In this paper, we present a 6.8-32 kbit/s scalable speech and audio coder using a modified-discrete-cosine-transform (MDCT)-based bandwidth extension on top of a 6.8 kbit/s code-excited-linear-prediction (CELP) coder. The proposed coder comprises a 6.8 kbit/s narrowband CELP as its core-layer and eight enhancement layers with the bitrates of 0.8, 1.2, 3.2, or 4.0 kbit/s. After encoding of a narrowband signal by the core-layer, the first enhancement layer extends the bandwidth of a narrowband decoded signal, and the other enhancement layers increase the fidelity of an extended wideband signal or robustness against frame erasure conditions. Subjective evaluation test results demonstrate that the proposed coder outperforms G.729.1 for music signals at 16 and 24 kbit/s in particular with competitive or even better performance in other conditions like clean speech, background noise, and frame erasure.
Bibliographic reference. Oshikiri, Masahiro / Ehara, Hiroyuki / Morii, Toshiyuki / Yamanashi, Tomofumi / Satoh, Kaoru / Yoshida, Koji (2007): "An 8-32 kbit/s scalable wideband coder extended with MDCT-based bandwidth extension on top of a 6.8 kbit/s narrowband CELP coder", In INTERSPEECH-2007, 1701-1704.