Additive Synthesis

Additive synthesis is one of the oldest and most researched types of audio synthesis. This technique was first used with church organs to accurately control the register-stops, as well as with the keyboard. The operation was quite simple. By pressing the keyboard’s keys and pulling several register-stops in different positions, the air released into the organ’s pipe. Around 1906, the Tel-harmonium synthesizer emerged. This device combined the sounds of several generators to create an additive tone. In the beginning, the additive synthesis approach was quite expensive, but it became more accessible as technology evolved. 

A Brief History on Additive Synthesis

The first additive synthesizers were quite complex, so many manufacturers were not willing to produce them. When software synthesis became popular, manufacturers started producing devices that offered a wide variety of sounds. The basis of additive synthesis lies upon the theory that nature creates sounds with simple sine waves which vary in both amplitude and frequency. These waves generate because of the vibrating properties of the object that produces the sound. Some of these waves have a harmonic connection to a fundamental tone. In other words, some people are able to perceive sounds as pleasant, while others perceive them as uncomfortable noise. Most complex sounds involve both noise and harmonic content.

The Physics Behind Additive Synthesis

The theory behind additive synthesis dates back to Joseph Fourier, a French mathematician. He theorized that a sound could be broken into a series of simple sine and cosine waves. This was the first attempt to explain additive synthesis.

A hardware-based additive synthesizer has up to six oscillators used as sound sources. Each oscillator connects to one or two envelope generators. On the one hand, the sounds produced by analog synths don’t always sound natural. On the other, digital oscillators are capable of mixing simple sine waves in real-time, thus creating complex waveforms. 

Re-synthesis is a technique that is closely related to additive synthesis. When using re-synthesis, the sample is loaded into the synth, and then analyzed and broken down in pieces. These envelopes and waves are common as a basis to create new sounds.

Final Observations

Additive synthesis is not quite popular within the audio universe because of two main reasons. First, because it’s essential that the user is familiar with the basic terminology of physics. Second, because of its time-consuming nature. Believe us: creating complex sounds with a wide variety of envelope generators and oscillators takes time.

If you’re interested…

If you wan to learn more about natural sounds, consult wavetable synthesis, which are the most popular synthesizers. Other kinds of synthesis you can learn from, too, are the granular and the subtractive.