Voice encoding and decoding on LPC2148

Hi All.

My task simplified can be displayed like this: I need to read voice from microphone using adc, encode it with some voice code, decode it, and put on the speaker using dac.

The controller is LPC2148

May be somebody know the voice codec wich can be compiled for this controller and can solve my task in the real time? May be somebody knows where I can download voice codec source adapted for such controllers?

Thank you.