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Appendix B Synthesizer Basics 495
Additive synthesis
Additive synthesis overview
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 approach, 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 diering 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 either have
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 Pro doesn’t provide a true additive synthesizer, but aspects of the additive synthesis
approach are used in Vintage B3 and all other drawbar organs. In Vintage B3 you start with a
basic tone and add harmonics to it, to build up a richer sound. The level relationships between
the fundamental tone and each harmonic are determined by how far you pull each drawbar
out. As Vintage B3 doesn’t provide envelope control over each harmonic, it is limited to
organ emulations.
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 even restructure a harmonic sound to make
it inharmonic, for example.