Modern digital hearing devices go far beyond simple sound-amplification devices. They may include extensive signal-processing algorithms adapted to the needs of the individual hearing impaired, and to the prevailing ambient acoustical conditions. This part of the HearCom projects concentrates on what types of algorithm are most effective for the individual hearing-impaired listener.
Apart from signal compression and frequency-dependent amplification tuned to the user's hearing profile, modern hearing aids and cochlear implants nowadays standardly incorporate several features to enhance the signal quality and listening effort in adverse listening conditions. Whereas mere compression and amplification might easily re-enable the hearing aid or cochlear implant user to maintain fairly normal conversation in relatively quiet environments, the intelligibility goes rapidly down in more challenging situations, such as environments with significant background noise or room reflections.
During the past decades large numbers of signal processing schemes have been proposed to re-establish intelligibility in such adverse listening conditions, some of them with great, other with limited success. In the HearCom project five different, representative classes of signal enhancement techniques are considered :
Both state-of-the-art solutions that are currently available in the most advanced hearing aid and cochlear implant devices, as well as some promising novel techniques are studied in the project. Several algorithm variants belonging to the above mentioned classes have been implemented and evaluated. These variants differ in their theoretical approach and in the precise settings of signal-processing parameters that control their behaviour.
Sound demo material has been prepared for each of the considered algorithms, except for feedback cancellation, which is, strictly speaking, not a true signal enhancement approach. Sound files are available for the following subset of test conditions:
|Room scenario||Single-channel noise suppression||Adaptive beamforming||Blind source separation||Coherence-based dereverberation|
|Low-reverberant room with stationary directional background noise||unprocessed.mp3 processed.mp3 more information||unprocessed.mp3 processed.mp3 more information||unprocessed.mp3 processed.mp3 more information|
|Living room with a directional music signal as background noise||unprocessed.mp3 processed.mp3 more information||unprocessed.mp3 processed.mp3 more information|
|Cafeteria with diffuse babble noise in the background||unprocessed.mp3 processed.mp3 more information||unprocessed.mp3 processed.mp3 more information||unprocessed.mp3 processed.mp3 more information|