Coding Wideband Speech at Narrow- Band Bit Rates

The 'rnuffl~d' quality of coded .peech, which arises from the handlimiling ofspeech to 4 kHz, can be reduced either by coding speed! with a wider bandwidth or by widcband enhancement of the narrowband coded speech. ThL~ paper investigates the limitations of wideband enbancement and pO)Ssibilities for its improvement A new wideband coding scheme is prop()sed thaI i. based 00 any narrowband coder, but augmented by wideband enhancement plus a few bits per frame ofhighband infonnation. The "cherne thus has a bit rate only slightly greater than that of the narrowband coder. Subjective listening tests show that tbis scheme can produce widchand speech of significantlyhigherqualitythanthenarrowband_'''''''_~,--~_'''_. ___ ~~ ________ ---'