This work describes a coder that works at bit rates of 9.6 Kbits/s to 32 Kb/s. Basically the system consist on a waveform DPCM coder with an improvement in the quantizer. This new feature consist on quantizing the prediction error taking into account its waveform characteristics. The prediction residual of a voiced signal is characterized by an energy sychronous with pitch. The envelope of this signal holds this information and can be used to quantize properly the prediction error. In this work a parametric version of the residual envelope is used in two ways: Dynamic bit assignment in time domain and adaptive control of the dynamic range of the quantizer.