DPLII was originally worked out as a blind upmixer using analog circuitry. See this interview with Jim Fosgate, who designed it: https://www.stereophile.com/in

DPLII was originally worked out as a blind upmixer using analog circuitry. See this interview with Jim Fosgate, who designed it: https://www.stereophile.com/interviews/1204fosgate/index.html https://www.stereophile.com/interviews/1204fosgate/index.htm... Later Fosgate worked with Roger Dressler at Dolby and Dolby's engineers converted the analog circuit to digital. See these two posts from Dressler for additional detail: https://www.avsforum.com/threads/dolby-pro-logic-ii-vs-dolby-digital.3270616/post-62424523 https://www.avsforum.com/threads/dolby-pro-logic-ii-vs-dolby... https://www.avsforum.com/threads/dolby-pro-logic-ii-vs-dolby-digital.3270616/post-62425841 https://www.avsforum.com/threads/dolby-pro-logic-ii-vs-dolby... The encoder came later, after the DPLII blind upmixer was already designed.