SIST EN 60118-2:2004/A2:2006

SLOVENSKI SIST EN 60118-2:2004/A2:2006

STANDARD
februar 2006
Slušni pripomočki – 2. del: Slušni pripomočki z vezji za samodejno krmiljenje
ojačenja – Dopolnilo A2 (IEC 60118- 2:1983/A2:1997)
Hearing aids - Part 2: Hearing aids with automatic gain control circuits; Amendment
A2 (IEC 60118- 2:1983/A2:1997)
ICS 11.180.15 Referenčna številka
SIST EN 60118-2:2004/A2:2006(en)
©  Standard je založil in izdal Slovenski inštitut za standardizacijo. Razmnoževanje ali kopiranje celote ali delov tega dokumenta ni dovoljeno

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NORME CEI
INTERNATIONALE
IEC
60118-2
INTERNATIONAL
1983
STANDARD
AMENDEMENT 2
AMENDMENT 2
1997-05
Amendement 2
Appareils de correction auditive –
Partie 2:
Appareils de correction auditive comportant
des commandes automatiques de gain
Amendment 2
Hearing aids –
Part 2:
Hearing aids with automatic gain
control circuits
 IEC 1997 Droits de reproduction réservés  Copyright - all rights reserved
International Electrotechnical Commission 3, rue de Varembé Geneva, Switzerland
Telefax: +41 22 919 0300 e-mail: inmail@iec.ch IEC web site http: //www.iec.ch
CODE PRIX
Commission Electrotechnique Internationale
K
PRICE CODE
International Electrotechnical Commission
Pour prix, voir catalogue en vigueur
For price, see current catalogue

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60118-2 Amend. 2 © IEC:1997 – 3 –
FOREWORD
This amendment has been prepared by the IEC technical committee 29: Electroacoustics.
The text of this amendment is based on the following documents:
FDIS Report on voting
29/350/FDIS 29/358/RVD
Full information on the voting for the approval of this amendment can be found in the report
on voting indicated in the above table.
____________
Page 3
CONTENTS
Add the title of the new clause 10 and the new annexes B and C as follows:
10 Frequency response of hearing aids with AGC circuits in operation
using steady-state broad-band signals
Annexes
B Smoothed data presentation
C Bibliography
Page 5
Add the following list of standards:
IEC 60118-0: 1983, Hearing aids – Part 0: Measurement of electroacoustical characteristics
Amendment 1: 1994
IEC 60711: 1981, Occluded-ear simulator for the measurement of earphones coupled to the
ear by ear inserts
IEC 61260: 1995, Electroacoustics – Octave-band and fractional-octave-band filters

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60118-2 Amend. 2 © IEC:1997 – 5 –
Page 9
3 Conditions
Delete 3.2
Renumber 3.3 to become 3.2
4 Explanation of terms
Add the following new definitions after 4.9 (page 3 in amendment 1):
4.10 Overall root-mean-square sound pressure level (overall r.m.s. SPL)
The root-mean-square sound pressure level with measurement bandwidth equal to the
frequency range covered by the one-third-octave frequency bands (see IEC 61260) from
200 Hz to 8 000 Hz.
4.11 One-third-octave band level
The level of that part of the signal contained within a band one-third-octave wide as defined
in IEC 61260.
4.12 Auto-spectrum (power spectrum)
The power spectrum of either the input signal (G ) to or the output signal (G ) from a
AA BB
hearing aid in the frequency domain. It is computed by multiplying the Fourier transform of
the signal by the complex conjugate of the Fourier transform of the same signal.
4.13 Cross-spectrum (G )
AB
The degree to which the same signal frequencies are mutually present in the input and
output of a hearing aid. It is computed by multiplying the complex conjugate of the Fourier
transform of the input signal to the hearing aid by the Fourier transform of the output signal
from the hearing aid.
4.14 Coherence
A number ranging from 0 to 1 showing to what degree the output from a hearing aid is
correlated to the input. Coherence for a random noise test signal is reduced by non-linearity
and by system noise. The coherence is calculated from the auto- and cross-spectrum
averages as follows:
2
G
AB
          Coherence =
GG•
AA BB
4.15 Synchronous analysis
Analysis which is synchronized with the period of the input signal, for example with the
periodicity of pseudo-random noise.

