Differential quantization of spectral parameters for CELP based coders in packet networks

Line Spectrum Frequencies (LSF) have been the current parameters to represent LPC coefficients in speech coding. Extensive research has been performed to exploit their interframe and intraframe correlations and quantize them more efficiently. Interframe coding of LSFs can cause error propagation when frame erasures occur. Since most LSF quantizers were designed with the primary concerns of bit-rate and complexity, less attention was paid to error propagation. In this paper, we consider the erasure performance of LSF differential scalar quantizer (DSQ) and compare it with the interframe coding method embedded in the ITU-T G.729 coder. Our results show that with only 13,7% % extra bit-rate, DSQ algorithm is much more robust to frame erasures and improvements in terms of average spectral distortion (Avg. SD) and Enhanced modified bark spectral distortion (EMBSD) tests under various packet loss conditions are obtained.