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Author Topic: Dolby SR-D or SDDS at 16 fps? Joe Beres Jedi Master Film Handler Posts: 606 From: Minneapolis, MN, USA Registered: Nov 2000 posted 01-22-2003 12:02 PM                     Please forgive my ignorance on the subject of digital soundtracks, but I'm curious about something. Let's say an archive restores an early silent film, maintaining the fill-frame 1.33 aspect ration, meant to be run at 16 fps. (Keeping in mind that it is frowned upon in the archive/restoration world to print up to 24 fps) Obviously, the analog soundtrack area is unavailable, but conceiveably an SR-D track (or SDDS), of a score for example, could be applied outside of the image. My question is would either of the digital tracks work at 16fps if recorded and encoded for that speed, or do they only work at or around 24 fps? I know that the lack of analog back-up could be an issue, and that most archives would never add a digital soundtrack to a print of a true silent film. However, i am curious about the logistics of the digital systems and whether this potentially could work or not.  |  IP: Logged Joe Redifer You need a beating today Posts: 12859 From: Denver, Colorado Registered: May 99 posted 01-22-2003 12:28 PM                        I would think so since they'd only have to worry about mono or stereo at best (not 5.1 or 8 channel). But the cost of designing new software and/or hardware to make it play would kind of make it not worth it, IMO. Why not just press "MUTE" on your processor and have true analog silence?  |  IP: Logged Paul Linfesty Phenomenal Film Handler Posts: 1383 From: Bakersfield, CA, USA Registered: Nov 1999 posted 01-22-2003 12:33 PM                     Actually, DTS timecode sounds like a good bet here. They already have a system that can be used for 16mm film.  |  IP: Logged Ian Price Phenomenal Film Handler Posts: 1714 From: Denver, CO Registered: Jun 99 posted 01-22-2003 12:43 PM                     But I'm betting that the DTS sync track is in the visible area of Full-Frame, Silent Speed film.  |  IP: Logged Lionel Fouillen Expert Film Handler Posts: 230 From: Belgium Registered: Nov 2002 posted 01-22-2003 12:45 PM                     From the little I know about movie digital sound, DTS would fit better than Dolby or Sony in my opinion. I wonder whether on-film digital sound could ever be possible at 16fps considering the reduced film length, not to mention the "perforation jump" of SR-D. This is an interesting topic. Any expert out there to think about it and share conclusions?  |  IP: Logged Daryl C. W. O'Shea Film God Posts: 3977 From: Midland Ontario Canada (where Panavision & IMAX lenses come from) Registered: Jun 2002 posted 01-22-2003 02:08 PM                        Depending on how the variable bitrate decoding is handled in the Dolby processor 16fps may or may not be possible. Since the easiest way to do variable bitrates (without building a ton more custom hardware) is with software, I'll assume that this is how it is done. That said, there's no reason why a firm-ware update couldn't make 16fps digital sound happen. Last time I tried something like this, I just had the sound totally drop-out anywhere under probably 20fps. AFAIK, the DTS track does fall on the Academy frame area. Since, AFAIK, the SDDS system is also variable bitrate, it should be able to do the same as I said about a Dolby processor.  |  IP: Logged John Pytlak Film God Posts: 9987 From: Rochester, NY 14650-1922 Registered: Jan 2000 posted 01-22-2003 02:53 PM                        The position of the (DTS) data track on 35mm prints is specified by SMPTE Recommended Practice RP115 as having a centerline that is 0.297 inches (7.54mm) from the reference edge of the print --- which would be in the projectable area of a full frame silent print.  |  IP: Logged Christopher Seo Jedi Master Film Handler Posts: 530 From: Los Angeles, CA Registered: Jun 99 posted 01-22-2003 03:04 PM                     The range of tolerated speeds for a DA20 was given as 21.4 fps - 25.7 fps. I can't recall if this was an inherent limitation of the hardware of the Cat. 670 video preamp/ADC card.  |  IP: Logged Bobby Henderson "Ask me about Trajan." Posts: 10973 From: Lawton, OK, USA Registered: Apr 2001 posted 01-22-2003 06:17 PM                     All three current digital audio systems would have to be modified into order to work with full aperture 35mm projection at 16fps. With DTS time code needing to be relocated to a different position, wouldn't that require a different kind of setup for recording the timecode? On normal prints, the time code is white against black. Wouldn't the film prints need some kind of dark background on the outer edge to hold the DTS timecode? Or would the DTS reader pickup the Morse Code looking data if it were printed in reverse? Dolby Digital and Sony SDDS would not track correctly since so many bits have to be coming in per second off the film for it to work. SRD and SDDS data is compressed and stored in packeted form. It is not linear like LPCM. My guess is SDDS just wouldn't work at all under 16fps. The 2.2 million bits per second of data both full quality and half quality tracks contain would need a smaller data spot to crunch that data down into 75% of the normal space. Dolby Digital would have a greater chance to work without modification. The theatrical system normally runs at 320kb/s with 550kb/s of data total for 24 frames. For 5.1, you could drop the bitrate down to 256kb/s (but it probably would not sound all that great). The best bet --if the theatrical systems can process it-- would be encoding a 192kb/s 2.0 mono/stereo track and using the remaining data space available for error correction.  |  IP: Logged Karen Hultgren Master Film Handler Posts: 492 From: Agoura Hills, CA, USA Registered: Mar 2000 posted 01-22-2003 08:00 PM                        DTS 16mm formatted film does not have any soundtrack printed on the film itself. The DTS timecode is printed where the mono track usually resides. So, when film is run, the optics picks up the timecode, feeds it to the DTS timecode preamp, Model 376, that conditions the timecode for processing by the DTS digital player. The 6-track digital soundtrack is contained on CD-ROM discs. The timecode tells the player when to play the discs and what to play off the discs. The process is normally used on new projects by film students and is a low cost solution for presenting 16mm films in 6-track digital sound. The speed you are referring to (16fps) is what we refer to as "special venue". We'd have to do some testing on that to be sure all would playback correctly. If you are truely interested in persuing this, please send me an email and I'll get you touch with our special venue guy. Karen at DTS khultgren@dtsonline.com  |  IP: Logged Scott Norwood Film God Posts: 8146 From: Boston, MA. USA (1774.21 miles northeast of Dallas) Registered: Jun 99 posted 01-22-2003 09:23 PM                        Why do we need digital sound with silents? Part of the fun is having live music performed as the film runs, and a real orchestra will sound better than any electronic reproduction system. Many silents are intended to be run with variable-speed projection, anyway, and not at a constant 16 or 18fps.  |  IP: Logged Joe Beres Jedi Master Film Handler Posts: 606 From: Minneapolis, MN, USA Registered: Nov 2000 posted 01-22-2003 11:31 PM                     It was just a point of curiosity for me. I didn't know what boundaries that technology itself has. It's kind of an unrealistic idea, but an interesting one, I think. I've been lucky to work in places that bring in musician(s) to play along with a silent film, but I'll probably never see some of the big budget silents performed with their original orchestral score. It would be interesting to see the image presented properly, but also hear what people would have heard at the film's premiere. I do agree though, there is nothing like the experience of seeing a silent film accompanied by a great musician or group.  |  IP: Logged John Hawkinson Film God Posts: 2273 From: Cambridge, MA, USA Registered: Feb 2002 posted 01-23-2003 12:09 AM                     You could probably also free-run an external music source, since the alignment is not that precise. How much smarts are in SRD readers, anyhow -- can you get raw access to the CCDs? If so, you could do 16fps 35mm with a Cat700 (+-1) and a DTS-6D with a little converter widget inbetween, just like DTS-16. Of course, at that rate, you might as well just use a shaft encoder. --jhawk  |  IP: Logged William Hooper Phenomenal Film Handler Posts: 1879 From: Mobile, AL USA Registered: Jun 99 posted 01-23-2003 02:06 AM                        Like Scott said, silent films were shot & are projected at different speeds. For the most part, only the earliets were 16-16 fps For the love of Mike, please don't run them at 16 or 18 fps. It was even expected at the time that in projection speed would be slightly faster than taking speed, & the slight speed increase was part of the "art" of movies. Anybody who's ever sat through Safety Last, Thief of Baghdad, etc. projected by someone who didn't do their homework well & insisted that silent movies are 16fps knows how much it makes you want to just start slapping the guilty. Those averaged around 24 fps. Something earlier like Birth of a Nation has much that was taken about 16 fps & was meant to be projected at about 18 fps. David Pierce's page at http://www.cinemaweb.com/silentfilm/bookshelf/#March1998 has info on this, & includes period instructions from different films for particular projection speeds. The projection speeds are feet per minute, so you must divide by 3.75 to get frames per second. And if you look at the later SMPE RP's for silents, you'll find an interval of from +/- 2 feet per minute to +/- 6 feet per minute! Which makes sense, since in the days of hand-cranked cameras & projection a couple of fps margin of error would be inevitable. When in doubt, run it at 24 fps. Unless it's real old stuff like BOAN or Lumiere's. Historically, the projection speed was what looked best to the projectionist, barring outside influences like the manager telling him to crank them through as fast as possible to get more shows in per day.  |  IP: Logged Michael Schaffer "Where is the Boardwalk Hotel?" Posts: 4143 From: Boston, MA Registered: Apr 2002 posted 01-23-2003 05:29 AM                        Theoretically, it should be possible to use SDDS at 16fps as the data blocks are adjacent to each other. While for Dolby Digital vertical tracking is provided by the perforations and the edge of the data blocks, with SDDS vertical sync is provided by patterns in the data blocks. However, the optical image of the blocks would have to be compressed by 1/3 so that the data is read at the rate specified for the system. That would require film stock with a very high resolution and quality. Also the pixels would be rectangular rather than square. But I think it could work as there is a zigzag pattern on the side of the track which is called the zipper track which regulates the electronic "shutter" of the CCDs. That means the zipper track tells the reader when to read a new line of pixels. BTW, neither Dolby nor SDDS use variable bitrates. It wouldn`t make sense to use variable bitrates if the playback speed is defined by the medium from which the data are read. As both systems use data compression, the goal is to use the limited data rate allowed by the playback medium as well as possible. Dolby uses a technique called Parametrical Bit Allocation. It shifts the amount of data dynamically between the channels depending on which channels need more information at any given moment. But that is not a variable bit rate. The information rate read from the print is constant.  |  IP: Logged

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