T T
4 © ISO 2016 – Tous droits réservés
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ISO/PAS 20065:2016(F)
3.19
pente de signal

rapport de la différence de niveau entre le niveau à bande fine maximal (3.22) d’une tonalité L et

Tmax

les niveaux à bande fine de la première ligne au-dessous/au-dessus de la tonalité à la différence de

fréquence correspondante
3.20
fréquence utile

fréquence de limite supérieure des composantes de signal utilisées pour l’évaluation

3.21
gamme d’investigation
gamme dans laquelle les tonalités sont étudiées dans le spectre de raies (3.12)
3.22
niveau à bande fine
niveau moyenné dans une raie spectrale (3.23)
3.23
raie spectrale

bande de fréquences de largeur de bande (3.17) ∆f (espacement des raies) (3.13) dans un spectre de

raies (3.12)
3.24
audibilité décisive
audibilité maximale (3.4) ∆L dans le spectre individuel j
4 Mode opératoire de mesurage
4.1 Généralités

Le mode opératoire de mesurage dépend des objectifs. Les exigences relatives à la mesure et à la

procédure d’évaluation en termes de choix du point de mesure, du moment et de la durée de la mesure,

du bruit perturbateur, etc., doivent être satisfaites.

La variable pour la détermination de l’audibilité des tonalités prédominantes est la pression acoustique

p(t). Pour l’analyse de la fréquence, le niveau de pression acoustique continu équivalent pondéré A L ,

Aeq

tel que donné dans l’ISO 1996-1, doit être déterminé pour les raies spectrales respectives. Si le spectre

est non pondéré (linéaire), alors il doit être corrigé avec la pondération A conformément à l’IEC 61672-1.

4.2 Instruments de mesurage

Des sonomètres qui satisfont aux ou qui dépassent les exigences de la Classe 1 de l’IEC 61672-1 doivent

être utilisés. Ceux-ci présentent une pondération en fréquence «A»/«LIN» ou «A»/«Z» avec une

fréquence limite inférieure égale ou inférieure à 20 Hz.

D’autres instruments tels que des enregistreurs (bande magnétique ou numérique) peuvent également

être utilisés. Les valeurs mesurées dérivées par les instruments d’enregistrement doivent se trouver

dans la plage de tolérance donnée dans l’IEC 61672-1.

L’analyse des composantes de fréquence dans les signaux de mesurage est effectuée au moyen d’un

analyseur de fréquence. L’espacement constant des raies Δf doit se trouver dans la plage comprise

entre 1,9 Hz et 4 Hz (compris). L’utilisation de la fenêtre de Hanning est obligatoire dans la présente

Spécification publiquement disponible. Pour le traitement ultérieur, il faut s’assurer que la numérisation

du signal de pression acoustique sur toute la plage dynamique utilisée a une résolution d’au moins 0,1 dB.

© ISO 2016 – Tous droits réservés 5
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ISO/PAS 20065:2016(F)

Avant un traitement ultérieur, le signal de mesurage analogique doit passer par un filtre passe-bas à

pente raide (filtre anti-repliement) afin d’éviter des erreurs dans l’analyse de fréquence. La fréquence

d’échantillonnage (voir 3.8) doit être égale à au moins deux fois la fréquence utile maximale présente

(voir 3.20). La fenêtre de Hanning doit être utilisée en tant que fenêtre temporelle pour réduire les

bandes latérales (voir 3.14).
4.3 Moyennage des spectres de base

Les spectres pour l’évaluation de la tonalité marquée doivent avoir une durée de moyennage d’environ

3 s. En raison de l’espacement des raies compris entre 1,9 Hz et 4 Hz (voir 4.2) et de la plage de

fréquences caractéristiques f de quelques kHz, les spectres de base fournis par l’analyseur de fréquence

ont une durée de moyennage inférieure à 1 s. Pour obtenir une durée d’intégration d’environ 3 s, un

certain nombre de spectres de base doivent être combinés. Cela doit être effectué ligne par ligne selon

la Formule (1):
 N 01,dL / B 
ij,
L = 10lg 10 dB (1)
 
j=1
 
L est le niveau de la raie spectrale ième du spectre jème;
i,j
N est le nombre de spectres combinés.
5 Évaluation
5.1 Informations générales

Le but de l’évaluation est d’établir l’audibilité ΔL. Le mode opératoire est identique pour les bruits

stationnaires et non stationnaires. Pour les tonalités qui peuvent tout juste être perçues, une croche

doit être adoptée comme une unité de temps adaptée à l’audition. Toutefois, des études approfondies

ont montré que la limite inférieure pour l’utilisation du mode opératoire est atteinte avec des durées de

moyennage d’environ 3 s. Des durées de moyennage plus courtes conduisent à des valeurs non justifiées

d’audibilité ΔL (trop élevées, mais aussi trop faibles). Les signaux qui ont une très grande dynamique en

niveau et/ou en fréquence, qui ne correspondent plus à un moyennage de 3 s, ne peuvent donc pas être

évalués à l’aide de la présente Spécification publiquement disponible. Les conditions qui suivent doivent

être satisfaites pour les mesurages.

