Magazine article American Cinematographer

Recording "Rollercoaster" Sound in Sensurround®

Magazine article American Cinematographer

Recording "Rollercoaster" Sound in Sensurround®

Article excerpt

A new and vastly more dramatic approach to recording this sensationally unique type of low-frequency sound that shakes the marrow in your bones

The first feature to utilize Sensurround was "EARTHQUAKE" and the second was "MIDWAY". At that time we did a fairly extensive modification of the Sensurround system in that we changed our control system so that we could have the transducers that are up in front of the screen operating, and/or the ones at the rear of the theater - but separately from each other. This made possible a front-only Sensurround.

This was quite important to us, because there were times, during dialogue sequences, when we wanted to have the Sensurround running, but did not want to have dialogue coming from the rear of the theater, because that is quite distracting. So we modified the equipment to maintain the perspective of sound at the front of the theater. At the same time, we incorporated a noise reduction system as part of the Sensurround equipment. All of the prints of "MIDWAY" and "ROLLERCOASTER" include the noise reduction system, which gives us a much larger dynamic range on the print.

For "EARTHQUAKE" we had a noise generator which was part of our control electronics in the theater, and that noise generator produced the large rumbling sound of the earthquake. At the time, that was the only way we could get a much louder sound than we required, but now we are able, on the optical track itself, to combine the normal sound track, the control frequencies (to control the frequent turning on and off of the Sensurround) and also have a dynamic range that allows us to put additional signals on which comprise the sound track that you hear, but expanded signals when played back, and many times louder than the normal sound track.

We've increased our headroom (or our added loudness) by about 20 dB and, at the same time, we've picked up about 15 to 20 dB margin to our noise floor, so that our track is much quieter. In both "MIDWAY" and "ROLLERCOASTER" there are some portions where, for an optical track, it's very, very quiet. Another good aspect of using this noise reduction system is that we are less bothered by scratches and film abrasions that occur on release prints. We don't hear as many of the scratches and ticks of the kind you usually hear on an optical sound track. As a result of that, we have been able to remove the traditional Academy Roll-off Filter (dating from the Research Council days), which is used as a standard roll-off on all optical reproduction systems. As a result, we've increased the frequency range of these optical tracks, producing an optical track that sounds more like a magnetic recording. We have a much better high-frequency response. Those are really the major improvements that we have made in the Sensurround system, from the technical standpoint.

All noise reduction devices work on what is basically a compression-expansion system. The tracks are compressed to a degree when recorded and, on playback, they are expanded. We tried the Dolby system, which is a very fine system which we use on certain music scoring sessions and that sort of thing, but for this particular application, the dbx system was found to be excellent. It gave us nearly a doubling effect of our dynamic range, so that instead of having the typical 45 to 50 dB dynamic range (which you have on an optical track, if it is really a good one), we wind up with about 65 to 80 dB - a considerable improvement.

We dub the picture in a normal fashion and wind up with a 3-strip magnetic track that includes sound effects, dialogue and music. That's a very normal sound track of the type that we can use to make a normal optical track for a release print that is destined for nonSensurround exhibition. When we make the Sensurround version, we reduce the level; we treat the mixed track with the dbx encoding process and then we add back onto that optical track certain effects - for instance, in "MIDWAY", the gun blasts - or, in "ROLLERCOASTER", the rumbles and these effects are not treated with the dbx compression system which you would normally use in recording. …

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