What are the different types of synthesis?

The synthesizer revolution started in the 1960’s with the invention of the Minimoog. Since then, there have been hundreds, possibly thousands of hardware and software-based synthesizers to hit the market. The purpose of this article is to help you get a better understanding of the common (and uncommon) methods by which these instruments synthesize their sounds.

What is subtractive synthesis?

We’ll start with the granddaddy of them all – subtractive synthesis. Subtractive synthesis was the most logical starting point for pioneering synthesizer inventors because, believe it or not, it’s the exact method humans use when singing, humming, or otherwise vocalizing sound.

To put into simple terms, there’s a sound source and a modifier. In the human example, the source is our vocal cords, the modifier is our mouth. For synthesizers, the oscillator is the source while filters act as the modifier.

The oscillator’s job is to produce a waveform such as a sawtooth, pulse, triangle, or square. Next, filters, envelopes, and other parameters are applied to etch out (subtract) certain frequencies until the desired sound is created.

What is additive synthesis?

Additive synthesis is a close cousin of subtractive synthesis. And as the name implies, this method involves adding frequencies rather than subtracting them. Synthesized sound is generated by stacking multiple sine waves until a harmonic structure is formed.
Additive synthesizers allow you to set the precise frequency and amplitude of each sine wave in the stack. In theory, any sound heard in nature can be perfectly recreated via additive synthesis. Practically speaking, however, most natural sounds would require hundreds of oscillators, making the process of “perfect” recreation extremely tedious.

What is resynthesis?

Resynthesis is additive synthesis with a twist. Both methods use a series of stacked sine waves to generate sound, however, synthesizers that use resynthesis recreate the harmonic structure of an input sound by analyzing its frequencies. In traditional additive synthesis, there is no input sound to recreate.

So, let’s assume you want to recreate an 808-inspired bass patch. With an additive synth, you “manually” stack your waves and use the synth’s various parameters to further shape the sound you want. In contrast, with a resynthesis synth, you simply upload a sample and allow the software to handle the task of synthesis.

What is wavetable synthesis?

Wavetable synthesis is a method in which a variable number of wave cycles are spread across a wavetable. When a key or chord is played the synthesizer uses different methods such as looping or pitch-shifting to make its way from one wave cycle to another, thus producing interesting harmonics.

Let’s break it down: Picture a sawtooth wave. What you should see is a repeating waveform with a sharp upward rise followed by a vertical drop from its peak. This rise and fall “loop” is known as a wave cycle. During the digital synth revolution of the late-1970’s computer memory and processing power were expensive. The inventor of wavetable synthesis realized that storing a single cycle of a waveform was more advantageous than generating and processing them on-the-fly.

Wavetable synthesizers are great for producing evolving pads, dynamic strings, and punchy bass sounds. Wavetable synthesis is often compared to Linear Arithmetic (LA) and Granular synthesis. These three methods do, indeed, share some common traits; yet, when you take a peek under the hood you’ll see that the similarities are only surface deep.

For example, LA synthesis was designed to use samples in a manner that emulates traditional instruments. Granular synthesis, on the other hand, is more akin to wavetable synthesis because it works by splitting a sound into many parts. These sound particles or “grains” are many times smaller than those used in wavetable synthesis. Even more, when a key is pressed the grains are rearranged in a manner that requires a ton of processing power, directly contradicting the design philosophy of wavetable synthesis.

What is frequency modulation synthesis?

Frequency modulation synthesis is in a class of its own. This technique was popularized by Yamaha and has become the most commercially successful synthesis method of all time (according to DX7 sales). FM synthesis works by using a carrier and a modulator. Harmonics are created when the frequencies of the carrier are modulated by the modulator.

FM-based synthesizers don’t sound like others. These synthesizers tend to have a more “electronic” or “digital” sound than most. And although pads, leads, and vocal sounds are possible, FM synthesis is really great when it comes to creating bright epiano, thick bass sounds, synthetic brass, and bells.

What is pulse code modulation synthesis?

Also known as sample synthesis, pulse code modulation (PCM) synthesis is a method which involves using samples instead of oscillators. If you didn’t know, a sample is a digital recording. It could be a piano, trumpet, cello, hand clap, or any other recording.
In recent years technology has progressed to the point where PCM-based instruments provide near-perfect replication of acoustic sounds. The use of innovative algorithms allows for seamless switching from one sample to another providing a truly authentic sound. In other words, nothing beats PCM-based synthesizers if you’re looking to mimic acoustic instruments.

What is phase distortion synthesis?

Phase distortion synthesis is different from other methods in the way the oscillator generates waves. It’s actually very simple; in short, a sine wave is bent into shape by the user to form new (or familiar) waveforms. Unlike traditional subtractive synths where you have a predefined set of waves to choose from, phase distortion synthesizers provide an unlimited number of waveforms from which your sound can be shaped.
Aside from the unbounded oscillator, phase distortion synths utilize many of the common parameters found on subtractive synthesizers.