Oscillator sync: Difference between revisions
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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
[[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
This effect may be achieved by measuring the zero axis crossings of the master oscillator and re-triggering the slave oscillator after every other crossing.
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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:[https://web.archive.org/web/20141010210716/http://dropmix.xs4all.nl/pipermail/synth-diy/2009-August/019132.html 2009, Aug, 019132]</ref><ref>Synth-diy:[https://web.archive.org/web/20141010210653/http://dropmix.xs4all.nl/pipermail/synth-diy/2009-August/019136.html 2009, August, 019136]</ref>
''See also [[Phase locked loop]]''
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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>http://www.music.mcgill.ca:[https://web.archive.org/web/20131006004705/http://www.music.mcgill.ca/~gary/307/week5/bandlimited.html bandlimited]</ref> or BLEP (band-limited step) must be adopted to avoid aliasing.<ref>http://www.cs.cmu.edu:[http://www.cs.cmu.edu/~eli/papers/icmc01-hardsync.pdf icmc01-hardsync.pdf]</ref>
In a digital oscillator, best practice is that the slave will not be reset to the identical phase each, but to a phase advanced by an equivalent time to the phase of the master at the reset. This prevents jitter in the slave frequency and provides truer synchronization.
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For digital implementation, note that none of the Threshold or Weak sync methods actually synthesize the waveform in a way different from Hard sync (rather, they selectively deactivate it).
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>
== Sync-based architectures ==
A variety of synthesis architectures are based on sync, often used in conjunction with [[
* [http://www.csounds.com/manualOLPC/vosim.html VOSIM]
* [[Physical modelling synthesis]]
==
* ''Digisound [http://www.digisound80.co.uk/digisound/other_documents/files/Guide_to_Synthesis.pdf Guide to Synthesis]'' by Charles Blakey, section 4.8
== References ==
{{From Wikipedia|Oscillator sync}}
{{reflist}}
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