ISO/TS 20065:2022

ISO/TS 20065:2022(E)
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ISO TC 43/SC 1/WG 45
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Date: 2022-09-28xx
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Acoustics –— Objective method for assessing the audibility of tones in noise –— Engineering
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method
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Acoustique — Méthode objective d'évaluation de l'audibilité des tonalités dans le bruit — Méthode Style Definition: Heading 6: Font: Bold
d'expertise
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ISO/TS 20065:2022(E)
© ISO 2022
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All rights reserved. Unless otherwise specified, or required in the context of its implementation, 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
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: +41 22 749 01 11
Email: copyright@iso.org
Website: www.iso.orgwww.iso.org
Published in Switzerland
ii © ISO 2022 – All rights reserved

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ISO/TS 20065:2022(E)
Contents
Foreword . iv
1 Scope . 5
2 Normative references . 5
3 Terms and definitions . 5
4 Measurement procedure . 10
4.1 General . 10
4.2 Measurement instruments . 10
4.3 Merging the basic spectra . 10
5 Evaluation . 10
5.1 General information . 10
5.2 Width Δf of the critical band . 11
c
5.3 Determination of prominent tones . 12
5.3.1 General information . 12
5.3.2 Determination of the mean narrow-band level L of the masking noise . 12
S
5.3.3 Determination of the tone level L of a tone in a critical band . 13
T
5.3.4 Distinctness of a tone . 14
5.3.5 Determination of the critical band level, L , of the masking noise . 14
G
5.3.6 Masking index . 15
5.3.7 Determination of the audibility, ΔL . 15
5.3.8 Determination of the decisive audibility, ΔL , of a narrow-band spectrum . 15
j
5.3.9 Determination of the mean audibility ΔL of a number of spectra . 17
6 Calculation of the uncertainty of the audibility ΔL . 17
7 Recommendations on the presentation of results . 20
7.1 Measurement . 20
7.2 Acoustic environment . 20
7.3 Instruments for measurement, recording and evaluation . 20
7.4 Acoustic data . 20
Annex A (informative) Window effect and Picket fence effect . 22
Annex B (informative) Resolving power of the human ear at frequencies below 1 000 Hz
and geometric position of the critical bands – corner frequencies . 25
Annex C (informative) Masking, masking threshold, masking index . 27
Annex D (informative) Iterative method for the determination of the audibility, ∆L . 28
Annex E (informative) Example for the determination of the tonal audibility . 33
Bibliography . 40
Foreword . iv
1 Scope . 5
2 Normative references . 5
3 Terms and definitions . 5
4 Measurement procedure . 10
4.1 General . 10
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ISO/TS 20065:2022(E)
4.2 Measurement instruments . 10
4.3 Merging the basic spectra . 10
5 Evaluation . 10
5.1 General information . 10
5.2 Width Δf of the critical band . 11
c
5.3 Determination of prominent tones . 12
5.3.1 General information . 12
5.3.2 Determination of the mean narrow-band level L of the masking noise . 12
S
5.3.3 Determination of the tone level L of a tone in a critical band . 13
T
5.3.4 Distinctness of a tone . 14
5.3.5 Determination of the critical band level, L , of the masking noise . 14
G
5.3.6 Masking index . 15
5.3.7 Determination of the audibility, ΔL . 15
5.3.8 Determination of the decisive audibility, ΔL , of a narrow-band spectrum . 15
j
5.3.9 Determination of the mean audibility ΔL of a number of spectra . 17
6 Calculation of the uncertainty of the audibility ΔL . 17
7 Recommendations on the presentation of results . 20
7.1 Measurement . 20
7.2 Acoustic environment . 20
7.3 Instruments for measurement, recording and evaluation . 20
7.4 Acoustic data . 20
Annex A (informative) Window effect and Picket fence effect . 22
Annex B (informative) Resolving power of the human ear at frequencies below 1 000 Hz
and geometric position of the critical bands – corner frequencies . 25
Annex C (informative) Masking, masking threshold, masking index . 27
Annex D (informative) Iterative method for the determination of the audibility, ∆L . 28
Annex E (informative) Example for the determination of the tonal audibility . 33
Bibliography . 40

