The Art of Synth Soloing: Modulation Basics

January 9, 2012
By Jerry Kovarsky

This new column will help you explore the art of synthesizer soloing in all its passionate glory. In coming months, we’ll explore sound design concepts for enhanced expression and point you toward other sources of inspiration. To kick things off, though, we’ll examine one fundamental of what makes the synthesizer such an expressive lead instrument: LFO-based modulation.

Push the Envelope
There are innumerable possibilities for a lead sound, but the constant is that it should have a steady sustain so you can bend notes and add expression by other means without the sound fading away. Start with a sound whose volume envelope has a fast attack time, decays only slightly (if at all) to a high sustain level, and has a relatively quick release (see Figure 1).
 
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 Fig. 1. Envelopes suited for leads in Waldorf Largo (left) and Rob Papen Blue (right).
 
With synths that have multi-breakpoint envelopes—or a “hold” segment between the attack and decay—you can give your attack a bit of extra punch before decaying slightly to your open sustain level. I first read of this in an article by Craig Anderton, who found an inherent (but non-adjustable) hold to be part of the “secret sauce” of the Minimoog. He recommends 20 to 25 milliseconds of “hang time” before the decay starts (See Figure 2). We now have a sustained sound that’s ready to be bent, tweaked, and shaped in of creative ways.
 
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 Fig. 2. The red box denotes a sliver of hold time between the attack and decay segments in Native Instruments Absynth.
 
Good Vibrations
The most common form of expression is adding vibrato, which is almost always assigned to a modulation wheel or joystick. Vibrato is achieved with an LFO routed to the pitch of the oscillator(s). It’s usually a sine or triangle wave, and moving the mod wheel or joystick forward increases the amount or depth of pitch modulation.

LFO speed is a matter of taste, but works well between 4.8Hz and 7.4Hz. Study how vibrato is used in the real world—listen to an opera singer and you’ll hear a very deep and often fast vibrato. Listen and watch a classical string player and you’ll see them wiggle their finger on the neck of their instrument at various speeds to match the music. Listen to a jazz trumpeter to hear one form of subtle vibrato speed/depth, then try some Mariachi music for the other extreme. Finally, check out guitar players to see and hear how they vary their vibrato: Eric Clapton is a master of expression, but then watch B. B. King’s fast, stinging approach to see how much variety there can be. Translate this to your synth programming to see how different speeds and depth ranges can (and should) be used.

Multi-Modulation
Most synths let you assign a controller to modulate more than one synth parameter at the same time. This is the secret to making a highly expressive sound that has depth and character. For the most part, this isn’t done at the level of physical controllers. There, you’re just assigning your wheel, joystick, or knob to send a MIDI continuous control (CC) message (CC1 is always modulation). You can often decide which CC a physical control sends, but that’s it. Making multiple parameters in your synth respond to the CC happens at the receiving end.

This might be done on each parameter page, but more commonly, there’s some sort of “modulation matrix” that lets you relate one source to multiple destinations. Different synths call it different things. Korg has AMS (Alternate Modulation System), Roland has Matrix Control, Logic’s ES2 soft synth has routing in the middle of the panel, Spectrasonics Omnisphere calls it the Mod Matrix (see Figure 3), and so on.
 
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Fig. 3. In better hardware and soft synths, a modulation matrix lets you affect multiple destinations (settings that affect the sound) from the same source (physical or virtual control).
 
Let’s apply this to modulate the LFO rate and depth simultaneously as the wheel or joystick moves up—one of my favorite vibrato tweaks. Assign an LFO in your synth to oscillator pitch (with the proper waveform and LFO rate discussed earlier), then assign the wheel or stick (CC1) to control the depth of this modulation. Next, assign CC1 to increase the rate ever so slightly. The result? Moving the control introduces vibrato, and as you’ll hear it also speed up the LFO rate. Experiment—I like the speed increase to begin only when I’ve moved the wheel about half of its travel, so very shallow amounts of LFO rate modulation are the answer.

Most synths have a delay in their LFOs, which lets you set a certain amount of time before modulation begins. (This is different from a delay effect in the effects section; see Figure 4.) This lets you add automatic but delayed vibrato so you can keep both hands on the keyboard. If you insist on complete control of when the modulation kicks in, consider using aftertouch instead of a wheel as your physical control for all of the above. This lets you keep your hands on the keys and frees up the mod wheel for something else.
 
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Fig. 4. Modulation delay parameters in GForce Minimonsta (left) and Korg M1 Legacy (right).     
 
Tremors: The Sequel
Another form of LFO modulation is tremolo. As opposed to vibrato, which affects pitch, tremolo creates a “pumping” of the volume of your sound. It’s commonly associated with breath-controlled instruments like woodwinds and has been applied in electric pianos like the Wurlitzer, Yamaha CP70B, and suitcase model Rhodes—the latter famously misnamed it “stereo vibrato.”

The main difference is that your modulation destination will be amp output, VCA gain, pre-filter mix level, or something similarly named, rather than oscillator pitch. Often, you’ll use a slower LFO than for vibrato, so you’ll need another free LFO to apply vibrato and tremolo independently. Another good choice is tempo-controlled rates, which let you sync the LFO to rhythmic values relative to the current
tempo: quarter-notes, eighths, sixteenths, and so on. Tremolo also works nicely as a delayed modulation, and you can try a square LFO wave instead of a saw or triangle for a more mechanical sound.

Next month, we’ll move into the art of the pitch bend. Enjoy!

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