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Posted by on Jul 1, 2013 | 0 comments

From Wax to Bits: Dynamics of the Film Sound Medium

Photo by flickr user Carbon Arc, and used under Creative Commons license.

Photo by flickr user Carbon Arc, and used under Creative Commons license.

As dynamics month comes to a close, I thought it would be fun to talk about the evolution of film sound mediums and how they impact dynamics. Since the widespread introduction of sync sound to films in the early 20th century, the technologies involved have changed quite dramatically. From experiments with wax cylinders and phonographs to magnetic tape and Dolby Digital, each evolution in sound technology improved fidelity and dynamics, giving sound designers greater power in creating artificial worlds and engaging the audience.

The Early Years

Almost as soon as motion pictures were introduced in the late 1800s, inventors and artists the world over began searching for a way of synchronizing sound with the images. Even Thomas Edison, inventor of the lightbulb and the phonograph, experimented with sound films. In 1894, The Edison Company and W. K. L. Dickson produced “The Dickson Experimental Sound Film,” a short film that made use of a wax cylinder phonograph recorded and played back with picture.

Although impressive for the day, Dickson’s film showcases some of the initial problems with sound for picture. Fidelity was a major issue, as phonographs of the era recorded sounds to the spinning cylinder mechanically without the aid of electronics. While this worked for music, speech was often unintelligible and lost in noise. Similarly, early phonographs were amplified only by a large conical horn, which was quiet and struggled to fill even the smallest of venues. It wouldn’t be until the early 1900s that electronic sound recording and amplification would become feasible, revolutionizing both the music and film industries.

In October of 1927, Warner Brothers released The Jazz Singer, the world’s first feature-length “talking picture”. Warner Brothers’ sound system, dubbed “Vitaphone”, utilized a 16-inch phonograph disc mechanically linked to the film projector. Both film and disc would be cued up to their respective start markers and then played back simultaneously, running together at a locked speed. Using some of the earliest condenser microphones and electronic recording technologies, Vitaphone records had less noise and greater intelligibility. Thanks to the electronic amplification systems, the discs were able to be heard in the largest of auditoriums. For the first time ever, audiences were given a feature film that could not only speak, but sing, loud and clear.

Unfortunately Vitaphone, like many other sound-on-disc systems, had some sync issues. Should a film reel break and get re-spliced, its accompanying disc would no longer match to picture. Additionally, after a number of plays the discs would begin to scratch, causing the needle to skip which in turn knocked the sound out of sync. While the Vitaphone had unprecedented clarity, these sync issues, as well as improvements to sound-on-film methods, would lead to its retirement in the early 1930s.


During the 1920’s, American inventor Lee DeForest was busy developing a sound-on-film system called “Phonofilm.” Phonofilm used a pair of electromagnetic ribbons and a light source to expose a barcode-like pattern of light and dark areas onto a film print next to the image. These lines would be read by a photoelectric sensor in the projector, which would then convert the varying levels of light into sound. With the sound directly on the film print, synchronization was no longer an issue; if the film needed to be cut, the sound would cut with it. Fox incorporated this “variable density” system into their own Movietone format, which served as the soundtrack for the early Movietone News newsreels.

However, variable density (and early optical systems in general) lacked the fidelity of the Vitaphone system. The photoelectric sensor would interpret film grain and dust as pops and hiss, increasing the noise floor and reducing available dynamics. Though systems were devised to combat this, such as Western Electric Noiseless, the high noise floors left little room for dynamic content. Despite this, variable density tracks were the predominant film sound format for many years. In the 1950’s, an alternate optical format, called “variable area,” began to take over. Instead of a barcode pattern, variable area tracks resembled a vertical waveform, where loud sounds took up more area on the soundtrack and soft sounds took up less.

While it had a similar frequency response to variable density (approximately 31Hz-12.5kHz), variable area systems weren’t as susceptible to film grain noise and made use of noise reduction technologies, like Dolby A and eventually Dolby SR. With the noise floor minimized, optical tracks were able to attain greater dynamics than ever before. Sound quality was further improved in the 1970s when stereo variable area tracks were introduced, providing even more creative possibilities and eventually paving the way to widespread use of surround sound.

As the film industry battled the threat of television in the 1950s, several large-format film systems emerged, introducing similarly large sound systems. Some of these systems, like Todd-AO and Super Panavision 70, used magnetic soundtracks. These 70mm film formats contained at least 6 tracks of audio with magnetic tape adhered to the outer edges of the prints. Magnetic soundtracks offered much better fidelity and dynamics compared to optical tracks, especially when utilizing noise reduction, but they were expensive and tended to deteriorate quickly. As large-format films became less common, magnetic sound-on-film all but disappeared. Multichannel film soundtracks, however, were here to stay.

The Digital Age

SDDS, Dolby Digital, Stereo Variable Area, and DTS timecode on a film print [via Wikipedia]

With the introduction of surround sound, it became necessary to create a new film sound delivery format for 35mm prints. While optical tracks could carry matrixed surround sound, they were still subject to optical’s limited frequency response and dynamics. During the late 1980s and early 90s, Dolby Laboratories, Digital Theater Systems, Inc, and Sony each developed their own digital formats for theatrical surround. Dolby’s format, Dolby Digital 5.1, encoded 6 discreet tracks of audio directly onto the film print. Instead of replacing the optical sound track, Dolby Digital was printed between the sprocket holes. A camera-like device would read the data as the film passed through the projector and send it to the decoder, which would then convert it to 6 discreet channels of sound for playback in the auditorium.

Sony’s system, “Sony Dynamic Digital Sound”, worked in much the same way, though it was capable of encoding up to 12 channels (7.1 surround plus backup tracks) and printed its data stream to the outer edges of the film print, much like Todd-AO’s magnetic tracks. DTS’s system (now Datasat) took a different approach; Instead of encoding the audio data onto the film itself, DTS instead printed a pulsed timecode track onto the print that controlled a CD-ROM drive. Each disc contained the encoded 5-channel mix and locked to the timecode for sync. The LFE, or “.1” channel, was derived from the low-frequency content of the surround tracks, making DTS a 5.1 system. While each format required their own separate readers and decoders, they could all co-exist on a single print alongside the variable-area analog tracks.

Thanks to digital’s super-low noise floor and huge dynamic range, sound designers could now work with material from the subtle to the overwhelming. Where soft sounds would be lost in the optical’s noise floor and loud sounds would crunch and overload, digital systems could be pushed further and harder. Scenes of action could be loud and raucous while emotional scenes of could be quiet and tender. The latitude possible with digital were nearly unlimited, especially when compared to Vitaphone and the first optical soundtracks.

As Digital Cinema Packages allow for uncompressed audio and super-wide channel formats like Dolby Atmos, quality and dynamics are now only limited by theater sound systems; no longer are the delivery mediums the limiting factors. In just over a century, film sound went from an impractical experiment to a major part of the moviegoing experience. From Dickson’s scratchy violin on a wax cylinder to the roar of the Tyrannosaurus in Jurassic Park, advances in technology have provided us larger dynamic space to work within when designing sound. This space is be exceptionally helpful in creating the realities of the film world, and used intelligently, make anything possible.



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