— L’incertitude élargie U de l’audibilité ΔL, avec une probabilité de couverture de 90 % dans un intervalle

de confiance bilatéral (voir l’Article 6) ne doit pas dépasser ± 1,5 dB. Cela est généralement le cas

avec l’évaluation d’au moins 12 spectres en bande fine moyennés décalés dans le temps. Lorsqu’il

y a moins de 12 spectres moyennés, alors l’incertitude doit être prise en compte, comme indiqué à

l’Article 6.

— Lorsqu’il existe d’autres états de fonctionnement, tous ces états doivent être couverts par les

spectres moyennés utilisés (voir l’Annexe E).

Les composantes tonales dans différentes bandes critiques sont évaluées séparément. Pour parvenir à

une conclusion sur la présence d’une audibilité tonale, seule la tonalité la plus marquée est considérée.

Lorsqu’un certain nombre de tonalités sont présentes dans une bande critique, une sommation d’énergie

de leurs niveaux de tonalités L est effectuée pour obtenir un niveau de tonalité L (voir 5.3.8).

Ti T

Une audibilité tonale est réalisée pour une tonalité uniquement si sa distinction (voir 3.18) est au moins

égale à 70 %. Cela signifie une largeur de bande maximale Δf dépendant de la fréquence de la tonalité

[voir Formule (9)] et nécessite une pente de signal (voir 3.19) d’au moins 24 dB/octave.

NOTE 1 Pour la distinction d’une tonalité, voir 5.3.4.
6 © ISO 2016 – Tous droits réservés
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ISO/PAS 20065:2016(F)

NOTE 2 Les multiples harmoniques d’une tonalité sont évaluées, indépendamment de cette tonalité, de façon

similaire à toutes les autres composantes du spectre.

Un exemple de programme de détermination de l’audibilité peut être téléchargé à partir de http://

standards.iso.org/iso/20065
5.2 Largeur Δf de la bande critique

La largeur Δf de la bande critique sur la fréquence de la tonalité f est donnée par la Formule (2):

c T
06, 9
 
 f /Hz
 
Δ=f 25,H07z,++50 10,,14 Hz (2)
c  
 1000 
 
 

En supposant une position géométrique des fréquences de coupure de la bande critique (voir l’Annexe B),

ces fréquences de coupure f et f sont dérivées comme suit:
1 2
ff=× f (3)
T 12
Δff+4
−Δf
f = + (4)
2 2
ff=+Δf (5)
21 c
5.3 Détermination des tonalités marquées
5.3.1 Informations générales

L’audibilité d’une tonalité est déterminée en utilisant le niveau de la tonalité L et le niveau de la bande

critique L du bruit de masquage dans la bande critique sur la fréquence de la tonalité f . La fréquence

G T

de toutes les valeurs maximales du spectre est considérée comme la fréquence de tonalité.

L’utilisation de la fenêtre de Hanning est recommandée à l’Annexe A. Avec des fonctions de fenêtrage

(à l’exception des fenêtres rectangulaires), la largeur effective de la bande passante d’analyse Δf est

supérieure à la largeur de bande Δf d’un filtre idéal (voir 3.13), c’est-à-dire que les bandes individuelles

sont ainsi superposées. Lors du processus de sommation, des composantes énergétiques sont comptées

plusieurs fois (voir l’Annexe A pour plus d’informations).

Dans un analyseur de fréquence, cette influence de la sommation (nombre de lignes > 1) est prise en

compte par le biais d’une valeur de correction; si l’addition de niveau est simulée par le programme

d’analyse, cette valeur de correction doit être prise en compte dans le programme de calcul, à la fois

dans la formation du niveau de tonalité [voir la Formule (8)] et dans le calcul du bruit de masquage [voir

la Formule (12)].
5.3.2 Détermination du niveau moyen en bande fine L du bruit de masquage

Le niveau moyen en bande fine L [voir la Formule (6)] est dérivé lors d’une procédure itérative à partir

des raies de la bande critique sur la raie objet de l’évaluation. La procédure commence par le calcul

de la moyenne de l’énergie de toutes les raies de la bande critique, à l’exception de la raie objet de

l’évaluation elle-même. Aux étapes suivantes, les niveaux des raies de la bande critique considérée ne

sont plus pris en compte dans la procédure de calcul de moyenne si leur niveau est supérieur à la valeur

moyenne de l’énergie déterminée à l’avance de plus de 6 dB. La procédure itérative est interrompue si

lors d’une étape d’itération, la nouvelle valeur de la moyenne énergétique est égale, avec une toléranc

...

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