Surround sound
Surround sound formats were used in movie theatres dating back to Disney's Fantasia, and became available to consumers in the late 80's. There are many formats of surround sound, differing based on the type of decoding processor they used. Dolby Pro Logic is one of the oldest processors, creating four channels, and Dolby Pro Logic IIx is one of the newest, creating seven or eight discrete channels. Competing technologies have complicated the purchasing decisions of consumers.