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Quick Guide To Synthesis

Analogue synthesis is not the only fruit. Many alternative types of synthesis are now possible with the advent of the computer. We examine a few that you might want to get your teeth into...

Analogue synthesis is far and away the most common form of synthesis in both hard and soft synths. However, there are several other types of synthesis which are becoming more accessible due to advances in computer technology.

The main difference between analogue synthesis and alternative forms is in the way the initial sound is produced, although some types of synthesis have other distinguishing features, too. In this feature we'll look at some of the more common alternative forms of synthesis you may come across.

First. we need to clarify the difference between digital and analogue synthesis. Technically, any form of synthesis that uses digital technology is digital, and synthesis that uses analogue circuitry is analogue - easy, innit! Therefore, all software synthesisers are technically digital even though they may emulate an analogue synthesiser. However, that won't stop us referring to an analogue technique as analogue even if it is generated with digital technology.

Subtractive synthesis

Subtractive synthesis takes a harmonically-rich sound and removes parts of it with filters. This is, in fact, the core method behind analogue synthesis - the source is typically a waveform such as sawtooth or square which is passed through filters to change the tone.

You can, however, apply a 'subtractive' filter to any sound source generated by any type of synthesis so if a synthesiser has a filter then that part of it at least is using Subtractive synthesis.

Additive synthesis

As you can probably guess, this is the opposite of Subtractive synthesis. Instead of starting with a complex waveform, Additive synthesis typically starts with the simplest wave of all - a sine wave - and adds several of them together to create more complex tones.

It is based on work done by the mathematician, Fourier, in the early 1800s when he proved that any waveform could be created by adding together sine waves of various frequencies and amplitudes. The main proviso is that the waveform must be cyclical or repetitive otherwise the sine waves which go to make it up would have to be constantly changing, too.

The principles behind Additive synthesis can clearly be seen by examining the make-up of typical analogue waveforms such as square, sawtooth, triangle and pulse. All of these can be 'constructed' from sine waves of different frequencies and amplitudes. However, although the original work involved sine waves, there no reason why more complex waveforms cannot be added to produce even more complex sounds.

You may be familiar with the Fourier Analysis display in audio programs such a WaveLab which show the individual frequencies that make up a sound. You can see from these displays that any but the simplest of sounds are quite complex and designing a friendly, comprehensive user interface for an Additive synthesis synthesiser is not easy. In fact, few companies tried.

The first, and possibly only, commercial Additive hardware synth of note was Kawai's K5 released in 1987 which offered 126 harmonics controlled from a large LCD. Innovative it was, but there has been little interest in hardware Additive synthesisers since. However, with today's modular soft synths such as Reaktor and Tassman, you could easily - we use this in a relative context here - pile oscillator upon oscillator to create a software Additive synth.

FM

FM or Frequency Modulation lead to the greatest synthesiser revolution we have ever seen. It was the foundation of Yamaha's ground-breaking DX7 released in 1983 and arguably the most popular synthesiser of all time. It was also, without doubt, the most difficult to program and it's a testimony to its sounds and not its programmability that musicians bought it in droves - and the vast majority never even attempted to program it!

FM synthesis was first proposed by John M. Chowning in 1973 in a paper in the Journal of the Audio Engineering Society. It was the first description of how a totally digital technology could be used to generate sounds using a manageable number of controls.

The core of the technology involves using the output of one oscillator called the Modulator to modulate the frequency of another oscillator called the Carrier. If you do this with genuine analogue waveforms you'll probably get sounds ranging from warbles to metallic and bell-like tones. However, more-stable digital oscillators give more control over the process and allow a wide range of timbres to be created from this apparently simple process.

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