An audio interface is a piece of computer hardware that allows the input and output of audio signals to and from a host computer or recording device.
Audio interfaces are closely related to computer sound cards, but whereas sound cards are optimized for audio playback an audio interface is primarily intended to provide low-latency analog-to-digital and digital format conversion for professional audio applications.[1]
Audio interfaces may include microphone preamps, as well as analog line inputs, DI inputs, and ADAT or S/PDIF digital inputs. Outputs are analog line, headphones and digital. They're typically available as external units, either as desktop devices or in a 19-inch rackmount format. Audio interfaces range from two channels in and out, to over 30.[2]