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Interference in Hearing Aids from Digital Wireless Telephones: Improved Predictive Methods

Interference in Hearing Aids from Digital Wireless Telephones: Improved Predictive Methods. H. Levitt, M. Bakke, Kozma-Spytek, L., Verhoff, J. Gallaudet University. Subjects. Number: 40 minimum in a balanced design Criteria for inclusion: Hearing aid wearer, uses cell phone,

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Interference in Hearing Aids from Digital Wireless Telephones: Improved Predictive Methods

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  1. Interference in Hearing Aids from Digital Wireless Telephones: Improved Predictive Methods H. Levitt, M. Bakke, Kozma-Spytek, L., Verhoff, J. Gallaudet University

  2. Subjects • Number: 40 minimum in a balanced design • Criteria for inclusion: • Hearing aid wearer, • uses cell phone, • age will not be a criterion for inclusion • Recruitment: • local hearing centers, • by newspaper advertisements, • HLAA e-newsletter • internet sites • Reimbursement: $12/hour or fraction thereof for participation.

  3. Stimuli • Stimuli: 5 forms of interference will be considered, 4 transmission technologies and 1 reference form of interference (HINT speech noise). • GSM (AMR, NB, Full Rate, 12.2 kb) • *iDEN • *CDMA (Full Rate) • UMTS (wideband CDMA, AMR, Full Rate, 12.2 kb) • * Waiting to hear from Kevin Butler from Sprint/Nextel regarding specific codec characteristics to use for iDEN and CDMA simulations

  4. Tests • Tests: Three computer tests will be administered • Threshold, • Boundary & • Speech Recognition

  5. Threshold Test • Simple adaptive procedure to determine the threshold S/N at which the subject is aware of noise. • The S/N will be adjusted accordingly until the specified number of reversal pairs has been obtained.

  6. Boundary Test • Adaptive procedure similar to the Threshold Test • Purpose: to determine the boundary SIR for different subjective ratings of sound quality • Trials for the 3 boundaries will be interleaved • Testing will continue until the specified numbers of reversals have been obtained for all 3 tests. • Using the categories from C63.19 • B1- Excellent Performance / Acceptable for normal use • B2 – Acceptable for normal use / Usable for a brief call • B3 – Usable for a brief call / Not usable

  7. Categories • 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. • NOT USABLE: With this level of noise, you would not be able to complete even a brief phone call. You could not accept this amount of noise for any type of phone use.

  8. Speech Recognition Test • Percent correct score for HINT test material at 2 fixed speech-to-interference ratios (SIRs) • SIRs correspond to best two boundaries (B1 and B2) • Direct-audio-input connection to Phonak behind-the-ear hearing aid fit to the subject’s hearing loss • Speech is prerecorded and passed through a codec or telephone band. • Codecs depend on type of technology (GSM, iDEN, CDMA & wideband CDMA).

  9. So far...

  10. Major issue at present • Choosing the best selection of parameters for technologies and codecs • Requests for information from industry have yielded some information • Information so far is incomplete

  11. Summary • 40 subjects with hearing loss • 4 technologies & reference noise • Tests • Thresholds • Boundaries between categories • Speech recognition for sentences • Problem: determining “best” parameters for technologies and codecs

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