Beyond Dolby (Stereo): Cinema in the Digital Sound Age

2. The Sound of 5.1: Aural Aesthetics

53 The Sound of 5.1: Aural Aesthetics The design, technical considerations, and specifications that went into the digital sound track are to provide a medium that theoretically has no limitation. The digital medium is not the restrictive part of the process anymore. Robert Warren, Dolby engineer When 5.1-channel digital surround sound (DSS) first appeared in the early 1990s, it offered filmmakers better dynamic range, more channels , and greater flexibility for placement of sounds within the multichannel environment. Few of these capabilities, however, could be exploited to their fullest at this early stage in the digital era. Relatively few exhibitors had installed DSS systems, so filmmakers had to ensure that their soundtracks would still play back acceptably when downmixed to Dolby Stereo, which far and away dominated the theatrical sound market. Today the landscape is quite different. The theater-building boom of the 1990s and audience preferences for digital sound systems made 5.1 the de facto standard for theatrical exhibition; the growth of DVD and accompanying explosion in home theater accomplished the same purpose in homes. With 5.1 digital surround sound the norm for both theatrical and home exhibition, contemporary filmmakers can feel reasonably confident in employing digital surround’s full capabilities 2 54 · Production and St yle without worrying about how their work will sound in Dolby Stereo or another less versatile format. The advent of digital surround certainly did not force filmmakers to change their stylistic or technical approaches—anything that could be done in the Dolby Stereo or monophonic eras could still be done with DSS. But just as football players and coaches alter their strategies to adapt to rule changes, changing a cinema technology (a “rule” of how movies operate) affects the stylistic choices filmmakers make (how they “play the game”). Film history is rich with examples of technology influencing aesthetics: sync sound, color, 3-D, and CGI all caused substantial changes to film style. This chapter will explore the new aesthetic possibilities offered by digital surround sound and consider how these possibilities can be—and already have been—exploited. Some Movies Get Louder . . . Digital surround sound provides a significantly larger dynamic range than Dolby Stereo and Dolby SR (the dynamic-range-enhanced version of Dolby Stereo). In lay terms, dynamic range is the difference between the loudest and softest sounds a system can reproduce. From a technical standpoint, it is measured in decibels (dB) and can be found by adding a format’s headroom (how much louder than a designated reference level a signal can be before it distorts or clips) to its signal-tonoise ratio (the distance between that reference level and the inherent noise of the system). The dynamic range of any format is dictated by a number of criteria that influence these two technical measures. For analog systems, one crucial factor is the amount of space available to record the audio data. In the case of a 35mm filmstrip, the Dolbyencoded soundtrack must fit into the narrow gap between image and sprocket holes, which is only about 2mm wide. Because of this limitation , Dolby SR film soundtracks only achieve a dynamic range of about 78 dB—far less than Dolby SR encoding offers in other formats with more space for the soundtrack.1 In contrast, all three digital surround formats have a dynamic range of over 100 dB. To put this into a practical context, listeners perceive a “doubling” in volume for each 10 dB a sound’s loudness increases ; hence a dynamic range of 100 dB provides more than a fourfold The Sound of 5.1 · 55 improvement over one of 78 dB in the difference between the loudest and softest sounds that can be produced. Sound engineer Robert Warren offers a useful analogy: “this digital bucket of water quantitatively could hold roughly five to ten times as much as the analog bucket of water.”2 Digital surround’s wide dynamic range means that within any given movie, it can include both very loud sounds and very soft ones, in theory surpassing the capabilities of Dolby Stereo and Dolby SR on both ends. On the high end of the volume spectrum, differences in headroom are particularly important, since the amount of headroom determines how much louder than its “average” volume level a soundtrack’s loudest parts can be. In the late sixties, monophonic sound had headroom of about 6 dB, meaning “the loudest sounds in...