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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 facilitate this, they combined samples
of the attack phase—the crucial part of a sound—with appropriate decay and sustain
phases.
Vector synthesis—used in the Sequential Circuits Prophet-VS and Korg’s
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 the 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 the beginning of this appendix, including the discussion about all sounds being a
sum of various sine tones and harmonics, for background information to provide insight
into additive synthesis.
In essence, you start out with nothing and then build up 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.
Depending on the sophistication of the additive synthesizer you are using, you will be
provided with individual envelope control over each sine wave, or you will be limited to
envelope control over groups of sine waves—one envelope per sound and its harmonics,
or all odd or all even harmonics, for example.
Logic Express does not contain any instruments that use additive synthesis methods.
Resynthesis
You can analyze the frequency components of a recorded sound and then resynthesize
(reconstruct) a representation of the sound using additive techniques. By calculating the
frequency and amplitude of each harmonic in the overall frequency spectrum of the
sound, an additive resynthesis system can generate a series of sine waves (with appropriate
levels over time) for each harmonic.
After the sound has been resynthesized in this fashion, you can adjust the frequency and
amplitude of any harmonic. Theoretically, you could restructure a harmonic sound to
make it inharmonic, for example.
Phase Distortion Synthesis
Phase distortion synthesis creates different waveforms by modifying the phase angle of
a sine wave.
370 Appendix Synthesizer Basics