Distortion synthesis is a group of
sound synthesis techniques which modify existing sounds to produce more complex sounds (or
timbres), usually by using
non-linear
In mathematics and science, a nonlinear system is a system in which the change of the output is not proportional to the change of the input. Nonlinear problems are of interest to engineers, biologists, physicists, mathematicians, and many other ...
circuits or mathematics.
[Nb. Some authors refer to these techniques as 'modulation synthesis'; e.g. Chapter 6 of ]
While some synthesis methods achieve sonic complexity by using many
oscillator
Oscillation is the repetitive or periodic variation, typically in time, of some measure about a central value (often a point of equilibrium) or between two or more different states. Familiar examples of oscillation include a swinging pendulum ...
s,
distortion methods create a
frequency spectrum which has many more components than oscillators.
Some distortion techniques are:
FM synthesis, waveshaping synthesis, and discrete summation formulas.
FM synthesis
Frequency modulation synthesis
Frequency modulation synthesis (or FM synthesis) is a form of sound synthesis whereby the frequency of a waveform is changed by modulating its frequency with a modulator. The frequency of an oscillator is altered "in accordance with the amplitude ...
distorts the carrier
frequency
Frequency is the number of occurrences of a repeating event per unit of time. It is also occasionally referred to as ''temporal frequency'' for clarity, and is distinct from ''angular frequency''. Frequency is measured in hertz (Hz) which is eq ...
of an oscillator by
modulating
In music, modulation is the change from one tonality ( tonic, or tonal center) to another. This may or may not be accompanied by a change in key signature (a key change). Modulations articulate or create the structure or form of many pieces, as ...
it with another signal. The distortion can be controlled by means of a modulation index.
The method known as
phase distortion synthesis
Phase distortion (PD) synthesis is a synthesis method introduced in 1984 by Casio in its CZ range of synthesizers. In outline, it is similar to phase modulation synthesis as championed by Yamaha Corporation (under the name of frequency modulation) ...
is similar to FM.
Waveshaping synthesis
Waveshaping
In electronic music, waveshaping is a type of distortion synthesis in which complex spectra are produced from simple tones by altering the shape of the waveforms.
Uses
Waveshapers are used mainly by electronic musicians to achieve an extra-ab ...
synthesis changes an original waveform by responding to its
amplitude
The amplitude of a periodic variable is a measure of its change in a single period (such as time or spatial period). The amplitude of a non-periodic signal is its magnitude compared with a reference value. There are various definitions of amplit ...
in a non-linear fashion. It can generate a bandwidth-limited spectrum, and can be continuously controlled with an index.
The
clipping caused by overdriving an
audio amplifier
An audio power amplifier (or power amp) is an electronic amplifier that amplifies low-power electronic audio signals, such as the signal from a radio receiver or an electric guitar pickup, to a level that is high enough for driving loudspea ...
is a simple example of this method, changing a sine wave into a square-like wave. (Note that direct digital implementations suffer from aliasing of the clipped signal's infinite number of harmonics, however.)
Discrete summation formulas
DSF synthesis refers to
algorithm
In mathematics and computer science, an algorithm () is a finite sequence of rigorous instructions, typically used to solve a class of specific Computational problem, problems or to perform a computation. Algorithms are used as specificat ...
ic synthesis methods which use mathematical formulas to sum, or add together, many numbers to achieve a desired wave shape. This powerful method allows, for example, synthesizing a 3-formant voice in a manner similar to FM voice synthesis. DSF allows the synthesis of
harmonic
A harmonic is a wave with a frequency that is a positive integer multiple of the ''fundamental frequency'', the frequency of the original periodic signal, such as a sinusoidal wave. The original signal is also called the ''1st harmonic'', the ...
and
inharmonic,
band-limited
Bandlimiting is the limiting of a signal's frequency domain representation or spectral density to zero above a certain finite frequency.
A band-limited signal is one whose Fourier transform or spectral density has bounded support.
A bandlimi ...
or unlimited spectra, and can be controlled by an index. As Roads points out, by reducing digital synthesis of complex spectra to a few parameters, DSF can be much more economical.
[C. Roads 1996, p.260-61.]
Notable users
Jean-Claude Risset was one notable pioneer in the adoption of distortion methods.
References
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External links
Sound synthesis types
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