This is topic Auto-switching of sound format, how does it work? in forum Film Handlers' Forum at Film-Tech Forum ARCHIVE.
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Posted by David Stambaugh (Member # 1102) on 03-09-2002, 06:19 PM:
Apologies in advance for asking a newbie-type question, but there are probably other lurkers here besides myself who are curious about this. I couldn't find a definitive explanation of this in a search.How is sound format switching done? Suppose you have a screen equipped with SDDS, DTS, and SR-D. You want to show the feature in SDDS, but maybe some of the trailers don't carry SDDS but do have SR-D, yet you want to show all of them in digital if possible. How is the switching between formats done? Other threads have mentioned using automation cues, or doing it manually (manual switching doesn't seem very practical if you have 20 screens to tend to). So in the real world, how is this normally handled? And is it possible to completely automate this to the point where you prioritize the formats, so if the sound track is present in the preferred format, that format is automatically used, but if it's not present the next highest priority format is used instead, and so on, with analog being the last-ditch fallback?
Enquiring minds want to know. 
Posted by Jon Bartow (Member # 241) on 03-09-2002, 10:05 PM:
Generally speaking (there are always exceptions of course) if you want to change from one digital format to another you must either change the format manually (i.e. go over and push the apropriate button) or have a cue set up in the automation.
*A cue being a mehtod of tripping the automation actually applied to the film ahead of time by the projectionist. (various cue types range from strips of sticky-backed foil that actually make electrical contact between two rollers, to proximity detectors that "sense" foil dots placed on the film, to bar-coded stickers that are read by a bar-code reader [bar codes are a United Artists Theaters speciality])
*Theater automations are essentially just industrial automations, very similar to any system running an assembly line, etc. When a cue is "read" by the automation it starts a series of timers and relays to control a pre-determined series of events (i.e. curtains, light levels, turret position, sound format, etc)
*The three digital systems (DTS, SR-D, SDDS) do not like being engaged with each other on the same screen at the same time without a controller to prevent interference with each others signals.
-DTS waits for a timecode to be read on the film and if the correct disc is in the player for that film (or trailer) it switches into DTS automaticaly
-SR-D can be set up to switch on in one of two ways: either it waits to receive a signal from the automation or it will engage as soon as it finds a SR-D sound-track on the print (this is referred to as "auto-digital" in the Dolby literature)
-SDDS IIRC behaves the same way as SR-D (either triggered by the automation or automatic) The SDDS DFP-D3000 will do a digital fallback structure incorporating all three Digital formats with a customer preset hierarchy of formats (i.e. SDDS -> SR-D -> DTS -> SR ) I've never seen it done with any other equipment but it is possible.
I'm sure others will have much more to add to this but it's a start
Jonathan
Posted by Brad Miller (Member # 2) on 03-09-2002, 10:34 PM:
Anything is possible, but each and every different model of cinema processor brings about it's own requirements for wiring and "rigging" to get the fallback structure you are inquiring about. Clearly the DFP-3000 is the easiest, but I still prefer the Dolby CP200.
Posted by Steve Kraus (Member # 476) on 03-10-2002, 12:17 AM:
Note that the separate (non-combo) SDDS processor is designed to be wired between the existing CP and the power amps. It contains its own house EQ and fader. Thus, when there is valid SDDS the signal is sent to the amps in place of the CP output. When/if SDDS drops out then the CP signal is passed. (It's not mandatory to wire it this way--one can leave the EQ and level flat and route it via the CP--but this is the norm.) Thus, with this arrangement SDDS would have priority and would take care of itself, regardless of what was happening back at the CP.
Posted by Steve Guttag (Member # 268) on 03-10-2002, 04:36 PM:
It is often possible (and it is the way I install multiple digitals) to pre-determine the preferred digital priority amungst the digital formats. Sometimes it takes some tricky wiring to get the priority the customer wants. The idea is that the operator threads all readers and if there is valid data on one or more digital systems, the cinema processor will use any or all digital system. If the one with the most priority fails, the next highest digital processor in the priority is already playing in digital to fall back on. How the three systems work (from a logic and channel standpoint) makes setting the priority levels easier or harder for different priorities.
Steve
------------------
"Old projectionists never die, they just changeover!"
Posted by David Stambaugh (Member # 1102) on 03-10-2002, 05:37 PM:
Thanks for the explanations, appreciate the info.
Posted by Scott Norwood (Member # 30) on 03-10-2002, 09:18 PM:
As a practical matter, BTW, no one really does this, at least not in multiplexes. For the most part, one usually just sets up the equipment for the digital format desired for the feature and plays the trailers and other material in either that same format or analog.At the risk of being tormented, I will add that my personal preference is to run trailers in analog and play only the feature in digital. I would feel differently if trailers were mixed better, but most of them are just too darn loud in any format, and the added dynamic range of the digital formats just makes this worse.
Posted by Jesse Skeen (Member # 586) on 03-10-2002, 11:24 PM:
OK Scott, I won't torment you, but the thing I've always liked about trailers since they started doing them in digital is how the music is usually kept out of the center channel. Makes for interesting listening through the booth monitors when they're set to center-channel only (the last theater I worked at I used this to uncover a few problems with the sound). I thought they were going to finally do something about the loudness issue, but guess that hasn't happened yet?
Posted by Brad Miller (Member # 2) on 03-11-2002, 03:52 AM:
Hey Scott, I agree with you and to this day still have the automations programmed to run trailers in SR at a lower volume (about 7-8db lower than the feature). If more cinema processors could be set up on a special format to run SR without sub or surround (like we did at Northpark), I would do that too.
Posted by Ken Lackner (Member # 1002) on 03-12-2002, 10:24 AM:
Quote: "The SDDS DFP-D3000 will do a digital fallback structure incorporating all three Digital formats with a customer preset hierarchy of formats (i.e. SDDS -> SR-D -> DTS -> SR ) I've never seen it done with any other equipment but it is possible."I have only worked with one multiple-digital screen. Back at my last theater, our largest house had a Sony DFP-D30000 system, along with a Cat. 701 and DA 20 for SRD. Sony was set up as the default with SRD as backup. Since nearly all trailers contain SRD, if there was a trailer that did not have SDDS, the system would fall back to SRD. I take it this is was a feature of the Sony system, right? How would you do it with, say, a Dolby processor?
Posted by Gordon McLeod (Member # 33) on 03-12-2002, 11:21 AM:
I could never quite figure out how kintek had there autosense in the KT800 that claimed it would autoselect a or sr stereo from mono
The stereo part could be done easily with a level/phase comparitor that switched as soon as there was a difference between the optical tracks but to be able to select the NR
Posted by Karen Hultgren (Member # 395) on 03-12-2002, 12:36 PM:
David,I think your questions on how digital units switch in has been answered. If you have any DTS questions, please let me know.
Karen at DTS
khultgren@dtsonline.com