Dolby™ Pro-Logic 2

Pro Logic II decoding reproduces 5.1-channel surround sound from any 2-channel sources: DVD, VHS, television broadcasts, radio, and CDs. Dolby Pro Logic II uses matrix decoding technology that has been dramatically improved over ordinary Pro Logic. With Pro Logic II, for instance, the Surround (Rear) channels are in stereo (only mono with Pro Logic) and playback covers the full frequency range (only up to 7 kHz with Pro Logic). These improvements let you enjoy a wide variety of 2-channel sources with the exciting effects of 5.1- channel surround sound.
It's not as good as discrete (Separate independent channel) formats like Dolby Digital and DTS, but it's more involving than ordinary stereo and a much better home cinema experience than Dolby Pro Logic