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Digital Sound - Formats Explained

Last Updated on April 19, 2024

Digital Sound and Digital Cinema

The movie theater industry transitioned to using Digital Cinema Projection systems, which means that film has been replaced by digital files provided by a computerized server. All Digital Cinema Projection systems output sound digitally, whether it is one channel or up to 12 channels that is allowed by the Digital Cinema specification.

The sound is compressed losslessly, which means that there is no compression used that removes any of the original sound that was produced in the studio. Think of film-based digital sound being similar to an MP3 file and digital cinema sound being like a multi-channel CD.

Immersive Sound Formats

Immersive sound formats are an upgrade to standard digital sound. These formats add more channels and/or layers to the soundfield, providing an enhanced experience over and above the more traditional surround sound presentation.

Digital Sound logoDigital Sound

All sound that you hear during a Digital Cinema presentation is stored and delivered digitally, as mentioned previously. Since this can be anywhere between 1-12 channels, it is up to the theater to specify if they are doing something other than the traditional, expected format of 5.1 channels (3 front, 2 surround, 1 subwoofer).

7.1 Channel Digital Sound

7.1 channel sound for Digital Cinema was introduced with the 2010 release of Toy Story 3. It splits the traditional two surround channels into four, so you now have two side surround channels (left and right) as well as two rear channels (left and right). This allows for more localization of sounds as they pan behind the listener and can help when action flies overhead, since the sound can move from in front of you to behind you, causing your brain to fill in the gap above you (to a certain extent).

This sound format does not have an official designation, so many theaters just refer to it as "7-channel digital sound" or something similar. It is marketed by Dolby Labs as Dolby Surround 7.1, even though no Dolby-specific technology or equipment is involved in the process (see below). We rely on the theaters to provide this additional information in the showtime comments. Just look beneath the showtimes to see designations for 7.1 channel digital sound.

Dolby Surround 7.1 logo Dolby Surround 7.1

In 2010, Dolby Labs worked in conjunction with Walt Disney Pictures and Pixar Animation Studios to introduce a new sound format with their release of Toy Story 3. Dolby Surround 7.1 takes the rear surround channel as described in Dolby Digital Surround EX (below) and splits it into two channels. Dolby Surround 7.1 is only available with Digital Cinema Projection systems.

An interesting note about this sound format is that the ability to produce 7.1 channels of sound is built into every Digital Cinema Projection system. Dolby Surround 7.1 is the marketing name that was given to the 7.1 channel sound format, but nothing about it is unique to Dolby technology or equipment.

If theaters indicate that their presentation is in Dolby Surround 7.1, we add the logo you see above to the showtimes for that movie at that theater.

Film-Based Digital Sound Formats

With the industry's transition to Digital Cinema Projection, film-based formats are becoming less common, but no less important. If you are seeing a movie in a film-based theater, you want to look for the logos below to make sure that you are hearing the best possible sound quality in the presentation. While most all theaters should be using one of the digital sound formats, it cannot be guaranteed. If you do not see one of the logos below in the showtimes, you might be disappointed with what you hear!

Dolby Digital Dolby Digital

Also known as SR-D, this system is manufactured by Dolby Labs, a very big name in audio technology. This sound system is capable of reproducing 6 distinct channels of sound. Left, Center and Right channels behind the screen. Left and Right surround channels, plus a low frequency channel for special effects, like explosions, etc...

These 6 channels of sound are encoded into a 2 dimensional code that is printed onto the film stock. Unlike the DTS system, there is no external CD player required. A special reader is mounted to the film projector that reads this code, converts it to sound we can hear and passes it to the amplifiers.

For those techies out there, the 2 dimensional code is printed onto the film stock in between the sprocket holes on one side. Due to the proximity of the data to the edge of the print, and the compactness of that data, some early Dolby Digital presentations were more subject to audio dropouts than DTS and SDDS presentations, since wear and tear on the print can cause the audio data to be lost for brief periods of time. This effect can be slight, or can be quite jarring, depending on the severity of the error. After a few years, the technology improved and awareness by theater personnel reduced these problems to nearly zero.

