Takahiro Unno

A robust narrowband to wideband extension system featuring enhanced codebook mapping

It is well-known that wideband speech (0-7 kHz) provides better quality and intelligibility than narrowband speech (300-3400 Hz), but typically only narrowband speech information is available in current wireless communication systems. Narrowband to wideband extension technology has been recently investigated to artificially generate wideband speech from narrowband speech for better speech quality and intelligibility. This paper presents a robust split-band narrowband to wideband extension system based on algorithmic enhancements to the codebook mapping technique for high-band parameter estimation. Numerical measurements confirm the performance improvements of the codebook mapping process, and informal listening evaluations show the potential of the system and its robustness to input distortions and non-speech input signals.

Improved frame erasure concealment for CELP-based coders

This paper describes new techniques for concealing frame erasures for CELP-based speech coders. Two main approaches were followed: interpolative, where both past and future information are used to reconstruct the missing data, and repetition-based, where no future information is required. Key features of the repetition-based approach include improved muting, pitch delay jittering, and LPC bandwidth expansion. The interpolative approach can be employed in voice over IP scenarios at no extra cost in terms of delay. Applied to the ITU-T G.729 ACELP 8 kb/s speech coding standard, both interpolation- and repetition-based techniques outperform standard concealment in informal listening tests.

A 4 kb/s hybrid MELP/CELP speech coding candidate for ITU standardization

This paper presents an improved 4 kb/s hybrid MELP/CELP speech coder submitted as a candidate for ITU standardization. The coder uses three modes: a high-quality MELP coder for strongly voiced speech frames, an ACELP coder with pitch prediction for weakly voiced frames, and a stochastic CELP coder for unvoiced frames. We present recent enhancements to this coder, both to improve speech quality and to reduce coder complexity. Previous lTU Selection Testing results on an earlier version of this coder showed that it met nearly all requirements for toll-quality speech, more than any other candidate. Our internal testing shows that the current reduced-complexity fixed-point coder maintains this high performance.