Speech Signal Enhancement by Information combining

Mobile phones as well as tablets are omnipresent and belong to everyday life. Today audiovisual communication takes place at different locations and in a large variety of acoustic environments. In consequence, the intelligibility as well as the quality of speech may significantly be degraded by ambient background noise. In order to improve speech intelligibility and to ensure a convenient communication with high audio quality, speech enhancement techniques are required. In this thesis all critical components contributing to the enhancement of the up-link signal are addressed: signal capturing at the acoustic frontend with a new near field beamformer, new codebook based speech and noise estimation procedure generating and exploiting reliability information, and actual noise reduction exploiting spectral dependencies of human speech. For the acoustic front-end of the digital processing chain a novel concept for the filter optimization of a near field beamformer is introduced. The optimization scheme allows to closely approximate a predefined reception characteristic which can be freely chosen according to the application. The output of the beamformer provides a preenhanced signal with improved SNR for subsequent singlemicrophone based speech enhancement.