Synthesizers come in an incredible variety of designs. At first glance, it might seem unlikely that they have anything in common. But once you understand a few central concepts, you’ll realize these instruments are much more alike than different. If you don't know anything about synthesizers, this is the place to start.
With the concepts below in mind, you'll begin to look at a synthesizer’s front panel and recognize how key functions are arranged, both in relation to each other and to the musician.
Modules: Pieces of the puzzle
Every synthesizer – often shortened to synth – can be thought of as a kind of puzzle: a set of pieces assembled in a particular way. We call these pieces modules.
A module can take many forms. It might be a physical box that you connect to other boxes with cables. The earliest commercial synthesizers were built this way – they were modular. A module could also be an electronic circuit, a chip, or even part of a software application. The simplest synthesizers may have only a few modules, while the most complex might contain hundreds.
What’s important is that each module represents one specific function the synthesizer performs – a single piece of the larger puzzle.
Before we start: Signal path
The signal path is the route that sound takes through the machine, from the moment it’s created to the moment it leaves. The actual machinery will be different for every synth, but there’s always a signal path, and nearly every synth uses some variation of the same one: VCO to VCF to VCA.
1) First, we create a sound wave as our raw material. We choose its waveform – the raw harmonic content we start with – and we control its pitch. We do this with a VCO.
2) Then, we change the tone of the sound wave over time, making the sound brighter or darker, which brings out or subdues parts of its harmonic content. We do this with a VCF.
3) Finally, we control the amplitude of the sound wave. Most obviously, we make it silent, then audible, then silent again: we divide it into individual notes. We do this with a VCA.
Front panel
Let's now take a look at the front panel of our synth below. The front panel of a synthesizer is where sound design is carried out. Each synthesizer will have its own particular set of modules, and a well-designed front panel allows the musician to access them all quickly and clearly.
A standard convention in front panel design is that the audio signal path flows from left to right. Non-audio elements are usually placed ‘out of the way’ of the audio path, so it’s easy to focus on one function at a time.
LFO
Modulation is a term that means ‘to control or influence.’ Everything that a synthesizer does to shape its audio is modulation – changing pitch by playing keys, altering timbre by turning knobs, or having modules like the Low-Frequency Oscillator (LFO) ‘turn the knobs for you’ using voltage control.
VCO
The Voltage-Controlled Oscillator (VCO) is where an audio signal is created for the synthesizer to use as raw material. A control voltage, such as a note played on a keyboard, instructs the oscillator to play a specific pitch. Traditional VCOs are analog electrical circuits, but some synthesizers have digital oscillators instead.
MIX
The Mixer is where the VCOs are blended, sometimes with the addition of noise and/or an external audio input signal, before entering the VCF. Some synths will have a specific central mixing area; others will simply place each sound source’s volume knob next to its other controls.
VCF
The Voltage-Controlled Filter (VCF) controls the tone of the sound in various ways, using an envelope or other modulation sources to change its tonal character over time. The change in tone from bright to dark, emphasiz-ing different harmonics in a sound, is central to how synths shape timbre.
ENV
An envelope is a modulation source that changes a sound over time, usually in response to playing the keyboard (starting and stopping each note). Envelopes can be used in a variety of ways, but the most common are the VCF envelope for cutoff frequency and the VCA envelope for signal level.
VCA
The Voltage-Controlled Amplifier (VCA) is the last stage of the audio signal chain. This is where the signal level of the sound is controlled before it is output from the synth. Often it will have no controls but a single volume knob (if even that) and a VCA envelope.
Left-hand controls
Left-hand controls are placed beside the keys, so the player’s left hand can add performance nuances such as pitch bend or vibrato while the right hand plays a melody. By far the most common are the pitch and modulation (mod) wheels, but they could also be joysticks, knobs, touch-sensitive ribbons, levers or something else.
Keyboard
The keyboard isn’t a requirement for a synthesizer; we just chose to focus on synths with keyboards for this book. Because synths are electronic, anything that generates an appropriate control voltage can play notes. However, keyboards are most common, a carryover from older electric pianos and organs. Some keyboards are sensitive to velocity (how hard you press a key) or pressure (how hard you press down on a key after you have pressed it). There are also automated ways to play melodies, such as sequencers.
Rear panel
The rear panel of a synthesizer is where other equipment connects to it. (Some synths have connections on the sides instead.) An audio output will always be present, but there can also be an audio input, as well as modulation inputs and outputs (analog or digital) to control the synth or have it control other devices.
In the following article in this series, we'll dive deeper into each section of the synthesizer and explore how it makes – and refines – sound.
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