Emotiva ERC-4 Differential Reference CD PlayerERC 4 Differential Reference CD Player and Digital Transport The Emotiva ERC 4 Differential Reference CD Player and Digital Transport combines a high quality digital CD transport and a superb balanced DAC (digital to analogue converter) in one convenient and attractive package. In addition to serving as an audiophile CD player and transport, the ERC 4 offers both Coaxial and Optical (Toslink) S PDIF digital audio inputs, so you can also use it as a