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Author
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Topic: 70mm sound
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Stephen Furley
Film God
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Posts: 3059
From: Coulsdon, Croydon, England
Registered: May 2002
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posted 11-12-2002 04:19 AM
On the one occasion that I have run 70mm, many years ago now, it was the original Todd-AO format, five screen channels, mono surround, no NR.I am totally confused about the later formats, much of what I have read seems to be conflicting. Can someone please give me a list of all magnetic formats which have been used on 70mm, format numbers, noise reduction, channel assignments, and which processors, and/or outboard adapters are needed to play them. I assume that DTS on 70 is the same format as on 35. What about CDS, were all CDS readers dual guage, the one I have seen was, or were there any 35 or 70 only versions? Was the sound format the same for both guages? How many channels was it? Thanks.
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Steve Kraus
Film God
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Posts: 4094
From: Chicago, IL, USA
Registered: May 2000
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posted 11-13-2002 01:51 AM
CDS was the same on both 35mm and 70mm except for data bits being 1.25X stretched vertically on the 70mm version due to the greater linear speed. Although the 70mm version was introduced first I think it is fair to say the 70mm dots were stretched as opposed to saying the 35mm dots were compressed since they were square on 35mm (14 x 14 microns) but rectangular on 70mm (17.5 x 14 microns). The CCD reader would "see" both tracks as being exactly the same.[Hmmm...does this predate and therefore invalidate that Dolby patent that seems to cover any digital sound system whose data simply gets stretched out on 70mm but is otherwise the same?] I believe the production model penthouse readers were all dual gauge. A web version of the CDS brochure with specs may be found here
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