v1.0 - 20050426

Document Cover Sheet

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

Document Title Report of magnetic speech level and S/N test methods and results for digital wireless speech and noise sources

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

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

Phone: 202-651-5676 Fax: 202-651-5476 Email: Linda.kozma@tap.gallaudet.edu

Distribution TR-41.N.n

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

The purpose of this experiment was 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. The slides describe the methods and results of the experiment in which digital wireless speech and noise sources were used.

Telecommunications Industry Association TR41.N.n-YY-MM-XXX

TEST PLAN GOAL: 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.

Test Plan 1S. Julstrom (Etymotic Research)

L. Kozma-Spytek (RERC Telecom Access) S. Isabelle (Motorola)

ParticipantsParticipation criteria: • must be adults, • must be daily hearing

aid users, • must use the telephone

(rather than TTY or Relay) regularly for most of their calls, and

• must primarily use the telecoil mode of their hearing aids for telephone calls.

Participant characteristics (n=12):• Age range: 40-79 years old (8F,

4M)• Hearing loss: 1 mild-moderate, 1

moderately severe, 7 severe, 2 profound, and 1 didn’t know

• Hearing aid use: >10 yrs.• Age of hearing aids: <6 yrs.• Hearing aid style: 11 BTEs, 1 ITE• Hearing aid type: 5 digital, 2

programmable, 5 analog• Voice telephone use: 10 daily, 2

several times a week• Speech over the Telephone: 3

Almost Completely Intelligible, 7 Mostly Intelligible, 2 Somewhat Intelligible

• Typical coupling mode: 10 t-coil, 2 w/o HA

(Note: The RF immunity of the hearing aids is not important for these tests since WDs or RF links are not used.)

Instrumentation

and

Test Set Up

Full-band speech at typical conversational level (~65 dB-SPL), with 200 Hz - 5 kHz pink noise recording at ITU-T P.56-measured level for level setting.

Vocoded speech at adjustable magnetic levels, with 1 kHz tone recording at the reference level for level measuring.

At center of circular coil:H(A/m) = N*I(A)/D(m)

Broadband noises at adjustable magnetic levels, with 1 kHz tone recording at their A-weighted, T-coil response levels for level measuring.

ACOUSTICREFERENCE

MAGNETICSPEECHSOURCE

MAGNETICNOISESOURCE

Signal Sources

Test Stimuli

Test Stimuli

Speech Sources• AMR MR12.2 codec• AMR MR12.2 codec• AMR MR12.2 codec• AMR MR12.2 codec• EVRC codec• VSELP codec• AMBE++ codec

Noise Sources• 100 Hz, 20% DC (Training)

• GSM (J-STD-007)

• UMTS (T1/T1P1/3GPP)

• Display• CDMA (TIA/EIA/IS 2000) • TDMA (TIA/EIA-136)

• iDEN

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

100 1 103

1 104

20

15

10

5

0

5

10

15

upper limitlower limit; fields exceeding -10 dB(A/m) at 1 kHzlower limit; fields between -10 and -13 dB(A/m) at 1 kHznominal optimum curve; 1st order rolloff corner = 1370 Hz

upper limitlower limit; fields exceeding -10 dB(A/m) at 1 kHzlower limit; fields between -10 and -13 dB(A/m) at 1 kHznominal optimum curve; 1st order rolloff corner = 1370 Hz

WD ABM1 |H| vs. Frequency

Frequency - Hz

Nor

mal

ized

|H| -

dB

100 1 103

1 104

20

15

10

5

0

5

10

15

Half-band integrated probe response; 1 kHz 1st order high-passNet speech response from nominal sourceHalf-band integrated probe response; 1 kHz 1st order high-passNet speech response from nominal source

Telecoil and Nominal Net Voice Response vs. Frequency

Frequency - Hz

Rel

ativ

e R

espo

nse

- dB

10 100 1 103

1 104

1 105

80

60

40

20

0

20

AweightdB freq q( )( )

freq q( )

Aweight f( )1.2589f

4

20.62

f2 1

f

12200

2

107.72

f2 737.9

2f

2

Perpendicular Transverse Longitudinal

Measuring Telecoil Orientation

Choosing the Source Orientation

Procedure for the Magnetic Matching Level Tests

Measure Telecoil Orientation.Select best orientation magnetic hat: 1 2 3Perpendicular Transverse Longitudinal

Subject adjusts hearing aid volume control for normal use in microphone mode with loudspeaker acoustic speech reference.

