Development and validation of a smartphone-based digits-in-noise hearing test in South African English

Objective: The objective of this study was to develop and validate a smartphone-based digits-in-noise hearing test for South African English. Design: Single digits (0–9) were recorded and spoken by a first language English female speaker. Level corrections were applied to create a set of homogeneous digits with steep speech recognition functions. A smartphone application was created to utilize 120 digit-triplets in noise as test material. An adaptive test procedure determined the speech reception threshold (SRT). Experiments were performed to determine headphones effects on the SRT and to establish normative data. Study sample: Participants consisted of 40 normal-hearing subjects with thresholds ≤15 dB across the frequency spectrum (250–8000 Hz) and 186 subjects with normal-hearing in both ears, or normal-hearing in the better ear. Results: The results show steep speech recognition functions with a slope of 20%/dB for digit-triplets presented in noise using the smartphone application. The results of five headphone types indicate that the smartphone-based hearing test is reliable and can be conducted using standard Android smartphone headphones or clinical headphones. Conclusion: A digits-in-noise hearing test was developed and validated for South Africa. The mean SRT and speech recognition functions correspond to previous developed telephone-based digits-in-noise tests.