Virtual Instruments — Synthesis

Moog Minimoog hardware synthesizer

The MiniMoog is among the most famous hardware synths in the world. Some software synths model hardware and others are completely new instruments.

Key Terms

Oscillator: The sound source of a synthesizer. This could be a simple waveform, a complex waveform, or a sample. The word “oscillator” tells us that it’s an electric signal that goes back and forth between a positive and a negative charge. In essence, this is all every sound wave is when it’s in an analog, electronic medium.

Low-Frequency Oscillator (LFO): An oscillator at such a low frequency that individual oscillations can be distinguished. It’s commonly used to affect other synth parameters to add movement to the sound (like vibrato).

Filter: We’ll go over specific filter types in the section on filter effects. Filters boost and/or cut bands of frequencies in a wave’s frequency spectrum. Equalization (EQ) is synonymous with filter.

Cut-off Frequency: The point in the frequency spectrum where a filter drops off. Often, this is where Resonance occurs—a narrow frequency boost, for musical effect.

Amplifier (Amp): An amplifier boosts a given current. In audio, it’s what allows speakers to run louder than a whisper; in synths, it’s basically a volume/gain knob, as it boosts the signal by a set amount.

Envelope: A set of parameters that affect the attack, sustain, decay, and release of a signal (ASDR). This is the key to having notes that reach their climax immediately or slowly, are long or short, fade out fast or slow, etc . . .

Wave Types for Oscillators

Oscillators can utilize simple waveforms, like a sine or square; however, there are infinite options. Most software synths come with a pre-defined set of waves in their “wavetable.” The simplest wave is a sine, which is what a circle would look like if it were linear— it goes up, then down in a perfect curve. Here are a few graphical representations of synth waves. These are taken from iZotope RX 6, which shows the wave itself as a blue line, then the intensity of each frequency in orange. You can see that a sine wave is a single frequency, whereas the rest have multiple harmonics.

A sine wave, shown in iZotope RX 6

This is a basic sine wave. All these examples were played in Native Instrument’s Massive.

A square wave from Massive

A pure square wave.

A triangle wave from Massive

A pure triangle wave.

A sawtooth wave from Massive

A pure sawtooth wave.

An example of an unmodulated wave from a wavetable

The Lunacy wave from Massive’s wavetable, without modulation; this one sounds similar to a bird chirp.

The beginning of the Harpolodic patch in Massive

By the time a wave has been joined with other oscillators and modulated in various ways, it resembles a regular sound wave. This is the first part of the Harpolodic preset from Massive.

What are the Types of Synthesis?

A quick look at the definitions of synthesis shows that it’s creating something new from either altering/combining simple parts, or degrading something complex.

Additive Synthesis: Oscillators are combined to create something new. For example, the timbre of instruments is dependent on variations in their upper harmonics. To create a specific instrument’s sound, you’d add sine waves at the right frequencies and velocities until it matches what you hear/analyze coming out of the real instrument. The algorithm that makes it possible to combine sine waves into a single wave is known as the Fourier Transform.

Subtractive Synthesis: This starts with a harmonically-rich wave (like a sawtooth or combination of oscillators), which is cut down into what the player wants. The Moog is a popular synth that uses this form of synthesis. An example is using a cut-off filter to throw out all the upper harmonics of a wave until only the fundamental remains, then modulating that with an LFO and an envelope to add vibrato and sustain.

Frequency Modulation (FM) Synthesis: This one takes a simple wave, then modulates it with another wave. It’s a vastly different process than other types of synthesis. The most famous, hardware synth to use FM synthesis is the Yamaha DX-7. NI’s FM8 is a modern software example. Ring Modulation is similar to FM, but it multiplies waves together; this boosts shared frequencies, among other things.

Sample-Based Synthesis: Simply put, this uses sampled audio as the oscillator. This opens up a whole new world of possibilities since you can start with something extremely complex and organic with little effort.

Granular Synthesis: This one has both practical and experimental implications. Audio is broken into tiny pieces (grains), then altered to taste. It can be a good way to speed up/slow down audio. It can also create completely new and crazy textures and noises.

Resources for this Section

Moog synths are as classic as they come. This page is a repository of historical assets about the company and their products.

This free, online synth provides a quick way to experiment with additive, subtractive, and FM synthesis.

This one is more immediately accessible. It more or less emulates a Theremin instrument, with four wave types.

This web-enabled example of speech synthesis is a great tool to show how each part of the mouth affects tone—and it’s hilarious.