Nice post, i too was gonna do this at some point but just never got round to it.
Just one thing that i feel may be usefull is to add in the different methods of synthesis, as this may be handy for some people when considering synths.
Subtractive: As already mentioned, this is the most common type of synthesis used and can be found on most if not all (depends on how you look at things) synthesizers to a degree. The basic principles are that you start of by creating a very harmonically rich sound source using oscillators with the waveshapes mentioned previously. Obviously this can give you a very full frequency spectrum which may or may not be desirable. The name is derived from the next part of the signal path in which the Filter (which can be any of the types previously mentioned or other types such as comb and formant) subtracts or "filters" frequencies from this harmonically rich source until the desired sound is achieved.
Additive: Additive synthesis is the direct opposite to subtractive synthesis. It is built around the principal that all sounds are created from a complex arrangement of sinewaves added together at different levels each with different envelopes. This method of synthesis does however produce very realistic and pleasing results although programming is slow and an in depth knowledge of a waveforms construction is needed if a user is attempting a specific waveform ie Square wave or triangle. Additive synthesis is rarely found in either Hardware or Software due to the sheer number of parameters needed to program a sound as there are likely to be more than 64 sine waves each with its own envelope and level control. creating an interface that is quick and easy to edit is not an easy task. The most simple additive synthesizer is the organ as it works on the same principal with each pipe (is that the right word?) creating its own sinewave(ideally).
Examples : Kawai k5000, Chameleon 5000.
Wavetable: Wavetable synthesis is a method of synthesis that came about in the 70s as a way of generating more complex waveforms than in the original analogue oscillator designs. Originally this consisted of a "look up" table containing many different waveforms and a user could select any of the waveforms in the same way that sine, saw etc could be. This method of synthesis however has much more potential as the table in which it is stored can be used in a number of ways. Firstly through the process of interpolation it is possible to "morph" between 2 different waveforms in 2 different positions within the table creating sweeping harmonic changes. This method can then be applied as a basic method of sample playback where by each position in the table is a different section of the sample. This was used to great effect before memory became cheap as it was possible to cycle through many positions in a table to build a sample and required much less space due to the fact that for example the sustain section could be a loop of only 2 positions where as a sample would take up a vast amount of cycles in order to do the same task.
This was used to great effect in synths such as the Wavestation.
Examples: PPG wave, Prophet VS, Waldorf wave/microwave, Access Virus Ti.
Sample based (PCM): im not gonna spend too long here as its pretty obvious, this is a case of playing samples back at different pitches etc and using the modifiers (EGs,LFOs, Filters) found in other forms of synthesis and can be considered as subtractive synthesis with a different generator.
Examples: EMU proteus, Roland D110.
Granular: Granular synthesis is a fairly new type of synthesis in terms of how long it has been commercially available and there are few hardware synthesizers that use this method of synthesis. This method uses the same idea as film, the human ear can only recognise new sounds every 10ms or so and so like film and the eye granular synthesis takes advantage of this fact by splicing together many small segments or "grains" of sound (this could be a sample for example) of around 10ms in length. This is done by effectively giving each grain an envelope, this could be considered the same as a crosfade between each grain resulting in a smooth transition undetectable by the human ear. The results can be shimmering pad sounds etc as the content of the signal can be harmonically very rich. this type of synthesis can be used as a form of subtractive synthesis in that the system is technically a tone generator and can be applied to the subtractive synthesis model using modifers like the ones previously stated.
Examples : Reason Malstrom, Reaktor library (forget the name of the synths but theres a couple in there), The access virus Ti also now has some form of granular oscillator but i have yet to find out if this is in the same vein or something quiet different.
FM: FM synthesis or Frequency Modulation, uses the same principals as FM radio however everything the FM radio tries to avoid is present in FM synthesis. In this model generally oscillators are referred to as Operators (this is due to Yamahas naming in the DX7 era). Each operator consists of an oscillator, EG and amp. Operators are then chained together in order to carry out the Frequency modulation. The way in which this works is that one operator will be the carrier and one will be the modulator (in a simple 2 operator system) the modulator will modulate the Frequency of the Carrier waveform, however unlike a standard LFO this modulation occurs at audio frequencies. In the most basic model (the original DX7) operators are only capable of generating sine waves. The reason for this is that as stated in additive synthesis more complex waves are generated from a collection of sinewaves, this when placed into the FM model creates more complex harmonics as each component(sine wave) of the complex wave (square for example) is modulated differently. Operators much like any other oscillator can be tuned, but generally have a wider tuning range as this when used as a modulator will have wildly varying effects on the carrier signal. Operators have EGs in order to emulate more complex sounds in which different harmonics enter at later points in time, emulating much the same effects as the additive model with sine wave components each with their own EGs. FM synthesis is one of the only synthesis methods which does not usually (and i say usually because the DX7 II did) fit into a subtractive "source and modifier" model as there are no filters. It is also one of the hardest to program as it is really non intuitive and requires a lot of time in order to grasp exactly what is going on due mainly to the fact that its principals are based main on maths. This being said it does have a character unlike any other, creating great percussion and bell/metallic sounds.
Examples : Yamaha DX7 I/II, NI FM7/8, Yamaha FB01, Yamaha TX series.
Vector: This is not a synthesis method in its own right, it is more of an addition made to a normal subtractive synthesizer in order to create a better sense of movement and a greater "hands on" approach to a sounds evolution. First used on the Sequential Circuits Prophet VS (VS standing for Vector Synthesis) this is basically a 4 way cross fader for fading between 4 sources (oscillators, samplers etc) with the centre point being all 4 sources at equal amplitude. the user can move from one corner to another also and this give a simple 2 way cross fade or across the centre for more complex fades. This can give a sound much like the sweeping of a wavetable although there are only 4 positions and thus 4 waveforms. However what it did allow (on the Pro VS anyway) was a user to create ever more complex waves by "blending" complex waves and then storing them ready to use to create the next complex wave. This has been a feature on many synths since such as the yamaha SY series and the Korg wavestation (this is due to the fact that after sequential went bust the team moved first to yamaha and then to Korg under Dave smith) The vector "mixer" is charcterised by its diamon shape and joystick. The diamond shape is actually only for cosmetic purposes.
Examples : Yamaha SY series, Prophet VS, Korg Wavestation, some of the newer korgs also have it (i think the OASYS and M3 feature it)
I will edit this to add in FM and other variants such as Phase distortion, vector and LA soon
|