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60118-2 Amend. 2 © IEC:1997 – 7 –
Page 15
Add, after clause 9, the following clause 10 (page 9 in amendment 1):
10 Frequency response of hearing aids with AGC circuits in operation
using steady-state broad-band input signals
10.1 General
The frequency response of electroacoustic systems, including hearing aids, has traditionally
been obtained using a swept pure tone input signal whose level is held constant while the
output of the system is measured over the frequency range of interest. However, other
methods have evolved for obtaining frequency responses of electronic systems as a result
of the recent proliferation of digital spectrum analysers that utilise steady-state broad-band
noise as one of their test signals. A time-stationary, steady-state broad-band noise, which is
more typical of the complex input signals that hearing aids are required to process in non-
laboratory real-world environments, may be a more suitable test signal for depicting
performance, particularly for those hearing aids with level-dependent gain circuitry.
For those hearing aids that do not have automatic gain control (AGC) or other forms of
adaptive signal processing circuitry, or for hearing aids having such circuitry but tested with
input levels below their activation point, the same frequency response should result,
whether a swept pure tone or broad-band noise is used, as long as the hearing aid is
operating linearly, and the signal-to-noise ratio is adequate. The method used shall be
stated.
IEC 60118-0 describes methods of measurements for the evaluation of the electroacoustical
characteristics of hearing aids employing swept pure tone signals. When testing hearing
aids with AGC or other non-linear circuits in action, the response at a given frequency will
depend on the way the measuring signal activates the non-linear element at the same
frequency.
In IEC 60118-2, Amendment 1, a method of measurement to characterize AGC hearing aids
is described. This method uses an AGC-activating pure tone signal with a fixed frequency,
and a swept pure tone signal with a 20 dB lower level for obtaining the frequency response.
Using this method, the effect of the non-linear element is controlled by the AGC-activating
signal alone, and is not influenced by the measuring signal.
This clause describes a method for the measurement of hearing aid frequency response
using a steady-state broad-band input signal and employing single or dual-channel spectrum
analysis to measure the frequency response.
The spectral characteristics of the specified test signal have been chosen to be in
conformance with the American standard ANSI S3.42 [1]*. This specification has been used
for many years to test hearing aids, and has been shown to represent a reasonable
compromise, ensuring sufficient signal-to-noise ratio in the high frequency area, and also to
some extent representing the spectral characteristics of speech.
_________
* Figures in square brackets indicate the references listed in annex C.

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60118-2 Amend. 2 © IEC:1997 – 9 –
Using this method, the non-linear element will respond to the broad-band signal, with
contributions from many frequencies, and not from an individual frequency component as
when using the methods in IEC 60118-0 or IEC 60118-2, Amendment 1.
Care should be exercised in interpreting measurements made with the steady-state noise
signal, because hearing aids whose frequency response is changed by the dynamic
characteristics of the input signal cannot be fully characterized by this almost time-invariant
signal. An example is hearing aids that have adaptive AGC time constants based on the
temporal pattern of the input signal.
This clause is basically in keeping with ANSI S3.42 [1] with regard to the test signal and the
frequency response measuring procedures. Important exceptions are the reference test gain
control position, which in this international standard is defined in accordance with
IEC 60118-0, Amendment 1, and the use of the IEC 60711 ear simulator. The coherence
function in connection with dual-channel measurements is used to validate the frequency
response measurements.
10.2 Test enclosure
The test enclosure shall fulfil the requirements specified in IEC 60118-0. The residual noise
at the test point shall give a signal-to-noise ratio in each one-third-octave band equal to or
greater than 10 dB, with a noise input signal as specified in 10.3.1.2 with an overall r.m.s.
level of 50 dB.
10.3 Test conditions
All sound pressure levels are referred to 20 μPa and abbreviated SPL. Reference is made
to IEC 60118-0 and IEC 60711. The comparison method (see 4.3 of IEC 60118-0) shall be
applied when using cross-spectrum measurements, and the substitution method (see 4.2 of
IEC 60118-0) when using auto-spectrum and swept filter measurements.
10.3.1 Noise input signal
10.3.1.1 Noise type and peak levels
Random noise or pseudo-random noise shall be used as input signals. The type of noise,
and its period shall be stated. The noise signal shall have a normal probability distribution
that is truncated so that the maximum peak signal level is 12 dB ± 3 dB above the r.m.s.
signal level. The noise shall be continuous, that is its level should be constant for a
sufficiently long time before each analysis period to allow any adaptive signal processing
element
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