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남현도,남일룡 단국대학교 1999 산업기술연구 Vol.1 No.-
This paper presents real-time implementation of a speech vocoder for ITU(International Telecommunications Union) H324 video telephony on the PSTN(Public Switched Telephone Network) using ITU G.723 16Kbps ADPCM(Adaptive Differential Pulse Code Modulation) algorithm. ITU H.324 is a new standard for low bit-rate multimedia communication that provides a foundation for interoperability and high quality video, voice and data based phone calls. The encoder using proposed algorithm accepts 8-bit PCM(Pulse Code Modulation) compressed sign민 and expends them to a 14-bit-per-sample for processing. The predicted values are subtracted from these 14-bit values to produced difference signals that are fed to the quantizer. Adaptive quantization is performed on the difference signals to produce a 2-bit output for transmission over the channel. At the decoder, the 2-bit transmitted values are used to update the inverse adaptive quantizer, whose output is a dequantized version of the difference signals. These dequantized values are added to the values generated by the adaptive predictor to produced the reconstructed speech signals. Computer simulations were performed to evaluate the performance of the speech vocoder that implemented by proposed algorithm.