Bsi bs en 60118 2 1996 (1999) bs 6083 2 1996

01285776 PDF BRITISH STANDARD BS EN 60118 2 1996 BS 6083 2 1996 Implementing Amendment No 1, not published separately IEC 118 2 1983 (including Amendments 1 1993 and 2 1997 to IEC 118 2 1983) Hearing[.]

Amendment No 1, not published separately

IEC 118-2: 1983

(including Amendments 1:1993 and 2:1997 to IEC 118-2:1983)

The European Standard EN 60118-2:1995 with the inclusion of

amendment A2:1997 has the status of a British Standard

ICS 17.140.50

BS EN 60118-2:1996

This British Standard, having

been prepared under the

direction of the Electrotechnical

Sector Board, was published

under the authority of the

Standards Board and

comes into effect on

15 September 1996

© BSI 06-1999

The following BSI references

relate to the work on this

standard:

Committee reference EPL/29

Draft for comment 84/20636 DC

British Association of OtolaryngologistsBritish Hearing Aid Industry AssociationBritish Medical Association

British Society of AudiologyBritish Telecommunications plcConfederation of British IndustryDepartment of Health

Department of Trade and Industry (National Physical Laboratory)Health and Safety Executive

Institute of AcousticsInstitute of Sound and Vibration ResearchInstitution of Electrical Engineers

Medical Research CouncilMinistry of DefenceRoyal Aeronautical SocietyRoyal National Institute for Deaf peopleSociety of Environmental EngineersUniversity of Exeter

Amendments issued since publication

Amd No Date Comments

9753 January

1998 Indicated by a sideline in the margin

PageCommittees responsible Inside front cover

BS EN 60118-2:1996

National foreword

This British Standard has been prepared by Technical Committee EPL/29 and is

the English language version of EN 60118-2:1996 Hearing aids Part 2: Hearing

aids with automatic gain control circuits, including amendment A2:1997

published by the European Committee for Electrotechnical Standardization (CENELEC) It is identical with IEC 118-2, second edition 1983, together with its Amendments 1:1993 and 2:1997, and supersedes BS 6083-2:1984, which is withdrawn

From 1 January 1997, all IEC publications have the number 60000 added to the old number For instance, IEC 27-1 has been renumbered as IEC 60027-1 For a period of time during the change over from one numbering system to the other, publications may contain identifiers from both systems

A British Standard does not purport to include all the necessary provisions of a contract Users of British Standards are responsible for their correct application

Compliance with a British Standard does not of itself confer immunity from legal obligations.

Cross-references

Publication referred to Corresponding British Standard

EN 60118-0:1993(IEC 118-0:1983) BS EN 60118 Hearing aids BS EN 60118-0:1993 Measurement of electroacoustical

IEC 263:1982 BS 6397:1983 Specification for scales and sizes for

plotting frequency characteristics and polar diagrams

IEC 268-8:1973 BS 6840 Sound system equipment

Part 8:1988 Methods for specifying and measuring the

characteristics of automatic gain control devices

a Superseded by EN 60118-1:1995 (IEC 118-1:1995), for which the corresponding British Standard

UDC 534.773.2:621.395.92:621.395.665:620.1:621.317.6 Supersedes HD 450.2 S1:1984 Descriptors: Electromedical device, hearing aid, automatic gain control, definitions, measurement procedures

English version Hearing aids Part 2: Hearing aids with automatic gain control circuits

(includes amendment A2:1997) (IEC 118-2:1983 + A1:1993 + A2:1997)

Appareils de correction auditive

Partie 2: Appareils de correction auditive

comportant des commandes automatiques de

gain (inclut l’amendement A2:1997)

(CEI 118-2:1983 + A1:1993 + A2:1997)

Hörgeräte Teil 2: Hörgeräte mit automatischer Verstärkungsregelung

(Enthält Änderung A2:1997) (IEC 118-2:1983 + A1:1993 + A2:1997)

