Field trials using a digital hearing aid with active noise reduction and dual-microphone directionality

In this study, we measured the effects of a digital hearing aid on speech recognition or reception in noise for two noise reduction concepts: active noise reduction by speech-sensitive processing (SSP) and improved directionality by a dual- or so-called twin-microphone system (TMS). This was conducted in a well-controlled clinical field trial in 16 hearing-aid users, using a single-blind crossover design. The hearing aid fitting was controlled by insertion gain measurements and measurements with loudness scaling. This study combined laboratory experiments with three consecutive field trials of 4 weeks each. We used performance measurements (speech recognition tests in background noise), paired comparisons, and self-report measurements (questionnaires). The speech recognition or reception tests were performed before and after each field trial, the paired comparisons were performed in weeks 4 and 12, and the questionnaires were administered after each field trial. For all subjects, results were obtained for three different settings: no noise reduction, SSP alone, and TMS alone. In the last week, we also performed speech recognition or reception tests in background noise with both noise reduction concepts combined. Three types of results have been reported: "objective" results from the critical signal to noise ratios for speech recognition or reception in different background noises for different settings and "subjective" results: paired comparisons and questionnaires. The subjective scores show the same trend as the objective scores. The effects of TMS were clearly positive, especially for the speech reception threshold tests and for the paired comparisons. The effects of SSP were much smaller but showed significant benefits with respect to aversiveness and speech perception or reception in noise for specific acoustical environments. There was no extra benefit from the combined effect of SSP and TMS relative to TMS alone.