-By Ioan Allen, Senior VP, Dolby Laboratories

Ioan Allen of Dolby Laboratories prepared this short article on theatre sound levels for a non-technical audience, not involved with the cinema industry. We thought this summary could be useful even for an industry audience, so Film Journal International is pleased to reproduce it here.

Cinema is a closed-loop system, unlike broadcast. The broadcaster has no control over how loud the consumer plays back his radio or TV, or how the tint/color control is set on the television. Cinema, on the other hand, has always attempted to replay the exact experience set by the filmmakers when the movie plays to its audience in the local cinema. In other words, the target has been to establish the light levels, color, sound levels, etc. in the cinema the same as those approved and established by the filmmaker. And the experience should be the same and as good in every cinema.

The criteria for sound levels, color, screen brightness, etc. are set by standards. These are established for movie production and exhibition by U.S. national standards bodies ANSI (American National Standards Institute) and SMPTE (Society of Motion Picture and Television Engineers) and internationally by the ISO (International Standards Organization).

Reference levels
Every projection room has a cinema audio processor which controls the sound for one screen. The vast majority of cinema audio processors have a volume control (commonly called the fader) scaled from zero to 10. Fader 7 is known as the reference level. From the mid-1970s on, a process was adopted to ensure that fader 7 means the same in every theatre. Test signals (known as pink noise) are used when the sound system is installed to calibrate the fader 7 sound-pressure level. There will still be loud movies and quiet movies—what this system ensures is that a film soundtrack created in a mix room in Hollywood which is set to fader 7 will sound at the same level in a theatre playing the same movie in New York when the fader in that cinema is also set to 7. The same matched levels apply not only in the U.S., but in virtually every country worldwide. A movie mixed in London should play at the same level when heard in Los Angeles.
This procedure is defined in the U.S. by SMPTE RP200 (Relative and Absolute Sound Pressure Levels for Multichannel Sound Systems) and internationally by ISO 22234.

Technology enables louder movies
There have been several technological steps in movie sound since the mid-1970s which have allowed the filmmaker to create increasingly dynamic movies—leading up to today’s powerful digital soundtracks. But it should be realized that it is not the cinema that determines the level—if the theatre plays the movie at fader 7, it will just be reproducing the level chosen by the filmmaker. And while an occasional rogue filmmaker will make an action film with an excessively loud soundtrack, most films play acceptably at the reference level. When a cinema does encounter a movie that seems to play too loud for its audience, a decision will be taken in that cinema to play the feature at a level lower than reference 7, at say fader 5 or 6.

1990s: Competitive trailers and loudness wars
Though many played satisfactorily at fader 7, the competitive nature of trailers meant that by 1996 some were painfully loud. Trailer finishers were reluctant to lower the level of their product for fear it sounded quieter than trailers from a competing studio. Many theatres had no method of automating the fader setting independently for the trailers and the feature (and indeed, many still don’t have the capability). And with 10 or even 20 screens in a multiplex site, there is no projectionist available to adjust the fader setting between trailer and feature. Complaints about the level of the trailers would result in the fader setting being lowered to 6, 5 or even 4, and this would be the level the feature played at—and this lowered feature level inevitably damaged the intelligibility of the dialogue. And there is no worse cinema audio problem than having the dialogue at too low a level—the “What did he say?” syndrome.

Recognizing that the situation was getting worse and worse, the major Hollywood studios created a group called TASA (Trailer Audio Standards Association). The group established a measurement technique called Leq(m), which measures the average level of a two or three-minute trailer. It should be noted that this is the actual level recorded onto the film, not the playback level in a cinema, which is still determined by the fader setting, in each individual auditorium, reference 7 or lower.

TASA established a maximum Leq(m) level permitted on a trailer—since 1999, every U.S. trailer has been checked for compliance (about 3,200 titles so far). The maximum permissible level has steadily been lowered—the loudest trailer today is constrained at 85 dB Leq(m), the equivalent of 50% of the level of the loudest trailers in 1996. The TASA measurements are submitted to the MPAA (Motion Picture Association of America), who will not issue a rating (green band) to a trailer that is louder than the standard. The Leq(m) procedure for loudness measurement is defined in ISO 21727: Method of measurement of perceived loudness of motion-picture audio material.

The Nielsen Survey and NATO
In 2004, Dolby Laboratories and Disney commissioned a Nielsen survey to assess the public’s view of the loudness of cinema material. With close to 3,000 respondents, 75% thought the level of trailers was about right, 4% thought the trailers were too quiet, and 21% thought the trailers were too loud. Over the first few years of implementation of the TASA program, the number of complaints about trailer sound levels received by NATO (the National Association of Theatre Owners) dwindled to virtually none. These two metrics suggest that trailers are now at or close to an acceptable level.

International trailers and commercials
The same method of measuring trailer loudness has been adopted in almost every country overseas, and 85dB Leq(m) is the permissible limit, as in the U.S. Additionally, all cinema commercials are constrained to a maximum of 82dB Leq(m) internationally—similar constraints have recently been announced in the U.S. by the CAC (Cinema Advertising Council).

Action trailer, quiet feature
Despite the fact that the existing procedures, both for set-up and playback level in the cinemas, and for measurement and constraint of the recorded level of the program, are working fine, two occasional problems remain. First, because of some production error, a rogue commercial or trailer could get through above the maximum level—but this happens so rarely as to be considered negligible. The regulations are so strictly enforced that in a couple of cases trailers have been remade (at considerable expense) in order to comply with TASA’s (and the MPAA’s) level regulations.

The second problem is more difficult, and practically impossible to solve. For example, let’s say that half the features are action films, and half are quiet, dialogue-based movies. We can assume the same mix of trailers. As a result, half of the time the trailer for an action film will immediately precede a quiet dialogue film. In this instance, the trailer will always sound louder than the feature. Even if there were a projectionist around to lower the level of this one trailer by hand, this lowering of level would take all the excitement out of the trailer and the artistic intent would not be preserved.

Presenting everything in the cinema at the correct sound level, and with adequate light on the screen, ensures a moviegoing experience superior to anything possible in the home—even in these days of home theatre!

Ioan Allen joined Dolby Laboratories in 1969. In addition to his work at Dolby, he is currently engineering director, motion pictures, for SMPTE, technical chairman of the Trailer Audio Standards Association (TASA), and serves as U.S. correspondent for the International Standards Organization (ISO) cinematography group (TC36). Allen is past president of the International Cinema Technology Association (ICTA) and past chairman of the SMPTE Audio Recording and Reproduction Technology Committee and Projection Technology Committee. He holds several patents and has authored and contributed to many journals and technical papers, and has received numerous awards over the years, including Scientific and Engineering Awards from the Academy of Motion Picture Arts & Sciences, and an Oscar.