What is the proper name for 'audio codec' ?
Codec is the proper name. It is also jargon in that laypersons do not know what it properly means.

Codec:


  a device or program that compresses data to enable faster transmission and decompresses received data.


Jargon:


  special words or expressions that are used by a particular profession or group and are difficult for others to understand


If you want to avoid the jargon, either explain what a codec is or simply refer to it by its definition.