G.723.1 Vocoder

GAO’s G.723.1 dual rate speech coder performs compression and decompression of 8 kHz speech signals. It encodes 16-bit PCM samples into 16-bit code-words yielding 10 or 12 code-words per 240 sample frames for the 5.3 Kbps and 6.3 Kbps channels respectively. GAO’s G.723.1 software has switchable transmission rates over 5.3 or 6.3 Kbps channels providing 4 kHz of quality speech bandwidth in conformance with the ITU-T standard. The higher bit rate has greater quality. The lower bit rate gives good quality and provides system designers with additional flexibility.

The ITU-T G.723.1 standard specifies a coded representation that can be used for compressing the speech or other audio signal component of multimedia services at a very low bit rate as part of the overall H.324 family of standards. This coder was optimized to represent high quality speech at the above rates using a limited amount of complexity. It encodes speech or other audio signals in frames using linear predictive analysis-by-synthesis coding. The excitation signal for the high rate coder is Multipulse Maximum Likelihood Quantization (MP-MLQ) and for the low rate coder is Algebraic-Code-Excited Linear-Prediction (ACELP).