SVD-Based Optimal Filtering Technique for Noise Reduction in Hearing Aids Using Two Microphones
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SVD-Based Optimal Filtering Technique for Noise Reduction in Hearing Aids Using Two Microphones Jean-Baptiste Maj Lab. Exp. ORL, Katholieke Universiteit Leuven, Kapucijnenvoer 33, 3000 Leuven, Belgium ESAT-SISTA, Katholieke Universiteit Leuven, Kasteelpark Arenberg 10, B 3001 Leuven, Belgium Email: [email protected]
Marc Moonen ESAT-SISTA, Katholieke Universiteit Leuven, Kasteelpark Arenberg 10, B 3001 Leuven, Belgium Email: [email protected]
Jan Wouters Lab. Exp. ORL, Katholieke Universiteit Leuven, Kapucijnenvoer 33, 3000 Leuven, Belgium Email: [email protected] Received 14 March 2001 and in revised form 30 October 2001 We introduce a new SVD-based (singular value decomposition) strategy for noise reduction in hearing aids. This technique is evaluated for noise reduction in a behind-the-ear (BTE) hearing aid where two omnidirectional microphones are mounted in an endfire configuration. The behaviour of the SVD-based technique is compared to a two-stage adaptive beamformer for hearing aids developed by Vanden Berghe and Wouters (1998). The evaluation and comparison is done with a performance metric based on the speech intelligibility index (SII). The speech and noise signals are recorded in reverberant conditions with a signal-to-noise ratio of 0 dB and the spectrum of the noise signals is similar to the spectrum of the speech signal. The SVD-based technique works without initialization nor assumptions about a look direction, unlike the two-stage adaptive beamformer. Still, for different noise scenarios, the SVD-based technique performs as well as the two-stage adaptive beamformer, for a similar filter length and adaptation time for the filter coefficients. In a diffuse noise scenario, the SVD-based technique performs better than the two-stage adaptive beamformer and hence provides a more flexible and robust solution under speaker position variations and reverberant conditions. Keywords and phrases: SVD-based technique, beamforming, noise reduction, hearing aids, speech intelligibility, diffuse noise.
1.
INTRODUCTION
A major problem for hearing impaired listeners is the understanding of speech in noise. Indeed, their speech reception threshold (SRT: defined as the sound-pressure level of speech at which 50% of the speech is correctly understood by the listener) in noise, interfering noises or competing speakers, is higher than for normal hearing subjects [1]. To compensate for this difference, several noise reduction strategies with one or multiple microphones have been developed. As for single microphone approaches, a noise reduction system in hearing aids is typically based on a hardware directional microphone. Some studies have shown that the directional microphone may give an SRT improvement of about 3 dB in difficult listening conditions [2, 3]. With other methods, such as spectral subtraction or Wiener filtering, an improvement in physical signal-to-noise ratio (SNR) has
been found, but unfortunately a similar improvement of the speech reception thresholds has not been
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