This European Standard was approved by CENELEC on 1994-03-08;

amendment A2 was approved by CENELEC on 1997-07-01 CENELEC

members are bound to comply with the CEN/CENELEC Internal Regulations

which stipulate the conditions for giving this European Standard the status of

a national standard without any alteration

Up-to-date lists and bibliographical references concerning such national

standards may be obtained on application to the Central Secretariat or to any

CENELEC member

This European Standard exists in three official versions (English, French,

German) A version in any other language made by translation under the

responsibility of a CENELEC member into its own language and notified to the

Central Secretariat has the same status as the official versions

CENELEC members are the national electrotechnical committees of Austria,

Belgium, Denmark, Finland, France, Germany, Greece, Iceland, Ireland, Italy,

Luxembourg, Netherlands, Norway, Portugal, Spain, Sweden, Switzerland and

United Kingdom

CENELEC

European Committee for Electrotechnical StandardizationComité Européen de Normalisation ElectrotechniqueEuropäisches Komitee für Elektrotechnische Normung

Central Secretariat: rue de Stassart 35, B-1050 Brussels

EN 60118-2:1995

© BSI 06-1999

2

Foreword

The text of the International Standard

IEC 118-2:1983, prepared by IEC TC 29,

Electroacoustics, was approved by CENELEC

as HD 450.2 S1 on 1984-09-11

This Harmonization Document was submitted to

the formal vote for conversion into a European

Standard and was approved by CENELEC

as EN 60118-2 on 1994-03-08

The text of amendment 1:1993 to the

International Standard IEC 118-2:1983 was

submitted to the formal vote and was approved

by CENELEC as amendment A1 to EN 60118-2

on 1994-03-08 without any modification

Having first withheld the publication

of EN 60118-2 and its A1, the Technical Board

of CENELEC has allowed on 1995-09-20 the

circulation of the definitive version

of EN 60118-2 with incorporation of its

amendment A1

The following dates were fixed:

Annexes designated “normative” are part of the

body of the standard In this standard, Annex ZA is

normative Annex ZA has been added by

The following dates were fixed:

Annexes designated “normative” are part of the body of the standard Annexes designated

“informative” are given for information only In this standard, Annex ZA is normative and

Annex B and Annex C are informative Annex ZA has been added by CENELEC

— latest date by which the

have to be withdrawn (dow) 1996-07-01

— latest date by which the amendment has to be implemented at national level by publication of an identical national

standard or by endorsement (dop) 1998-04-01

— latest date by which the national standards conflicting with the amendment have to be withdrawn (dow) 1998-04-01

4.1 Automatic gain control (AGC) 5

4.2 Steady-state input/output graph 5

4.3 Lower AGC limit or AGC threshold 5

4.4 Compression ratio (between specified

input sound pressure level values) 5

4.5 Dynamic output characteristics 5

4.8 AGC activated frequency response 6

4.9 Operating frequency range of the AGC 6

4.10 Overall root-mean-square sound

pressure level (overall r.m.s SPL) 6

4.11 One-third-octave band level 6

4.12 Auto-spectrum (power spectrum) 6

4.13 Cross-spectrum (GAB) 6

4.15 Synchronous analysis 6

5 Steady-state input/output graph 6

5.1 Graph showing the relation between

input sound pressure level and output

sound pressure level 6

8 Effect on steady-state and dynamic

performance with respect to variation

in battery or supply voltage 8

9 AGC activated frequency response of

hearing aids with a single channel

AGC circuit in operation using pure

10 Frequency response of hearing aids

with AGC circuits in operation using

steady-state broad-band input signals 9

PageAnnex A (informative) Examples of

employing digitally controlled input SPL and a band rejection filter 15Figure 5 — Nominal values with upper

and lower limits (± 2 dB) for one-third-octave band levels of the noise input signal at the

Table 1 — Nominal values for the one-third-octave band levels of the noiseinput signal at the test point 11

4 blank

1 Scope

1.1 This standard applies to the hearing aids of any

type with automatic gain control (AGC) circuits

This standard gives uniform methods for specifying

dynamic and static performance characteristics of

hearing aids with AGC circuits together with the

relevant methods of measurement for these

characteristics

This standard is confined to a description of the

different characteristics and the relevant methods

of measurement It does not attempt to specify

performance requirements

1.2 This standard includes devices which have

compression and/or limiting properties with respect

to the envelope of the input signal Devices which

control the long-term average output level are also

included

a) AGC is employed to obtain compression, or the

reduction of the dynamic range of the sound at

the output, with the object of preserving the

integrity of the input waveform

b) AGC circuits instead of clipping devices are

often used for limiting purposes

A limiting effect occurs when the input/output

characteristic flattens out at higher input levels

Limiting action is mainly used as a means of

preventing excessive output sound from the hearing

aid from reaching the listener’s ear

1.3 This standard does not include:

a) Expanders

b) Clipping devices, which cut off the signal peaks

above a certain level; such devices differ basically

from AGC circuits, which, in a steady state, tend

to preserve the waveform of the input signal

NOTE An AGC circuit with very short recovery time may

cause considerable distortion, especially in the low-frequency

range This should be given special attention.

