Oscillator Drift

Also called “frequency drift” this is an unintended offset of a voltage-controlled oscillator (VCO) from its nominal frequency — basically, the oscillator goes out of tune! Drift can be caused by numerous factors, including component aging, changes in temperature that alter the crystal regulating the oscillator, or problems with a voltage regulator, which controls the bias voltage to the oscillator. Modern digitally controlled oscillators don’t drift, as their digital clocks can calibrate them automatically. However, this drift is sometimes considered musically desirable, and various parameters can be used to emulate this effect.