Sound synthesis is the electronic production of sounds—starting from their basic properties, such as sine tones and other simple waves.
Synthesizers are so named because they can emulate, or synthesize, a wide variety of sounds—such as the sound of another instrument, a voice, a helicopter, a car, or a dog bark. Synthesizers can also produce sounds that don’t occur in the natural world. The ability to generate tones that cannot be created in any other way makes the synthesizer a unique musical tool.
The simplest form of synthesizer would be a basic sine wave generator that provided little or no control over pitch. Unfortunately, you could not use such a simple synthesizer to synthesize anything except a sine wave.
Combining multiple sine generators with pitch control, however, can produce many interesting and useful tones.
In a synthesizer, the task of tone generation falls to a component known as an oscillator. Most synthesizer oscillators generate harmonically rich waveforms, such as sawtooth, triangle, square and pulse waves. These waves are named due to the resemblance of their shapes to the teeth on the blades of a saw, to triangles, to squares, and so on. For information about the most common synthesizer waveforms, see Oscillators.
Sculpting the fundamental tone and related harmonics into another sound is achieved by routing the signal from one component, also known as a module, to another in the synthesizer. Each module performs a different job that affects the source signal.
In a modular synthesizer, this routing is achieved by physically cabling modules to each other. In most modern synthesizers, however, the signal routing between modules is internally prewired and is typically changed using switches, knobs, and other controls.
For a discussion of the various synthesizer components and how they interact with each other to control and shape your sound, see How Subtractive Synthesizers Work.
Synthesizers have been around for much longer than you may think. In the days that preceded the use of digital technology, all electronic synthesizers were analog. And prior to the use of electricity, synthesizers were actually mechanical. If you’re interested in learning more, see A Brief History of the Synthesizer.
An analog synthesizer combines voltage-controlled circuits—such as oscillators, filters, and amplifiers—to generate and shape sounds. The amount of voltage is typically related directly to the waveform pitch, with higher voltages equalling higher pitches.
In a digital synthesizer, the signal flow is digital. Binary descriptions of the signal—a string of zeros and ones—are fed from one algorithm to another.
Some synthesizer designs feature digital oscillators—which generate signals that are sent to analog filters—and amplifiers. The main advantage of this approach is that digital oscillators don’t drift in pitch, a problem that analog oscillators are often notorious for.
A virtual analog synthesizer is a digital synthesizer that mimics the architecture, features, and peculiarities of an analog synthesizer. The behaviors and functions of the oscillators, filters, and other modules that you would find in an analog synthesizer are emulated by computer algorithms.
The ES1 is a great example of a virtual analog synthesizer. Its virtual signal flow is that of a typical analog synthesizer, but all the signal processing—the virtual oscillators and so on—is performed by the central processing unit (CPU) of your computer.
The ES1 includes some of the desirable idiosyncrasies of particular analog circuits—in cases where they tend to sound nice, such as high oscillator levels overdriving the filter. And undesirable analog synthesizer phenomena, such as the habit of going completely out of tune, are not simulated.
Virtual analog synthesizers have a few other advantages over their analog counterparts:they’re completely programmable (you can save sound settings), they can be completely automated (you can record and play back fader and knob movements), and they are often multi-timbral (you can play different sounds at the same time, on different instrument channels). Aspects such as polyphony (the ability to play multiple notes) and velocity sensitivity are found in most virtual analog synthesizers but in very few analog instruments.