ETSI ETS 300 488 ed.1 (1996-01)

SLOVENSKI STANDARD
SIST ETS 300 488 E1:2003
01-december-2003
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Terminal Equipment (TE); Telephony for hearing impaired people; Characteristics of

telephone sets that provide additional receiving amplification for the benefit of the

2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

Copyright Notification: No part may be reproduced except as authorized by written permission. The copyright and the

Whilst every care has been taken in the preparation and publication of this document, errors in content,

typographical or otherwise, may occur. If you have comments concerning its accuracy, please write to

"ETSI Editing and Committee Support Dept." at the address shown on the title page.

Foreword .......................................................................................................................................................5

Introduction....................................................................................................................................................5

1 Scope ..................................................................................................................................................7

2 Normative references..........................................................................................................................7

3 Definitions and abbreviations ..............................................................................................................7

3.1 Definitions ............................................................................................................................7

3.2 Abbreviations .......................................................................................................................7

4 Sending characteristics .......................................................................................................................8

4.1 General ................................................................................................................................8

4.2 Sensitivity frequency response ............................................................................................8

4.3 Sending Loudness Rating....................................................................................................8

5 Receiving characteristics.....................................................................................................................8

5.1 General ................................................................................................................................8

5.2 Sensitivity frequency response ............................................................................................8

5.3 Receiving Loudness Rating .................................................................................................8

5.4 Restoring normal receive amplification................................................................................9

6 Other characteristics ...........................................................................................................................9

6.1 Sidetone...............................................................................................................................9

6.2 Stability.................................................................................................................................9

6.2.1 Analogue and digital sets ................................................................................9

6.2.2 Additional stability test ...................................................................................10

6.3 Echo path loss ...................................................................................................................10

6.3.1 Echo Return Loss (ERL) ...............................................................................10

6.3.2 Weighted Terminal Coupling Loss (TCLw) ...................................................10

6.4 Distortion............................................................................................................................10

6.4.1 Sending .........................................................................................................10

6.4.2 Receiving.......................................................................................................10

6.4.3 Sidetone ........................................................................................................10

6.4.4 Sending power handing capability.................................................................10

6.4.5 Receiving power handling capability .............................................................11

6.5 Noise..................................................................................................................................11

6.5.1 Sending .........................................................................................................11

6.5.2 Receiving.......................................................................................................11

6.6 Acoustic shock...................................................................................................................11

7 Testing methods................................................................................................................................11

7.1 Analogue telephones .........................................................................................................11

7.2 Digital telephones ..............................................................................................................12

7.3 Summary of test methods..................................................................................................13

Annex A (normative): Packaging, labelling and user instructions .........................................................14

A.1 Packaging and labelling ....................................................................................................................14

A.2 User instructions................................................................................................................................14

A.3 Product suppliers information............................................................................................................14

Annex B (informative): Bibliography........................................................................................................15

History......................................................................................................................................................... 16

This European Telecommunication Standard (ETS) was produced by the Terminal Equipment (TE)

Technical Committee of the European Telecommunications Standards Institute (ETSI).

This ETS specifies the requirements for telephones with receive amplification intended to aid the hearing

impaired. A significant proportion of the population is disabled by varying degrees of hearing loss, often

associated with a reduction of speech discrimination ability. Amplification can only replace the lost

The group most likely to receive the greatest benefit from the use of a telephone with additional receive

amplification are those with moderate to severe hearing losses in the range of 35 dB to 80 dB.

In setting the numerical values in this ETS, consideration has been given to the fact that the sound

pressure levels at the ear during a telephone conversation can be up to 30 dB above those occurring in

normal face-to-face conversation (at 1 metre distance). As hearing impaired people do not necessarily

have elevated thresholds of loudness discomfort, some form of output limitation will be required. Recent

work has indicated that Automatic Gain Control (AGC) may provide a better means of limitation than peak

clipping. In addition, it is recognized that in order to give maximum intelligibility to some hearing impaired

Two types of application are envisaged. Firstly, where the telephone is to be used in the main by a hearing

impaired person, secondly where it will be used by persons with a range of hearing acuity. In the first case

it will be advantageous to maintain the receive amplification (the level of which is selected by means of a

volume control set by the hearing impaired user) when the handset is replaced. In the second, it may be

preferable to arrange that the additional amplification is brought into use by the operation of a latching

switch that automatically resets the gain to nominal level when the handset is replaced in its rest position.

The use of voice switched attenuation, perhaps 10 dB to 12 dB, may be necessary to provide protection

against instability, in particular for the first case, and could also improve the discrimination against the

It is estimated that with the provision of additional amplification to the levels recommended below, possibly

up to 80 % of hearing impaired users would benefit even when not using their hearing aids to couple to the

telephone set. If a hearing aid is worn in addition and inductive coupling is also provided, then the

proportion of hearing impaired users who will be able to have satisfactory telephone conversations will

increase further. It is, however, pointed out that with a high gain setting selected, the sound level and/or

inductive field at the earphone may be considerably higher than normally experienced by hearing aid

microphones and/or inductive pick-up coils and, on short telephone connections in particular, there is a

very real possibility of overloading the input stages of the hearing aid. For this reason, this ETS permits

the Receiving Loudness Rating (RLR) to be adjusted to be quieter than the requirements of the relevant

The inclusion of additional receiving amplification does not reduce or replace existing technical standards

that apply to a handset. Additional receiving amplification may be combined with other additional

functionality, such as inductive coupling or additional earpieces, provided specifically for people with

This ETS specifies the electro-acoustic performance characteristics of telephony terminals which are

intended for direct application to the ear (e.g. traditional handsets, operators' headsets) and which

provide, at the earphone, additional amplification in the receiving direction compared with the Receiving

This ETS applies to telephony terminals that can be connected to the Public Switched Telephone

Network (PSTN) or the coincident S and T reference point of the basic access of the Integrated

Hands free or loudspeaking devices and extra amplification in sending for the benefit of people having

This ETS incorporates by dated and undated reference, provisions from other publications. These

normative references are cited at the appropriate places in the text and the publications are listed

hereafter. For dated references, subsequent amendments to or revisions of any of these publications

apply to this ETS only when incorporated in it by amendment or revision. For undated references the latest

additional receiving amplification: A facility provided in a terminal whereby the gain in the receiving

direction from telephone line to ear may be increased (or decreased), relative to that required by the

relevant terminal standard, for the purpose of enabling the user to select, within certain limits, his/her

relevant terminal standard: A standard which would apply if the terminal concerned did not provide

voice switching: A process of automatically inserting attenuation into either the send or receive path (e.g.

The sending characteristics shall meet the requirements of the relevant terminal standards both with and

When in the sending condition, the sending sensitivity frequency response shall fulfil the requirements of