Dunedain said:
This 70mm stereo soundtrack sounds interesting, in that it's apparently just like the 93 Definitive Collection laserdisk soundtrack, but with no added sound effects. So it's an authentic theatrical soundtrack? What source was used to get this 70mm stereo soundtrack, is it complete? Does it sound as good as the Definitive Collection does (in terms of overall quality)?
I'll give a brief summary here, but you should read this thread for a much more detailed accounting: http://originaltrilogy.com/forum/topic.cfm/Star-Wars-1977-70mm-sound-mix-recreation-stereo-and-51-versions-now-available/topic/11348/
The term 'stereo 70mm' is a bit misleading, I suppose, because it is not actually a theatrical sound mix--it is the 1993 Definitive Collection PCM track with certain sections replaced by the 35mm stereo mix, in order to remove the extra, unnecessary sound effects. 70mm prints of Star Wars never had stereo mixes, they all contained six-track discrete channel audio, which in today's terms could be called a 4.2 format. That is to say, four full range channels (left, right, center, surround) with the remaining two devoted exclusively to bass content. The '93 DC mix was created by downmixing the 70mm version into stereo, and then adding extra sound effects on top of it; hence the 'stereo 70mm' sounds more like the original, but not exactly as it was.
The 5.1 version comes significantly closer to the theatrical mix by adding a custom LFE channel, derived mainly from the 1997 special edition, but adjusted considerably for optimal integration into the rest of the audio. The surround sound element can also be obtained from the stereo version by using a receiver with Prologic II or a similar upmixer, but the 5.1 is needed to hear the extra bass content, which by all accounts was a very important aspect of the way the film sounded back then. Again, note that aside from the powerful bass, removal of extra sounds, and being pre-upmixed in software, the majority of it will sound exactly the same as the Definitive Collection mix. It's about as close to the original as you can get short of a transfer of the real thing.