We propose a robust artificial bandwidth extension (ABE) technique to improve the narrowband speech signal quality using enhanced excitation estimation and spectrum envelope. For excitation estimation, we use a whitened narrowband excitation signal, generated by passing the excitation signal through a whitening filter. An adaptive spectral double shifting method is introduced to obtain an enhanced wideband excitation signal. For envelope estimation, we propose an enhanced combined method using the codebook and linear mapping. The proposed ABE system is applied to the decoded output of an adaptive multi-rate (AMR) codec at 12.2 kbps. We evaluate its performance using spectral distortion, wideband perceptual evaluation of speech quality, and a formal listening test. The objective and subjective evaluation confirm that the proposed ABE system provides better speech quality than that of AMR at the same bit rate.
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