From what I can remember, it's the Dolby "Surround Sound".
From wikipedia:
http://en.wikipedia.org/wiki/Dolby_Stereo#Dolby_Surround"Dolby Surround' was the earliest consumer version of Dolby's multichannel analog film sound format Dolby Stereo.
When a Dolby Surround soundtrack is produced, four channels of audio information—left, center, right, and mono surround—are matrix-encoded onto two audio tracks. The stereo information is then carried on stereo sources such as videotapes, laserdiscs and television broadcasts from which the surround information can be decoded by a processor to recreate the original four-channel surround sound. Without the decoder, the information still plays in standard stereo or monaural. The Dolby Surround decoding technology was updated during the 1980s and re-named Dolby Pro Logic. The terms Dolby Surround and LtRt are used to describe soundtracks that are matrix-encoded using this technique."
I've got a whole bunch of Telarc CDs and they sound great on my 2 channel system.
HsvHeelFan