Dracula (1979) original Dolby Stereo track preservation

[pipefan413]

So for old movies recorded in dolby stereo
Are they mixed with 4 discrete channels?
If that's so all the 5.1 "remixes"  would be a little closer to the original mix

... How?

First off, if the contents of the actual audio mix are themselves modified then there is no way they are authentic (changed sound effects etc. as often seen in 5.1 remixes).

Secondly, I don't really get what you mean by them being "mixed with 4 discrete channels". Yeah, they'd be mixing a 4-channel master, but that would get matrix-encoded down using the Dolby Motion Picture Matrix system to turn it into 2 channels for distribution on prints etc. The channels, as both I and @Onti have said previously, were Left, Right, Centre (derived from L+R), and Surround (a single channel derived from L+R and phase inverted, though there's a wee bit more to it than that). Obviously this is not the same as 5.1, which is instead Left, Right, Centre, Left Surround, Right Surround, and Low Frequency Effects (the ".1"). This was all done in the analogue realm with equipment like the Dolby SEU4 matrix encoder, and monitored through corresponding analogue equipment like the Dolby SDU4 matrix decoder, in order to check that the decoded 4:2:4 mix still sounded good and reasonably close to the original 4-track input. If not, they'd fiddle with the encoder until they ended up with a 4:2 encoded track that sounded as representative of the discrete 4-channel input as reasonably possible. Incidentally, I have one of these, as do at least two other people on this forum that I know of (wouldn't be surprised if others do too). I'm planning on recording some stuff through two different hardware decoders as soon as I have some other equipment to capture and test them with, which should be very very soon!


I've already tried to explain this as clearly as I thought I could, but I feel like you're missing some part of it so I'll try this again in a slightly different manner. The original 4 channels are turned into 2, but those 2 cannot be turned back into the original 4 in such a way that they sound exactly the same, they are somewhat different but are nonetheless 4 channels of different audio (it isn't just the 2 channels duplicated or whatever). Maybe you need to do some research about the Dolby MP Matrix, same as I did myself not too long ago. The idea is that they were trying to store a 4-channel mix in a way that would fit on the limited space available in the optical soundtrack area at the side of a 35 mm film print; there's not enough space for 4 optical tracks, so they reduced it down from 4 to 2 using a fairly clever matrix encoding algorithm which would allow them to later read those 2 channels and convert them back to 4 again during playback in the theatre. This is known as a number of things depending on context and what you're trying to put the focus on, e.g. Dolby Motion Picture Matrix (the actual matrix encoding system), Dolby Stereo (the theatrical version of the tech), Dolby Surround / Pro Logic (early home video implementations of the same concept), 4:2:4 (referring to turning 4 channels into 2 then back into 4) and so on.

It doesn't exactly help that a lot of the terminology around this particular topic is messy as hell. Dolby now has two completely different products called Dolby Surround, for instance: one is the very first home version of the theatrical Dolby matrix decoding system (most commonly known as Dolby Stereo), and the other is the most recent version of their matrix decoder/upmixer, which came in with the Dolby Atmos generation of home video AV receiver tech. The two are completely different, though! The original Dolby Surround is only capable of turning 4:2 matrixed tracks into 3 channels, at best with a "phantom" centre, possibly because it was cheaper/simpler to use less complex equipment to turn 2 channels into 3 (L/R/S), possibly because people probably didn't really have centre speakers at that point anyway, and possibly a bit of both. By contrast, the latest Dolby Surround is basically more interested with making audio stored as a small number of channels (e.g. 2) sound "good" through many-speaker setups by turning those 2 channels into many more, so if you have 5 main speakers and a subwoofer it'll turn 2 channels into 5.1, if you have another 2 speakers on top of that you'll get 7.1, and so on... point being, this is not an accurate representation of the originally designed 4:2:4 matrixed-then-dematrixed process because obviously L/R/C/S is not the same as L/R/C/Lss/Rss/Lsr/Rsr/LFE or whatever else it's trying to cater for. So... yeah, I get that it's kinda confusing.

If you have specific questions I'll be happy to help, I'm just kinda struggling to get what you guys are asking at the moment and I think it might be because there's some fundamental stuff missing from what you've read/understood thus far and it might help to do some reading on the subject before jumping to any conclusions (such as supposing that 5.1 remixes are faithful to Dolby Stereo because Dolby Stereo is created from 4-track sources).