This paper proposes a bandwidth extension (BWE) method for the AMR narrow-band speech codec using steganography, which is called steganographic BWE herein. The high-band information is embedded into the pitch delay data of the AMR codec using an extended quantization-based method that achieves increased embedding capacity and higher perceived sound quality than the previous steganographic method. The target bit-rate mode is below 7 kbps, the level below which the previous steganographic BWE method did not maintain adequate sound quality. The sound quality of the steganographic BWE speech signals decoded from the embedded bitstream is comparable to that of the wide-band speech signals of the AMR-WB codec at a bit rate of less than 6.7 kbps, with only a slight degradation in the quality relative to speech signals decoded from the same bitstream by the legacy AMR decoder.
Bibliographic reference. Nishimura, Akira (2009): "Steganographic band width extension for the AMR codec of low-bit-rate modes", In INTERSPEECH-2009, 2611-2614.