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ISO/TS 20065:2022(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 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/patentswww.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 of the voluntary nature of standards, the meaning of ISO specific terms and
expressions related to conformity assessment, as well as information about ISO's adherence to the World
Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT), see
www.iso.org/iso/foreword.htmlwww.iso.org/iso/foreword.html.
This document was prepared by Technical Committee ISO/TC 43, Acoustics, Subcommittee SC 1, Noise.
This Technical Specificationfirst edition of ISO/TS 20065 cancels and replaces the Publicly Available
Specification ISO/ISO/PAS 20065: 2016, which has been technically revised primarily editorially to
provide a clearer technical specification standard that can be more easily implemented in software.
The main changes are as follows:
— Guidanceguidance on residual sound (clause 5.3.1));
— Aa file containing a number of other example audio files and a guidance document can be downloaded
from https://standards.iso.org/iso/20065https://standards.iso.org/iso/20065 (from “Prominent
tones in wind turbine noise Round robin test IEC 61400_-11, ISO /PAS 20065”)”);
— Editorialeditorial changes for clarity and to meet the latest ISO standards, including definitions,
measures, formulae, allignedaligned and streamlined terminology, and additional background
information.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at
www.iso.org/members.htmlwww.iso.org/members.html.
© ISO 2022 – All rights reserved v

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TECHNICAL SPECIFICATION ISO/TS 20065:2022(E)

