Phonetic vocoder assessment

The efficiency of phonetic vocoders stems from the fact that the only transmitted information is the index of the recognised units and the corresponding prosodic parameters. Hence, speaker recognisability is one of the main issues in this class of coders. Our approach to minimise this drawback was to include some speaker adaptation capability. The purpose of this paper is two-folded: on one hand, to describe the recognisability and intelligibility tests that were performed with our phonetic vocoder with and without speaker adaptation; on the other hand, to present our recent developments of this coder, using the SpeechDat corpus for Portuguese, that includes telephone calls from 5000 speakers. This allowed us to generate improved HMM models, codebooks, and quantization tables, and to investigate the performance of the coder in non-clean environments and with a much wider speaker population.

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