This paper describes an artificial bandwidth extension (ABE) method that generates new high frequency components to a narrowband signal by folding specifically gained subbands to frequencies from 4 kHz to 7 kHz, and improves the quality and intelligibility of narrowband speech in mobile devices. The proposed algorithm was evaluated by subjective listening tests. In addition, rarely used conversation test was constructed. Speech quality of 1) narrowband phone call, 2) wideband phone call, and 3) narrowband phone call enhanced with ABE were evaluated in conversational context using mobile devices with integrated hands-free (IHF) functionality. The results indicate that in IHF use case, ABE quality overcomes narrowband speech quality both in car noise and in quiet environment.
Bibliographic reference. Laaksonen, Laura / Myllylä, Ville / Niemistö, Riitta (2011): "Evaluating artificial bandwidth extension by conversational tests in car using mobile devices with integrated hands-free functionality", In INTERSPEECH-2011, 1177-1180.