This paper presents a bit-rate conversion system for an efficient communication between two CVSD systems with different bit-rates. To ensure the robustness to external noises, the presented system is implemented in digital domain using a general purpose digital signal processor (DSP). In order to overcome the problems caused by different bit-rate and time-constants, several methods are considered in this study. In addition, a significant simplification of the system complexity is obtained by introducing the IIR filter to the decimation/interpolation process. The use of the IIR filter provides comptational advantages over the conversion system employing FIR filters, because the linear phase is not a critical issue in this application. By modifying the algorithm based on the IIR filter, a 3- channel full-duplex conversion algorithm was successfully implemented on a single DSP. Experimentals results are presented to exihibit the consistent and reliable performance of the bit-rate conversion system.