Ljunggren Audio

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Eurorack DIY

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VCOs & other soundsources


A voltage-controlled oscillator or VCO is an electronic oscillator that produces cyclical waveforms with frequency controlled by a voltage input. Usually some or all of the following waveforms are available - sine, triangle, square and sawtooth, although sometimes the tri/saw/ramp outputs are merely "waveshaped" alternatives of the same output controlled manually and/or by cv.



The oscillator frequency is varied by an applied control voltage, which though not necessarily different to any other cv, will generally be of a standard designed to produce accurate pitch-tracking across a 12 semitone per octave musical scale:


* Eurorack uses a 1v/Oct standard,

* Buchla use 1.2v/Oct

* some even use volts/hertz


Usually modulating signals may also be fed into the VCO to cause frequency modulation (FM), pulse width modulation (PWM) and forms of syncronisation. It is worth noting some VCOs can act as low frequency oscillators and may have built in waveshaping, Ring Modulation and/or sub-oscillators etc.


Sub-oscillators: a sub-oscillator is a part of the VCO that generates a tone (usually a squarewave) at a pitch usually one or more octaves lower than that of the main VCO.






self osc filters: