Digital hearing aids introduce a delay between the direct sound entering the ear and the processed sound delivered by the device. In open-fit designs, this can lead to comb-filter effects, which distort sound quality. Most previous studies on hearing aid processing delay focused on identifying the upper limit of tolerable delay (typically 5–10 ms). This thesis is among the first to systematically explore the lower limit—specifically, whether very short delays (≤0.5 ms) offer perceptual advantages, thereby shifting the focus from “how much delay is too much” to “how little delay is enough for optimal sound quality”.

Study II focused on how processing delay influences the perception of one’s own voice—a common source of dissatisfaction among hearing aid users. Using wearable hearing aids with delays of 0.5, 5, and 10 ms, participants evaluated how their voice sounded in real time. The shortest delay (0.5 ms) was consistently preferred over the longest delay (10 ms). A customized version of the Own Voice Qualities (OVQ) questionnaire revealed that longer delays led adverse effects on the perception of tonality, reverberation, and own-voice sound quality. Interestingly, unlike in Study I, SRD ability did not predict delay preference in this context, suggesting that own-voice perception may rely on different auditory cues.

In summary, short processing delays, particularly around 0.5 milliseconds—are consistently preferred over longer delays. Participants’ ratings showed that 10 ms delay was associated with adverse effects on reverberation, tonality perception, and overall own-voice sound quality. Since own-voice perception plays a crucial role in hearing aid satisfaction, these findings highlight the importance of minimizing delay. Notably, real-life user preferences aligned with laboratory results, reinforcing the clinical relevance of short-delay hearing aids for improving everyday listening experiences.

If you are interested in more details about the study, see the attached thesis below.