Ever played with an additive synthesiser that can resynthesise an audio file? If so, all this may seem quite familiar. Indeed, at their core, additive resynthesisers work in much the same way as dedicated spectral synths. Both employ FFT to examine an existing sound, allowing access to smaller harmonics or groups of harmonics.
Note that while additive synthesis can be viewed as a form of spectral synthesis, it can differ in that an additive resynthesis isn’t merely accentuating or attenuating existing harmonics, but actually analysing a sound and rebuilding it as a collection of individual sine waves. Each of those sine waves needs its own oscillator, and more oscillators mean a more detailed representation of the sound being (re) synthesised. Early additive synths offered a limited number of oscillators and less realistic recreations of a given sound. Happily, with modern computers, such limitations are mostly used for the sake of user-friendliness.
Traditionally, additive synths present the harmonic content in play as a collection of vertical bars or sliders that represent the static state of each partial’s amplitude, while familiar envelopes are provided to control that amplitude (and other things) over time. While these methods offer detailed control, they can be tedious to use. The payoff comes in the ability to do more than simply alter an existing sound, but to thoroughly transform that sound into any other sound, one partial at a time.
A primary distinction between a spectral synth like iZotope’s Iris 2 and an additive synth such as VirSyn’s Cube is that the latter can be used to build sounds from scratch using individual sine waves, rather than relying on imported or analysed content.
Some additive synths – like Apple’s Alchemy – blur the line by offering spectral editors alongside more traditional additive editors.
Editing a spectral image is quite similar to editing a resynthesised sound in an additive synthesiser