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Sync can have two different meanings, depending on whether we’re talking about oscillators or about clock signals.

Some oscillators support a mode where they reset their waveshapes to the beginning when they receive a signal (usually a pulse or the rising edge of a square wave). The oscillator being synchronized is sometimes referred to as the “slave” oscillator. That sync signal comes from a second oscillator (sometimes called the “synchronizing” oscillator), usually tuned to a lower frequency than the one being synchronized. If there is not a precise octave relationship between the two oscillators, the result is a modified waveform that has been reset prematurely, following the frequency of the second oscillator. You can create some very cool “ripping” sounds by modulating the frequency of the slave oscillator; a simple AD envelope works well.

There are two types of sync: hard and soft. Hard is where the slave oscillator always resets when the master tells it to, no matter what. Soft is where the slave oscillator only resets when it is close to the end of its own wave, meaning it ignores the sync signal unless the two oscillators are tuned close to some octave interval.

In the context of timing, when you are synchronizing sequencers or drum patterns, it is common to send a master timing or sync signal around the modular for all the relevant modules to follow. This is typically a gate or trigger signal (beware of triggers that are too short in duration; some modules might miss the sync pulse – fortunately gate extenders exist). It can be a pulse that goes to a high voltage every note (such as a quarter or eighth note) of the overall pattern; it can be a clock going at a higher speed such as the common 24 ppqn (pulses per quarter note) used by MIDI and Roland DIN Sync compatible gear. This clock is tied to the desired tempo, and varies with the tempo (as opposed to video rate or sample rate synchronization, which tends to be a steady speed).

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