Microphone array system for speech enhancement in a motorcycle helmet

Document type: Researchreports
Full text:
Author(s): Per Cornelius, Nedelko Grbic, Ingvar Claesson
Title: Microphone array system for speech enhancement in a motorcycle helmet
Translated title: Mikrofon array system för talförbättring i en motorcycle hjälm
Series: Research Report
Year: 2005
Issue: 5
ISSN: 1103-1581
Organization: Blekinge Institute of Technology
Department: School of Engineering - Dept. of Signal Processing (Sektionen för teknik – avd. för signalbehandling)
School of Engineering S- 372 25 Ronneby
+46 455 38 50 00
Authors e-mail: pco@bth.se, ngr@bth.se, icl@bth.se
Language: English
Abstract: In this report a real case study of the sound environment within a helmet while driving motorcycle is investigated. A solution to perform speech enhancement is proposed for the purpose of mobile speech communication. A microphone array, mounted onto the face shield in front of the user's mouth, is used to capture the spatio-temporal properties of the acoustic wave ¯eld inside the helmet. The power of the spatially spread noise within the helmet is small when standing still while it may heavily exceed the power of the speech when driving at high speeds. This will result in dramatically reduced speech intelligibility in the communication channel. The highly dynamic noise level imposes a challenge for existing speech enhancement solutions.
We propose a subband adaptive system for speech enhancement which consists of a soft constrained beamformer in cascade with a signal-to-noise ratio dependent single microphone solution. The beamformer make use of a calibration signal gathered in the actual environment from the speaker's position. This calibration procedure e±ciently captures the acoustical properties in the environment. Evaluation of the beamformer and the single microphone algorithm, both as either parts by them selves and as a cascaded structure, together with the optimal subband Wiener solution is presented. It is shown that a cascaded combination of the calibrated subband beamforming technique together with the single channel solution outperforms either one by it self, and provides near optimal results at all noise levels.
Subject: Signal Processing\Beamforming
Signal Processing\Speech Enhancement
Keywords: Speech enhancement, Beamforming, adaptive filtering, subband filtering
URN: urn:nbn:se:bth-00272