Virtual Instruments — Synthesis
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
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.
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.