Acoustics –— Objective method for assessing the audibility of
tones in noise –— Engineering method
1 Scope
This document describes a method for the objective determination of the audibility of tones in
environmental noise.
This document 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.
Note: NOTE The procedure has not been validated below 50 Hz.
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The method presented herein can be used in continuous measurement stations that work automatically.
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2 Normative references
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The following documents are referred to in the text in such a way that some or all of their content
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constitutes requirements of this document. For dated references, only the edition cited applies. For
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undated references, the latest edition of the referenced document (including any amendments) applies.
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ISO 1996-1, Acoustics — Description, measurement and assessment of environmental noise — Part 1:
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Basic quantities and assessment procedures
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IEC 61672-1, Electroacoustics — Sound level meters — Part 1: Specifications
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3 Terms and definitions
Formatted: English (United States)
Formatted: Adjust space between Latin and Asian text,
For the purposes of this document, the terms and definitions given in ISO 1996-1 and the following apply.
Adjust space between Asian text and numbers
Unless otherwise stated, the reference level for dB values in these definitions is 20 µPa.
Formatted: Font: Times New Roman, 12 pt, English
ISO and IEC maintain terminology databases for use in standardization at the following addresses:
(United States)
— ISO Online browsing platform: available at https://www.iso.org/obphttps://www.iso.org/obp Formatted: English (United States)
Formatted: Adjust space between Latin and Asian text,
— IEC Electropedia: available at https://www.electropedia.org/https://www.electropedia.org/
Adjust space between Asian text and numbers, Tab
stops: Not at 19.85 pt + 39.7 pt + 59.55 pt + 79.4 pt
NOTE Unless otherwise stated, the reference level for decibels (dB) values in these definitions is 20 µPa.
+ 99.25 pt + 119.05 pt + 138.9 pt + 158.75 pt +
178.6 pt + 198.45 pt
3.1
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tone
sound characterized by a single-frequency component or narrow-band components Formatted: English (United States)
Formatted: Hyperlink, English (United States)
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ISO/TS 20065:2022(E)
3.2
tone frequency
f
T
frequency of the spectral line (3.23) (or mid-band frequency of the narrow-band filter), to the level of
which the tone (3.1) contributes most strongly
Note 1 to entry: Tone frequency is expressed in hertz (Hz.).
3.3
tone level
LT
energy summation of the narrow-band level (3.22) with the tone frequency (3.2), f , and the lateral lines
T
about f , assignable to this tone
T
Note 1 to entry: Tone level is expressed in decibels (dB.).
Note 2 to entry: If the critical band (3.5) for the frequency, fT, 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 3 to entry: The method for the determination of the tone level, LT, of a tone in a critical band is described in
5.3.3.
3.4
audibility
ΔL
Audibility of tones is the arithmetic difference between the tone level (3.3), L , and the masking threshold
T
(3.15), ′
L
T
Note 1 to entry: Audibility is expressed in decibels (dB.).
Note 2 to entry: The method for the determination of the decisive audibility (3.24), ΔL , of a narrow-band spectrum
j
(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
c
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: Critical band is expressed in hertz (Hz.).
Note 2 to entry: This characteristic of a critical band (see also References [34] and [45]) holds only for a restricted
sound level range. This dependence is neglected here.
3.6
mean narrow-band level of the critical band
L
S
energy mean value of all narrow-band levels (3.22) in a critical band (3.5), except for the spectral line for
the frequency, f , under consideration and all lines that exceed this mean value by more than 6 dB
T
Note 1 to entry: Mean narrow-band level of the critical band is expressed in decibels (dB.).
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ISO/TS 20065:2022(E)
Note 2 to entry: The method for the determination of the mean narrow-band level, L , of the masking noise is
S
described in 5.3.2 and Annex D (iterative method).
3.7
critical band level
L
G
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: Critical band level is expressed in decibels (dB.).
Note 2 to entry: See narrow-band level (3.22) and Annex C for masking.
Note 3 to entry: For the definition formula for L , see Formula (12).
G
3.8
sampling frequency
f
S
number of samples taken per second
Note 1 to entry: Sampling frequency is expressed in hertz (Hz.).
Note 2 to entry: The analogue data provided continuously are converted into samples through sampling at discrete
time intervals for digital processing.
Note 3 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
S
[fS ≥ 2 fN, see also aliasing (3.9), antialiasing filter (3.10) and useable frequency (3.20)]. Discrete Fourier Transform
(DFT) analyzersanalysers 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 (fS/2) is also known as the Nyquist frequency.
