In this paper, the performances of PCM/ADPCM transcoding systems are analyzed. The coders studied are the 64 kbit/s PCM with μ-255 companding law and the 32 kbit/s ADPCM proposed by Cummiskey et al. The theoretically predicted performance agrees closely with the results of computer simulation for a wide range of input signal level. According to the results, the performance degradation resulting from the code conversion process appears to be minimal for the single tandem case. However, for the case of multiple tandem code conversions, the performance becomes significantly degraded as the number of tandem coders increases. The overall performance of the transcoding system depends largely on the performance of the coder that is inferior to the other coder being cascaded.