Upmixing is a term used in audio engineering. It refers to the mixing up of audio channels.
Upmixing is the process of making more audio channels out of a given number of audio channels. This allows audio content from stereophony, which works with two audio channels, to be converted into surround sound with 5.1 or 7.1 audio channels so that it can be played back on the surround speakers- center, center left, center right, rear left, rear right, and subwoofer. Audio components for upmixing are called upmixers.