Predicting performance on the digits-in-noise test in noise and reverberation using the speech transmission index

This study investigated the effects of noise and reverberation on recognition of Dutch digits-in-noise (DIN) test triplets. The findings demonstrate that the STI_DIN, an adaptation to the standard speech transmission index (STI), provides a reliable, low‑error predictor of DIN test performance in conditions with noise and/or reverberation when only a single speech recognition threshold (SRT) measurement in noise is completed. To achieve this, twenty-four normal-hearing (NH) adults completed adaptive SRT measurements in noise-only, reverberation-only and combined noise and reverberation conditions using unprocessed (UP), low-pass filtered (LPF) and cochlear implant vocoded (CI_voc) speech materials. Standard STI values differed across conditions and overestimated the detrimental effect of reverberation on recognition. The STI_DIN, derived from the magnitude cross power spectrum (mCPS) of reverberated DIN test triplets and unprocessed triplets, was applicable for T₆₀ reverberation times up to 12 s. STI_DIN values remained constant across conditions, showing no significant main effect of condition for any of the unprocessed and processed speech materials. The results show that when an SRT_n measurement in noise-only is obtained using DIN test triplets (i.e., the clinical standard), the STI_DIN can be used to predict the SRT in other listening conditions with noise and reverberation. The root‑mean‑square error between measured and predicted SRTs was 0.92 dB, and 95 % of predictions deviated <1.7 dB from the measured values in conditions with noise and/or reverberation.