Low Frequency Oscillators
Another control waveform that is commonly available on synthesizers is the ‘random’ waveform.
This is also sometimes known as ‘sample and hold’, often abbreviated to S/H. The reason for
this is because in the really early days of sound synthesis when synthesizers were modular
(and huge!), there was a device that could ‘sample’ a signal
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and hold that sampled value for a
period of time set by a clock signal. When the clock advanced a cycle, the next sampled value
was read out. When the sample input was derived from a random noise generator and the clock
source was a repeating LFO square wave, the output was a totally random, stepped control
signal:
HOLD
CLOCK
These days, whilst the method of producing random control waveforms is achieved differently,
the resulting effect is exactly the same and when fed to the oscillators, this will cause random,
repetitive jumps in pitch and when fed to a filter, will cause random, repetitive changes in tone.
Another common parameter found on LFOs is a DELAY control. This causes the control
waveform to fade in gradually after a note-on is received:
Note on
Level
DELAY TIME
TIME
How is this useful? Well, with most instruments, vibrato is not always on - it tends to be gradually
introduced during the course of a note. Think of a violinist or an opera singer - they start at a
certain pitch and then gradually add vibrato. The LFO DELAY parameter allows us to simulate
this (although it must be said that vibrato effects are more naturally controlled with a
performance controller such as the modulation wheel).
The V-Station has two independent LFOs available which may be used to modulate different
synthesizer sections and each LFO can run at different speeds.
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The term ‘sample’ in this context is not to be confused with the more recent meaning of
recording sounds digitally and playing them back from a music keyboard.
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Synthesis Tutorial
