compression for cinema

rob spence · August 2, 2011

Hi

I'm having to do my own audio mastering for a festival ( because of no funds ) and it will be shown on cinema screens...Dolby Sterio is needed. Can anyone tell me if I need to compress the track and if so which method is best.

Im using Soundtrack Pro.

cheers.

Hal Smith · August 2, 2011

Hi

I'm having to do my own audio mastering for a festival ( because of no funds ) and it will be shown on cinema screens...Dolby Sterio is needed. Can anyone tell me if I need to compress the track and if so which method is best.

Im using Soundtrack Pro.

cheers.

Modern "Dolby Stereo" soundtracks require Dolby SR processing which is a specific companding system. You need Dolby gear to do it correctly. Dolby SR is a surround system, if you have a Left-Center-Right-Rear produced master, A Dolby box will encode it correctly for theatre surround sound reproduction.

Everything Dolby is a very controlled system with very precise requirements for track preparation, etc. I have seen the basic Dolby SR encoding processors on eBay for $200-300. That gear assumes you're sending it Dolby standard level tracks to encode L-C-R-S correctly to two tracks (Lt and Rt in Dolby nomenclature) for film sound tracks. The basic matching SR decoder will cost about the same but I'd want a theater processor and monitoring system to quality control tracks, that's what the big boys use in their re-recording studios. The simpler SR processors like the CP-50 have been going in the $300-400 range recently but they may or may not have two CAT 280T Dolby SR cards in them, a lot of them will have the older CAT 22 Dolby A cards. The "official" way of switching between Dolby A and SR in the older boxes was to have an SRA5 accessory chassis with two CAT 280T's in it but there's nothing wrong with manually swapping out 22's for 280T's as needed.

See my recent post at: http://www.cinematography.com/index.php?showtopic=52793&pid=355574&st=0entry355574 for more information on theater reproduction.

There is a treasure trove of information on Dolby's gear and proper recording and playback setup on their website. http://www.dolby.com/professional/services/index.

If you register at www.film-tech.com there's a large collection of manuals there for the older Dolby gear.

Dolby tracks on release media requires their professional license. I suspect Dolby has some sort of free or very cheap limited license for festivals and student projects. I also suspect if you sold a short to HBO with unlicensed SR tracks on it, Dolby just might come looking for you.

Chris Millar · August 3, 2011

Dolby SR and Dolby SRD - two different things ;)

Hal Smith · August 3, 2011

Dolby SR and Dolby SRD - two different things ;)

His posts talks about Dolby Stereo which I assumed to mean he was talking about analog A or SR tracks. I doubt if there are any festivals out there that require Dolby Digital, AKA SRD for submissions.

Chris Millar · August 3, 2011

Dang it!

Yes, you're quite right

I was referring more to the Spectral Recording side of the process it as opposed to the surround and so on:

http://www.dolby.com/DocLibTechLanding.aspx?taxid=182

But I made a smarty pants mess of myself

rob spence · August 3, 2011

Thanks for the replies, much appreciated. Looks like its technically out of my area to achieve it...we'll probably

have to get it professionally finished...any ideas on any Uk companies that are not too expensive?

Hal Smith · August 3, 2011

But I made a smarty pants mess of myself

There's nothing more embarrassing than an errant post. I know, I've done it myself enough times. :(

Having a complete Dolby A/SR/SRD system in my home theatre out in the shop is why I've learned as much about Dolby as I have.

I started with a half dead CP-200 that even has the accessory chassis for playing 70mm magnetic tracks, fixed it thanks to Dolby support who gave me(!) a service extender card, got a SRA-5 with the SR cards in it off eBay, found a cheap DA-10 SRD decoder on eBay, got incredibly lucky by buying a box of miscellaneous theatre sound gear cheap off a guy here in OKC that had a brand new, current model CAT 702 SRD reader hidden at the bottom of it. I've since retired the CP-200 and I'm using a simpler, much smaller CP-55 that I modified per Dolby for split surround.

I'm using five JBL 12" control room monitors for speakers and 750 watts or so worth of power amplification in the system. The weekend I finished it all I ran my print of "Master and Commander, Far Side of the World" for my daughter-in-law and her hubby. I cherish his comment: "It sounds like a real theater". It should...it's all real theater gear except for my JBL's which are physically smaller than what theaters run, but then the shop is only 1200 square feet.

Alex Donkle · August 5, 2011

Definitely a good call on getting it professionally finished.

Films are not technically compressed and/or mastered like music is. They are mixed by ear, and then Dolby (if you want to use their name, they require actually doing the transfer themselves) does the process as Hal suggested with the only goal of making a good recording of the final mix. For Dolby Digital, there are VERY specific requirements on the physical room, speaker, calibration, ect... that you can mix in. Dolby Stereo I'm not sure whether they have those same requirements, but in either case you really need a calibrated studio to mix sound on any film project.

In music, mastering is usually another layer of the art that adds its own tweaks.

On who to contact for a low budget Dolby mix in the UK? Can't think of anyone off hand, however I would check at these two forums that are more dedicated to film post sound. Tons of guys there who can at least point you in the right direction.

http://duc.avid.com/forumdisplay.php?f=8

http://www.gearslutz.com/board/post-production-forum/

Edited August 5, 2011 by Alex Donkle