Hello from Elmer the Projectionist.

The Basics of Theatrical, Stereo Sound

Cinema Sound Before the 1990s
The Start of Dolby Digital
DTS and SDDS Digital Sound Formats
The Channels of "5.1 Audio"
What's the difference?
The Pros and Cons of DTS
The Pros and Cons of Dolby Digital
The Pros and Cons of SDDS
5.1 Digital Audio Comes Home
Multichannel Digital Audio in 1999
Frequently Asked Questions

Cinema Sound Before the 1990s
For most of us, the dawn of widespread, practical, stereo cinema sound happened in the late 1970s when the Dolby System blossomed into the national scene. The basic system for 35mm, "Dolby Stereo" in the 1970s was a four-channel scheme, featuring three channels behind the screen and a fourth channel played through an array of speakers on the side and rear walls of the theatre. Because the rear, "surround" channel was spread to several speakers, it had a spacious characteristic which lent itself to natural, ambient sound effects like wind sounds, city noises, etc. It could also be used for the occasional, directional effects like the sound of a spacecraft flying out over the audience.

A typical layout for theatrical, 4-channel sound. Please note: The exact number of surround speakers carrying "channel 4" sound may vary. I'm sorry I didn't have time to make this drawing to scale and to paint it.

The 70mm system featured six channels of high-quality audio, with a total of five channels behind the screen and, once again, a single surround channel spread through the side and rear speakers of the auditorium. Because of the added audio capacity, the 70mm format was used extensively for Hollywood musicals in the 1950s and 1960s and for grand, epic films like Lawrence of Arabia. Large-format cameras were used for the cinematography and, in general, those 70mm presentations were both visually and aurally spectacular. However, in the mid-1960s, film printing technology progressed to the point where it became practical and cost-effective to film a given movie in a 35mm wide-screen process and then "blow it up" to 70mm for the theatrical release. The visuals were less exciting than a true, 70mm presentation, but the filmmakers could still take advantage of the improved sound of the 70mm presentation. Over the years, 70mm cameras fell into disuse and any innovations in camera technology were only developed for 35mm cameras or for "special venue" presentations like IMAX or amusement park rides. Generally, there was no call for new, state-of-the-art 70mm cameras for regular, theatrical features.

In 1978, with the release of Superman, The Movie, a "stereo surround" layout became available with the 70mm format, giving a "Left Surround" and a "Right Surround" channel instead of a single surround channel (Some have claimed that this introduction didn't happen until the 1979 release of Apocalypse Now). However, not many films presented in 70mm through the 1980s incorporated this "split surround" option and, instead, used the traditional, 70mm, six-channel format. It's a sad fact that basically all of the 70mm theatrical presentations you may have seen in the 1980s were just films shot in 35mm and released in 70mm to take advantage of the sound system. There was a marked difference in the visual splendor of a film which was actually filmed in the 70mm format.

In 1989, Columbia Pictures released a restored edition of Lawrence of Arabia and viewers agreed that its true, 70mm images were breathtaking. At about the same time, the top manufacturers of motion picture cameras, Arriflex and Panavision, announced the introduction of brand new, 70mm cameras with all the state-of-the-art features cinematographers enjoyed in the most advanced 35mm cameras. It was thought that this would mark a revival of the 70mm format and the return of the kinds of spectacular images which had been available in those classic musicals and epic films. But it was not to be. The only major theatrical film to be photographed in 70mm in the early 1990s was Ron Howard's underwhelming Far and Away. Within a year of that film's release, Dolby and other companies introduced advances in Digital Sound for 35mm releases and, suddenly, the 70mm theatrical format was all but declared dead.

A typical layout for theatrical, 70mm sound with a single surround channel. Please note: The exact placement and number of surround speakers may vary.

