Synthesis
From DNBWiki
Method used by an electronic instrument to generate sound.
Contents |
[edit] Subtractive Synthesis
Subtractive synthesis is the process of mixing harmonicly rich waveforms and subtracting frequency content using filters. Rich waveforms include the saw wave, square wave, triangle wave and the pulse wave. Filters include low pass, high pass, band pass and notch.
See also:
Additive Synthesis; Frequency Modulation (FM) Synthesis; Wave Table Synthesis; Granular Synthesis;
[edit] FM Synthesis
Frequency modulation synthesis is performed by controlling the frequency of an oscillator (called the carrier) with the amplitude of another oscillator (called the modulator). It is a very versatile method of synthesising a rich tone that has simple parameters and is computationally cheap.
Basic parameters are carrier frequency, modulation depth, and modulation frequency. The modulation frequency divided by the carrier frequency may be referred to as the harmonicity ratio, while the ratio of the modulation depth divided by the carrier frequency may be refered to as the modulation index.
[edit] The science bit:
In the simplest example, the carrier wave and the modulator wave are both sine waves. When the frequency of the carrier wave is modulated by a small amount at a low rate a vibrato or wavering pitch is heard. As the frequency of the modulating increases to that of the carrier a rich tone is heard. A frequency analysis (frequency against amplitude) will show a center frequency (that of the original sine wave) and an infinite number of so-called side-bands spread at frequency distances equal to the frequency of the modulating wave and amplitudes related to the modulation depth (precisely calculated using [functions]). Side bands of negative frequency are heard at equal positive frequency but phase reversed. The harmonicity ratio defines the spacing of the side bands relative to the carrier so when it is an integer a simple harmonic tone is produced. A value of one produces harmonics at similar frequencies (note: but of differing amplitudes) to that of a saw wave. A value of two produces harmonics ar similar frequencies to that of a square wave (ie only at odd number frequency multiples of the carrier). Non integer frequencies produce complex, bell-like tones.
[edit] History:
FM synthesis was discovered by John Chowning at Stanford University while fiddling with vibrato at extreme settings. The story goes that none of the major synthesiser manufacturers were interested in it until Yamaha licensed the technique and used the principle in their DX7 and subsequent X series synthesisers.
[edit] See also
[edit] Wavetable Synthesis
nb Not necessarily a complete or completely accurate description
Wave table synthesis (or waveshaping synthesis) involves mapping the samples of an input wave to an output wave according to the values in a lookup table or transfer function. A simple lookup table where x (input) = y (output) results in no change to the sound. Non linear lookup functions result in harmonic distortion. Control of the amplitudes of each harmonic created can be acheived by weighted summing of Chebyshev polynomials of the first kind. Functions that are symmetrical about the y axis produce waves that contain only even numbered harmonics, while functions with rotational symmetry about the origin produce waves with only odd numbered harmonics.
[edit] related Wikipedia articles:
[edit] Granular Synthesis
Granular synthesis is a technique use to create sounds that have a wide spectrum but do often not have a 'base frequency' so the sounds are more atmospheric. Those grains can also be used to modulate other sounds and the grains can also be modulated themselves to get different sound.
[edit] Granular synthesis on the web
[edit] Additive Synthesis
Also called Fourier Synthesis, is a type of synthesis which produces a new sound by adding together two or more audio signals. The "classical" form of additive synthesis, still used on some synthesizers, may be called "harmonic synthesis." Here the sources added together are simple waves (for example, sine waves) and are in the simple frequency ratios of the harmonic series. The resultant absolute amplitude is the sum of the amplitudes of the individual signals. The resultant frequency is the sum of the individual frequencies taking into account the effects of constructive and destructive interference. This is potentially a very powerful technique, as it was shown well over 200 years ago by the Frenchman, Francois Baptiste Joseph Fourier that any periodic sound (i.e., pitched sound) can be represented by the sum of simple sine waves. In practice, however, the approach can be extremely time-consuming since often hundreds of harmonics may be used to create a complex sound.
