Quality assessment of CS-ACELP

The CS-ACELP (Conjugate-Structure Algebraic Code-Excited Linear Prediction) algorithm approved as 8kbit/s Speech Coding Draft Recommendation G.729 by ITU (International Telecommunication Union) is designed to have quality no worse than current Recommendation G.726 ADPCM (Adaptive Differential Pulse Code Modulation) at 32kbit/s. This paper presents the results of subjective quality tests for characterizing G.729 using Japanese, English, French, German and Italian speech. The CS-ACELP codec achieves commercial telephone quality under channel error-free conditions. It meets all the requirements under random-bit-error conditions against various input levels including two-stage transcoding. Furthermore, it is less sensitive than ADPCM to the burst errors that occur in mobile radio channels.