Additive Synthesis

Stack sine waves one by one and write the harmonic structure directly.

Related

TimbreEqualizerOrganModern

The question

If every timbre splits into sines, why not stack them instead of filtering or FM? Additive synthesis is that direct route.

How it works

A periodic wave can be written as a fundamental plus its harmonics. Each partial has its own frequency, amplitude and phase. Place partials on integer multiples and the result has pitch; place them between multiples and it reads as a bell or metal. The drawbar organ is clearest, where each drawbar sets one harmonic group. Additive resynthesis analyses a sound into partials and rebuilds it. More partials mean a finer spectrum and more computation.

Settings and what you hear

Partial levels set brightness and weight. Strong odd partials give a hollow, woody tone; adding even partials fills it out. High partials that decay fast make a bright head, dark tail; partials that ring together sound like an organ. Slight detuning makes partials beat and widens the tone. Phase shapes the transient but matters less when steady.

What to listen for

Hear the drawbar organ and notice that thickness comes from the partial mix, not from a filter sweep. Then hear the bell, where many high partials decay quickly and the strike darkens at once. Finally hear the church organ, dense in the low register and clearer up top.

Common misconceptions

That additive only makes organs, when it also makes bells and metal; that more partials are better, when too many turn harsh; that phase does not matter, when it shapes the attack.

Sources

• Curtis Roads, The Computer Music Tutorial — additive synthesis checked, not quoted
• Jean-Baptiste Fourier, Théorie analytique de la chaleur — harmonic decomposition background checked, not quoted

Used for fact-checking only; all prose is original.