Info iconThis preview shows pages 1–2. Sign up to view the full content.

View Full Document Right Arrow Icon

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: MULTI-MICROPHONE NOISE REDUCTION TECHNIQUES FOR HANDS–FREE SPEECH RECOGNITION –A COMPARATIVE STUDY– Joerg Bitzer y , Klaus Uwe Simmer z and Karl-Dirk Kammeyer y y University of Bremen, FB–1, Dept. of Telecommunications P.O. Box 330 440, D–28334 Bremen, Germany, email: [email protected] z Aureca GmbH, Mozartstrasse 26, D–28203 Bremen, Germany, email: [email protected] ABSTRACT In this paper we will describe different multi-microphone noise reduction techniques as for example front-end systems for a command speaker-independent word recognizer in an office environment. Our focus lies on examining the recog- nition rate if the noise source is not gaussian and stationary, but a second speaker in the same room. In this case standard noise reduction techniques like spectral subtraction will fail, and only multi-microphone techniques can raise the recog- nition rate by using the spatial information of the speakers. We will compare the delay-and-sum-beamformer, different superdirective solutions and the post-filter approach. Our results show that these techniques are the right choice for hands–free speech recognition systems. Furthermore, we will give a deeper insight into the superdirective design for microphone arrays. 1. INTRODUCTION More and more users of personal computers work with speech recognition devices to control their systems. The input mi- crophone is almost always headset mounted. This restric- tion is very uncomfortable. To avoid this restriction, hands– free devices are the right choice, but the recognition rate decreases dramatically, as the signal-to-noise ratio (SNR) decreases. Many publications address this problem with the focus on broad-band, slowly varying noise. Single- and multi-microphone approaches are known [1, 2, 3, 4]. This contribution deals with the problem of a second speaker in the same room. Therefore, the interference signal is coloured and non-stationary. For a two-channel system a possible so- lution is published in [5]. This algorithm is a derivation of a two-channel generalized sidelobe canceller [6]. But it can be shown that this kind of algorithms fails in reverberant environments [7]. In this contribution we will focus on non- adaptive solutions. In section two we describe the differ- ent approaches for multi-microphone noise reduction tech- niques. Especially the superdirective design is explained and a design procedure based on the coherence function is given. Section three shows the results of the noise reduction experiments. 2. NOISE REDUCTION ALGORITHMS Noise reduction in a reverberant environment is a difficult problem. We will focus on multi-microphone algorithms which have good capabilities to suppress diffuse noise....
View Full Document

{[ snackBarMessage ]}


This preview shows document pages 1 - 2. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online