RWTH Aachen
Institute for Communication
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Intelligibility Assessment of a System for Artifical Bandwidth Extension of Telephone Speech

Florian Heese, Bernd Geiser, and Peter Vary
Book Title:
Proceedings of German Annual Conference on Acoustics (DAGA)
Event Date:
Mar. 2012


Techniques for artificial bandwith extension (ABWE) aim to extend the limited audio bandwith (0.3 kHz - 3.4 kHz) of current narrowband telephone systems towards the wideband frequency range (0.3 kHz - 7 kHz). Several previous studies already report a consistent quality advantage of the enhanced signals over narrowband speech. In this contribution we want to evaluate an ABWE algorithm under realistic conditions and assess its impact on the speech intelligibility. In a first step, the parameter settings of a given ABWE algorithm (more than 200 possible parameter combinations) have been optimized by using instrumental speech quality measures such as the (differential) log spectral distortion (LSD). Then, to subjectively evaluate the identified algorithm configuration, a listening test (modified rhyme test) has been conducted. Therefore, real narrowband telephone recordings and their processed ABWE version have been used. In addition realistic background noise environments (e.g., babble noise and car noise) have been created. The test stimuli have been encoded with the ITU-T G.722 codec and presented to the subjects using standard DECT+/CAT-iq wideband handsets under controlled conditions. An improved speech intelligibility was found in noisy environments. The results of the intelligibility test are, for reference, compared with objective speech intelligibility measurements.

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