Dolby Digital Surround EX Dolby Digital Surround EX

In 1998, Dolby Labs and LucasFilm announced a new enhancement to Dolby Digital called Dolby Digital Surround EX. This format extrapolates a rear center channel from the two side channels, adding another source of sound inside the theater. The first movie to feature the EX format was Star Wars I - The Phantom Menace.

For more information, you may want to visit Dolby's web site. The first Dolby Digital Surround EX processor, the SA-10, is capable of a dynamic range of 88dB.

Datasat Digital Sound Logo Datasat Digital (aka DTS Digital DTS Digital)

DTS stands for "Digital Theater Systems" which is now known as Datasat Digital Sound. This sound system is capable of reproducing 6 distinct channels of sound. Left, Center and Right channels behind the screen. Left and Right surround channels, plus a low frequency channel for special effects, like explosions, etc...

These 6 channels of sound are recorded onto compact discs similar to music CDs found in the home. Two discs are used for most movies. The sound is synchronized with the picture by means of a timecode that is printed onto the film stock itself. A special reader is mounted to the film projector that reads this timecode and tells the CD player what it should be playing at any given time.

For those techies out there, the time code is printed onto the film stock between the picture and the optical audio tracks. We have found in our experiences that DTS presentations are some of the most solid. We have not attended a DTS presentation where the audio was lost during any point of the film, which causes us to seek out DTS presentations whenever possible!

 

DTS Digital ES DTS Digital ES

There is an enhancement to DTS that performs the same functions as Dolby Digital EX, and that format is known as DTS-ES. Some theaters may (incorrectly) label this format as DTS EX, due to its similarity to the Dolby product.

According to the DTS web site, it is "fully compatible with all current 5.1 digital formats and systems, and DTS-ES also provides event closures to trigger dramatic trailer and feature effects, such as strobe lights, lasers, and more." The center surround channel is derived from the right surround and left surround channels on ES-encoded soundtracks, just like Dolby Digital EX does. For future applications, a top surround channel is also derived. According to the DTS web site, the DTS-ES surround processor is capable of a dynamic range of >100dB.

 

SDDS Digital SDDS Digital

Stands for "Sony Dynamic Digital Sound". This sound system is capable of reproducing sound in two configurations. One with 8 distinct channels of sound. Left, Center-Left, Center, Center-Right and Right channels behind the screen. Left and Right surround channels, plus a low frequency channel for special effects, like explosions, etc...

The other has 6 distinct channels of sound. Left, Center and Right channels behind the screen. Left and Right surround channels, plus a low frequency channel for special effects, like explosions, etc...

Most installations use the 6-channel configuration. The 8-channel configuration is used only when the screen is large enough to handle the additional speakers between the screen. These 6 or 8 channels of sound are encoded into a code that is printed onto the film stock. Similar to the Dolby system, there is no external CD player required. A special reader is mounted to the film projector that reads this code, converts it to sound we can hear and passes it to the amplifiers.

For those techies out there, the codes are printed onto the film stock outside the sprocket holes on both sides.

SDDS presentations are rare in many markets, so our experience with SDDS is limited. Even though the data for SDDS is in the most vulnerable location (on the outside edge of the print), we have not found that theaters have as many problems with sound dropouts on SDDS presentations as on Dolby Digital presentations. Due to the limited experience we have with this format, it is difficult to draw solid conclusions of the reliability of SDDS presentations.

Failsafe or fall back systems

All three digital sound formats have a fall back system in place in the event that the coded information on the print becomes unreadable for some reason, or if there is some other breakdown in the reader. (or the CD player goes bad in the DTS system)

Both the DTS and Dolby Digital systems will fall back to playing the old analog audio tracks. The SDDS system will first fall back to a duplicate coding on the other side of the print and if that fails, or if the reader fails, then it will fall back to playing the old analog audio tracks.

All three systems will return to playing the digital information once the problems have gone away or have been corrected.

What About THX?

THX is not a digital sound format, but rather a certification for movie theaters that dictates the quality of the construction, the components used, and a calibration of the sound system that is repeated on a yearly basis. THX makes digital sound better!

For more information about THX, please see What is THX?




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