10.6

721Logic Pro Instruments
Wavetable, Vector, and LA synthesis
Wavetable synthesis uses a number of different single-cycle waveforms, laid out in what is
known as a wavetable.
Playing a note on the keyboard triggers a predetermined sequence of waves. In general,
this is not a stepped transition but rather a smooth blend from one waveform into another,
resulting in a constantly evolving waveform. Multiple wavetables can also be used
simultaneously—either played one after the other, or blended together—resulting in more
harmonically complex waveforms.
A single wavetable can emulate filter cutoff with a series of bright, less bright, then dull-
sounding waveforms played in sequence—which resembles a reduction of the filter cutoff
frequency in a subtractive synthesizer.
Wavetable synthesis isn’t well-suited for emulating acoustic instruments. It is noted for
producing constantly evolving sounds; harsh and metallic, or bell-like sounds; punchy
basses; and other digital tones.
Wavetable synthesis was championed by the PPG and Waldorf instruments. ES2 and Retro
Synth include a number of wavetable features. Alchemy takes this a step further with
granular synthesis which shares some aspects with wavetable synthesis. See Granular
synthesis.
Roland LA (Linear Arithmetic) synthesizers such as the D-50 work on a similar principle. In
these synthesizers, complex sampled attack phases are combined with simple sustain or
decay phases to create a sound. In essence, this is a simple wavetable that consists of two
samples.
Where LA and wavetable synthesizers differ is that the latter were designed to create
new, original, digital sounds. LA synthesizer designers, in contrast, wanted to emulate real
instruments using a minimum of memory. To achieve this goal, they combined samples of
the attack phase—the crucial part of a sound—with appropriate decay and sustain phases
that were played with filtered sawtooth or pulse waves.
Vector synthesis—used in the Sequential Circuits Prophet-VS and Korg Wavestation—allows
you to move through wavetables and sequences arranged on a two-dimensional grid (two
different vectors, or less technically, on the X or Y axis). The main benefit of this approach
is that the balance between samples and waves is achieved in real time by moving a
joystick. You can also use ES2 to perform vector synthesis by modulating the Oscillator Mix
(Triangle) parameter with the Vector Envelope.
Additive synthesis
Additive synthesis could be considered the reverse approach to subtractive synthesis. See
Sound basics overview, Tones, overtones, harmonics, and partials, and How subtractive
synthesizers work.
To obtain an insight into the additive synthesis method, consider the fact that all sounds
are a sum of various sine tones and harmonics.
In additive synthesis, you start out with nothing and build a sound by combining multiple
sine waves of differing levels and frequencies. As more sine waves are combined, they
begin to generate additional harmonics. In most additive synthesizers, each set of sine
waves is viewed and used much like an oscillator.