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v1.0 - 20050426 D ocum entC over Sheet ProjectN um ber PN -3-X X X X (leave blank ifunknow n ornotapplicable) D ocum entTitle Prelim inary ResultsofH LA A 2006 Subjective Testing forH earing A id – Cordless Phone M agnetic Com patibility Requirem ents Source S. Julstrom (Etym otic Research), L. K ozm a-Spytek (RERC Telecom Access), and S. Isabelle (M otorola) C ontact N am e:Linda K ozm a-Spytek Com plete A ddress:G allaudetU ;RERC Telecom A ccess/Tech. A ccess Program ;800 Florida A ve, N E; W ashington, DC 20002 Phone:202-651-5676 Fax: 202-651-5476 Em ail: Linda.kozm [email protected] D istribution TR-41.3.9 ForIncorporation Into TIA Publication X ForInform ation Intended Purpose ofD ocum ent (Selectone) O ther(describe)- The docum ent to w hich this cover statem ent is attached is subm itted to a Form ulating G roup or sub-elem entthereofofthe Telecom m unications Industry A ssociation (TIA )in accordance w ith the provisionsofSections6.4.1–6.4.6 inclusive ofthe TIA Engineering M anualdated M arch 2005, allof w hich provisionsare hereby incorporated by reference. A bstract Results of the HLAA 2006 subjective testing are sum m arized including inform ation on hearing aid telecoilorientations and ranges ofuser-prefered telecoilm agnetic signallevels and S/N ratios to inform the developm entofhearing aid/cordlessphone m agnetic com patibility requirem ents. Telecommunications Industry Association TR41.3-06-08-009-L
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V1.0 - 20050426 Telecommunications Industry AssociationTR41.3-06-08-009-L.

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Page 1: V1.0 - 20050426 Telecommunications Industry AssociationTR41.3-06-08-009-L.

v1.0 - 20050426

Document Cover Sheet

Project Number PN-3-XXXX (leave blank if unknown or not applicable)

Document Title Preliminary Results of HLAA 2006 Subjective Testing for Hearing Aid – Cordless Phone Magnetic Compatibility Requirements

Source S. Julstrom (Etymotic Research), L. Kozma-Spytek (RERC Telecom Access), and S. Isabelle (Motorola)

Contact Name: Linda Kozma-Spytek Complete Address: Gallaudet U; RERC Telecom Access / Tech. Access Program; 800 Florida Ave, NE; Washington, DC 20002

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

Distribution TR-41.3.9

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

Results of the HLAA 2006 subjective testing are summarized including information on hearing aid telecoil orientations and ranges of user-prefered telecoil magnetic signal levels and S/N ratios to inform the development of hearing aid/cordless phone magnetic compatibility requirements.

Telecommunications Industry Association TR41.3-06-08-009-L

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ORIGINAL TEST PLAN GOAL: “In support of the Jan. 17, 2006 PINS, to determine the ranges of user-preferred telecoil magnetic signal levels and S/N ratios, according to the measurement specifications and criteria laid out in ANSI C63.19. Some additional information will be gained on hearing aid telecoil orientations.”

Preliminary Results: Subject Testing forHearing Aid – Cellphone/Cordless Phone

Magnetic Compatibility Requirements

S. Julstrom (Etymotic Research) L. Kozma-Spytek (RERC Telecom Access)

S. Isabelle (Motorola)

TESTING CONTINUATION: Following initial testing at Etymotic Research and the presentation of the initial results to the C63.19 working group, the number of test subjects was expanded from 12 to 57 with additional testing at Gallaudet University (n=19) and the 2006 HLAA convention (n=26). Two representative cordless phone interferences were added for the final HLAA round of testing.

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Perpendicular (Axial) Transverse (Radial 1) Longitudinal (Radial 2)

First Step: Measure the telecoil orientation.

Second Step: Choose the appropriate “magnetic hat”.

The test subjects first filled out an extensive questionnaire. Then . . .

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HA Telecoil Orientation Results:

Of 69 hearing aids tested for orientation•66 were BTE (behind-the-ear)•3 were ITE (in-the-ear)

Of the 57 subjects tested•The transverse hat (radial 1) was used 53 times.•The longitudinal hat (radial 2) was used 1 time.•The perpendicular hat (axial) was used 3 times.

