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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 (3.729 ACELP 8 kb/s speech coding standard, both interpolation-and repetitionbased techniques outperform standard concealment in informal listening tests.

WIDEBAND CODER OVERVIEWThis paper presents a multi-rate wideband speech coder with bit ratcs from 8 to 32 kbls. The coder uses a splitband approach, where the input signal, sampled at 16 kHz, is split into two equal frequency bands from 0-4 kHz and 4-8 kHz, each of which is decimated to an 8 kHz sampling rate. The lower band is coded using the Adaptive Multi-rate (AMR) family of high-quality narrowband speech coders, while the higher band is represented by a simple but effective parametric model. A complete solution including t h s wideband speech coder, channel coding for various GSM channels, and dynamic rate adaptation, easily passed all Selection Rules and ranked second overall in the recent 3GPP AMR Wideband Sclection Testing. Besides high performance, ad&tional advantages of the embedded split-band approach include ease of implementation, reduced complexity, and simplified interoperation with narrowband specch coders.

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