Oscillator sync: Difference between revisions

'''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|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 frequency input. 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.

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.

This form of oscillator sync is more common than soft sync, but is prone to generating [[aliasing]] in naive digital implementations.

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>

;Reversing sync

;Threshold or Weak sync

:*Hard sync which is disabled when the frequency or amplitude of the slave crosses a user-defined threshold.

:*Hard sync which is disabled when the frequency of the slave extends too high above or too far below the frequency of the master.

:*Hard sync which is disabled when the frequency of the slave is lower than the frequency of the master.

:The phase of the slave is advanced by some amount when the master oscillator level crosses some threshold. Used for audio synthesis, this may give an audible effect similar to soft sync.

:When the master oscillator crosses some threshold, the normal reset of the slave is disabled: it will stick at its final level, positive or negative. When the master crosses back over some threshold, the slave is reset.

: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.

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.

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]