I started paying attention to this stuff back when Dolby Pro Logic was new, which was a pretty clever way to get surround effects using only left and right audio channels. Left and right channels went directly to the front left and right speakers, but it also compared wave forms coming from the left and right channels. Any wave forms that matched got sent to the center channel (like most on-screen dialog) and any that mismatched got sent to the rear surround speakers (noise, ambience, etc). It wasn’t perfect by any measure, but it was a pretty clever hack.
I always thought backwards-compatible FM stereo was pretty cute — transmit L+R channels as before, so they can be picked up and played without trouble with mono equipment, and transmit L-R separately. Just add or subtract to get the L or R channels.
I started paying attention to this stuff back when Dolby Pro Logic was new, which was a pretty clever way to get surround effects using only left and right audio channels. Left and right channels went directly to the front left and right speakers, but it also compared wave forms coming from the left and right channels. Any wave forms that matched got sent to the center channel (like most on-screen dialog) and any that mismatched got sent to the rear surround speakers (noise, ambience, etc). It wasn’t perfect by any measure, but it was a pretty clever hack.
I always thought backwards-compatible FM stereo was pretty cute — transmit L+R channels as before, so they can be picked up and played without trouble with mono equipment, and transmit L-R separately. Just add or subtract to get the L or R channels.
I knew there was some magic going on with DPL, but I never guessed quite how they did it—that was a surprisingly simple approach in the end!