This paper describes a new database of binaural room impulse responses (BRIR), referred to as the Aachen Impulse Response (AIR) database. The main field of application of this database is the evaluation of speech enhancement algorithms dealing with room reverberation. The measurements with a dummy head took place in a low-reverberant studio booth, an office room, a meeting room and a lecture room. Due to the different dimensions and acoustic properties, it covers a wide range of situations where digital hearing aids or other hands-free devices can be used. Besides the description of the database, a motivation for using binaural instead of monaural measurements is given. Furthermore an example using a coherencebased dereverberation technique is provided to show the advantage of this database for algorithm evaluation. The AIR database is being made available online.
The ability of the human auditory system for sound localization mainly depends on the binaural cues, especially interaural time and level differences (ITD and ILD). In the context of digital hearing aids and binaural audio transmission systems, these cues can be severely degraded by independent bilateral signal processing such as dereverberation or noise reduction. This contribution presents a novel two-stage binaural dereverberation algorithm which explicitly preserves the binaural cues. The first stage is based on a statistical model of the room impulse responses (RIR) and comprises a spectral subtraction rule which reduces late reverberation only. It includes a smoothing process of the spectral gains to reduce musical tones. In a second stage, the residual reverberation is attenuated by a dual-channel Wiener filter. This is derived from a coherence model of the reverberant sound field taking into account shadowing effects of the head. The overall binaural-input binaural-output structure efficiently reduces both early and late reverberation. In experiments as well as informal listening tests using measured binaural room impulse responses, the proposed algorithm significantly improves speech quality according to objective and subjective measures. His research interests cover the areas of single-and multichannel speech enhancement algorithms including noise suppression and dereverberation. MagnusSchäfer received the Dipl.-Ing. degree in information and communication technology from RWTH Aachen University, Aachen, Germany, in 2006. He is currently pursuing the Ph.D. degree at the Institute of Communication Systems and Data Processing, RWTH Aachen University. His research interests cover the areas of singleand multichannel speech and audio coding as well as speech enhancement. Thomas Esch (S'07) received the Dipl.-Ing. degree in information and communication technology from
This paper discusses the application of noise reduction algorithms for dual-microphone mobile phones. An analysis of the acoustical environment based on recordings with a dual-microphone mock-up phone mounted on a dummy head is given. Motivated by the recordings, a novel dual-channel noise reduction algorithm is proposed.The key components are a noise PSD estimator and an improved spectral weighting rule which both explicitly exploit the Power Level Differences (PLD) of the desired speech signal between the microphones. Experiments with recorded data show that this low complexity system has a good performance and is bene cial for an integration into future mobile communication devices.
Abstract-A novel semi-analytical signal processing model for the binaural coherence of homogeneous isotropic noise fields is presented in this contribution. This is derived from a simplified geometrical model of the human head, where the shadowing between the left and right ear is modeled by two nonreflecting circular plates. Based on Kirchhoff's diffraction theory, it is shown how the corresponding coherence is calculated. This model can be used as part of various binaural signal processing algorithms, such as speech enhancement for digital hearing aids or binaural speech transmission systems. In experiments using an artificial head in a highly reverberant environment, it is confirmed that the proposed theoretical model shows a good match with the coherence obtained from measurements.Index Terms-Binaural, head shadowing, head-related, Kirchhoff diffraction theory, noise field coherence.
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