In　this　paper,　an　efficient　transcoding　algorithm　between　AMR-NB　and　G.729ab　is　proposed.　The　proposed　algorithm　further　elaborates　on　solutions　when　a　DTX　function　is　adopted　between　the　source　and　destination　coding　systems.　When　neither,　either　or　both　of　the　source　and　destination　coding　systems　adopt　the　DTX　function,　the　proposed　algorithm　can　carry　out　the　transcoding　operation　between　the　two　coding　systems　efficiently.　When　neither　of　the　two　coding　systems　adopts　the　DTX　function,　transcoding　methods　in　different　domains　are　proposed.　A　scalable　distortion　measure　method　based　on　parameter　domain,　specifically　related　to　codebook　gain　conversion,　is　proposed　to　keep　the　amplitude　of　synthesized　speech.　The　effect　on　subjective　speech　quality　due　to　the　amplitude　of　synthesized　speech　is　cancelled　out　by　using　the　proposed　method　and　the　computational　complexity　is　reduced　as　well.　When　either　or　both　of　the　two　coding　systems　adopt　the　DTX　function,　depending　on　the　type　of　the　destination　frame,　transcoding　methods　between　speech　frames　and　non-speech　frames　are　proposed.　When　the　frame　is　declared　as　an　erased　frame,　a　linear　prediction-based　pitch　recovery　and　transcoding　method　is　used　in　this　paper.　By　employing　the　proposed　algorithm　in　transcoders,　complexity　is　reduced　by　about　26-82%　and　quality　is　also　improved　compared　to　the　conventional　DTE　method.　(C)　2010　Elsevier　B.V.　All　rights　reserved.