Robustness of CELP coders.

A Code-Excited Linear Predictive (CELP) coder can provide high quality speech at 8 kbps, and is being considered for mobile telephony applications. In this memorandum we examine the robustness of the CELP coder, such as its ability to cope with non-speech and corrupted speech inputs or to survive errors in the transmission of the coder parameters. It was found that the coder is robust for different kinds of input signals, but was extremely sensitive to channel errors. In this memorandum we first show how we determined the error sensitivity of each coder parameter and identified the error propagation mechanisms. Next, we show that with relatively simple measures the effect of bit errors can be significantly reduced. Moreover, we demonstrate that repetition of the coder parameters from the most recent error- free frame is an effective technique to compensate for bit errors.