65 of the 69 measured aids had orientations in the plane of the side of the head at some angle from the vertical; that is, in a radial, not axial orientation. The next slide shows a histogram of these radial angles, along with a graph showing that the vast majority of these are covered well by a transverse orientation field (parallel to the top of the handset). Only a couple of outliers respond primarily to a longitudinal field.

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Plane-of-Head HA Telecoil Orientations(64 BTE, 1 ITE)

0

2

4

6

8

10

12

14

-90 -75 -60 -45 -30 -15 0 15 30 45 60 75 90

degrees from vertical (positive is top angled forward)

freq

uen

cy o

f o

ccu

ren

ce

Relative Sensitivity to Transverse and Longitudinal Handset Telecoil Signals (assuming 25 degree handset angle from hor.)

-20

-15

-10

-5

0

5

-90 -75 -60 -45 -30 -15 0 15 30 45 60 75 90

HA telecoil degrees from vertical (positive is top angled forward)

dB transverse

longitudinal

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Magnetic signal source with perpendicular (axial), transverse (radial) and longitudinal (radial) components

HA telecoil with a vertical orientation

Relative sensitivity of HA telecoil (with a vertical orientation) to transverse radial component of magnetic field (with 25º handset angle from horizontal) is reduced ~1dB from maximum coupling

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Third Step: After finding the level of magnetic speech signal that matches a 65 dB-SPL acoustic speech signal for their hearing aid, the subject finds their preferred “most comfortable” magnetic telephone coupling level (MCL).

The graph below shows that the subjects preferred to magnetically match 65 dB-SPL speech.

Most Comfortable Magnetic Telephone Coupling Level compared to the 65 dB-SPL Acoustic Speech Matching Magnetic Level

0

5

10

15

20

25

-12.5 -10.0 -7.5 -5.0 -2.5 0.0 2.5 5.0 7.5 10.0 12.5

MCL - acoustic matching level (dB)

Fre

qu

en

cy

of

se

lec

tio

n

Note: The -12.5 dB outlier came from the test subject who required the second strongest magnetic signal to match 65 dB-SPL, a level that would definitely result in hearing aid magnetic input overload. Reducing the magnetic signal well below that level apparently resulted in a more “comfortable” level (presumably less distorted).

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Fourth Step: In addition to choosing a magnetic level to match 65 dB-SPL acoustic speech and a preferred MCL, the subjects also choose minimum and maximum acceptable magnetic speech levels. All this data is summarized in the graph below, which shows how far the MCL is above (white bars) or below (black bars) the 65 dB matching level and the range of acceptable levels.

Evidently, hearing aids in the field have widely varying telecoil sensitivities in relation to their microphone sensitivities.

57 Test Subject's Magnetic Speech Level Rangesin order of ascending 65 dB-SPL level match

-50

-40

-30

-20

-10

0

10

1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35 37 39 41 43 45 47 49 51 53 55 57

dB

(A/m

)

65 dB SPL Match Max Accept. Min Accept. MCL

-18 dB A/m (ANSI C63.19)

-25 dB A/m (ANSI 3.22)

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Fifth Step: For each noise type, the subjects select their noise tolerances for the clearly defined “usable”, “normal use”, and “excellent performance” categories and the tester finds their objective noise-in-the-presence-of-speech threshold.

Instructions for Magnetic S/N Tests

Excellent Performance - You would find a phone with this level of noise to be highly usable. You would have no complaints about this amount of noise for extended phone calls.

Acceptable for Normal Use – You would find this level of noise to be acceptable for normal, regular use of a phone. You would accept this amount of noise for an extended phone call without becoming tense or tired.

Usable for a Brief Call - With this level of noise you could successfully complete a brief phone call. However, you would not accept this amount of noise for normal, regular phone use.

