Quality and computation load reduction achieved by applying smart transcoding between CELP speech codecs

The increasing number of standardized speech codecs implies interoperability issues between networks deploying different and sometime incompatible standards. To assure interoperability, transcoding from one codec format to another is necessary at gateways between networks. This transcoding reduces speech quality, involves computation load and additive delay. Recently, a fair amount of work has been conducted on studying alternative transcoding methods reducing complexity and delay. In this context this paper further elaborates on some alternative solutions. It presents for each of them an evaluation of quality in relation with complexity reduction. The impact of frame lost and cascading transcoding on such smart solutions is also discussed. The obtained panel of results allows clear statements on the properties and highlights the interest of smart transcoding in terms of quality, complexity and delay reduction.