Does a DCP Have to Have Surround Sound?

The original surround sound

Digital Cinema Packages do not demand surround sound audio, but it’s a good idea. And they should never be in stereo in most cases.

How Are Speakers Set Up in Cinemas?

The vast majority of theatres in the world are set up for “5.1” Surround sound. Three speakers are at the front of the theatre (A “Left”, “Center”, and “Right” speaker). Two are at the back (A “Left Surround”, and “Right Surround”). Those are the 5 speakers in the 5.1. The “.1” refers to a special speaker only used to make low rumbling noises. This “Low-frequency effects” speaker handles things like explosion sound effects.

Other setups (like 7.1 or 11.1) have more speakers (like “side”, or “ceiling” positions). Some new systems (like Dolby ATMOS) have even more flexibility, and allowing for various numbers of speakers.

It’s also important to note that while we say “speaker”, we actually mean “channels.” Each channel can use more than one speaker. For example, many theatres use several small speakers for “left surround” and “right surround” – even though they’re all playing the same sounds. So just counting speakers doesn’t tell you how many channels of sound a theatre is actually using.

How are Movies Mixed?

Typically in a film, all the dialogue is only on the “Center” channel. These speakers are usually behind the screen (which has holes for sound to get through). With this setup speech and other key information, always seems to come right from the screen (where the audience is looking).

(Creative commons photograph by Kenneth Lu, used with permission.)
(Creative commons photograph by Kenneth Lu, used with permission.)

The other speakers are usually only used for music and sound-effects. This lets sound mixers create an immersive space which can fill the theatre. However, they don’t have to worry about where exactly the audience is sitting.

Why Isn’t Stereo a Good Option For DCP

Stereo (or 2.0 sound) only uses two Channel – “Left” and “Right”. In many theatres, the Left, and Right speakers are also behind the screen with the Center speaker. But in some cases (especially smaller multiplex cinemas, or multipurpose theatres often used by festivals), the Left and Right speakers can actually be on the side walls (or split across several speakers, in various locations).

A DCP with a stereo mix can be confusing in those venues. It can sound like dialogue is coming from two (or many) places at once, even from behind the audience.

Even worse stereo DCPs also suffer from “phasing” problems. Phasing occurs when there are small delays between two or more speakers playing the same signal. In some types of sound (music and sound effects) this is usually not noticeable (or sounds like a slight echo or reverb). However our brain is very picky about human speech and phased dialogue can sound very distorted and be extremely difficult to understand. That’s why dialogue always should always exist only on the center channel.

(Creative commons photograph by Kenneth Lu, used with permission.)

Trying to play stereo properly in a surround theatre is usually a very frustrating experience for a filmmaker (and for an audience too)! While most equipment will attempt to play it – 2.0 audio is not a valid option under the DCP technical specification.

What are the official audio layout options for DCP

To be valid DCPs need to have Mono (1.0), L/C/R (3.0), or Surround (>5.1) audio. Most awards programs, festivals, theatre chains, and distributors require DCPs that meet this requirement.

My Movie Only Has a Stereo Mix, What Can I Do?

So what are the options for a filmmaker who only has a stereo mix for their film but needs to create a DCP?

The easiest option is to combine both the stereo tracks together to make a single Mono track. 1.0 sound only uses the one Center channel speaker. All sounds play through the one position, from the screen. While this does avoid technical problems it only uses one speaker in the theatre and most films will sound quiet and “thin”. As well environment noise (the audience, other movies next door) will be much more noticeable.

A better option is to “upmix” to try and create a Surround sound track from a stereo source. In an upmix, an audio team does their best to remove all dialogue from the stereo. Afterwards, the remaining sounds are “shaped” to all the channels, and the dialogue restored only on the center channel. When done well, the result is a full surround sound experience.

How Good Can an Upmix Sound?

An artificial mix will never sound as clean as an original surround mix done by a human engineer. An original mix can place every single sound anywhere in the soundscape (like a plane flying in from only the left speakers, or a distant explosion only in the rear surrounds). An upmix has to make compromises. Trying to unmix audio is like trying to unscramble an egg. However, the quality of upmixes has greatly improved in the last couple of years due to recent advances in audio technology. The upmix team at now uses neural network (artificial intelligence) algorithms in our tools and is getting results that would have been impossible only a few years ago. We have even done upmixes for test screenings of large feature films where the crew of the film didn’t realize it was an artificial mix. And upmixing is much faster, and a fraction of the cost, of a traditional surround mix.

Don’t Just Do It For the Audience

Surround sound will always provide a better in-theatre experience. Unlike home theatre, large cinemas are unforgiving to stereo or mono material. And there are reasons to make sure your DCP is in surround beyond audience experience. It’s often required for major film festivals, distributors, and most major industry awards – so if you have aspirations for your film, why not make sure it’s done right to begin with!

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