Abstract
This study investigates a band extension technique for the narrow-band telephony speech encoded with G.711, the most common codec employed in digital speech communications such as IP telephony services. The proposed technique employs full wave rectification that nonlinearly generates high-band overtones. In order to improve the conventional technique, this study investigates the possibility of a subband gain control based on the transmission of side information by using steganography. From the subjective evaluation, it is indicated that the proposed technique may potentially outperform the conventional technique.