Dr. Michael Nasief :: Publications:

Speech coding is the process of converting voice signal into digital form in a few bits as possible. The newly developed Code Excited Linear Prediction “CELP” coders is one major type of the parametric coders which combines between low data rates and good speech quality. Most of these coders have been built initially for 7 languages not included Arabic language or its dialects. It is known that the speech quality is directly proportional to the data rate but what is the effect of the change of the spoken language or accent? This paper is made to answer on three main questions. The first question is; what is the effect of the language or accents on CELP coders? Moreover what will happen if the speech is compressed more by lower data rate coder and at the same time the language is other than English? Finally if there is an effect, so what is the defective part in the coder? Extensive testing is done on 3 coders ITU G.711, ITU G.723.1 and 3GPP AMR with changing the spoken language. The outputs were compared with the ITU PESQ algorithm. It has been proved that the speech quality will be slightly degraded when using languages other than English. Also the quality is dramatically decreased as the compression ratio increased which will be rather lower and unstable for Arabic or Cairo accent. Finally it is found that the main problem was in the Linear Prediction vector quantization CodeBook and has been verified by the MFCC for English, Arabic and Cairo accent with LBG algorithm.