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Moogerfooger Madness
Harness the Power of Moog Music's Moogerfoogers
What does the term “voltage control” mean to you? If you’re only experienced with digital synthesizers, chances are slim you know much about it. In fact, since the introduction of MIDI in 1983, few synthesizers use voltage control beyond the input for a sweep pedal. Such a pedal is typically used to control volume, although some synths allow you to assign a pedal to control parameters such as the portamento rate or filter cutoff frequency.
Such simplicity and inflexibility isn’t the case for an analog modular synthesizer, which virtually lives on control voltages. The creation of even a simple sound on a modular takes a handful of patch cords, and dozens of cords are required for complex patches. While that may sound daunting, consider the power and possibilities such a system provides: Many sound developers turn to modular synthesizers to create sonic events and textures that can’t be produced any other way, even in a digital environment.
Bob Moog poses with Keith Emerson’s modular Moog system--“The World’s Most Dangerous Synth”--in August 1999. The multitude of colorful patch cords gives an indication of the number of cords required to set up a complex patch on a modular synthesizer.
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With the CP-251 Control Processor and the Moogerfooger line of effects processors--the MF-101 Lowpass Filter, MF-102 Ring Modulator, MF-103 Twelve-Stage Phaser, and MF-104 Analog Delay--Moog Music has re-introduced the power and flexibility inherent in analog modular synthesizer systems. But before you can realize the potentials, it’s best to understand the underlying principles of voltage control.
Control Voltage
In electronic music terms, a control voltage is an electric signal that you route to a destination such as a voltage-controlled oscillator, amplifier, or filter (VCO, VCA, or VCF, respectively). You might think of voltage as electrical pressure, which is used to control--or modulate--some aspect in the destination device. When you apply different voltages to a VCO, the oscillator’s pitch will vary. Route a control voltage into the frequency cutoff of a lowpass VCF and you can modulate the brightness of the audio signal traveling through the filter. Audio signals passing through a VCA will come out louder the greater the control voltage you pump into the amplifier; lower the control voltage and the signal will get quieter. Even the audio signal itself is an analog voltage.
A control voltage is an analog signal. What’s the main difference between analog and digital? While an analog signal is capable of continuous fluctuations, digital data is quantized into discrete steps.
In an analog audio system, fluctuations in voltage are analogous to changes in air pressure in a wind instrument. Parameters such as oscillator pitch and LFO speed are modulated by analog control voltages in an analog synthesizer. Conversely, digital music equipment uses microprocessors to store, retrieve, and manipulate information about sound in the form of numbers, and typically divides potentially continuous fluctuations in value (such as amplitude or pitch) into discrete quantized steps.
The types of control-voltage sources and the destinations to which CV signals can be applied depend on the system you’re making music with. If you have any of the Moogerfooger products, you get a good selection of both--and the possibilities increase exponentially when you combine multiple Moogerfoogers. Such a combination makes for an effects-processing system with which you have realtime dynamic control. Include an MF-101 Lowpass Filter or MF-102 Ring Modulator--either of which can serve as an audio source--and you have a functional modular synthesizer.
Let’s take a look at the sources and destinations found in a typical modular system, as well as those inherent in all five of the Moogerfoogers, then discuss what the heck you can do with all this fun stuff.
Generic CV Sources & Destinations
Devices that generate control voltages come in numerous shapes and sizes. Prior to the introduction of MIDI, keyboards were designed to output discrete stepped voltages to trigger specific pitches in a VCO. Analog sequencers worked the same way. Play a note on a CV keyboard or advance an analog sequencer by one step, and either device will output a specific, steady-state voltage.
Two of the most creative CV sources in a synthesizer are the envelope generator and low-frequency oscillator (EG and LFO for short). An EG outputs a continuously variable voltage that changes over time. This voltage is typically applied to a VCA or VCF to shape the volume or timbre of a sound; VCO pitch is another potent destination, so you can get programmed pitchbends. EGs range in complexity from a two-stage attack-decay envelope to a multi-stage envelope with independent rate and level parameters for each step and flexible envelope-looping options.
Attack, Decay, Sustain, Release.
LFOs usually provide an assortment of waveforms to choose from. Most commonly you get sine, triangle, sawtooth, reverse sawtooth, pulse, and square (a pulse wave with a 50% duty cycle). Like an EG, an LFO outputs continuously varying voltages, but they fluctuate periodically. While these fluctuations usually occur at a rate that’s much slower than an audio VCO, some LFOs can oscillate at rates that extend into the audible range (higher than 20Hz). Depending on the destination being modulated, this can lead to very interesting timbral results. Typical destinations for LFO signals are VCOs for vibrato or note trills, VCAs for tremolo, and lowpass VCF cutoff frequency for fluctuations in treble harmonic content.
Triangle waveform Sawtooth waveform Square waveform
Somewhat related to the LFO is sample-and-hold (S&H), which might appear as a separate synthesizer circuit or as an LFO waveform. Technically, S&H works by sampling an input voltage when triggered, passing this voltage through unchanged to its output, sampling another input voltage, and so on. The resulting S&H output is a CV signal that jumps from one value to the next in a random manner. Apply the S&H CV to a VCO, VCA, or VCF and you’ll get some unpredictable but often effective results.
sample-and-hold shape
The final group of CV sources falls in the manually controlled category. They include pitchbend and modulation wheels, joysticks, ribbons, two-dimensional touchpads, knobs, sliders, and sweep pedals. The voltages generated by these devices are continuously variable and change according to user interaction. When you want realtime hands-on or foot control of parameters such as volume, pitch, LFO rate, and modulation depth, these work very well.
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