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Waveforms

Basic VCO waveforms, top to bottom: Square wave, 25% duty cycle pulse wave, sine wave, triangle wave, sawtooth wave. All from a Synthesizers.com Q106 VCO.

A particular periodic cycling wave, with a particular harmonic content and a particular appearance on an oscilloscope. Several widely used waveforms are generated by the VCOs (or digital equivalent) of synths that use subtractive methods; these are used because their harmonic content reacts well to filtering to produce a variety of useful timbres. They are often named by their visual appearance on a scope screen, and on panel legends, switches or jacks to access different waveforms may be labeled by a drawing or representation of the shape, rather than the name. These commonly used shapes include:

  • Pulse wave, which contains large amounts of odd-number harmonics. The harmonic content is easily varied by pulse width modulation.
  • Sawtooth wave (also known as the ramp wave), which has a strong second harmonic, with higher harmonics declining in amplitude in an exponential curve. The sawtooth wave is the basic waveform generated by most VCO cores.
  • Triangle wave, a waveform containing little of higher-order harmonics. Among other uses, it is better suited to techniques like frequency modulation, which add a lot of harmonic content.
  • Sine wave. This one is different because it contains no harmonic content, only a fundamental. It might be used to reinforce the harmonic content of other waveforms, for frequency or amplitude modulation, or for additive synthesis. Filtering a pure sine wave is of no use, since it has no harmonics to filter.

All of the above are also useful for control signals for modulating other signals, and are often found as output options of low frequency oscillators.

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