2 Object

2.1 The purpose of this standard is to facilitate

measurements of certain characteristics of hearing

aids with AGC circuits that are not described

elsewhere in IEC Publication 118-0: Hearing Aids,

Part 0: Measurement of Electroacoustical

Characteristics, and which are considered necessary

for a physical description of the function of the

automatic gain control

2.2 In general, the methods of measurement

recommended are those which are considered to be

the most directly related to the characteristics This

does not exclude the use of other stated methods

which will give equivalent results

3 Conditions

3.1 General conditions

Reference is made to IEC Publication 268-8: Sound System Equipment, Part 8: Automatic Gain Control Devices

Measurements other than those described herein and that are stated in IEC Publication 118-0 can be performed in accordance with that publication, but with AGC operating, provided the operating conditions are stated

3.2 Throughout this standard, all sound pressure levels are referred to 20 4Pa

4 Explanation of terms

4.1 Automatic gain control (AGC)

A means in a hearing aid by which the gain is automatically controlled as a function of the magnitude of the envelope of the input signal or other signal parameter

NOTE Throughout this standard, reference is made to the use

of acoustic inputs However, where appropriate, additional measurements may be made with an electromagnetically induced input.

4.2 Steady-state input/output graph

The graph illustrating the output sound pressure level as a function of the input sound pressure level for a specified frequency, both expressed in decibels

on identical linear scales (Figure 1, page 12)

4.3 Lower AGC limit or AGC threshold

The input sound pressure level which, when applied to the hearing aid, gives a reduction in the gain of 2 ± 0.5 dB with respect to the gain in the linear mode (Figure 1)

4.4 Compression ratio (between specified input sound pressure level values)

Under steady-state conditions, the ratio of an input sound pressure level difference to the corresponding output sound pressure level difference, both expressed in decibels (Figure 1)

4.5 Dynamic output characteristics

The output sound pressure envelope shown as a function of time when an input sound signal of a predetermined frequency and level is modulated by

a square envelope pulse with a predetermined pulse amplitude (Figure 2, page 13)

EN 60118-2:1995

4.6 Attack time

The time interval between the moment when the

input signal level is increased abruptly by a stated

number of decibels and the moment when the

output sound pressure level from the hearing aid

with the AGC circuit stabilizes at the elevated

steady-state level within ± 2 dB (Figure 2, page 13)

4.6.1 Attack time for the normal dynamic

range of speech

The attack time, as defined in Sub-clause 4.6,

when the initial input sound pressure level

is 55 dB and the increase in input sound pressure

level is 25 dB

4.6.2 High level attack time

The attack time, as defined in Sub-clause 4.6,

when the initial input sound pressure level

is 60 dB and the increase in input sound pressure

level is 40 dB

4.7 Recovery time

The time interval between the moment when the

stated input signal level is reduced abruptly to a

level a stated number of decibels lower after the

AGC amplifier has reached the steady-state

output under elevated input signal conditions,

and the moment when the output sound pressure

level from the hearing aid stabilizes again at the

lower steady-state level within ± 2 dB (Figure 2)

4.7.1 Recovery time for the normal dynamic

range of speech

The recovery time, as defined in Sub-clause 4.7,

when the initial input sound pressure level

is 80 dB and the decrease in input sound pressure

level is 25 dB

4.7.2 High level recovery time

The recovery time, as defined in Sub-clause 4.7,

when the initial sound pressure level is 100 dB and

the decrease in input sound pressure level is 40 dB

4.8 AGC activated frequency response

The frequency response when the AGC circuit is

activated by a specified AGC activating signal

4.9 Operating frequency range of the AGC

For a specified input sound pressure level, the

frequency range in which the AGC threshold is

reached or exceeded

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 (GAA)

to or the output signal (GBB) from a 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 (GAB)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:

Coherence =

4.15 Synchronous analysis

Analysis which is synchronized with the period of the input signal, for example with the periodicity of pseudo-random noise

5 Steady-state input/output graph

5.1 Graph showing the relation between input sound pressure level and output sound pressure level

The graph shall have the input sound pressure level

as abscissa and the output sound pressure level as ordinate, both expressed in decibels on linear scales having divisions of identical size

NOTE In the input/output graph of an AGC device, different portions may be distinguished:

— Below the lower AGC limit the slope is essentially 45° (linear amplifier mode).

