In most cases, surround sound systems rely on the mapping of each source channel to its own loudspeaker. Matrix systems recover the number and content of the source channels and apply them to their respective loudspeakers. With discrete surround sound, the transmission medium allows for (at least) the same number of channels of source and destination; however, one-to-one, channel-to-speaker, mapping is not the only way of transmitting surround sound signals.
The transmitted signal might encode the information (defining the original sound field) to a greater or lesser extent; the surround sound information is rendered for replay by a decoder generating the number and configuration of loudspeaker feeds for the number of speakers available for replay – one renders a sound field as produced by a set of speakers, analogously to rendering in computer graphics. This "replay device independent" encoding is analogous to encoding and decoding an Adobe PostScript file, where the file describes the page, and is rendered per the output device's resolution capacity. The Ambisonics and WFS systems use audio rendering; the Meridian Lossless Packing contains elements of this capability.
