Designing For The Surround Switch
Surround Professional - October 1998
Audio production beyond two-channel stereo was once mainly a concern for audio professionals in the film industry. That industry standardized a means of production whereby the final audio elements are produced and monitored in an environment that physically and acoustically resemble the commercial cinema houses that are the final venue for the product. This level of control allows for a high degree of confidence that the audio playback heard by the audience in the cinema will be reasonably close to what the audio production team intended.
The proliferation of surround product is requiring many audio professionals to rapidly come to grips with a formidable new set of tools and requirements. The diversity of the existing and emerging formats and increasingly competitive requirements for surround audio to enhance them have contributed to something of a state of anarchy when it comes to surround production and playback methods and standards (or lack of standards).
The previously described "apples-to-apples" playback transportability as used in film production is not possible in most cases involving these newer formats. Since the final target of most of them is in the home, the conditions where end-user playback of surround media takes place varies to the extreme. Although manufacturers of consumer surround equipment normally include documentation with recommended setup and calibration methods, it is likely that the speakers will be placed where they best fit with the furniture and levels will be set where they "sound good". These factors cannot be controlled by the audio production team, but they must be considered (and sometimes simulated if possible) during the course of a project.
Take Control
The production monitoring environment, however, is within the control of the professional audio community. Let's address some of the acoustical and operational factors that must be considered in the design of a control room for surround production use. Not surprisingly, the requirements of surround audio production necessitate a number of alterations to the traditional two-channel school of control room design. Seating layouts must be balanced with the acoustical treatments, speaker placement and ergonomic design to accommodate all those in the room who must be able to make critical judgments during production playback.
A surround mixing control room should be sized to provide the best possible monitoring and working environment for all who are regularly involved in production in that room. There is no magic formula for a perfect surround control room that can instantly solve everyone's audio production requirements. The dimensions of an optimal surround mix room may be as small as a one person "5.1 nearfield cockpit" in a mobile production truck or as large as a 200-seat traditional cinema mixing theater. Both are appropriate for their intended use and can provide reference-quality surround monitoring when designed properly. The relationship of the primary monitoring position (engineer), secondary monitoring positions (producers, directors, etc.) and monitors in a surround production environment is considerably more complex and critical than is the case for a stereo-only monitoring environment.
Control rooms for surround monitoring require less reflective reinforcement from the room than typical stereo control rooms in order to avoid interference with the surround field. Still, the largest amount of acoustic energy will come from the front speakers, and considerable stereo production will continue for some time. It is possible to achieve a diffuse field from the back of the room appropriate for stereo and monaural monitoring without adversely affecting the function of the rear monitors during surround projects. The key to achieving this acoustical balance is careful management of the surround monitors' energy to avoid unwanted interaction with the rear wall acoustical treatment.
In the design of a surround sound control, the physical space and monitors must be treated as an integral system. Careful analysis of the individual room and its physical and acoustical relationships with the listener(s) and monitors will determine the appropriate treatment. Proper balance and placement of absorptive, reflective and diffusive surfaces are just as important in a surround control room as they are in a traditional stereo control room. The addition of center, surround and subwoofer sources demands attention beyond what is necessary in strictly stereo rooms regarding the positions and directional characteristics of the monitors. Monitor type, placement and mounting method, and the location and type of acoustical treatments in the room must all be evaluated to assure the best balance of timbre between the monitors. In some cases, electronic equalization may be required to achieve the best results.
Don't make the mistake of disregarding stereo and monaural production requirements when designing and configuring a facility for surround use. The need to monitor in stereo and mono, as well as surround formats, will remain for the foreseeable future. Portable radios, clock radios, televisions and automobiles will continue to have stereo and monaural playback systems. It is necessary to have the ability to critically monitor either a separate stereo or mono mix and/or how the surround mix "folds down" under control of the format being used (Dolby Digital, DTS, SDDS, etc.).
What About The Monitors?
Controversy rages regarding the "right" monitors, placement and methods for monitoring and producing surround audio. Designing monitoring flexibility into the control room can provide the ability to adapt to varying philosophies and standards as they develop. The ability to accommodate multiple locations for surround monitors (especially side and rear) can address several concerns. As an example, a primary monitoring position for the engineer may be set up "by the book" for ITU-R BS.775-1 monitor geometry. This configuration can place the rear monitors forward of the producer's desk, seriously degrading the ability to make mix decisions from that location. In this case, the engineer could be given the ability to switch to different or additional surround monitors when monitoring from the producer's position is required.
Formats, equipment and methods for surround audio production are evolving at a breakneck pace. The emergence of this magazine is evidence of that trend and is a welcome forum to help advance the art and technology of surround audio production. There are still many who, when looking for answers, find still more questions while trying to understand and make maximum use of the "surround dimension" in professional audio. The next few years will inevitably see many widely diverging opinions and methods concerning surround sound the professional audio arena.