The Start of Dolby Digital
Dolby's "AC-3" digital sound format was the first to allow a single film print to carry both analog and digital sound information without the two formats interfering with each other. A theatre equipped for analog sound can show the same print as a theatre equipped for Dolby Digital sound. This breakthrough made the format far more practical than previous attempts at introducing widespread, digital sound to the cinema. The Dolby Digital system was tested in selected theatres before its official launch in 1992. A few public screenings of Star Trek VI: The Undiscovered Country and Newsies were presented in California without any advertisements that they were, in fact, Dolby Digital presentations. Researchers gathered data from those screenings to assess the durability and reliability of the format and then, with the release of Batman Returns, the format was officially made public. But this new sound format would not go unchallenged.

DTS and SDDS Digital Sound Formats
In 1993, with the release of Jurassic Park, the Digital Theatre Systems (DTS) format was introduced. A few days later, the Sony Dynamic Digital Sound (SDDS) format was introduced with the release of The Last Action Hero. Each of these new formats retained the traditional, analog 4-channel soundtrack on the print and, like the Dolby Digital system, they were programmed to default to analog sound in case of technical difficulties during the digital playback. All three digital systems were a vast improvement over analog sound, but the three were not compatible. Cost considerations forced studios and theatres to choose which, if any, of the new digital formats they would be using. For a while, certain studios and theatres had exclusive deals with one of the three sound format providers and, away from cities like Los Angeles, New York and Chicago, movie fans were left wondering if their favorite films would be released in a digital format compatible with their local theatres.

The Channels of "5.1 Audio"
Both Dolby Digital and DTS offer what's called a 5.1-channel presentation. The ".1" in that designation refers to a subwoofer-only channel for Low Frequency Effects or "LFE" sounds. The other five channels are the Left, Center and Right channels behind the screen and the Left and Right surround channels on the side and rear walls of the cinema. The dynamic range of digital sound produces both improved clarity and the kind of powerful, rumbling bass which most viewers had never experienced in a theatre before digital sound was available. Audiences can actually "feel" the T-rex approaching, for example. The use of a designated, subwoofer-only channel also gives film sound technicians more artistic control over exactly when the viewer will "feel" the sound. In sound systems which use subwoofers without a discrete, subwoofer channel, all bass sounds below a certain frequency are automatically routed to the subwoofer. A dedicated subwoofer channel allows more exact control, reserving subwoofer usage only for specific, powerful effects (For example, you can "feel" the dinosaur but you won't have to "feel" an actor speaking with a deep voice).

A typical layout for theatrical, "5.1" digital sound. The exact placement and number of surround speakers may vary.

The SDDS system goes a couple of steps further than Dolby Digital and DTS in that it's a 7.1 channel system, incorporating certain concepts from the classic, 70mm days. With SDDS, there can be five channels behind the screen in addition to the two surround channels and a dedicated subwoofer channel. However, not many films are created with the full, "8-channel" sound mix, even if they are released in SDDS. In most cases, today's films are mixed for a 5.1 presentation no matter which digital sound format is used in the theatrical release.

A typical layout for eight-channel, SDDS sound. The exact placement and number of surround speakers may vary.

What's the difference?
There are varied opinions about which of these three, digital sound formats is the best. Since most of us are limited in the number of available presentations of a given film in a given format, I'm content to know that I'm listening to a Digital presentation, no matter what the format. They're all better than analog. However, I do have my favorites among these competitors. Each format has its own advantages and disadvantages, both in technical terms and in terms of the strength of the companies which stand behind the technology.

The Pros and Cons of DTS
DTS is what's known as a "double system" because the sound and the picture are contained on two, separate mediums. With DTS, the actual film print contains an analog, back-up, four-channel soundtrack and, next to it, there's a "time code" which is read by a pick-up device on the projector. This time code is then sent to a DTS CD-ROM drive to ensure that the sound played from a special, DTS CD remains synchronized with the picture (The DTS CD is, of course, completely incompatible with a regular CD player, a computer CD-ROM drive, a DVD-ROM drive or a DVD player). So the disadvantage of the system is that there might be reliability problems with the CD-ROM drive or with the DTS CD staying in sync with the picture or, if there's any loss of signal between the projector's time code reader and the DTS CD drive, the digital audio will be lost completely. However, I should note that after more than 5 years of DTS in theatrical usage, reliability problems are very rare. The advantage of DTS over Dolby Digital is that it has a relatively low "compression ratio" when the 5.1 audio is squeezed onto those little Compact Discs. Most audio purists (including Steven Spielberg himself) seem to agree that DTS offers the truest fidelity when compared with the original, master sound recordings at the mixing stage (They have better ears than I do). Also, in comparison to the other formats, DTS equipment seems to be the least expensive for theatres to install.

