Enhancing quality of CELP coded speech via wideband extension by using voicing GMM interpolation and HNM re-synthesis

This paper presents a procedure to improve the quality of narrowband (0–4khz) CELP coded speech. The procedure is based to refine the pitch periodicity and reinsert the high frequency components (4–8khz) in the narrowband CELP decoded speech. The narrowband CELP decoded speech is first analyzed with Harmonic+Noise analyzer and Lowband information are extracted. By exploiting the Lowband spectrum envelope and V/UV information, the highband (4–8khz) spectrum envelope is recovered statistically by using a voiced/unvoiced gaussian mixture model with interpolation. Lowband information along with the estimated highband information is then fed to the Hannonic+Noise synthesizer to re-synthesize a wideband speech. The objective and subjective tests are performed to evaluate the quality of the re-synthesis wideband (0–8khz) speech. The results of the above experiments show that the re-synthesis wideband speech is pleasant to listen with crispy characteristics and preferred over the CELP coded speech.