determining a suitable step size modulation function and maximum step size that will induce better snr for the frame it is corresponding to and encoding for each of the frames with its respective suitable step size modulation function and maximum step size the quality of the processed voice signal is therefore improved and the quantization error thereof is minimized application_number US 386308 A description fig3 shows a waveform of an ordinary voice signal 100 which has the property of miner variation within a short time period for the inherent characteristics of a voice signal the signal 100 is divided into a plurality of frames each of them has very similar signal characteristics thereof and the signal within a frame can be encoded with a same step size modulation function without introducing much distortion in this embodiment for simplicity the length of each frame is l in alternative embodiments however the frame length l of the voice signal 100 can be variable for example according to the amplitude range and variation of the voice signal 100 with a frame as a unit the signal 100 is pre coded in advance and formal encoded thereafter as shown in the flowchart of fig4 in this embodiment there are k given maximum step sizes maxstepsize 1 maxstepsize 2 maxstepsize k in order of from small to.