The Pros and Cons of Dolby Digital
Dolby Digital has the disadvantage of using the highest compression ratio of the competing formats. Audio purists complain that some fidelity is lost in the process of encoding and then decoding the digital information. Dolby dismisses that complaint because they've studied the way human hearing works and have developed a "psychoacoustic" process which, they claim, compensates for the high compression ratio. You'll just have to listen and judge for yourself, I guess. Also, there can be problems during "reel changes" about once every twenty minutes during a film's presentation. Depending on how the projectionist splices a film's reels together, the splicing tape may cause the sound to briefly default to analog. This problem can easily be avoided by a conscientious projectionist. The obvious advantage of Dolby Digital is the worldwide support of the Dolby company, with its proven track record for innovation and technical support for theatre operators. Also, the fact that the Dolby Digital tracks are contained on the film ensures that there will never be sync problems.

The Pros and Cons of SDDS
To be honest, I don't know what the compression ratio is for SDDS. I've heard claims that SDDS has a 1:1 compression ratio, which means there's no compression happening at all. This is very impressive to the purists. Another advantage of SDDS is that, in addition to the digital soundtrack on the film print, there is a back-up analog stereo soundtrack and a back-up SDDS digital soundtrack. SDDS is the only format capable of 8-channel sound. However, there are only a handful of theatres in the world which can present this 8-channel audio. The rest are generally equipped for 5.1 presentation of SDDS. In fact, the SDDS processor has a built-in "fold down" feature which can convert the 8-channel mix to a 5.1 mix or even to a 4-channel mix, depending on how an individual theatre is configured. At the vast majority of SDDS theatres, however, you will be hearing a 5.1 presentation. The disadvantage of SDDS is that it's so closely linked to Sony theatres and its studios (Columbia, Tristar, etc.). This simply means that other studios and other theatre chains are less likely to enthusiastically support this format than they are the other formats, especially when you consider that this is the most expensive format for a theatre to purchase and install. Also, I've read countless complaints from projectionists who feel SDDS has serious hardware reliability problems.

5.1 Digital Audio Comes Home
With the home video releases of True Lies and Clear and Present Danger, we saw the introduction of 5.1 audio for the home theatre enthusiast. The first company to release a home 5.1 format was Dolby, followed by DTS (It appears that Sony has no plans to develop a home version of SDDS). Home Dolby Digital and DTS were first available to laserdisc enthusiasts and now, finally, they are both available on DVD. Of course, in order to hear these impressive sound formats at home, you'll need a laserdisc or DVD player which can provide the 5.1 digital information and you'll need a home theatre receiver which can process the 5.1 digital sound. Since Dolby Digital and DTS are still incompatible with each other, you'll have to match the formats in your player (whether it be laserdisc or DVD) and your receiver. Laserdisc and DVD players which provide 5.1 audio also provide Dolby Pro-Logic (four channel) sound as a back-up. So, if you happen to buy a player which can give 5.1 sound but you still have a Pro-Logic or 2-channel stereo receiver (get out of the stone age, people!) then you can still enjoy high-quality stereo sound until the day you upgrade your receiver. Never assume you can't enjoy laserdiscs or DVD until you can afford to spend thousands of dollars on some wildly extravagant home theatre system. Don't be intimidated by the elaborate and expensive home theatre displays at your local electronics store or in a real estate agent's Model Home. The beauty of most of these systems is that you can build them in steps as your budget allows. For a few hundred dollars, you can have a good player and several discs now. And, until you add more hardware, you can enjoy great movies at home... movies which will only get better as you upgrade your system.

A typical layout for a home theatre, 5.1 digital audio sound system.

