As a saxophonist, the first time I heard a keyboardist use LFO vibrato I almost choked. That was a long time ago, but in most synth patches, the LFO is still used for a steady pitch warbling that is laughable. In this article, I'll discuss how you can get more musical pitch modulation out of an LFO (using a bit of imagination), as well as other ways to broaden the LFO's horizons.
FIG. 1: Breakpoint envelopes (from top to bottom) control channel one Main and Mod oscillator pitches, lowpass filter cutoff FIG. 1: The Voltage Processor on the Arturia ARP 2600 V lets you combine modulators and audio signals in novel ways.
When an acoustic instrumentalist creates vibrato, pitch isn't the only thing that's varied. Timbre and volume also vary, and in different proportions, depending on whether the vibrato is created with the lip, diaphragm, wrist, or throat. You can emulate those playing techniques with a sine-wave LFO.
The Real Deal
You can create timbral variation by mapping the LFO to modulate the cutoff frequency of your synth's filter. Set the default cutoff frequency and modulation amount so that the effect is subtle — too much modulation will create a wah-wah sound.
For volume dynamics, map the LFO to modulate the amplifier's output level, but again, keep it subtle to avoid a tremolo effect. You might even mix in a little noise, keeping the level low enough to be noticeable at only the loudest point of the LFO cycle. Properly done, that adds a subtle breathiness to the sound and gives it an organic character.
Instrumentalists often slightly delay the onset of vibrato, allowing the tone to settle in first. If your LFO has a delay control (sometimes called hold), you can use that; otherwise, you might be able to apply an envelope generator with a slow attack to the LFO frequency or modulation amount. All these techniques are illustrated in Web Clip 1.
A preprogrammed LFO will do the job, but there's no substitute for real-time expressive control. You can achieve that by using MIDI controllers. For example, mapping the Modulation Wheel to control LFO amount is a much more natural way to delay the onset of vibrato. If your synth has a MIDI Learn mode, setting up the mapping is a piece of cake. Even if you need to dive into the manual to find out how to set it up, it's well worth the effort.
In Web Clip 2, I mapped the same controller to LFO frequency and filter-modulation amount, so as I raised the slider, I got a faster and more pronounced timbral variation. The low static drone starts to shift slowly, morphing into a rhythmic pulse and then into a wild effect — all under the control of a single slider on my keyboard.
The Arturia ARP 2600 V's Voltage Processor allows you to combine modulation and audio signals in novel ways (see Fig. 1). In Web Clip 3, I set up oscillator VCO2 as an LFO to modulate the amplitude of oscillators VCO1 and VCO3, which are tuned an octave apart. I inverted the polarity of the modulation applied to the higher-pitched oscillator, causing the sound to morph between the two octaves. As a variation, you can modulate the amplitude of only one oscillator, so that one tone stays constant while the other comes and goes. It's a good idea to map a MIDI controller either to the speed or to the amount of the modulation; otherwise, the effect becomes monotonous on sustained notes.
Many programmers apply a slow LFO in small amounts to vary pitch in order to keep a patch from sounding too mechanical. If doing that makes the patch seem out of tune, try applying the LFO to only one oscillator in a multi-oscillator patch. The static oscillators maintain the pitch center, while the modulated oscillator introduces a variable sonic grind. Choose your LFO frequency and amount carefully to avoid obvious beating between the oscillators. You may also find that you prefer a triangle wave to a sine wave for that effect.
Although I've only talked about applying the LFO to pitch, filter cutoff frequency, and amplitude, any target is fair game. Most synths now offer some form of modulation matrix that lets you target a variety of parameters, including the settings of other modulators. Experiment a bit, and you'll be surprised by what you can get out of the lowly LFO.
Brian Smithers teaches audio workstations at Full Sail Real World Education and music technology at Stetson University. He is the author of Sonar 5 Ignite! (Thomson Learning, 2005).