Variable bit‐rate CELP coding of speech with phonetic classification
Erdal Paksoy, A. Gersho, Krishnaswamy Srinivasan · European Transactions on Telecommunications · 1994
Abstract A variable bit‐rate speech coder intended for digital cellular applications is described. A voice activity detection algorithm is used to distinguish active speech from background noise. Each frame of active speech is further classified to distinguish between three phonetic categories: voiced, unvoiced, and onset. Each input frame is assigned one of five bit rates according to voice activity and phonetic classification and coded using an analysis‐by‐synthesis algorithm tailored to the needs of the class that it belongs to. The resulting coder, calledVariable Rate Phonetic Segmentation, produces good quality speech at an average bit‐rate below 3 kbit/s when operating with a voice activity factor of 0.5. Informal subjective quality assessment for speech in clean and noisy backgrounds indicates a performance that is comparable to the TIA standard QCELP algorithm while operating at a 25% to 40% lower average bit rate.