CELP-BASED SPEECH COMPRESSOR

摘要

A high quality low bit rate audio codec having a reproduced voice quality that is comparable to that of a full rate codec compresses audio data sampled at8 Khz e.g., 64 Kbps PCM to 4.2 Kbps or decompresses it back to the original audio or both. The accompanying degradation in voice quality is comparable to the standard 8.0 Kbps voice codes. This is accomplished by using the same parametric model used in traditional CELP coders but determining quantizing encoding and updating these parameters differently. The low bit rate audio decoder is like most CELP decoders except that it operates in two modes depending on the received mode bit. Both pitch prefiltering and global postfiltering are employed for enhancement of the synthesized audio. In addition built-in error detection and error recovery schemes are used that help mitigate the effects of any uncorrectable transmission errors.