Synthesizer Part 5 (Synthesis)

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Synthesizer synthesis

Since the invention of the synthesizer, different forms have been developed for sound generation; some syntheses can be realized analogously and digitally, while others can only be used digitally.
The additive and subtractive synthesizer synthesis will first be analyzed and described, but also other types of synthesizer synthesis such as FM synthesis, wavetable synthesis, granular synthesis or physical modeling will be outlined in their basic features and functionalities.

Additive synthesis

The additive synthesis is based on the reversal of an analysis named after Jean Baptiste Joseph Fourier. Fourier was a French mathematician and physicist who lived from 1768 to 1830 and created a mathematical procedure that allowed to dissect a periodic vibration into fundamental vibration and its harmonic vibration. In terms of a sound, this means that it can be broken down into the fundamental tone and its overtones, its sine frequencies. In contrast to this principle, however, this also means that one can assemble a sound from such sounds by adding them. The fundamental tone usually gives the pitch, the overtones form the timbre. The connection between timbre and overtones was discovered by Hermann Ludwig Ferdinand von Helmholtz (1821-1894), an extremely versatile scientist. Based on the assumption of the relationship between timbre and overtones, sine waves are theoretically the basis for the formation of infinite frequencies. In an additive synthesis, this method is technically as financially extremely expensive. Since one of its own oscillator caused sinusoidal vibrations, which should form the desired overall sound, it would have to be controlled by an enormous number of parameters.
It’s not such a big problem with digital synthesizers, except perhaps a financial one. Because here is technically feasible what the computer can afford. Finally, a not to be underestimated advantage of additive synthesis needs to be mentioned. It lies in its accuracy and subtlety, with which it can bring sonic changes that can also be accurately detected by the human ear.

Subtractive synthesis

Instead of combining partials, the subtractive synthesis changes what is not to be heard through the filter, envelope generator and amplifier, in other words: a harmonic rich in overtones is reworked with the mentioned modules in order to make the sound as desired. The subtractive synthesis is to be carried out both analogously and digitally. Its sequence is as follows: A voltage controlled oscillator produces an overtone-rich frequency – usually a triangular, square or saw tooth wave. A voltage controlled filter removes certain harmonics; in most cases low-pass filters are used; rarely are high-pass and bandpass filters used. The whole thing is then routed through a Voltage Controlled Amplifier and processed on the loudspeaker for the human ear.

FM synthesis

Frequency modulation synthesis, called FM synthesis for short, is based on the fact that an oscillator produces a carrier oscillation that is frequency-processed by a second oscillator. The FM synthesis can be implemented both analog and digital.

Wavetable synthesis

A wavetable is a digital collection of secured waveforms that can be altered in different ways, allowing for a large range of sounds. The synthesis was first used on a PPG Wavecomputer 360, a completely digitally controlled device by the inventor Wolfgang Palm. Click here to learn more about the wavetable synthesis.

Granular synthesis

Granular synthesis combines the sound with the tiniest of stored sound particles. It allows the pitch of an audio signal to be changed without modulating its length.

Physical modeling

Physical modeling is a method to play on a virtual instrument. It is based on a synthesis method that does not start with the generated waveform, but with what the generator of the waveform looks like. So for the synthetic trumpet, not the waveform is directly is replicated but the construction of it. Click here if you want to learn more about physical modeling.

The end

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Click here to read the first part of the synthesizer series.
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Click here to read the third part of the synthesizer series.
Click here to read the forth part of the synthesizer series.

6) Brockhaus encyclopedia
7) Audio Encyclopedia by Andreas Friesecke