3.10
antialiasing filter
low-pass filter
ideal filter that allows 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
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ISO/TS 20065:2022(E)
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 DFT analyzersanalysers 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
N
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. Regarding the Fast Fourier Transform,
10
the value of N generally 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 document.
Note 2 to entry: DFT 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).
Note 3 to entry: Line spectrum is sometimes referred to as frequency spectrum.
3.13
line spacing
frequency resolution
distance, between adjacent spectral lines (3.23), where the line spacing in the DFT is given by
∆=ff / N
S
where
 f is the sampling frequency (3.8);
S Formatted: Pattern: Clear
 N is the block length (3.11).
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Note 1 to entry: Line spacing is expressed in hertz (Hz.).
Note 2 to entry: In this document, the line spacing is 1,9 Hz ≤ Δf ≤ 4,0 Hz.
3.14
time window
time data set of the signal segment (block length) (3.11) that is multiplied by a weighting function
(window function)
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ISO/TS 20065:2022(E)
Note 1 to entry: In accordance with the definition of the Fourier integral, a prerequisite of the DFT 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 Functionfunction.
Note 2 to entry: For more information on window and weighting functions, see, for example, Reference [56] and
Annex A.
3.15
masking threshold
′
L
T
audibility (3.4) threshold for a specific sound in the presence of a masking sound (masker)
Note 1 to entry: Masking threshold is expressed in decibels (dB.).
Note 2 to entry: See Annex C for more information on the audibility threshold and the masking noise.
3.16
masking index
a
v
arithmetic difference between the masking threshold (3.15), L′ , and the critical band level (3.7), L , of
G
T
the masking noise
Note 1 to entry: maskingMasking index is expressed in decibels (dB.).
Note 2 to entry: For frequency-dependent masking index, a , masking and masking noise, see Annex C.
v
3.17
bandwidth
frequency bandwidth
frequency range of a number of adjacent spectral lines (3.23)
Note 1 to entry: Bandwidth is expressed in hertz (Hz.).
Note 2 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 prominence of a tone based on a bandpass noise to the prominence of a sinusoidal tone
of the same tone frequency (3.2), f , and same tone level (3.3), L
T T
Note 1 to entry: Distinctness is expressed in %.percentage (%).
3.19
edge steepness
slope of the level difference between the maximum narrow-band level (3.22) of a tone, LTmax, and the
narrow-band levels of the first line below/above the tone to the corresponding frequency difference
Note 1 to entry: Edge steepness is expressed in decibels per hertz (dB/Hz.).
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ISO/TS 20065:2022(E)
3.20
useable frequency
f
N
upper limit frequency of the signal components used for evaluation
Note 1 to entry: Useable frequency is expressed in hertz (Hz.).
3.21
investigation range
frequency range within which tones are investigated in the line spectrum (3.12)
Note 1 to entry: Investigation range is expressed in hertz (Hz.).
3.22
narrow-band level
averaged level within a spectral line (3.23)
Note 1 to entry: Narrow-band level is expressed in decibels (dB.).
3.23
spectral line
frequency band of bandwidth (3.17), ∆f (line spacing) (3.13), in a line spectrum (3.12)
Note 1 to entry: Spectral line is expressed in hertz (Hz.).
3.24
decisive audibility
ΔL
j
maximum audibility (3.4), ∆L in the individual spectrum, j
Note 1 to entry: Decisive audibility is expressed in decibels (dB.).
3.25
mean audibility
ΔL,
energy average of decisive audibility (3.24)), ΔLj, calculated for each narrow-band averaged spectrum
Note 1 to entry: Mean audibility is expressed in decibels (dB.).
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
Formatted: Pattern: Clear
analysis, the A-weighted equivalent continuous sound pressure level, L , as given in ISO 1996-1, is
Aeq
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toshall be established for the respective spectral lines. If the line spectrum is unweighted (linearLIN or
Z), then it shall be corrected to A-weighting in accordance with IEC 61672-1. Formatted: Pattern: Clear
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ISO/TS 20065:2022(E)
4.2 Measurement instruments
Sound level meters that meet, or exceed, the requirements of Class 1 in IEC 61672-1 shall be used. These
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have a frequency weighting “A”/“LIN” or “A”/“Z” with a lower limit frequency equal to, or below, 20 Hz.
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Additional instruments such as recording instruments (digital or magnetic tape) may also be used. The
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measured values derived through recording instruments shall lie within the tolerance range given in
IEC 61672-1.
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Analysis of frequency components in the measurement signals is performed using a frequency Formatted: Pattern: Clear
analyzeranalyser. The constant line spacing, Δf, shall lie in the range 1,9 Hz to 4 Hz (inclusive). The use of
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the Hanning window is mandatory in this document. 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 Hann
...