— Above this limit, the graph curves over in a portion having

a decreasing slope, often followed by another portion having a nearly flat slope (AGC mode).

— At very high input levels, a flat or sloping portion may be followed by a portion with a steeper slope, generally due to saturation of the AGC circuit.

5.2 Methods of measurement

The gain control is adjusted to its maximum setting

Any adjustable gain control after the AGC-loop

shall be adjusted in such a manner that overload of

the hearing aid is avoided

An input sound signal of frequency 1 600 Hz

or 2 500 Hz when appropriate, is applied at the

lowest possible level consistent with an adequate

signal-to-noise ratio of preferably more than 10 dB

The input sound pressure level is increased up

to 100 dB in sufficiently small steps, and the

corresponding output sound pressure level is

measured after steady-state conditions have been

reached The graph is plotted with the input sound

pressure level as abscissa and the output level as

ordinate, as described in Sub-clause 5.1.

Where separate adjustable controls exist, such

as AGC, gain or output controls, which will

influence the shape and other characteristics of the

steady-state input/output graph, it is recommended

that input/output graphs be plotted, when useful,

for various additional stated setting of such

controls

6 Dynamic output characteristics

6.1 Characteristics to be measured

The purpose of this test is to determine the dynamic

characteristics of the AGC circuit, particularly

attack and recovery times It should be emphasized

that all these characteristics will depend on test

frequency as well as on such factors as signal level,

control settings and battery voltage

6.2 Methods of measurement

6.2.1 Dynamic output characteristics for

speech levels

At the maximum setting of the gain control an input

signal of 1 600 Hz or 2 500 Hz when appropriate

with a sound pressure level of 55 dB is applied Any

adjustable gain control after the AGC loop shall be

adjusted in such a manner that overload of the

hearing aid is avoided

This signal is modulated by a square envelope pulse

raising the input level by 25 dB The pulse length

shall be at least five times longer than the attack

time being measured If more than a single pulse is

applied, the interval between two pulses shall be at

least five times the longest recovery time being

measured

NOTE 1 This test may be carried out at various control settings

as stated in Sub-clause 5.2.

NOTE 2 If lower gain control settings are applied, the method

of obtaining these settings shall be clearly specified.

NOTE 3 The loudspeaker employed for the measurement of

dynamic output characteristics as in Clause 6 must be

NOTE 4 The output signal should be monitored on a device such as an oscilloscope, the time constants of which are considerably shorter than those being measured.

NOTE 5 When very short response times are to be measured, the response time of the source shall be reported.

NOTE 6 For half-wave rectifying AGC circuits, the attack time

is dependent upon the polarity of the first half wave of the test signal after the onset of the modulating square wave envelope Depending upon the polarity, a shorter or longer attack time will occur This is best demonstrated in the case of an instantaneous rise in the amplitude occurring at a zero crossing of the test signal.

6.2.2 Dynamic output characteristics for high level input

At the maximum setting of the gain control an input signal of 1 600 Hz or 2 500 Hz when appropriate with a sound pressure level of 60 dB is applied Any adjustable gain control after the AGC loop shall be adjusted in such a manner that overload of the hearing aid is avoided This signal is modulated by

a square envelope pulse raising the input level

by 40 dB The pulse length shall be at least five times the attack time observed

If more than a single pulse is applied, the interval between two pulses should be at least five times the longest recovery time being measured

NOTE See Notes 1 to 6 of Sub-clause 6.2.1.

7 Non-linear distortion

7.1 Transients

The signal may be distorted during the attack time and recovery time by transients as well as by unwanted low-frequency modulation caused by instabilities The effect of these phenomena on the listener is not sufficiently understood to allow a recommendation for measuring transient distortions to be made

7.2 Harmonic distortion 7.2.1 Characteristics to be specified

The purpose of this test is to determine the harmonic distortion as a function of the input sound pressure level after steady-state conditions have been reached

7.2.2 Methods of measurement

Harmonic distorsion is measured in accordance with the test procedure described in

IEC Publication 118-0

NOTE This test may be carried out at various control settings

as mentioned under Sub-clause 5.2.

