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'''Oscillator sync''' is a feature in some [[synthesizer]]s with two or more [[oscillator]]s. One oscillator will restart the [[period]] of another oscillator, so that they will have the same base
[[frequency]]. This produces a particular type of sound, rich with [[harmonics]], harsh but musical. The oscillator that resets the other oscillator(s) is called the master, and an oscillator that is reset by another oscillator is called a slave. The [[timbre]] can be altered on the slave oscillator by varying its input frequency. There are two common forms of oscillator sync which appear on synthesizers: ''hard sync'' and ''soft sync''. Soft sync is a term used for a variety of mechanisms.
== Hard sync ==
In a hard sync setup, the slave oscillator is forced to reset to some level and [[phase]] (for example, zero) with every cycle of the master regardless of position or direction of the slave [[waveform]], which often generates asymmetrical shapes.
The master oscillator's pitch is generated by user input (typically the synthesizer's [[keyboard]]). The slave oscillator's pitch may be [[musical tuning|tuned]], or detuned from this frequency, or may remain constant. Every time the master oscillator's cycle repeats, the slave is re-triggered, regardless of its position. If the slave is tuned to a lower frequency than the master 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 slave oscillator often causes unnatural timbres and the impression of [[harmony]].
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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 some usage, soft sync means a sync intended to nudge and lock the slave oscillator into the same or an integer or fractional multiple of the master oscillator frequency when they both have similar phases.<ref>Synth-diy:[http://dropmix.xs4all.nl/pipermail/synth-diy/2009-August/019132.html 2009, Aug, 019132]</ref><ref>Synth-diy:[http://dropmix.xs4all.nl/pipermail/synth-diy/2009-August/019136.html 2009, August, 019136]</ref>
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:In this method, the current wave completes but a new waveform is generated at the sync pulse. The tail of the old wave and the new wave are output summed if they overlap.
== Aspects of digital implementation ==
Naive approaches to sync in digital oscillators will result in [[aliasing]]. Methods such as [[additive synthesis]], BLIT ([[Band limited]] Impulse Train)<ref>www.music.mcgill.ca:[http://www.music.mcgill.ca/~gary/307/week5/bandlimited.html bandlimited]</ref> or BLEP (band-limited step) must be adopted to avoid aliasing.<ref>www.cs.cmu.edu:[http://www.cs.cmu.edu/~eli/papers/icmc01-hardsync.pdf icmc01-hardsync.pdf]</ref>
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Overlap sync is primarily a digital technique with simple implementation, such as used in [[formant wave-function synthesis]] (''fonction d'onde formantique'' or FOF).<ref>www.gersic.com:[http://www.gersic.com/dspwiki/index.php?title=Physical_Modeling_Synthesis Physical Modeling Synthesis]</ref> An analog implementation could be a highly damped sine oscillator excited by the reset pulse.
== Sync-based architectures ==
A variety of synthesis architectures are based on sync, often used in conjunction with [[amplitude modulation]], [[frequency modulation]] or [[phase modulation]]. Such architectures include
* [http://www.csounds.com/manualOLPC/vosim.html VOSIM]
* [[Physical modelling synthesis]]
{{From Wikipedia|Oscillator sync}}
== See also ==
* ''Digisound [http://www.digisound80.co.uk/digisound/other_documents/files/Guide_to_Synthesis.pdf Guide to Synthesis]'' by Charles Blakey, section 4.8
== References ==
{{reflist}}
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