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All About Additive (Part 2) | |
Article from Music Technology, May 1988 |
In the final part of a look into the world of additive synthesis, Chris Meyer explains the different approaches to additive synthesis adopted by various manufacturers and which synths have employed them.
We conclude our series on additive synthesis and resynthesis by defining some of the terms involved and surveying a selection of "additive" machines.
Renowned for their sampling, the Fairlights also boast additive synthesis - the Series II in particular attempted to marry sampling and additive synthesis as closely as possible. You were supposed to select a sample rate based on the pitch of the sound so that one wave would fit into 128 samples. Then the Fairlight would make a Fourier analysis of each waveform to determine its harmonic spectrum. You could then alter this harmonic spectrum, or create one from scratch by drawing a wave-to-wave amplitude envelope for each harmonic (up to 64) of the sound. The sound was then "computer crunched" into a sample (or back into one). This made it an early additive sample machine, and also, since you could start with a sample and edit its spectrum, a resynthesis sampler.
The PPG Wave was one of the first wavetable synthesisers. A number of waveforms were set end to end, and envelopes, LFOs, velocity, pressure and so on, determined which waveform was played at any given moment. The waves could have smooth progressions from one shape to another, or sudden jumps. The Waveterm, which was a sampling and editing terminal for the Wave, allowed you to create waveforms (using additive synthesis) and design progressions. This qualifies it as an advanced additive wavetable synthesiser.
A wavetable synthesiser, this. The VS's voice structure contains four oscillators per voice which can be mixed in real time (with envelopes, aftertouch, a joystick and so on). You can create new waveforms by mixing four existing waveforms (including sine waves) together. Because you can create waveforms (and later dynamically mix them), harmonic progressions could be set up, making this an advanced additive wavetable synthesiser. Each wave can be treated as four "groups" of harmonics that can be faded against each other - this over-generalises the harmonic progression of a real sound a bit, but is still useful. Waveforms may also be sent to the VS using the MIDI Sample Dump Standard.
Like Korg's DSS1, this is a sampler that encourages you to turn it into a wavetable synthesiser. It has a section where you can define the harmonic content of a wave, thus qualifying it as an additive wavetable machine when used in this mode.
- Kawai K5
The voice structure of Kawai's additive machine is related to that of the Prophet VS, in that it has four oscillators per voice. But where the VS mixed the four waveforms through what is in essence a quad panner, each oscillator has its own envelope, modulation and so on. (You can define the waves produced by these oscillators by determining the relative strengths of up to 63 harmonics. Kawai present this system as 63 harmonics that can be fed through one of four envelopes.) This ends up being a simplification of a full additive machine - as opposed to having to construct an envelope for each harmonic, there are only four to deal with. No, this doesn't give the "full" power of additive (and this is still technically an advanced additive wavetable machine); but sometimes all that power can be too laborious to deal with. Like the VS, the K5 may also receive waveforms as samples over MIDI (using a Kawai SysEx message, not a MIDI Sample Dump), making it possible to take snapshots of a sample, modify them, and transfer them to the Kawai - a crude form of resynthesis.
- E-mu Systems Emax SE
E-mu has just freshened up their popular sampling keyboard with a software update that includes a "spectrum interpolation synthesis" module. In essence, this is an additive synthesis software package that resides inside the Emax. Sounds may have up to 24 harmonics, and are divided into 24 time slices (which unfortunately seem to have a fixed position in time). The amplitude and pitch of envelope of each harmonic may be created by either editing its status per time slice or by "drawing" its profile with the data entry slider while the Emax clicks off time. The transition from time slice to time slice may be smooth or abrupt.
The harmonic content of the sound at each time slice is called a "spectrum", and these may be copied to other spectrum locations. Frequency ratios of the partials may also be defined (although they must be integers at the slice if you intend to copy it to another location - as described last month, having something like 3/2 sine waves per wavelength ends up a little distorted). You may also draw the amplitude of each harmonic at a given time slice. The result may then be crunched into a sample that the Emax will play back, which qualifies it as an additive sample machine. Having controls over all the parameters that additive synthesis requires is difficult for any interface; the SE does a commendable job in making it relatively easy.
- Technos Acxel
Whereas the Fairlight is a sampler that borrowed additive techniques (and eventually resolved things into samples), the Technos is a true additive synthesiser/resynthesiser that uses samples as the starting point for its sounds. It has a large number of oscillators that can have any of 32 different preset waveshapes (including sine), or you can draw your own. These may have their frequency ratio set, and multistage (up to 1024 point) envelopes for pitch and amplitude may be constructed. The number of harmonics per voice is adjustable from eight to 128 (32 is the default). Lots of processing is available besides simple additive construction, such as digital filtering, FM, modulation and so on. Since all these parameters are being executed in real time, full real-time control over the sound is available. An additional highlight of the Acxel is The Grapher - a visual interface that you can touch and trace out new curves on.
ADDITIVE SYNTHESIS IS ultimately very powerful, but that power only comes with many, many parameters to manage. Implementing all this power is a difficult and expensive proposition in terms of both hardware and software. Consequently, a lot of manufacturers are going to shout "additive" and "resynthesis" when, in fact, they're only calling on part of the power of additive synthesis. But remember, that pigeon-holing a machine doesn't diminish its musical usefulness.
This is the last part in this series. The first article in this series is:
All About Additive
(MT Apr 88)
All parts in this series:
Part 1 | Part 2 (Viewing)
Understanding the DX7 (Part 1) |
A Handy Way To Solve Sticky Control Problems |
The Sensuous Envelope Follower |
![]() Rock Around the Clock |
It's Cee Zee! (Part 1) |
Hands On - Emu Emax II |
Dave Bristow on the Yamaha DX7 - Yamaha DX Keyboards |
Synth Computers |
Sounds Natural - The Acoustic Guitar (Part 1) |
Technically Speaking |
'Wee Also Have Sound-Houses' |
The Ins and Outs of Digital Design |
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Feature by Chris Meyer
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