In sonic art and electroacoustic music, synthesis is the act of creating sound through mechanical or computational means. This is in opposition to ways which we have primarily examined up to this point in the semester of capturing sound using a microphone, then processing and utilizing it in the DAW.
The Tone Generator plugins from last week are examples of synthesis in action. These generators can create one of six sounds (sine wave signal, saw up/down wave signal, triangle wave signal, square wave signal, and white noise). Each of the signals that the generator creates are synthesized from computational means that calculate the signal and then create it from nothing.
In the early days of sonic art and electroacoustic music synthesis techniques were rather simple, involving oscillators, filters, and delays. However, by the mid-20th century engineers such as Robert Moog and Don Buchla were working to create massive, modular synthesizers, capable of creating other-wordly sounds.
Basic Synthesis Concepts
Additive vs Subtractive Synthesis
Generally, there are two broad categories of sound synthesis, Additive Synthesis and Subtractive Synthesis.
As you can potentially imagine, Additive Synthesis creates sounds by adding oscillators or other sound generating devices together.
Although additive synthesis is a fairly straight forward concept, and seems logical, it was not the predominate form of synthesis. Although it is rather easy to ad a few sine wave oscillators together, to create complex sound may mean adding hundreds or thousands of them together. In the earlier days of synthesis, especially when everything was an analog electrical component, this was impractical at best and realistically financially impossible.
Instead, engineers favored subtractive synthesis, which works under the assumption that a complex signal will be created (such as a noise generator) and then filters will be used to remove sound until what is left is desirable.
Modulation
One way of creating complex signals we have not talked about yet (in addition to using signals such as noise, or saw/triangle/pulse waves) is through modulation. In this scenario, one sine wave is used as the input to another sine wave. Typically, this modulating signal will either effect the amplitude of the carrier signal (which would then be known as amplitude modulation, or AM Synthesis) or the frequency (known as frequency modulation, or FM Synthesis).
Envelopes
Another basic synthesis concept that you need to know about is that of envelopes. An envelope is essentially a “shape” which contains and defines some parameter of a sound. (Think of a hand-written letter’s envelope, which contains the letter itself.)
The most basic type of envelope that gets used in synthesis defines the amplitude of a sound. By defining the amplitude of the sound, an envelope is used to create the beginning, middle, and end of a sound event (or a note).
Envelopes can have all kinds of shapes and parameters. However, knowing that initially, we will use envelopes to define a sound event’s amplitude, there a few specific qualities of sections to think about. From a basic level, we can think of a note as having a beginning (or attack) and end (or release). So, a basic envelope may look like the following;
However, as you will hear in the video, this creates a rather artificial and stiff sound. Instead, we may want an attack that is much shorter, resulting in a more natural sound. This might look like;
This is all fine and dandy, however, we may want to be able to define sound events that sustain (i.e. not always increasing then decreasing in amplitude). This would be known as a sustain section. When combined with an attack and release, this creates a basic ASR or Attack, Sustain, Release Envelope.
This sustain allows for a sound event or note to be held as long as is necessary.
In the real-world when analyzing sounds, you will notice that after the initial attack, most sounds have a loss of energy before they stabilize at their sustain level. This is known as the decay. The decay occurs directly after the initial attack, and allows a sound to appear as though it has been struck or some amount of energy has been exerted to create the sound.
Together, these four sections create the ADSR Envelope (standing for Attack, Decay, Sustain, Release Envelope.) This is a standard envelope shape in sonic art and electroacoustic music.
Artists Working With Synthesis
One of the first commercially successful compositions for synthesizer was by Morton Subotnick, who used a Buchla Synthesizer to compose Silver Apples of the Moon. Please read about Mort, his work, and then listen to this piece.
- Morton Subotnick on 50 years of Silver Apples of the Moon (Please note, there are a number of videos within the article you should watch.)
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Please also read the chapter on Synthesis in the Indiana University textbook. Read the technical information closely. When they start talking about VCV Racks, you can choose whether you want to continue following along or not.