What are the different types of synthesizers?

What are the different types of synthesizers?

Ever hear of people posting about Additive Synthesis? Talking about partials and overtones and want to know what the crack is?

It's simple. Not all synthesizers work the same. In fact there are many different ways to create a sound, from Subtractive to Phase Distortion and more here we take a look at the most common types of ways to make a sound electronically and talk a bit about each.

Subtractive synthesis explained

Subtractive synthesis is arguably the most common synthesis methodology.

Developed to commercialisation with huge success in the 1960s by Bob Moog, it uses oscillators to create electrical soundwaves which can then be manipulated to alter their pitch, frequency content and amplitude over time.

There are a few key components of any subtractive synthesizer. These are:

* Oscillator * Filter * Amp * LFO

 The basic function of these is to sculpt and take away (hence subtract) from the original raw sound.

Lets provide A real world analogy for how Oscillators combine with Filters to create alternate sounds:

Image the filter is akin to your lips around an open mouth screaming a continuous note, closing or pursing your lips closes up the harmonics of the sound, varying the degree in which you open or close your mouth or how you shape your lips whilst closing your mouth all has a audible effect on that raw sound. This is essentially the fundelmental principle of how the oscillator and filter work in subtractive synthesis.

Popular for their simplicity in output of sound they are a great choice for a first synth and incredible versatile at a wide range of sounds.

Audio demo of subtractive synth sounds - FXPansion Strobe2 presets - a synth as simple as it gets for subtractive.


Additive synthesis explained

Additive synthesis is a sound synthesis technique that creates timbre by adding sine waves together.

An additive synthesiser has multiple oscillators. Each oscillator creates a simple sine wave. The user is able to set the frequency and amplitude of each sine wave and then mix them together in varying degrees to build a harmonic structure.

By combining these sine waves together a complex waveform can be formed.

History has shown us it's actually quite challenging to design a simple and practical interface for additive synthesis.

Audio demo of additive synth sounds from Kawai KS5000S Presets


FM (Frequency Modulation) synthesis explained

FM Synthesis is similar to Additive synthesis in that it uses 6 sine wave creating oscillators, each of which can have their frequency, amplitude and envelope set by the user. In FM, oscillators are called Operators.

 It differs from additive in that rather than combining the sine waves together, the output of one operator is sent to modulate another operator. The second operator then modulates a third operator and so on until a complex waveform is produced by the final oscillator in the chain known as the Output Operator.

The oscillators can be routed through each other in varying ways, this can be called "patterns" or 'algorithms' and each algorithm presents a different series of internal routing.

The most well know example of FM synthesis would by the Yamaha DX7, popular during the 80's and early 90's 

It can be found in software form in many VSTi synths, most notably Native Instruments FM8

Audio demo of some FM Synth sounds from Yamaha DX7 presets


Sample Based Synthesis explained

The Fairlight CMI is probably the most well known early attempt at Sample based synthesis but at the time it was held back by it's huge cost.

It wasn't until the late 80s in where increased demand for more affordable synthesise technologies that could produce a range of analogue, digital and natural sounding tones allowed Synth giants such as Korg and Roland to commercially develop the M1 and D-50 respectively.

A sample based synthesiser uses pre-recorded samples stored in memory as sound sources. 

Originally, due to the expense of memory chips, only small capacity memory was able to be cost effectively fit into devices. So it was not possible to use or hold a library of full length high quality samples on a singular device.

To overcome this, designers found ingenious ways to cram more sound possibilities in without impacting sound quality too much such as by just storing the attack and a portion of the sustain of the sound. The sustain section is then looped to create the illusion of a longer sample. This worked well because most of the identifiable character of a sound is derived from its initial attack timbre. However, the more slowly evolving timbre of the sustain and decay parts of some sounds aren't able to be accurately or realistically reproduced by looping a short sample. To mask this the sustain sample is processed through conventional subtractive filters and amplifiers which create the illusion of a natural evolving decay.

Audio demo of Sample based synth sounds from Izotope Iris 2 Presets


Wavetable, wave sequencing & vector synthesis explained

Wavetable synthesis is not unlike Sample based synthesis in that the sound of an existing instruments single note is sampled and parsed into a sequence of indexed tables of samples aka wavetables,

There can be dozens or hundreds of wave shapes in an indexed table. As a note or sound is triggered, sweeps can occur that move from one wave shape to the next with digital interpolation occurring between shapes. This process can then be processed such as by being modulated by an LFO or triggered by an envelope that mimics traditional ADSRs found in subtractive synthesis.

Popular hardware wavetable synths include the Korg Wavestation and the Sequential Circuits Prophet VS. Korg have even reimagined an updated version of their Wavestation Synth in the form of the Wavestate.

Both these synthesisers employed a joystick controller which controlled the vector mix of waves over time. With the joystick in the default central position, an equal mix of all waves is heard but as it is moved away from this position the mix changes. This mix can be automated over time with a mix envelope and each wave can be modulated differently to change, for example, its pitch.

A modern example of a Software based VSTi Wavetable Synthsizer is Serum by Xfer

Audio demo of some wavetable synth sounds from Arturia Pigment Presets


Phase distortion (PD) synthesis explained

Phase distortion synthesis is a synthesis method introduced in 1984 by Casio via its CZ range of synthesizers

Phase distortion is a form of synthesis, which uses an algorithm to create a sine wave, and then uses a second algorithm to distort the shape of this sine wave to create a completely new waveform.

Imagine increasing the amplitude of a single sine wave until it clips and distorts and starts sounding more harmonically rich like a square wave. This is a good example of the phase distortion process.

It is best used when added to other forms of synthesis, such as Frequency Modulation, where the ability to create waveforms which are variations of sine waves is particularly useful for creating new tones.

Excellent audio demo of Phase Distortion Synth Sounds from the Casio CZ-1 

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