V1.0 - 20050426 Telecommunications Industry AssociationTR41.3-05-11-XXX.

v1.0 - 20050426

Document Cover Sheet

Project Number PN-3-0219

Document Title Digital Cordless Phone and Hearing Aid Interference: Subjective and Objective Studies

Source RERC on Telecommunications Access

Contact Name: Linda Kozma-Spytek Complete Address: Gallaudet University, 800 Florida Ave, NE, Washington DC 20002

Phone: 202-651-5676 Fax: 202-651-5476 Email: [email protected]

Distribution TR-41.3

For Incorporation Into TIA Publication X For Information

Intended Purpose of Document (Select one) Other (describe) -

The document to which this cover statement is attached is submitted to a Formulating Group or sub-element thereof of the Telecommunications Industry Association (TIA) in accordance with the provisions of Sections 6.4.1–6.4.6 inclusive of the TIA Engineering Manual dated March 2005, all of which provisions are hereby incorporated by reference.

Abstract

Provide abstract of document here.

This power point presentation includes: 1) results from a statistical analysis of subjective ratings data on digital cordless phone and hearing aid interference obtained during the 2005 SHHH convention and 2) partial, preliminary results from an in-progress, objective study of the output of hearing aids coupled to digital cordless phones.

Telecommunications Industry Association TR41.3-05-11-XXX

Digital Cordless Phone and Hearing Aid Interference:Subjective and Objective

Studies

Linda Kozma-SpytekRERC on

Telecommunications Access

Phone Selection Select cordless phones that produce varying amounts of

interference at the output of hearing aids coupled in microphone and telecoil modes

Select cordless phones that represent current off-the-shelf models as well as solution phones from different manufacturers

Select cordless phones that represent current digital transmission frequencies and technologies (i.e., 2.4 & 5.8 GHz; DSSS & FHSS)

FHSS DSSS

2.4 GHz 4

5.8 GHz 1 3

Microphone(dB SPL)

Telecoil(dB SPL)

Solution Phone A 0, -1 -1, 2

Off the Shelf Phone B 1, 2 3, 5

Solution Phone C -2, 1 5, 6

Solution Phone D 1, 2 7, 7

Off the Shelf Phone E -1, 2 8, 10

Off the Shelf Phone F 2, 2 9, 12

Off the Shelf Phone G 0, 1 14, 15

Off the Shelf Phone H 1, 4 18, 19

Differences between the RMS output of two digital BTE hearing aids alone and when coupled to test phones on a live call/no signal

Participants:• 5 HA Microphone users; 27 HA Telecoil users

Stimuli:• long recorded phone conversation between a male and female speaker• hearing aid and/or telephone VC was adjusted in order to achieve a comfortable listening level for speech using the preferred ear for telephone listening

Procedure:• One training run using the corded, landline control phone with a rotary dial handset VC• Randomized presentation of the control and test phones• For each phone condition, participants rated their listening experience on 4 scales

• Loudness of Speech(7 pt scale; 1=inaudible, 4=comfortably loud, 7=too loud)

• Intelligibility - %age of words understood in the conversation(5 pt scale; 1=<20%; 3=41-60%; 5=>80%)

• Annoyance due to Interference(6 pt scale; 0=no interference, 3=annoying, 5=unbearable)

• Usability (4 pt scale; 1=highly usable, 4=not usable)

• For each phone condition, participants were asked whether they would purchase the phone under test given the amount of interference perceived

Test Friedman Friedman Friedman Friedman Cochran

Scale Loudness Intelligibility Interference Usability Purchase

Mic(n=5)

.293 .052 .229 .127 .912

Telecoil(n=27)

.000** .000** .000** .000** .000**

Overall Significance of Phone

for HA Mic & Telecoil Users

**sig. (p<0.01)

Loudness Intelligibility Interference Usability Purchase

Phone A 0.01 0.00 0.03 0.00 0.32

Phone C 0.32 0.13 0.00 0.03 0.00

Phone D 0.10 0.00 0.00 0.03 0.00

Phone E 0.00 0.00 0.00 0.00 0.00

Phone F 1.00 0.00 0.00 0.00 0.00

Phone G 0.76 0.00 0.00 0.00 0.00

Phone B 0.00 0.00 0.00 0.00 0.00

Phone H 0.00 0.00 0.00 0.00 0.00

sig. (p<0.01) Friedman Friedman Friedman Friedman Cochran

Significance Results for Pairwise Comparisons between the Control Phone and Each Test Phone