7.3 Intermodulation distortion

Intermodulation distortion is measured in accordance with the test procedure, described

in IEC Publication 118-0

EN 60118-2:1995

8 Effect on steady-state and dynamic

performance with respect to variation

in battery or supply voltage

In accordance with IEC Publication 118-0,

Sub-clause 7.8, it is recommended that the change

in the following performance parameters be tested

with respect to variation in battery or supply

voltage: steady-state input/output graphs as

mentioned in Clause 5, dynamic-output

characteristics, attack and recovery times as

mentioned under Clause 6, and non-linear

distortion as mentioned in Clause 7.

9 AGC activated frequency response

of hearing aids with a single

channel AGC circuit in operation

using pure tone signals

9.1 Introduction

9.1.1 Measurement below the AGC threshold

It is important to know the frequency response of

hearing aids when the automatic gain control is

active Measurements carried out in accordance

with 7.4 of IEC 118-0 can be employed, provided

that the input signal levels at all measuring

frequencies are below the AGC thresholds

9.1.2 Measurement above the AGC threshold

When measurements are taken above the AGC

threshold with moderately slow scanning speeds

and the attack and decay times in current use, they

can be considered at any frequency as steady-state

measurements

From the set of comprehensive frequency response

curves obtained using this method of measurement,

a steady-state input/output graph can be

constructed for any frequency

9.2 General conditions

Throughout this standard all sound pressure levels

specified refer to 20 4Pa When appropriate, sound

pressure level will be abbreviated SPL

NOTE Throughout the standard, reference is made to the use of

acoustic input However, when appropriate, additional

measurements may be made with electromagnetic or electric

inputs in accordance with IEC 118-1 and IEC 118-6.

Test results obtained by the substitution method

(see 4.2 of IEC 118-0) shall be considered basic.

9.3 Test equipment

The test equipment shall comply with clause 5

of IEC 118-0 Figure 3 and Figure 4 give schematic

illustrations of the measuring equipment

A tracking bandpass filter, centred at a centre

frequency fc, shall be inserted in the measuring system The 3 dB bandwidth shall not be greater than 10 % of the centre frequency, and the 20 dB bandwidth shall not be greater than 20 % of the

centre frequency For frequencies higher that 4 fc or

less than fc/4,fc being the centre frequency, the attenuation shall be greater than 40 dB For

frequencies higher than 8 fc or lower than fc/8, the attenuation shall be equal to or greater than 60 dB

NOTE In certain cases it may be necessary to use a filter with

an attenuation higher than 40 dB or 60 dB, respectively, in order not to increase the frequency range relative to the activating frequency where no reliable results can be obtained.

When automatic swept frequency recording using a compressor system to maintain a constant input sound pressure level is employed, a second tracking bandpass filter complying with the specifications given above shall be inserted in the feed-back loop

NOTE When synchronizing the tracking bandpass filter to the swept frequency, consideration should be given to the influence of the transmission time from the sound source to test point, the bandwidth of the filter and the scanning speed.

Alternatively, a band rejecting filter tuned to the AGC activating signal frequency and having an attenuation equal to or greater than 50 dB at the

centre frequency (fc) may be employed For

frequencies greater than 1,05 fc or less than fc/1,05, the attenuation shall be less than 3 dB

9.4 Test conditions

The AGC control should be set for maximum AGC effect (i.e lowest AGC threshold) Otherwise the test conditions shall comply with the specifications

stated in clause 6 of IEC 118-0, as applicable, The

settings shall be stated

9.5 Measurement

Data should be quoted for that part of the frequency range between 200 Hz and 8 000 Hz over which the output of the hearing aid falls by at least 10 dB when the signal sources are switched off

9.5.1 Determination of the operating range of the AGC

Test procedure

a) Adjust the gain control to full on and set other

controls in accordance with 9.4 of this standard.

b) Apply a sinusoidal input signal and vary its frequency, keeping the input SPL constant

at 50 dB, 60 dB, 70 dB, 80 dB and 90 dB or until the AGC threshold has been exceeded

c) Plot the output SPL versus frequency at a constant input SPL for each of the input sound pressure levels