Apply magnetically coupled speech to hearing aid in telecoil mode at -25 dBA/m (nominal match to 65 dB-SPL).

Subject adjusts the magnetic level to subjectively match the 65 dB-SPL acoustic level.

Procedure for the Magnetic Speech Level Tests

Subject adjusts the magnetic speech level to their preferred, most comfortable listening level.

Subject then adjusts the magnetic speech level to their lowest acceptable level and highest acceptable level, with the order of these level adjustments counterbalanced across subjects.

Tester resets the magnetic level to the subject's previous MCL and reconfirms setting by having subject rate the speech on a loudness scale.

Instructions for the Magnetic Speech Level Tests

• Most Comfortable Speech Level – your preferred, most comfortable listening level for an extended telephone call.

• Minimum Acceptable Speech Level – the quietest setting you would consider usable for an extended telephone call.

• Maximum Acceptable Speech Level – the loudest setting you would readily tolerate for an extended telephone call.

Axial & Radial

Ambient Magnetic Noise LevelsEquivalent 1 kHz Field Srength (telecoil response)

-70

-65

-60

-55-50

-45

-40

-35

-30

dB

(A/m

)

C-weighted

A-weighted

Procedure for Magnetic S/N Tests

Tester uses adaptive procedure to find subject’s magnetic noise level threshold in the presence of the speech.

Select randomized noise source with corresponding speech source at MCL (1 of 6).

With speech at their self-selected MCL, the subject adjusts the magnetic noise level to:

their highest usable level, their highest normal use level,

their highest level for excellent performance.The level adjustments are accomplished in the order given above or

reversed with order counterbalanced across noise sources and subjects. Once each magnetic noise level adjustment is complete, subjects rate the

speech in noise on an annoyance scale and a usability scale.

Provide training for magnetic S/N tests.

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.

GSM Noise:Speech and Noise Levels for Minimum Category Ratings

-60

-50

-40

-30

-20

-10

0

10

1 2 3 4 5 6 7 8 9 10 11 12

dB(A

/m)

MCL speech

"usable" noise

"normal use" noise

"excellent performance" noise

noise threshold

ambient magnetic noise level

Minimum S/N for a "Usable" Rating

0

10

20

30

40

50

60

1 2 3 4 5 6 7 8 9 10 11 12

test subject

dB

Display

CDMA

GSM

iDEN

TDMA

UMTS

Minimum S/N for a "Normal Use" Rating

0

10

20

30

40

50

60

1 2 3 4 5 6 7 8 9 10 11 12

test subject

dB

Display

CDMA

GSM

iDEN

TDMA

UMTS

Minimum S/N for an "Excellent Performance" Rating

0

10

20

30

40

50

60

1 2 3 4 5 6 7 8 9 10 11 12

test subject

dB

Display

CDMA

GSM

iDEN

TDMA

UMTS

Signal (MCL) to Threshold Ratios

0

10

20

30

40

50

60

1 2 3 4 5 6 7 8 9 10 11 12

test subject

dB

Display

CDMA

GSM

iDEN

TDMA

UMTS

Minimum S/N Ratios (Each data point represents an average judgement

across the 6 noise types. For each performance category, these average S/N ratios are rank ordered from low to high.)

0

10

20

30

40

50

60

dB

"Usable"

"Normal Use"

"ExcellentPerformance"

Signal (MCL) toNoise ThresholdRatios

25

15

Lower Category Boundary needed to include:

Usable Normal Use Excellent Performance

70% of the observations

20 dB S/N 27 dB S/N 34 dB S/N

(30 dB S/Nθ) *

80% of the observations

23 dB S/N 29 dB S/N 37 dB S/N

(34 dB S/Nθ) *

90% of the observations

27 dB S/N 34 dB S/N 42 dB S/N

(37 dB S/Nθ) *

*Note: The effective limit for the excellent performance category is the threshold of audibility for the noise in the presence of the intended speech signal at the subject’s most comfortable listening level.

(n=71/performance category)

Minimum S/N Ratios