The portion of a voltage controlled oscillator which generates the initial waveform, from which all of the other waveforms that the VCO outputs are derived. The two parts of a basic VCO core are a circuit that charges a capacitor at a rate determined by the input control voltage, and a timing mechanism that "resets" the waveform back to its starting point by discharging the capacitor. There are two basic types, which are named after the waveforms they produce: the sawtooth core and the triangle core. Each has their virtues and disadvantages, and aficionados will argue over which produces the best sounding VCO, but the sawtooth core is more commonly used because it is a simpler circuit.