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 Harmonic+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.