Oscillator sync is a feature in some synthesizers with two or more VCOs, DCOs, or "virtual" oscillators. As one oscillator finishes a cycle, it resets the period of another oscillator, forcing the latter to have the same base frequency. This can produce a harmonically rich sound, the timbre of which can be altered by varying the synced oscillator's frequency. A synced oscillator that resets other oscillator(s) is called the master; the oscillators which it resets are called slaves. There are two common forms of oscillator sync which appear on synthesizers: Hard Sync and Soft Sync. According to Sound on Sound journalist Gordon Reid, oscillator sync is "one of the least understood facilities on any synthesizer". Hard Sync The leader oscillator's pitch is generated by user input (typically the synthesizer's keyboard), and is arbitrary. The follower oscillator's pitch may be tuned to (or detuned from) this frequency, or may remain constant. Every time the leader oscillator's cycle repeats, the follower is retriggered, regardless of its position. If the follower is tuned to a lower frequency than the leader it will be forced to repeat before it completes an entire cycle, and if it is tuned to a higher frequency it will be forced to repeat partway through a second or third cycle. This technique ensures that the oscillators are technically playing at the same frequency, but the irregular cycle of the follower oscillator often causes complex timbres and the impression of harmony. If the tuning of the follower oscillator is swept, one may discern a harmonic sequence. This effect may be achieved by measuring the zero axis crossings of the leader oscillator and retriggering the follower oscillator after every other crossing. This form of oscillator sync is more common than soft sync, but is prone to generating aliasing in naive digital implementations. Soft Sync There are several other kinds of sync which may also be called Soft Sync. In a Hard Sync setup, the follower oscillator is forced to reset to some level and phase (for example, zero) with every cycle of the leader regardless of position or direction of the follower waveform, which often generates asymmetrical shapes. In some cases, Soft Sync refers to a process intended to nudge and lock the follower oscillator into the same or an integer or fractional multiple of the leader oscillator frequency when they both have similar phases, similar to a phase-locked loop. Reversing