NIDRR – Gallaudet Research Update

1. NIDRR – Gallaudet Research Update Hearing Aid (HA) and Cochlear Implant (CI) users provided subjective ratings of usability for speech-to-interference ratios (SIRs) presented in a single-interval, forced-choice adaptive procedure. The subjective rating categories were developed to correspond to the usability category ratings of ANSI C63.19, as set forth in its Sections 7 and 7.2.

2. The specific category descriptions for each SIR judgment were: 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.

3. Two types of calibrated A-weighted test signals were employed: telephone voice-band speech and wide-band interferer noise. The speech employed during the testing was the same as used by Nabelek, et al. (2006) for the Acceptable Noise Level test procedure. It consists of a reading of a descriptive travelogue of the Arizona area by one male talker. 

4. The interferer noises were generated from simulations of the RF signal envelope for three common digital wireless transmission technologies. These wide-band noises were paired with telephone voice-band speech samples coded to match the noise types, according to each technology’s specification. The specific speech and noise source pairs used were: AMR MR12.2 codec with GSM (J-STD-007) AMR MR12.2 codec with UMTS (T1/T1P1/3GPP) EVRC codec with CDMA (TIA/EIA/IS 2000)

5. The speech was presented through a direct audio input connection for HA users and in the soundfield for CI users at the subject’s Most Comfortable Listening Level (MCL). MCL was determined using a manual procedure in which the level of the speech was adjusted up and down until the participants responses converged on the mid-point (i.e., “comfortable” rating) of a 7-point loudness scale.

6. With the speech at MCL, the level of the interferer was varied adaptively in order to find the SIRs corresponding to the boundaries between the four ANSI C63.19 usability categories. Three adaptive searches were performed simultaneously with trials for the boundaries randomly interleaved. Testing continued until four reversals per boundary were obtained. For each noise type, the audibility threshold in the presence of speech was determined through the use of an automated, adaptive up-down procedure. The threshold search continued until four reversals were obtained.