Subtractive: Introduction

Subtractive synthesis is probably the most famous and most popular method of sound synthesis. The basic idea is to generate spectra with rich spectral content which are then shaped afterwards by filters. Although the possibilities of subtractive synthesis are quasi-unlimited, especially when combined with other methods, the principle can be exlpained with three groups of functional units:

Generators

  • Oscillators
  • Noise Generators
  • ...

Modulators

  • LFO (Low Frequency Oscillators)
  • Envelopes (ADSR)
  • ...

Manipulators

  • Filters (VFC)
  • Attenuators (VCA)
  • ...

[Fig.1] gives an overview how these functional units are arranged in a subtractive synthesizer. Modulators and generators overlap, since they are interchangeable in many aspects.


/images/Sound_Synthesis/subtractive/subtractive-figure0.png
[Fig.1] Functional units in subtractive synthesis.

Like with all methods for sound synthesis, the dynamic change of timbre is an essential target for generating the desired sounds. [Fig.2] shows a more specific signal flow which is a typical subtractive synth patch for generating lead or bass sounds.

  • A VCO is manipulated by a VCF and then attenuated by a VCA.
  • The VCO has a sawtooth waveform.
  • The cutoff frequency of the VCF and the amplitude of the VCA are controlled with individual envelopes.
  • If ENV2 has a faster decay than ENV1, the resulting sound is the typical thump.

/images/Sound_Synthesis/subtractive/subtractive-figure1.png
[Fig.2] Subtractive patch for bass and lead synths, as used in the Faust example.


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