Subtractive synthesis

Subtractive synthesis is a method of synthetic sound generation and is used for example in synthesizers.

Principle of operation

In the subtractive synthesis, an oscillator generates (eg VCO) a sonic raw material which by sound-altering modules (filters, envelope generators, amplifier modules, etc.) is then reworked. The desired sound is achieved by filtering out the unwanted frequency components from the most harmonically rich spectrum of the oscillator or lowered ( = subtraction).

Oscillators

The raw materials are the most oscillators, the following shapes are available:

• Sawtooth, brilliant sound that contains all the naturally occurring overtones. Works well for Mimicking string instruments ( Sample here )
• Rectangle, clarinet -like nasal tones up that contains only the odd harmonics. Works well to imitate sounds flötennähnliche ( Sample here )
• Triangle, hollow sound that almost only contains the first five harmonics. Works well to thicken surface sounds ( Sample here )
• Sine, " round " sound, which consists of only a root. In practice, the sound of a tuning fork comes pretty close to a sine. Since a pure sine wave contains no harmonics, the sound can not be changed ( Sample here ) by linear filtering.

The AI ( Advanced Integrated ) and AI Square synthesis of Korg, such as the Korg X5, in principle, a Subtractive synthesis, in which instead of such raw material right sounds ( waveforms, waveform ) are used, which are in a sample ROM.

The frequency spectrum generated by the oscillator may be affected by other parameters. Distributed here are the pulse width modulation of the square wave forms, a plurality of modulation ring oscillators, the frequency modulation of two oscillators and the synchronization of two oscillators, usually referred to briefly as sync.

You can also alter the symmetry of a wave in Tonverlauf and so, for example, have a high-pitched, asymmetrical sawtooth wave continuously into a smooth, symmetrical triangular wave and thus a very dynamic timbres course produce ( Synthesizer Workstation Pro).

Filter

The filter comes as vielseitigst usable variant of the low-pass filter ( Sample here ) is of particular importance. Many synthesizers have only a low-pass filter. Other forms are high-pass filter ( Sample here ), band-pass filter (a combination of high-pass and low-pass, Sample here ), notch filter ( Sample here) and comb filter.

The most important parameter is the filter cut-off frequency ( engl. cutoff ). The frequencies above the cutoff frequency are not completely removed, but increasingly attenuated with increasing distance from the cutoff frequency. How quickly the overtones are quieter, depends on the so-called slope of the filter, the (dB / octave) is given in decibels per octave. A high slope leads to awesome- sound gradients, low to soften the tone curves. Most synthesizers have low-pass filter with a slope 12 to 24 dB / octave.

The corner frequency of the filter and thus the tone shaping can be controlled in most synthesizers, both manually as well as automated controls via filter EG or LFO modulators such. Filters also tend to have a so-called resonance (English Emphasis or Contour ), which is also manually or automatically controlled. The response raises amplitudes of the frequencies around the cutoff frequency, making the sound thin and nasal ( Sample here).

Most audible is subtractive sound shaping for flat sounds in which tones while holding the filter cut through the sound spectrum is unstable ( Sample here).

Other occurrences

The human voice produces its sounds by means of a kind of subtractive synthesis. The larynx produces it in a harmonically rich sound, which is then filtered through the mouth. A lower cut-off frequency has the "U". Here almost all harmonics are cut off so that almost only remains of the pure sine wave tone. An overtone-rich sound that is filtered only slightly, is the " A".