9
Synthesis Tutorial
LFOs - Memories - Summary
Like the Envelope Generators, the LFO section on a synthesizer is a
Modulator. That is to say, instead of forming a part of the sound syn-
thesis process, it is used instead to modify (modulate) other synthesiz-
er sections. For example, altering the Oscillator pitch or Filter cutoff fre-
quency.
Most musical instruments produce sounds that vary not just in volume
but also in pitch and timbre. Sometimes this variation can be quite sub-
tle, but still contribute greatly towards shaping the final sound.
Where an Envelope is used to control a one-off modulation which
occurs during the lifetime of a single note, LFOs modulate by using a
cyclic repeating wave pattern. As discussed earlier, Oscillators produce
a constant waveform which can take the shape of a repeating sine
wave, triangle wave etc. LFOs produce waveforms in a similar way, but
at a frequency normally too low to produce an audible pitched vibration
that the human ear can perceive. In fact, LFO actually stands for Low
Frequency Oscillator.
The waveforms generated by the LFOs may be fed to other parts of
the synthesizer to create the desired movements in the sound
The K-Station has two independent LFOs available which may be used
to modulate different synthesizer sections and run at different speeds.
A typical waveshape for an LFO would be a Triangle wave. Imagine
this slow moving wave being applied to an Oscillator’s pitch. The result
would be that the pitch of the Oscillator slowly rises and falls above
and below its original pitch.
This would simulate, for example, a violinist moving a finger up and
down the string of the instrument whilst it is being bowed. This subtle
up and down movement of pitch is referred to as the ‘Vibrato’ effect.
Similarly, if the same LFO were applied to the Filter Cutoff frequency
instead of the Oscillator pitch, a similar wobbling effect known as ‘wow-
wow’ would be heard.
As well as LFOs being available to modulate different sections of the
synthesizer, additional Envelopes may also be used simultaneously.
Clearly the more Oscillators, Filters, Envelopes and LFOs there are in
a Synthesizer, the more powerful it becomes.
The first generation of synthesizers, produced many years ago were
large modular machines where each part of the synthesizer was
housed in a separate unit (block). These blocks could only be physical-
ly connected together by combinations of cables known as patch leads.
A typical sound produced by this method would often involve connect-
ing dozens of patch leads.
Every time a new sound was required, the leads would have to be
physically disconnected and reconnected. The positions and connec-
tions of the leads would have to be noted down on paper if there was
to be any hope of creating that particular sound ever again! If not
reconnected in exactly the same way, the sound would be lost forever.
Modern machines such as the K-Station have all the blocks in one
compact unit and the sound generating or modulator blocks are
arranged in a sensible fashion. Front panel switches and knobs deter-
mine how each block functions and where the sound modifying blocks
such as the LFOs and Envelopes are routed, instead of having to
physically connect them externally with cables.
Additionally, the settings of these front panel controls (which of course
determine the current sound or ‘patch’) may then be stored in memory
locations in the machine which can be recalled at any time.
An Analogue synthesizer can be broken down into five main sound
generating or sound modifying (modulating) blocks.
1 Oscillators that generate Waveforms at a certain
pitches.
2 A Mixer that mixes the outputs from the Oscillators
together.
3 A Filter that removes certain harmonics, which changes
the characteristic or timbre of the sound.
4 An Amplifier that is controlled by an Envelope
generator, that alters the volume of a sound over
time when a note is played.
5 LFOs and Envelopes that can be used to modulate
any of the above.
Much of the enjoyment to be had with a Synthesizer is with experi-
menting with the factory preset sounds and creating new ones. There
is no substitute for ‘hands on‘ experience. Experiments with altering
knobs and buttons will eventually lead to a fuller understanding of how
the various controls alter and help shape new sounds.
Armed with the knowledge in this chapter, and an understanding of
what is actually happening in the machine when tweaks to the knobs
and buttons are made, the process of creating new and exciting
sounds will become easy - Have fun.
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