Digital Signal Processing for Hearing Instruments

Abstract

Hearing, as a prerequisite of listening, presumably represents the most important pillar of human's ability to communicate with each other. Hence, engineers of all denominations, physicists, and physicians have always been creative both to improve the environmental conditions of hearing and to ameliorate the individual hearing capability. Digital signal processing for hearing instruments has been an active field of research and industrial development for more than 25 years. As a result, these efforts have eventually paid off and, thus, opened big markets for digital hearing aids and cochlear implants which, in turn, promote and accelerate related research and development. Certainly, the present state-of-the-art of hearing instruments has highly profited from efficient small size technology with very low power consumption mainly developed for portable communication equipment, advanced digital filtering and filter banks, as well as speech processing and enhancement devised for modern speech transmission and recognition. Moreover, these examples of cross-fertilisation exploiting synergies are continuing and expanding on a large scale. To promote the aforementioned cross-fertilisation, the goal of this special issue on Digital Signal Processing for Hearing Instruments (DSPHI) has been to collect and present the latest state-of-the-art research in signal processing methods and algorithms used in or suitable for hearing instruments, as well as in related design approaches and implementations. Just four years ago, in this journal a first special issue on this topic was published, underlining the importance and activity of this challenging field of research: EURASIP Journal of Applied Signal Processing 2005:18. This special issue on DSP for Hearing Instruments gathers 16 articles. Again, it reflects various aspects of multiple disciplines needed for the treatment of hearing impairment. In fact, the included papers address a variety of approaches, algorithms, and designs applicable to hearing instruments that are all amenable to DSP implementation. The papers in this issue are organized according to their focus of research, since some of these contributions encompass multiple topics. To this end, we have combined the contributions to the following classes: (i) head-related transfer functions and filter banks (2 articles) embracing all DSP inherent to hearing instruments, (ii) noise reduction and speech enhancement (8 articles) encompassing combinations with other algorithms, beamforming, and related measurement procedures, (iii) feedback cancellation (1 article), (iv) sound classification (2 articles), (v) cochlear implants (2 articles), and (vi) personal hearing system (1 article). The paper entitled "Database of multichannel in-ear and behind-the-ear head-related and binaural room impulse responses" (H. Kayser et al.) offers a database of head-related impulse responses (HRIRs) and binaural room impulse responses (BRIRs). These data are measured with three-channel behind-the-ear (BTE) hearing aids and an in-ear microphone at both ears of a human head-and-torso-simulator. The database provides a tool for the evaluation of multichannel hearing aid algorithms in hearing aid research.