Transcoding of Narrowband to Wideband Speech

Transcoding is required to facilitate the communication of compressed speech between networks that have adopted opposing speech coding standards. The traditional transcoding technique of tandem conversion by decoding from the old standard and then re-encoding with the new standard suffers from unacceptable delay and complexity. For real time applications, delay and complexity can be reduced by performing transcoding in the bit stream domain. This paper describes techniques for transcoding between narrowband and wideband speech coding standards. In particular, an examination of the performance of bit stream mapping approaches to transcoding from the ITU-T G.729 narrowband speech coder to the ITU-T G.722.2 wideband speech coder is presented. Results for the proposed transcoder compared with a tandem transcoder indicate significant reductions in computational complexity however speech quality results less satisfactory. It is concluded that an ideal transcoder must consider the interaction of all speech parameters to ensure satisfactory speech quality.