by Cindy Hill on Feb 3, 2011 at 1:14:49 pm
My colleagues and I are working on a feature-length documentary and are considering mixing in Dolby 5.1. I have two fairly basic questions. What happens to the mix when your film is played in a venue that is not equipped with surround sound and does one need to fill the sound space at all times to avoid dead zones? Sorry if my phrasing is off. This is all very new to me.
There are different surround formats, not all of them involving Dolby, so it's important to first determine the destination of your mix.
If this will go straight to DVD, you can encode your mix to the Dolby AC-3 format with many media applications, including Compressor. The AC-3 format has its own downmix facilities, so it will fold down the 5.1 mix to stereo if only stereo playback is available. Some people rely solely on that, while other also include a dedicated stereo mix on another audio track of the DVD. Both work, and the AC-3 folddown usually sounds pretty good.
If this will go to theatres for screening, things get a little more complicated. You have to know from the theatres which format they want. More and more of them are asking for DCP (Digital Cinema Pack), which are normally created by a specialist post-house. In that case, you have to send out the discrete audio channels for the creation of the DCP, so Dolby are not involved in the process at all on your end. The ingest department of theatre chains can usually refer you to a post house for the DCP.
If an analog print will be created, you'll probably need a Dolby DMU to create the MO Disk used at the print master stage. Now you're opening a whole new can of worms. Dolby do not sell the DMU, they lend it to approved facilities. That means you have to establish a contact with your Dolby rep, have them come in and approve your mix room with all their gear. That normally involves some room treatment and EQ'ing, which normally involves a sizeable investment on your part. Then, they will lend you a DMU and you'll have to pay the royalties for every show you encode. The setup of the DMU and the learning of it is not trivial either. If you have to go down this road, I strongly suggest you find a local sound post house that already has the DMU so they can create your master for you from your final mix. If you can find your local Dolby rep, they're usually very helpful with this kind of thing and can steer you in the right direction.
If you can send in HDCam SR, you just have to dump your discrete audio tracks on it, so Dolby are not involved. You would be responsible for creating the stereo downmix, in this situation.
The DMU has mixdown facilities as well and creates a stereo-compatible mix from the 5.1 when you encode.
As for aesthetic considerations, you shouldn't strive to fill in spaces just to fill in spaces. It should be natural-sounding, while steering clear of gimmicky use of the surround channels. This is a much deeper subject that isn't even settled amongst pro mixers, so it's hard to give steadfast rules on it.
Good luck. If you have further questions, fire away! If you know your output format, we can streamline this mass of information down a bit.
For material intended for DVD, I'd go for a dialnorm of -27, mainly because it's what most broadcasters we go to air on ask for, so the workflow can stay the same. I'm kind of lazy that way. I think it's what most people are using on commercial DVD's, too. Others I know work to -24, as that's another pretty common spec. I've never really investigated the sonic difference between the two, I basically read the specs and stick to them. I almost never work on material intended solely for DVD and am usually working to broadcaster specs.
For the creation of the LtRt, I normally use the DMU. I just have to open up a stereo track in PT and can record it in real-time while proofing the final mix. I use Neyrinck for Dolby-E and love it, so SoundCode would surely be my first port of call for a software LtRt solution as well. For straight downmixing duties, I use Waves M360.
The DMU CPU is the Dolby Mastering Unit (or something to that effect). It's the box we use to encode mixes for the analog print masters to go out to theatres. I don't think Dolby promote it at all, since it can't be bought from them.
When you enter a partnership agreement with Dolby, you buy the remote and meter bridge for it and can request a unit whenever you have a master to do. We happen to be lucky here as we have one of the regional units almost permanently in the rack. It's a big 4U box half-full of emptiness, really, once you open it up. You basically have I/O for 10 channels of AES/EBU plus timecode, the encoder CPU itself, an MO-Drive for the masters and connections for lots of different remotes and meters you could have attached. This is the sole bit of equipment I can think of that uses MO-Disks as its medium. Encoding is a real-time operations, akin to any recording locked to timecode and is done simultaneously in Dolby Digital, EX or not (SRD format), and LtRt (SVA format). We send the MO Disk to whatever facility is doing the print masters. Once every few months, a Dolby rep will stop by and take the logs on the DMU, to be sure you paid all your encoding royalties. There's no getting around them.
We tend to use the DMU a bit less since more projects go out as DCP only, but many still go out dual-format.