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Speech SourcesAMR MR12.2 codecAMR MR12.2 codecAMR MR12.2 codecEVRC codecAMBE++ codec

AMR MR12.2 codecVSELP codec

ADPCM codec (32kb/s)

ADPCM codec (32kb/s)

Noise Sources100 Hz, 20% DC (Training)

GSM (J-STD-007) UMTS (T1/T1P1/3GPP)

CDMA (TIA/EIA/IS 2000) iDEN

DisplayTDMA (TIA/EIA-136)

FHSSDSSS

n5757575757

3130

2626

Note: Time intermittency effects of the interference were not considered. All noise types were presented as continuous interfering signals.

Test Stimuli

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S/N Results

To most directly address the standards’ S/N requirements, the results can be viewed as the ratio of MCL to the category noise rating levels. In interpreting these S/N numbers, it is important to remember that the signal (MCL) levels are average speech levels measured per ITU P.56. These levels are typically ~15 dB lower than the signal level as measured per FCC Part 68. The noise levels are the 1 kHz equivalent A-weighted telecoil response levels.

There is considerable subject-to-subject variation in the S/N category boundary judgments. This variability is smoothed by displaying the results as a cumulative distribution.

The following graph shows the results plotted this way for the “normal use” category. The other categories show similar results, but shifted up or down.

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Some differences among the noise types are apparent. The cordless modulation noises, at least with the relatively small sample of subjects tested, seem to require S/N’s similar to the cellphone noise types with the higher S/N requirements.The fact that the various noise types do not all show the same measured S/N needs indicates that the present noise measurement (A-weighting) does not fully account for the subjective annoyance characteristics of a given noise type. For example, the noise measurement underestimates the annoyance of cordless types and UMTS, and overestimates that of TDMA and display noise. While A-weighting may be a good first step towards the proper subjective level modifier, it probably is not the final answer. If the ideal noise measurement parameters could be found that accurately modeled noise annoyance and audibility, all the noise types, including future ones, would plot the same.

Minimum S/N for a "Normal Use" Rating

-10

0

10

20

30

40

50

60

0% 20% 40% 60% 80% 100%

subjects meeting criteria

S/N

- d

B

Display

CDMA

GSM

iDEN

TDMA

UMTS

DSSS

FHSS

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This graph plots the average cumulative distributions for the six cellphone noise types and the two cordless noise types. (Display noise is lumped in with the cellphone noise types, although it is potentially relevant for cordless, too.)

Average Minimum S/N Across Cellphoneand Cordless Phone Noise Types

-10

0

10

20

30

40

50

60

0% 20% 40% 60% 80% 100%

subjects meeting criteria

S/N

- d

B

Cellphone "usable"

Cellphone "normal use"

Cellphone "excellentperformance"

Cellphone Speech (MCL)to Threshold Ratio

Cordless "usable"

Cordless "normal use"

Cordless "excellentperformance"

Cordless Speech (MCL)to Threshold Ratio

From the far right of the graph, it can be seen that some subjects “required” S/N’s greatly in excess of their objective noise threshold S/N’s. (For whatever reason, they felt they needed to turn the “noise” knob way down.) Allowing for that oddity, a S/N requirement of 30 dB (45 dB with signal measured per Part 68) does not appear out of line.

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Summary:• The overwhelming majority of hearing aids tested had a generally vertical

orientation, emphasizing the importance of testing the transverse orientation (radial 1; parallel to the top of the handset). A phone should produce this field with good quality when positioned normally.

• The preponderance of subjects prefer their magnetic level at a 65 dB-SPL equivalent. The magnetic level to achieve that varies widely among hearing aids, but the C63.19 established -18 dB(A/m) minimum should cover all the reasonably adjusted ones, with some margin.

• 30 dB S/N (45 dB with signal measured per Part 68) is a justifiable minimum requirement (with the noise level measured A-weighted).

• A-weighting is a good start as a subjective noise level modifier, but there is still enough variation among the various noise types to justify looking for a better or more complete future calculator of annoyance/audibility.

• Noise tolerance is related to noise audibility threshold, independent of noise type or the subject’s hearing dynamic range. (Discussed more in the additional material following.)

Note: This is a preliminary presentation of results and is not intended for wider distribution or publication at this time. A formal paper is planned.

