A novel transcoding scheme from EVRC to G.729ab

In this present day of Internet and wireless it has become increasingly important to have an interoperable communication between these two systems. It is obvious that at the present environment a direct speech transcoding scheme holds the key for the efficient and seamless transmission of speech communication between the two systems. This paper presents a direct speech transcoding scheme from the CDMA (code division multiple access) standard EVRC (enhanced variable rate codec) to the ITU (International Telecommunication Union) standard G.729ab. The EVRC is developed by Lucent and adopted as TIA/IS 127 standard by TIA (Telecommunications Industries Association). It is the most widely used speech codec for the present CDMA mobile systems. Again, it is also a very competent candidate for the 3rd generation mobile system for speech coding for its high quality. The ITU standard G.729ab is the de facto workhorse for low bit rate speech coding over VOP (voice over packet) networks. The motivation behind this transcoding scheme is to transform the EVRC parameters into the G.729ab parameters directly without going through the whole process of decoding the EVRC parameters and then encoding the resultant synthetic speech using the G.729ab encoder so that it improves the delay characteristics and also the quality of the speech. In the same time this approach also results in considerable savings in computations.