Oscillator

Most synth sounds start at an oscillator; the main exception is noise, the hiss behind hi-hats and wind effects. The oscillator produces a wave that repeats over and over, and the number of repeats per second sets the pitch. A4 is a wave repeating 440 times a second (440 Hz); A3, an octave down, repeats 220 times. The shape of each cycle, called the waveform, sets the raw tone before anything else touches it: a sine sounds pure, a sawtooth bright and buzzy.

Everything after the oscillator reshapes that wave. A filter can darken it and an envelope gives it a start and an end, but the pitch comes from the oscillator.

Oscillator controls and what they do

• Wave or Shape picks the starting tone. Switch a held C3 from sine to saw and a soft hum turns into a bright buzz.
• Octave, coarse and fine tune move the pitch. Coarse tune usually steps in semitones; fine tune moves in cents, hundredths of a semitone.
• Level sets how loud that oscillator is when a synth has more than one.

Many synths give each voice two or three oscillators. Tune two sawtooths a few cents apart and they drift in and out of step with each other, which gives the thick, moving sound behind big pads. That trick is detune, and making a synth sound bigger walks through it. Tune the second oscillator 7 semitones up (a fifth) and every note becomes a stack: play C3 and you hear C3 and G3 together. At 12 semitones up (an octave), C3 brings C4 with it.

On hardware you will see VCO (voltage-controlled oscillator, the analog kind) and DCO (digitally controlled oscillator, an analog oscillator kept in tune by a digital clock, as in Roland’s Juno-60). Software synths call them oscillators, or Osc for short.

In Gelato Synth, the Osc A page holds the main oscillator with Shape, Level and Glide, a slide from one note to the next that is also called portamento. The Osc B page adds a second oscillator with its own Shape, a Ratio from x0.5 to x8, Detune of up to 50 cents either way, and a Hear B slider that sets how much of it you hear. For the path from oscillator to speaker, see how synthesizers work.