Multichannel Digital Audio in 1999
Advances in sound technology will continue. In the coming years, Digital TV and High Definition TV broadcasts will be available throughout the United States. Those broadcasts will be capable of delivering Dolby Digital 5.1 audio. So, imagine watching such high quality entertainment as, for example, The Jerry Springer Show with a high definition picture and words bleeped out all around your listening room!

With the release of Star Wars Episode One: The Phantom Menace we witnessed the introduction of a sound format called Dolby Digital Surround EX. This system uses matrix encoding and decoding to add a third surround channel to the 5.1 system, creating a 6.1 sound scheme. Just like the front of the theatre, the rear has a Left, Center and Right audio channel. The new center, rear channel will give soundtrack designers even more artistic options... but the effect may be subtle if you're already sitting right in the middle of the theatre. Time will tell how much this "EX" system will revolutionize the world of theatrical sound. Incidentally, if a theatre is set up correctly, the "EX" equipment is fully compatible with DTS and SDDS digital sound too. So, you can have three surround channels no matter which digital format you're using.

The layout of the new, Dolby Digital Surround EX theatrical sound system is basically like this, although the exact placement and number of surround speakers may vary.

Click Here for an official list of what is required for a theatre to become THX-certified.

Q: Which is better, THX or DTS?
A: There's no need to have one without the other. The THX program can be applied to DTS, Dolby, and SDDS equipment. The best theatres will feature THX standards and at least one of those digital sound formats together. When you're looking for a great theatre near you, look first for the "THX" designation in their advertisements or on the sign in front of the building and then look for the DTS, Dolby or SDDS logo to go with that theatre. Remember, the THX theatres are more likely to have superior seating layouts, superior projectors and much more than just a good sound system (But I'm afraid the THX program has nothing to do with the quality of popcorn).

Q: Do I need THX in my home theatre?
A: It's up to you to decide what you really need. Of course, you will pay more for home theatre equipment which carries the THX logo and you will get a product which is built to a higher standard than other equipment from the same company. Personally, I hate to see people who are scared of high prices and decide that they can never afford a good home theatre. Prices are always getting better on electronics. Perhaps you can't afford the same thing you saw in the bells-and-whistles demonstration room at your local stereo shop, but some of the less expensive (and non-THX) equipment also sounds great! Until you can afford that dream home theatre you've seen, think about a simple, Dolby Pro-Logic Surround Sound set-up or a modestly priced 5.1 audio set-up. No matter how you build the system and no matter how much you spend, it will be better than listening to those tiny speakers which are built into your TV.

Q: What about THX-certified software?
A: This is one of my favorite things about home THX. The THX mastering program has given us the absolutely best home video versions of some of my favorite movies. If I had to choose between a 5 year-old laserdisc of a movie or the new, THX remastered version, I'd definitely go for the THX version. The people putting together this software definitely go the extra mile to ensure better sound and picture quality. Granted, there are still lots of great laserdiscs and DVDs which don't carry a THX label on the package and there are some movies which you simply can't find in a THX-mastered video version. But if I wanted to buy a movie right now and then I found out that a new, THX-mastered version were being released three months from now... I'd definitely wait for the THX version. You can enjoy the benefits of THX-certified software even if you will never own any THX hardware.

Q: Movies are already really loud. Why do they keep adding more speakers?
A: It's true that today's theatre sound systems are a lot more powerful than the sound systems of just a few years ago, but the problem of movies being "too loud" isn't caused by too many speakers. The point of multi-channel, digital sound systems isn't just to make movies louder. The clarity and dynamic range of digital sound can make a flute solo sound better than ever too. The problem is that certain, "flashy" filmmakers want to shake you out of your seat and the sound system allows them to do it. The people who create movie trailers are especially guilty of abusing the technology of modern digital sound. You should be pleased to know that Dolby Laboratories and theatre operating organizations are currently investigating this problem and will be issuing their recommendations to the sound technicians back in Hollywood. Sound mixing is still an art and, of course, some people are better at it than others. Rest assured that the people making these movies have listened to them and, as long as you're going to a good theatre, you are getting the presentation they intended for you to hear. Please direct your complaints directly back to the filmmakers in Hollywood.

The Amazing Jessie (I've met this dog!)

© 2008