We propose a blind bandwidth extension (BWE) technique that improves the quality of a narrow-band speech signal using time domain extension and spectral envelope prediction in the frequency domain. In the time domain, we use a spectral double shifting method. Further, a new spectral envelope predictor is introduced in the frequency domain. We observe less distortion when the attribute is transferred from low to high frequency, instead of reflecting the original high band. The proposed blind BWE system is applied to the decoded output of an adaptive multi-rate (AMR) codec at 12.2 kbps to generate a high-frequency spectrum from 4 to 8 kHz. The blind BWE was objectively evaluated with the AMR and AMR wideband codecs and subjectively evaluated by comparing it with the AMR.
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