Dolby Mix stage requirements for surround

Noiz2

Sound Ninja
Perhaps this should be a sticky?
There is a lot of talk about surround on micro budget projects and a "I can mix this on my computer speakers" attitude that I hear a lot. I'm not talking so much about this board as about people I talk to in person about projects.

So just to be clear about things, below is not what Dolby want's you to have it's what you MUST have or they won't let you do DD. So before you go and say I can do DD Surounf inside FCS take a read because you can't.



Theatrical Sound Production Facility Requirements

1. Introduction

Dolby Production Services contracts services and encoding equipment to content owners and
distributors wishing to release their theatrical program in a Dolby format. To ensure the highest
quality and reliability, Dolby requires that these services take place in an audio production facility that
meets the minimum requirements outlined below.

Facilities wishing to be considered for Dolby approval should contact Dolby Production Services.

2. Room Design

2.1. The room must be large enough to accommodate at least “Mid Field” monitoring. The minimum
acceptable room dimensions are 20’ long (Screen to Rear Wall) by 13’ wide with a 9’ ceiling
height. The optimum mix position is located 2/3 the length of the room away from the screen. In
the minimum sized 20’x13’ room, this position is 13’-4” from the screen.

Refer to chart below for acceptable room dimensioning ratios. The shaded area represents
acceptable conditions, whereas the straight line represents the optimum ratio.

3. Speakers

3.1. The screen speakers (Left, Center, and Right) must be the same make and model and must be
behind a perforated projection screen. The screen speakers should be able to reproduce
frequencies +/-3dB from 40 Hz to 16 kHz without assistance (satellite systems utilizing a
subwoofer to achieve full range are not acceptable for use as the screen speakers). The screen
speakers must be able to produce “clean” sound pressure levels (peaking) up to 105dBC SPL.
The location of the Left and Right speakers should not subtend an angle greater than 45
degrees from the mix position. The speaker cabinets should also be mounted at the same
vertical height, which should be mid-screen, for all screen channels.

Rev 20080213 Page 1 of 3




3.2. There must be at least (2) pairs of surround speakers mounted along the sidewalls to create an
effective surround “array”. Larger mixing rooms will have several surround pairs that cover
listening areas in front of and behind the mix position. In smaller rooms, the first pair of
surrounds must be slightly in front of the mix position. The second surround pair should be
slightly behind the mix position.

Mix stages that are to be equipped for Dolby Digital Surround EX must also have at least (1)
pair of surround speakers mounted on the rear wall. A separate two-channel amplifier must also
power the rear surround speakers to allow proper Surround EX monitoring.

For smaller mix rooms, surround speakers should never be directly “on axis” with the mix
position. The surround speaker array must be able to produce “clean” sound pressure levels
(peaking) up to 105dB SPL.

3.3. There must be a separate subwoofer capable of producing an equalized response of 25Hz-
120Hz +/- 3dB. The subwoofer must also be able to produce “clean” sound pressure levels
(peaking) up to 115dBC SPL.

4. Equalization & Delay

4.1. The speaker system must be equalized to the ISO 2969 “X” curve. There must be 1/3 octave or
parametric equalization inserted before the screen channel amplification to accomplish this
equalization. For the surround channels, single octave EQ is acceptable but not recommended.

4.2. If the distance from the mixer to the screen is more than 1.5 times the distance from the mixer to
the surrounds, a suitable delay line should be inserted (Pre-EQ) into each surround channel
monitoring path. It is recommended that the delay line is patchable so that it can be inserted in
the recording chain should a separate picture and track screening master be required.

4.3. A parametric EQ of at least one but preferably more bands and a 120 Hz low pass filter (Pre-EQ)
should be inserted in the LFE (subwoofer) monitor path. The LFE filter should be a 3rd order
Butterworth filter set with a crossover point at 120 Hz. Higher order filters are acceptable, but
lower order filters can cause incorrect perception of the LFE channel. Also, it is recommended
that the 120 Hz low pass filter is patchable so that it can be inserted in the recording chain
should a separate picture and track screening master be required.

5. Level

5.1. After proper equalization, the monitor levels need to be calibrated to 85 dBC SPL for each
screen channel (L,C,R), 82 dBC for each surround channel, and +10 dB in-band gain (RTA
method) referenced from the center channel for the subwoofer. A compliance check of EQ and
levels by a Dolby engineer must be performed prior to commencement of each contracted mix.

5.2. The sound system must be designed to provide a minimum headroom specification of +20dB
above normal reference level for each channel.

5.3. The console monitor section must have a multi-channel assignable fader with at least six inputs
and outputs. The monitor section must also provide a ‘fixed reference level’ mode for proper
listening levels when mixing and print mastering.

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6. Equipment

6.1. Dolby will supply a Digital Mastering Unit (DMU) to approved 5.1 mixing studios IF the length of
the film is 40 minutes or more. For short subjects or trailers, the film must be mastered to a
digital multitrack format and transferred at an approved Dolby Digital transfer facility..

