Digits in Noise Speech Reception Thresholds in Ambient Noise

The study was approved by the Committee for the Protection of Human Subjects, the Institutional Review Board at Dartmouth College (Hanover, NH). Twenty children and 20 adults were recruited. Those who self-reported having hearing loss or ear pathology were excluded. Written informed consent was obtained. The Digits in Noise (DIN) test was administered via the hearWHO application on a tablet according to the application recommendations and protocols. To replicate a community screening environment, ambient noise was be presented as speech babble (4-talker babble, developed for the QuickSIN test, Etymotic Research). All testing was completed in a sound booth (single wall, Industrial Acoustics Company) using a calibrated GSI-61 audiometer with attached CD player for the background babble noise. The subject was seated in the sound booth in a measured location facing two calibrated loud speakers at 45 degrees azimuth. Each subject first performed the DIN test using commercially available standard-issue insert headphones (JBL TUNE 210) in the absence of ambient noise as a reference measurement. These headphones were chosen because they are likely to be used in the field, readily available, and simulate community-based screening. The DIN test was repeated to confirm test-retest variability. After the two DIN tests in quiet, the subject repeated the DIN test in the presence of ambient noise. Ambient noise was presented through calibrated soundfield speakers at sound levels of 45, 50, 55, 60, 65, and 70 dBA in a random order to minimize learning effect. The protocol was repeated using over-the-ear headphones (Sennheiser HD 202). Headphone order was randomized for each subject. The raw DIN score, which ranged between 0-100, was displayed on the app at the conclusion of each test and recorded for each ambient noise level. At the conclusion of the study, the raw DIN scores were converted to SRTs with the assistance of the hearX group.