Originally Posted by Sam Ash
Furthermore, I still prefer DPLII for up-mixing 2 channel music to 7.1 channels, I really don't like how DSU up-mixes music to any number of channels. Can you shed some light on this Roger, I know you were part of the DPLII DNA.
I can shed on this, but it might not be light.
I'm not going to do this subject justice, but that won't stop me from providing an answer.
1) The goals of the DSU and PLII designers were significantly different. PLII was designed by Jim Fosgate first as a music processor, the culmination of his many years in that pursuit. It was aimed at processing 2-ch sources into 5 outputs (and a couple years later to 7 with PLIIx). Based only on my speculative observations, DSU appears to have been designed to take 5.1 movies to "new heights" with 7.1.4 or more speakers. It does that admirably well.
2) The underlying upmixing techniques are very different. PLIIx uses wideband logic steering. The dominant sounds control the process, so less dominant sounds fall where they may -- which usually means they are redistributed. For example, the main singer stays up front but background singers spread into the surrounds. If you listen to the surrounds with the fronts muted, you still get a stereo effect.
DSU uses multiband processing. It's very sophisticated in its ability to "de-compose" sounds based on spectrum and correlation index. In some senses it works like magic, it's so adept at separating coherent elements from spatial, uncorrelated elements. That, in my opinion, is its undoing for stereo music applications. I suspect it was tasked with handling 2-ch music, partly because PLIIz could not go far enough, and partly because it was time to use technology originated within Dolby.
At the risk of gross oversimplification, with DSU the vocalist and background singers stay up front, and what is left for the surrounds is the pure uncorrelated stuff. That tends to be a directionless, amorphous cloud of sound with a tilt toward the higher frequencies (where things are naturally less correlated). If you listen to the surrounds alone, it's not mono, but it's not stereo in the usual sense either.
I hope this makes sense.