TECHNICAL ISO/TS
SPECIFICATION 20065
First edition
Acoustics — Objective method for
assessing the audibility of tones in
noise — Engineering method
Acoustique — Méthode objective d'évaluation de l'audibilité des
tonalités dans le bruit — Méthode d'expertise
PROOF/ÉPREUVE
Reference number
ISO/TS 20065:2022(E)
© ISO/TS 2022

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ISO/TS 20065:2022(E)
COPYRIGHT PROTECTED DOCUMENT
© ISO 2022
All rights reserved. Unless otherwise specified, or required in the context of its implementation, 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
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: +41 22 749 01 11
Email: copyright@iso.org
Website: www.iso.org
Published in Switzerland
ii
PROOF/ÉPREUVE © ISO 2022 – All rights reserved

---------------------- Page: 2 ----------------------
ISO/TS 20065:2022(E)
Contents Page
Foreword .iv
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Measurement procedure . 6
4.1 General . 6
4.2 Measurement instruments . 6
4.3 Merging the basic spectra . 6
5 Evaluation . 6
5.1 General information. 6
5.2 Width, Δf , of the critical band . 7
c
5.3 Determination of prominent tones . 8
5.3.1 General information . 8
5.3.2 Determination of the mean narrow-band level of the critical band, L , of
S
the masking noise . 8
5.3.3 Determination of the tone level L of a tone in a critical band . 9
T
5.3.4 Distinctness of a tone . 10
5.3.5 Determination of the critical band level, L , of the masking noise . 10
G
5.3.6 Masking index . 11
5.3.7 Determination of the audibility, ΔL . 11
5.3.8 Determination of the decisive audibility, ΔL , of a narrow-band spectrum . 11
j
5.3.9 Determination of the mean audibility, ΔL, of a number of spectra .13
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 audibility .29
Bibliography .35
iii
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ISO/TS 20065:2022(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 of the voluntary nature of standards, the meaning of ISO specific terms and
expressions related to conformity assessment, as well as information about ISO's adherence to
the World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT), see
www.iso.org/iso/foreword.html.
This document was prepared by Technical ISO/TC 43, Acoustics, Subcommittee SC 1, Noise.
This first edition of ISO/TS 20065 cancels and replaces ISO/PAS 20065:2016, which has been technically
revised.
The main changes are as follows:
— guidance on residual sound (5.3.1);
— a file containing a number of other example audio files and a guidance document can be downloaded
from https://standards.iso.org/iso/20065 (from “Prominent tones in wind turbine noise Round
robin test IEC 61400-11, ISO/PAS 20065”);
— editorial changes for clarity and to meet the latest ISO standards, including definitions, measures,
formulae, aligned and streamlined terminology, and additional background information.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www.iso.org/members.html.
iv
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TECHNICAL SPECIFICATION ISO/TS 20065:2022(E)
Acoustics — Objective method for assessing the audibility
of tones in noise — Engineering method
1 Scope
This document describes a method for the objective determination of the audibility of tones in
environmental noise.
This document 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 captured, then this method cannot replace subjective evaluation.
NOTE The procedure has not been validated below 50 Hz.
The method presented herein can be used in continuous measurement stations that work automatically.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements of this document. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any amendments) applies.
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.
ISO and IEC maintain terminology databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at https:// www .electropedia .org/
NOTE Unless otherwise stated, the reference level for decibels (dB) values in these definitions is 20 µPa.
3.1
tone
sound characterized by a single-frequency component or narrow-band components
3.2
tone frequency
f
T
frequency of the spectral line (3.23) (or mid-band frequency of the narrow-band filter), to the level of
which the tone (3.1) contributes most strongly
Note 1 to entry: Tone frequency is expressed in hertz (Hz).
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3.3
tone level
L
T
energy summation of the narrow-band level (3.22) with the tone frequency (3.2), f , and the lateral lines
T
about f , assignable to this tone
T
Note 1 to entry: Tone level is expressed in decibels (dB).
Note 2 to entry: If the critical band (3.5) for the frequency, f , under consideration contains a number of tones,
T
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 3 to entry: The method for the determination of the tone level, L , of a tone in a critical band is described in
T
5.3.3.
3.4
audibility
ΔL
Audibility of tones is the arithmetic difference between the tone level (3.3), L , and the masking threshold
T
′
(3.15), L
T
Note 1 to entry: Audibility is expressed in decibels (dB).
Note 2 to entry: The method for the determination of the decisive audibility (3.24), ΔL , of a narrow-band spectrum
j
(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
c
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: Critical band is expressed in hertz (Hz).
Note 2 to entry: This characteristic of a critical band (see also References [4] and [5]) holds only for a restricted
sound level range. This dependence is neglected here.
3.6
mean narrow-band level of the critical band
L
S
energy mean value of all narrow-band levels (3.22) in a critical band (3.5), except for the spectral line for
the frequency, f , under consideration and all lines that exceed this mean value by more than 6 dB
T
Note 1 to entry: Mean narrow-band level of the critical band is expressed in decibels (dB).
Note 2 to entry: The method for the determination of the mean narrow-band level, L , of the masking noise is
S
described in 5.3.2 and Annex D.
3.7
critical band level
L
G
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: Critical band level is expressed in decibels (dB).
Note 2 to entry: See narrow-band level (3.22) and Annex C for masking.
Note 3 to entry: For the definition formula for L , see Formula (12).
G
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3.8
sampling frequency
f
S
number of samples taken per second
Note 1 to entry: Sampling frequency is expressed in hertz (Hz).
Note 2 to entry: The analogue data provided continuously are converted into samples through sampling at
discrete time intervals for digital processing.
Note 3 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
S
the time signal [ f ≥ 2 f , see also aliasing (3.9), antialiasing filter (3.10) and useable frequency (3.20)]. Discrete
S N
Fourier Transform (DFT) analysers 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.
S
3.10
antialiasing filter
low-pass filter
ideal filter that allows 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 DFT analysers 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
N
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. Regarding the Fast Fourier
10
Transform, the value of N generally has the integer of power of 2. It has a value, for example, of N = 2 = 1 024
data points.
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ISO/TS 20065:2022(E)
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 document.
Note 2 to entry: DFT 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).
Note 3 to entry: Line spectrum is sometimes referred to as frequency spectrum.
3.13
line spacing
frequency resolution
distance, between adjacent spectral lines (3.23), where the line spacing in the DFT is given by
Δff= /N
S
where
f is the sampling frequency (3.8);
S
N is the block length (3.11).
Note 1 to entry: Line spacing is expressed in hertz (Hz).
Note 2 to entry: In this document, the line spacing is 1,9 Hz ≤ Δf ≤ 4,0 Hz.
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 DFT 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 [6] and
Annex A.
3.15
masking threshold
′
L
T
audibility (3.4) threshold for a specific sound in the presence of a masking sound (masker)
Note 1 to entry: Masking threshold is expressed in decibels (dB).
Note 2 to entry: See Annex C for more information on the audibility threshold and the masking noise.
3.16
masking index
a
v
′
arithmetic difference between the masking threshold (3.15), L , and the critical band level (3.7), L , of
T G
the masking noise
Note 1 to entry: Masking index is expressed in decibels (dB).
Note 2 to entry: For frequency-dependent masking index, a , masking and masking noise, see Annex C.
v
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3.17
bandwidth
frequency bandwidth
frequency range of a number of adjacent spectral lines (3.23)
Note 1 to entry: Bandwidth is expressed in hertz (Hz).
Note 2 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 prominence of a tone based on a bandpass noise to the prominence of a sinusoidal
tone of the same tone frequency (3.2), f , and same tone level (3.3), L
T T
Note 1 to entry: Distinctness is expressed in percentage (%).
3.19
edge steepness
slope 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
Note 1 to entry: Edge steepness is expressed in decibels per hertz (dB/Hz).
3.20
useable frequency
f
N
upper limit frequency of the signal components used for evaluation
Note 1 to entry: Useable frequency is expressed in hertz (Hz).
3.21
investigation range
frequency range within which tones are investigated in the line spectrum (3.12)
Note 1 to entry: Investigation range is expressed in hertz (Hz).
3.22
narrow-band level
averaged level within a spectral line (3.23)
Note 1 to entry: Narrow-band level is expressed in decibels (dB).
3.23
spectral line
frequency band of bandwidth (3.17), ∆f (line spacing) (3.13), in a line spectrum (3.12)
Note 1 to entry: Spectral line is expressed in hertz (Hz).
3.24
decisive audibility
ΔL
j
maximum audibility (3.4), ∆L in the individual spectrum, j
Note 1 to entry: Decisive audibility is expressed in decibels (dB).
3.25
mean audibility
ΔL,
energy average of decisive audibility (3.24), ΔLj, calculated for each narrow-band averaged spectrum
Note 1 to entry: Mean audibility is expressed in decibels (dB).
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ISO/TS 20065:2022(E)
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, shall
Aeq
be established for the respective spectral lines. If the line spectrum is unweighted (LIN or Z), 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
analyser. 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 document. 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 analyser 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):
1 N
01,dL / B
 