0%

20%

40%

60%

80%

100%

Soft - Inaudible Comfortably Loud Loud - Too Loud

** ** **

Loudness Ratings by Phone

** = sig. different from Control phone (p<0.01)

0%

20%

40%

60%

80%

100%

control phoneA

PhoneC

PhoneD

PhoneE

PhoneF

PhoneG

PhoneB

PhoneH

<40% 40-60% > 60%

**

****

** ** ****

Intelligibility Ratings by Phone

** = sig. different from Control phone (p<0.01)

0%

20%

40%

60%

80%

100%

No Interference Not Annoying Mildly Annoying Annoying - Unbearable

Ratings of Annoyance due to Interference by Phone

** **

** ** **

**

**

** = sig. different from Control phone (p<0.01)

0%

20%

40%

60%

80%

100%

Control PhoneA

PhoneC

PhoneD

PhoneE

PhoneF

PhoneG

PhoneB

PhoneH

No Interference - Not Annoying Mildly Annoying Annoying - Unbearable

** **

** ** ** **

Ratings of Annoyance due to Interference by Phone

** = sig. different from Phones C&D (p<0.01)

0%

20%

40%

60%

80%

100%

Control PhoneA

PhoneC

PhoneD

PhoneE

PhoneF

PhoneG

PhoneB

PhoneH

Highly Usable Minor Limitations Major Lim. - Unusable

Usability Ratings by Phone

no sig. difference

** = sig.<0.01Usability x Loudness

Usability x Intelligibility

Usability x Interference

Wireline 0.207 0.639** 0.158

Phone A 0.616** 0.734** 0.276

Phone C 0.671** 0.839** 0.744**

Phone D 0.441 0.538** 0.496**

Spearman Correlations for Usability Ratings

0%

20%

40%

60%

80%

100%

yes

no

Purchase Decision by Phone

** ** ** **

**

** **

** = sig. different from Control phone (p<0.01)

0%

20%

40%

60%

80%

100%

No Interference - NotAnnoying

Mildly Annoying Annoying -Unbearable

yes

no

7% - yes

93% - no

77% - yes

23% - no

Purchase Decision as a Function of Interference Rating

Data for the sample of HA users tested suggest that:

1) cordless telephone interference is likely to be primarily a baseband magnetic problem affecting hearing aid telecoil users

2) the annoyance ratings and purchase decisions due to interference by hearing aid telecoil users for Phone A are not significantly different from those of the control phone

3) the solution implemented in Phone A either eliminates perceived interference or reduces perceived interference to a level that is detectable, but not annoying for hearing aid telecoil users

4) an objective measure correlating to an interference rating of 1 (Not Annoying – I can detect interference but it is not at all annoying.) would establish a performance requirement for cordless telephones that will produce a subjective experience with regard to interference equivalent to landline corded phones

5) Phone A provides evidence for the technical feasibility of designing a digital cordless phone to meet this performance requirement

ANSI C63.19 E-Field/H-Field

Frequency Range (MHz) 1800 - 2100

Dipole Position Tip Center

Hearing Aid 1 (D/ITE) M4 M4

Hearing Aid 10 (D/ITE) M4 M4

Hearing Aid 8 (D/ITE) M3 M3

Hearing Aid 5 (D/BTE) M3 M3

Hearing Aid 9 (D/BTE) M2 M2

Hearing Aid 7 (D/BTE) M2 M2

Hearing Aid 2 (A/ITE) M1 M2

Hearing Aid 3 (DP/BTE) Failed Failed

Hearing Aids BTE ITE

Analog 0 1

Digitally Programmable

1 0

Fully Digital 3 3

Objective Testing

Objective MeasurementsCharacterize hearing aid output when coupled to

the control and test phones Hearing Aids (programmed/constant VC)

Microphone & Telecoil coupling modes Phones (normal use position re HA)

Off, Minimum VC & Maximum VC Measures (w/o speech through phones)

RMS (dB SPL) Spectrum

Measures (w/ speech through phones at Min. VC only) SIR

Replications for select conditions

Preliminary results from the objective measures suggest:

Cordless telephone interference appears to be primarily an audioband magnetic problem for hearing aids in telecoil coupling mode.

However, it appears that for some hearing aids with very low RF immunity (i.e., M1 or poorer re ANSI C63.19 in the high band), interference may be generated in hearing aids using microphone coupling.

Considerations re the development of the in-band magnetic noise standard for telephone wireless handsets:

1) Implementation of the standard by industry

2) Product identification/labeling

3) Dissemination of information for consumers and consumer organizations

4) Participation in C63.19

5) Monitoring new/emerging technologies for the potential to produce interference in hearing aids – either in-band magnetic or RF generated

This research was supported by the Rehabilitation Engineering Research Center on

Telecommunications Access. The RERC on Telecommunications Access is a joint project of the Trace

Center, University of Wisconsin, and the Technology Access Program, Gallaudet University. The RERC is

funded by the National Institute on Disability and Rehabilitation Research in the U.S. Department of

Education, under grant number H133E040013.  However, the opinions and content are those of the grantees and do

not necessarily represent the policy of the U.S. Department of Education.