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Random Bursts

December 1, 2005

FIG. 1: This Arturia Minimoog patch uses noise to modulate the filter cutoff -frequency. The amount of modulation is controlled by the Mod Wheel.

Although recording engineers view noise as something to avoid, it has great creative potential for the synthesist and sound designer. Wind, thunder, surf, bomb blasts, snare drums, and hand claps are all easily created on any synthesizer that has a noise generator. But in addition to that, noise can be used to enhance pitched sounds in a variety of interesting ways.

Color Me Noise

You're probably familiar with the use of colors to describe different types of noise: white, pink, red, and more rarely, blue. White noise is a collection of randomly occurring frequencies equally weighted over the audible frequency spectrum. Pink noise is essentially white noise that has been lowpass filtered, so it rumbles along with muted high-frequency content (see Web Clip 1).

As you continue to lower the boom on the high-frequency content of noise, the signal eventually becomes inaudible; however, it is still usable as a randomly fluctuating control signal. (On some synths, that is called slow random to distinguish it from audio-range noise.) Slow random imparts a wobbly, nervous character to whatever parameter it modulates (see Web Clip 2).

Noise as a Modulation Source

Minimoogs aren't known for creating grungy sounds, but you can take this classic synth in new sonic directions by modulating the filter cutoff with audio-range noise. The effect of noise modulation on filter cutoff is similar to distortion: grunging up notes when the cutoff frequency is low, and emphasizing the resonant quality of the filter when its cutoff is higher.

I created the example in Web Clip 3 using the Arturia Minimoog (see Fig. 1). As with its hardware predecessor, the OSC3 Mix pot determines the mix of control sources for pitch and filter modulation. This control pans between the Mini's noise source and its third oscillator, traditionally used in its LO range to act as an LFO. In my patch, the OSC3 Mix pot is fully clockwise (noise only), Oscillator Modulation is turned off, and Filter Modulation is turned on. You can vary the modulation amount to get just the right level by using the Mod Wheel.

Adding Noise to the Mix

The effect of modulating a filter's cutoff frequency with audio-range noise differs decidedly from adding noise to the audio signal. Web Clip 4 demonstrates a Korg OASYS patch in which white noise is mixed with the oscillators as the audio source. That emphasizes the sound of the enveloping of the filters without creating the pseudo-distortion effect heard in Web Clip 3.

I suggest dialing in some noise to enhance sharply enveloped, resonant-filtered bass sounds. The only downside to this technique is that the patch can become noisy. You can often tame the undesirable side effects of added hiss or rumble with some creative equalizing. (None of the Web Clips associated with this article have been equalized.)

FM-eral Uses of Noise

You can use noise as the modulator in FM patches to produce eerie, atmospheric sounds such as submarine sonar pings and vocal choir impressions. Because noise is a complex modulator, it is best used to modulate a sine wave or some other low-harmonic-content waveform. Noise modulation adds an evocative dimension to the sound, giving it a mysterious reverb quality (see Web Clips 5 and 6).

My favorite way to use noise is an effect I call ripping vibrato. I use white noise and triangle LFO to modulate pitch, and I route the Mod Wheel to control the amount of modulation. Adding noise gives the vibrato a distinctive chorusing and ripping character (see Web Clip 7).

On basic synths, noise modulation is typically limited to frequency and filter cutoff. But if you have access to a modular synth such as Arturia's Moog Modular V or synth construction software like Native Instruments' Reaktor, try using noise to modulate other parameters. For example, using enveloped red noise to modulate amplitude produces a typical brass-instrument-style spit tone.

Peter Schwartz is a composer, arranger, and keyboardist living in upstate New York. His analog synth programming is featured in the factory patches of the new Korg OASYS.

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