Just to be clear, I don't use any DSP over the multichannel stuff either. However, since the advent of HT, I've become spoiled in that I cannot tolerate a 2 channel movie soundtrack any more.
Pyrrrho, I never had the chance last night to experiement with DPL and DPLII . I'm buying the 2nd Hunger Games and watching that tonight. However, I will experiment with the DPLII hppefully this weekend.
The vast majority of the old stuff will be DPL encoded, not DPL II encoded. DPL II, when applied to those old things that are DPL encoded, will be sort of a combination of decoding and extra processing.
Here you can read about DPL and how it works:
http://www.dolby.com/uploadedFiles/Assets/US/Doc/Professional/208_Dolby_Surround_Pro_Logic_Decoder.pdf
Here is a relevant quote on the
encoding of DPL:
Before we discuss decoders, however, it is necessary to see how the MP Matrix encoder works. Referring to the conceptual diagram in Fig. 1 (below) the encoder accepts four separate input signals, left, center, right, and surround (L, C, R, S), and creates two final outputs, left-total and right-total (Lt and Rt).
The L and R inputs go straight to the Lt and Rt outputs without modification. The C input is divided equally to Lt and Rt with a 3 dB level reduction (to maintain constant acoustic power in the mix). The S input is also divided equally between Lt and Rt, but it first undergoes three additional processing steps:
• Frequency bandlimiting from 100 Hz to 7 kHz.
• Encoding with a modified form of Dolby B-type noise reduction.
• Plus and minus 90-degree phase shifts are applied to create a 180 degree phase differential between the signal components feeding Lt and Rt.
It is clear that there is no loss of separation between the left and right signals; they remain completely independent. Not so obvious is that there is also no theoretical loss of separation between the center and surround signals. Since the surround signal is recovered by taking the difference between Lt and Rt, the identical center channel components in Lt and Rt will exactly cancel each other in the surround output. Likewise, since the center channel is derived from the sum of Lt and Rt, the equal and opposite surround channel components will cancel each other in the center output.
The ability for this cancellation technique to maintain high separation between center and surround signals requires that the amplitude and phase characteristics of the two transmission channels be as close as possible. For instance, if the center channel components in Lt are not identical to the ones in Rt as a result of a mismatch in channel balance, center information will come out of the surround channel in the form of unwanted crosstalk.
For what DPL II does, you can read this:
http://www.pacificav.com/library/Dolby Surround Pro Logic Operation.pdf
Although Dolby says it is fine to "decode" DPL encoded material with DPL II, properly speaking, it is not simply
decoding; it is applying DSP processing to the signal as well. As you can see from the information regarding the encoding of DPL, the surround is mono, and there is no encoding of different information for the right and left rear channels. Yet DPL II will give you different sound from the right and left surround, which means it is not simply decoding the signal, but is applying extra DSP to the process. If you want it decoded and nothing else, you must use DPL, not DPL II. However, many people like the effect of DPL II on DPL encoded material (just like many people like other DSP effects), so you should use whatever you like.
