Outer Limits

Nov 1, 2007 12:00 PM, By Brian Smithers

           

How to use good sound design in your music post-production work.

BONUS MATERIAL
Web Clips: Listen to audio clips that demonstrate special effect sounds created with pitch- and formant manipulation, reversing, editing, vocoders, subtractive synthesis, and more

Landing the Mothership

To create a sound for a biomechanical mothership, I turned to my cats. A cat's purr is a mysterious yet comforting sound, until you scale it up to the size of a tiger looking for lunch. It's also a complex timbre with which to work.

FIG. 4: A fundamental technique amid all the space-age tools: zero-crossing edits make for a seamless loop of cat purrs without requiring any crossfades.

Cats don't purr on demand, however, so I had to be sneaky. For several days, I kept my M-Audio MicroTrack 24/96 handheld recorder close at hand, waiting for an opportunity. It came in the middle of the night, when two of our three feline companions took turns stealing my pillow. Pleased with themselves, they purred victoriously as I reached out to my nightstand for my recorder and slowly brought it in close to their smug whiskers.

A cat's purr continues seamlessly as the cat breathes, but its timbre changes between inhale and exhale. I started by editing out all the inhales from a particularly vigorous episode. With some careful old-fashioned zero-crossing edits, I created a seamless drone that sounded more like the thrum of a giant spaceship and less like a happy Himalayan (see Fig. 4).

To make the sound much bigger than life, I dropped the pitch several semitones with Digidesign's Time Shift plug-in. I followed that with some heavy compression with Sonnox's Oxford Dynamics and Inflator. The compression leveled out the volume fluctuations to create a steadier engine sound. Inflator has a way of adding more beef to a sound without actually making it louder.

Digidesign's Hybrid synthesizer provided the mechanical part of the engines. I adapted a drone preset by modulating the pitch of two oscillators with separate semirandom LFOs. The third oscillator provided mostly noise, with the whole thing being lowpass filtered pretty heavily. The resulting timbre held only a hint of pitch, especially when played in the lowest octave.

I created escort ships with another Hybrid patch using its various envelopes to drop the pitch and lower the filter cutoff as the ships pass by. Small amounts of pan automation for each note — each note being an escort — contribute to the illusion of motion. I had to draw each pan curve meticulously by hand to keep the tail of one ship from jumping to the position of the next ship (see Fig. 5). Had I printed each ship to its own track, or at least enough tracks to ensure that no two adjacent or overlapping ships shared a track, the panning would have been easier. My work flow is necessarily shaped by the tools at hand, however, so I tend to conserve tracks when working in Pro Tools M-Powered, which supports only 32 audio tracks.

FIG. 5: Layers of sound, each with one or more automation envelopes, combine to create the sound of a spaceborne warship passing overhead.

There's one special fighter that flies by at about 25 seconds — it sounds a bit like a Formula One car. I chose another organic sound to call attention to it and to imbue it with a hint of emotion. It's the sound of another of our cats getting annoyed at the recorder, a delicious meow that I massaged into a flyby. First I molded the timing of the sound in V-Vocal, working it like a lump of Play-Doh until it had the right velocity. I used V-Vocal's pitch and volume envelopes to get the Doppler shift right. When working with pitch- and time-manipulation plug-ins, I am always listening carefully for the point at which the algorithm “breaks.” The sound gets grainy and artificial, and I have to pull back the effect or try another plug-in. For this task, V-Vocal allowed me all the headroom I needed, and its graphic interface made the job a snap.

I bounced the clip and exported it into Pro Tools, where I doubled it and transposed the copy an octave down to give it bulk. I bused the two tracks to an aux, where I added a chorus with the Short Delay plug-in. The chorus gives the sensation of the beating of two engines, a sound that pilots know well and the rest of us recognize at least subconsciously. The fighter's trajectory was achieved with a bit more-dramatic panning than the escorts, another subtle sign that it is special. Web Clip 3 is the final 40-second sequence.

Bring Down the House

Recording an avalanche is tricky business, what with the risk of death and all that. With a bit of imagination and the right tools, however, a world-class landslide can be created in the studio — or, in this case, the kitchen.

As I held the microphone as close as practical, my ever-patient wife poured 4 pounds of cat food from one container into another over and over. Predictably, this drove our cats into a feeding frenzy, so I retreated to my studio and left Barb to appease them. I imported the files into Pro Tools and auditioned them for the best bits, editing and naming them as I went.

FIG. 6: Sometimes a heavy hand is warranted, as with these three EQ plug-ins adding up to 10 dB of low bass to the primary rumble tracks.

Although Digidesign has introduced two more-sophisticated time/pitch plug-ins, its original Pitch Shift has two appealing features. First, it allows you to defeat time correction, creating an old-fashioned varispeed-style effect. Second, its Accuracy slider lets you optimize the algorithm for sound or rhythm. In this case, I chose to optimize sound and slowed down various regions by as much as 4:1.

The slowed-down cat food did a pretty good job of imitating falling rocks, but creating a compelling avalanche requires enough bottom end to give the impression of the earth belching. For this, I turned to Way Out Ware's TimewARP 2600. I created a simple patch that blends all three oscillators, each set to a different low base pitch. I set the initial filter cutoff to about 100 Hz. The thing that really made the earth move was patching the noise generator to the filter cutoff. This made the timbre shift unpredictably, lending the sound the sort of natural chaos it needed. This flexible architecture is one reason modular or semimodular synths like the ARP 2600 and its clones are so powerful for sound design. I played this sound in real time to create accents that help steer the intensity.

The core sound of the avalanche was complete: two copies of the lowest-pitch cat food region, offset by several seconds and panned stereo left and stereo right, complemented by a synthesized rumble. Each part was heavily EQ'd to emphasize its low end (see Fig. 6). The painstaking work, however, was yet to come.

I had succeeded in creating an avalanche ambience without any clear and present danger. The basic cat-food-turned-landslide regions were in stereo, and, panned to opposite sides, they established a good three-dimensional environment for the landslide. Next I needed to get up close and personal with some heavy rocks.

Pro Tools always deals with stereo regions as multimono files, so creating a mono region from a stereo region is as simple as dragging one channel from the region list to the tracklist. I harvested a handful of such regions that had been pitch-shifted less severely than the “rumble” regions. Each occupied its own mono audio track so it could be mixed individually. I hand trimmed each region to an appropriate length and hand drew volume and pan automation to make it come crashing into the picture.

Sonnox's Oxford Reverb includes a preset called Canyon, and it proved to be just the thing to keep things rumbling through the surrounding mountains. Web Clip 4 is the result of all this faking and tweaking.

Postscript

Note the recurring application of basic synthesis techniques. Even when a synthesizer is not directly involved, you'll need to apply volume and pan envelopes and automate effects parameters — after all, life is never static, so why create static sounds?

Given a Hollywood budget, I would have done a few things differently, such as experimenting with different brands of cat food — perhaps even dog food. Seriously, though, the common thread through all these examples is the triumph of imagination over money. If you listen carefully to the sounds around you and take note of their distinctive characteristics, you will start to hear the possibilities in a chair squeaking or crickets chirping. Almost any sound can be pressed into service if you break it out of its original context. To a good sound designer, there are no ordinary sounds.

Brian Smithers is the author of Mixing in Pro Tools: Skill Pack (Thomson Learning, 2006). He would like to thank his family, friends, and pets for their contributions to this article.

BONUS MATERIAL
Web Clips: Listen to audio clips that demonstrate special effect sounds created with pitch- and formant manipulation, reversing, editing, vocoders, subtractive synthesis, and more