Here's That Grainy Day

Feb 1, 2007 12:00 PM, By Jim Aikin

Granular synthesis is often used in academic and experimental music but isn't found in many commercial synthesizers. The sounds it produces are somewhat unsettling rather than smooth, but if you're looking for fresh sound effects, granular techniques can be a potent resource.

With granular synthesis, a source sample is sliced into tiny grains, usually between 1 and 50 ms long. The sound is then created by mixing the grains back together. A number of parameters can be modulated. For example, the length of the grain, its pitch, and its starting point (the spot in the original sample from which each grain is drawn) can be changed while the sound is playing.

Grain States

You may want to consider using Csound (www.csounds.com) to explore granular synthesis. The site is free, it's powerful, and it includes sophisticated granular synthesis tools. On the downside, Csound is not well suited for live performance and can be difficult to learn.

An easier way to try out granular synthesis is to use the Sampler plug-in available as an optional add-on for Ableton Live 6. Sampler doesn't provide full-on granular synthesis, but it can produce a surprising range of tones that use granular concepts. You can develop rich, sustained tones that evolve smoothly and gradually, burbling nonsense vocal textures, or thick crackling masses.

The Source

Any sample can be used as a source, but the best sounds are a few seconds in length, have a continuous high-amplitude level, and have lots of variation in tone color. I created the audio examples for this column by recording my own voice speaking a phrase, and then compressing it substantially to get a more uniform level. The audio examples and the Live project used to generate them are in Web Clips 1 and 2 on the EM Web site.

In Live 6, I created an Instrument Rack, loaded an instance of Sampler into the rack, and dragged my source sample into Sampler. Using an Instrument Rack makes it easier to create layers, each of which can have its own effects, and to assign modulation routings that can be saved with the rack preset.

Gran-diose

On the Sample tab in Sampler, set a short loop that starts somewhere in the middle of your sample, as shown in Fig. 1. Give it a healthy crossfade value, so as to smooth the edges of the grains, and set the Sustain Mode to either forward or back and forth. If you play Sampler from the keyboard at this point, you'll hear a static tone.

The parameters under the Sample tab can't be modulated directly, but they're available as destinations under the Modulation tab. There, two LFOs and an auxiliary envelope can modulate loop start and loop length. I like setting the LFOs to slow rates to achieve gradual changes.

To animate the tone of your short loop, activate LFO 2, choose Loop Start as destination A, and set the modulation amount for destination A to about 10 percent. This value is a percentage of the sample length, so changing the Sample End parameter in the Sample page will affect how much modulation you get.

The key to developing good granular sounds is experimentation: keep fiddling with parameters until you get a sound you like. By assigning a macro knob in the Instrument Rack to LFO rate, you can move from a smooth, short loop to longer stutters while a note is sounding.

Modulation to the Max

Sampler gives you three ways to modulate the loop start or length from an external MIDI source. You can assign your mod wheel to a macro knob in the Instrument Rack that contains Sampler, assign the mod wheel to a Sampler parameter directly, or switch to Sampler's MIDI tab and choose a parameter such as Loop Start or Loop Length as a destination. (Some of these MIDI routings override others.)

For more-complex sounds, try adding Live's Grain Delay effect to Sampler's output, then modulate a couple of its parameters from a macro knob. You'll be amazed at the richness of the sound textures you can create.

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Jim Aikin writes regularly for EM, Mix, and other music-technology magazines.