6.2. Studios that are approved to use the Dolby DMU mastering system must also meet certain
business requirements (films per year) to be considered for a permanent installation. For studios
not meeting these business requirements, Dolby supplies a traveling DMU on a “per-mix” basis.

6.3. The “Dolby Surround Tools” plug-in for ProTools can not be used to create an Lt/Rt during the
final film print master. This plug-in does not facilitate the proper metering and processing needed
during mastering. Although the plug-in cannot be used for print mastering, it can be used for pre-
mixing. Also, any analog tape machines being used for the mix should be equipped with Dolby
SR noise reduction

Note: Dolby Laboratories, Inc. Model CP650 is a recommended cinema processor for decoding many
formats such as: Dolby Digital Film Soundtrack, SR/A Optical Film Soundtrack, and Digital 5.1 and
Lt/Rt Studio Masters.
 
This certainly eliminates some folks from delivering DD but it seems to be based upon strict requirements needed for a quality production. Any idea what the theory is on the distance requirements, that seems to be the tough one for really small studios.
 
If you don't meet the requirements you don't get certified for DD and you can't mix it. It's easy to enforce since a Dolby guy has to come out with the Dolby recorder to actually capture the mix that goes back to Dolby to be processed. For Matrixed surround it's laxer, though not much - mostly that the surrounds are mono. Dolby doesn't have to be there to capture the mix but the EULA on the Dolby boxes forbid you to mix a project till it has a signed license from Dolby, and they can pull the encoding cards if they catch you cheating.

You can encode with an alternate matrix system like SRS. They have cheaper licenses and you can in theory do it on any stage or room. BUT the Dolby specs are there for a reason and not getting at least close to them is just asking for a mix that will not play back well in theatres.
 
This certainly eliminates some folks from delivering DD but it seems to be based upon strict requirements needed for a quality production. Any idea what the theory is on the distance requirements, that seems to be the tough one for really small studios.

And not mentioned but a DD license runs $12,000+ so DD is out for a lot of folks anyway.

The reason for the distance/ size requirements is that this is for theatrical work. You can't mix for a large space in a small space. Well actually you can IF you know how it's going to translate AND you check it in a big space. But you can't reliably mix for theatres in a small space, things just change too much with size. THX has even whackier requirements for space. THX wants to see a min volume, but it doesn't need to be in the usable room, it can be above a false ceiling??? So you will find some small THX "certified" mix rooms that seem too small but they will have a space above the ceiling that sometimes is as big as the mix room itself. As a former physics major it makes no sense to me at all but it is what it is and having that THX bug is a selling point.
 
I've seen this spec document before, and I have to say first of all that it's absolutely wonderful that these kinds of standards exist, unlike in the music recording business where there are none. The saddest consequence there is the ascension of the truly tragic "volume wars" (i.e. 'maximizers' set to "kill") which has for all intents and purposes destroyed the fidelity of modern pop music CDs. But that's another topic...

It's fascinating to see how this very well intentioned (and, evidently, well implemented) standard came to be through one fundamental force: Dolby won't license the use of its DD logo (and its DD hardware) unless you have a properly calibrated mixing environment. Hooray! Fidelity insurance! Or as close as we'll ever come to it...

The specs as listed above, given the theater environment for which they're intended, is IMO a paragon of good sense. The numbers make sense, and the results should be beneficial to all movie viewers and sound mix personnel, not just Dolby themselves (who clearly benefit too). Sure, it presents a dilemma for the likes of me, with an 11x13 nearfield-only control room in my own studio (although I freelance at the big joints); I can't get a Dolby license to mix post in my studio. But...I can still do it, and do it well if I'm very careful and thorough (something I try very hard to do always). Then, as long as I bring what I do to a Dolby certified post room to finish, I should be good to go.

So that's my little conceptual workaround - design a 5.1 mixing environment that *works* (and I'm almost there now), which is all Dolby really wants anyway - the actual mix is almost entirely up to the taste of those involved. This should be fine for anything I do straight to DVD/Blu-Ray when the "DD" logo isn't needed. When it is, after completing the mix to about a 90% level in my control room, I can take my PTHD files to a DD licensed studio, finish it in a far shorter time than it would have taken from scratch, and walk out with a DD approved version that's affordable on an indie budget.

Hopefully, I don't need too much of a talking down on this, but I'm listening if I do... : )
 
Ted, if you can get results, then why not? After engineering around town for many years I'm sure you know the who & how to get the job done correctly: IMO good strategy. It would seem like any difficulty in translating the mix might be in a few minor EQ & level adjustments, and that's just a small fader touch away.

I'm wondering how folks have the perforated screens & projectors with their speakers set up behind the screen at the mid screen level. That's an interesting but for most cases, appropriate spec.

I once watched a bit of a movie from behind the screen at a theater, what an interesting experience. You can see the audience looking right at you and all their responses. A small video camera back there recording would be a great way to gather & gauge audience reactions for testing a WIP.
 
I once watched a bit of a movie from behind the screen at a theater, what an interesting experience. You can see the audience looking right at you and all their responses. A small video camera back there recording would be a great way to gather & gauge audience reactions for testing a WIP.

Great idea! I bet it's been done many times... : )
 
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