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Addendum: Relationship of noise tolerance to noise audibility threshold Analysis of the results showed that noise tolerance for the various category ratings for a given noise type is directly related to the subjects' noise audibility threshold for that noise type, but not to any other evident characteristic of the noise type or, surprisingly, to the subject’s hearing dynamic range to any significant degree (as represented by their MCL to threshold ratio).

In relation to the objective noise threshold, there is no significant difference among the noise types, no matter how their levels are measured. This can be clearly seen by re-visiting the “normal use” cumulative distribution graph, but now plotting in terms of the ratio of the rated category noise level to the objective noise threshold.

Maximum Noise-to-Threshold Ratiofor a "Normal Use" Rating

-30

-20

-10

0

10

20

30

40

0% 20% 40% 60% 80% 100%

subjects meeting criteria

dB

Display

CDMA

GSM

iDEN

TDMA

UMTS

DSSS

FHSS

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That the ratios of the category ratings to the objective noise threshold shows little, if any correlation to the subject’s hearing dynamic range can be seen by plotting the individual subject’s ratios, ordered by their dynamic range (MCL to threshold ratio).

(Subject responses placing some of their “requirements” well below their objective noise threshold are clearly evident in the graphs.)

The slopes of the trend lines are near zero, showing a consistent relationship to the noise threshold, but little relationship to the MCL above threshold.

Speech (MCL) and Noise to Threshold RatiosDSSS Noise

-30

-20

-10

0

10

20

30

40

1 6 11 16 21 26

ordered test subjects

dB

speech (MCL)

"usable"

"normal use"

"excellent performance"

Linear ("usable")

Linear ("normal use")

Linear ("excellentperformance")

Speech (MCL) and Noise to Threshold RatiosCDMA Noise

-30

-20

-10

0

10

20

30

40

1 6 11 16 21 26 31 36 41 46 51 56

ordered test subjects

dB

speech (MCL)

"usable"

"normal use"

"excellent performance"

Linear ("usable")

Linear ("normal use")

Linear ("excellentperformance")

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Speech (MCL) or Noise to Threshold RatioDSSS Noise

0

2

4

6

8

10

-35

-30

-25

-20

-15

-10 -5 0 5

10

15

20

25

30

35

40

45

50

dB

fre

qu

en

cy Speech (MCL)

"usable"

"normal use"

"excellent performance"

Speech (MCL) or Noise to Threshold RatioCDMA Noise

02468

101214

-35

-30

-25

-20

-15

-10 -5 0 5 10 15 20 25 30 35 40 45 50

dB

freq

uen

cy

Speech (MCL)

"usable"

"normal use"

"excellent performance"

The two graphs at the right are histograms of the ratio of the subjects’ rating responses (MCL or noise) to their objective noise thresholds, for two representative noise types.

They illustrate that the category noise ratings maintain a consistent average relationship to the noise threshold across noise types, even in the midst of significant subject variability.

The similarity of the graphs is evident.

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With all eight noise types added in, the resultant smoother, more “bell-like”, the curves are matched here with best-fit normal distribution curves. These latter curves discount the influence of the extreme negative outlier data points far below objective threshold.

The lower graph shows the consistency among noise types of the means and standard deviations of the noise category boundary ratings relative to noise threshold.

A reasonable judgment for the three noise categories could be that for "excellent performance", the noise should not be greater than noise threshold (i.e., inaudible); for "normal use", ~4 dB above threshold; and for "usable", ~10 dB above threshold.

Speech (MCL) and Noise to Threshold RatiosAverages and Standard Deviations

-20

-10

0

10

20

30

40

Dis

play

CD

MA

GS

M

iDE

N

TD

MA

UM

TS

DS

SS

FH

SS All

best

fit

Speech (MCL)

"usable"

"normal use"

"excellent performance"

Speech (MCL) or Noise to Threshold RatioTotal for All 8 Noise Types, with Best Fit

Normal Distribution Curves for Noise Ratios

0

10

20

30

40

50

60

-35

-30

-25

-20

-15

-10 -5 0 5

10

15

20

25

30

35

40

45

50

dB

fre

qu

en

cy

Speech (MCL)

"usable"

"normal use"

"excellent performance"

mean 10, std.dev. 6

mean 4, std. dev. 4

mean 0, std. dev. 3