“…The bandwidth extension is then divided into two separate tasks: spectral envelope extension and excitation signal extension. Early studies employ codebook mapping techniques for spectral envelope extension, using two codebooks representing narrowband and wideband spectra H. Wang is with the Department of Computer Science and Engineering, The Ohio State University, OH 43210, USA (e-mail: wang.11401@osu.edu) E. W. Healy is with the Department of Speech and Hearing Science and the Center for Cognitive and Brain Sciences, The Ohio State University, Columbus, OH 43210, USA (e-mail: healy.66@osu.edu) D. L. Wang is with the Department of Computer Science and Engineering and the Center for Cognitive and Brain Sciences, The Ohio State University, Columbus, OH 43210, USA (e-mail: dwang@cse.ohio-state.edu) [52], [58]. Through training, the best matching entry in the wideband codebook to the narrowband codebook is used to generate the spectral envelope.…”