ij,
L = 10 lgd10 B (1)
i  ∑ 
j=1
 N 
where
th th
L is the level of the i spectral line for the j spectrum, in dB;
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
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ISO/TS 20065:2022(E)
lead to unjustified values of audibility, ΔL (too high, but also too low). Signals that have very high level
and/or frequency dynamics that no longer correspond with a 3-second averaging can, therefore, not be
evaluated using this document. 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).
Tones in different critical bands are evaluated separately. To arrive at a decision on whether an
assessment has to be made, only the critical band with the most pronounced tone is considered (see
5.3.8).
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).
Ti T
An assessment 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
R
steepness (see 3.19) of at least 24 dB/octave.
The mean audibility, ΔL, which is the conclusive result of this method for the noise to be assessed, is
determined by averaging in energy terms the decisive audibility ΔL calculated for each narrow-band
j
averaged spectrum. In this averaging, the ΔL , the maximum audibility in each line spectrum, is used
j
regardless of the frequency of the tone. Because the aim of this method is to estimate the annoyance
of a noise containing tones relative to a noise without tones, not the annoyance of a tone at a particular
frequency.
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 line spectrum.
A sample program to determine audibility can be downloaded from https:// standards .iso .org/ iso/
20065. This is based on ISO/PAS 20065. It is useful for validating proprietary analysis codes.
5.2 Width, Δf , of the critical band
c
The width, Δf , of the critical band about the tone frequency, f , is given by Formula (2):
c T
06, 9
2
 
f /Hz
 
T
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
2 2
−Δf Δff+4
()
c cT
f = + (4)
1
2 2
ff=+Δf (5)
21 c
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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 line
T
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
e
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 analyser, this influence of summation (number of lines >1) is taken into consideration
through a correction value; if the level addition is simulated by the analyser 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)].
The measurement is to be made where possible at such times that tones from sources of residual
sound are not present as these can impact the assessment of the source of specific sound under
investigation. Justification of the selection of the measurement time period is to be reported. Where
not possible, the influence of t
...