Environmental conditions and acoustic transduction in hands-free speech recognition

Hands-free interaction represents a key-point for increase of flexibility of present applications and for the development of new speech recognition applications, where the user cannot be encumbered by either hand-held or head-mounted microphones. When the microphone is far from the speaker, the transduced signal is affected by degradation of different nature, that is often unpredictable. Special microphones and multi-microphone acquisition systems represent a way of reducing some environmental noise effects. Robust processing and adaptation techniques can be further used in order to compensate for different kinds of variability that may be present in the recognizer input. The purpose of this paper is to re-visit some of the assumptions about the different sources of this variability and to discuss both on special transducer systems and on compensation/adaptation techniques that can be adopted. In particular, the paper will refer to the use of multi-microphone systems to overcome some undesired effects caused by room acoustics (e.g. reverberation) and by coherent/incoherent noise (e.g. competitive talkers, computer fans). The paper concludes with the description of some experiments that were conducted both on real and simulated speech data. (C) 1998 Elsevier Science B.V. All rights reserved.