X

Appendix B Synthesizer Basics 489
Common modulation sources
The main envelope generator of the synthesizer not only controls levels over time, but it also is
often used to modulate other sound parameters when you press or release keyboard keys. Many
synthesizers, such as ES2, feature multiple envelope generators.
The most common use of envelope modulation is to control the lter cuto and resonance
parameters with the keyboard velocity or keyboard scaling modulation sources (see Modulation
overview on page 487).
A modulation source found on nearly all synthesizers is the LFO (low frequency oscillator). This
oscillator is used only as a modulation source and does not generate any audible signals that
form part of your actual synthesizer sound, because it’s too low to be heard. It can, however,
aect the main signal by adding vibrato, lter sweeps, and so on.
Common LFO controls
•
Waveform: Allows you to choose the type of waveform—triangle waves and square waves
are common.
•
Triangle waves are useful for lter sweeps—slow changes to the lter cuto frequency—or
when simulating an ambulance siren—slow changes to the oscillator frequency.
•
The square waveform is useful for rapid switches between two dierent pitches, such as
vibratos or octaving.
•
Frequency/Rate: Determines the speed of the waveform cycles produced by the LFO. When it
is set to low values, very slow ramps are produced, making it easy to create sounds such as
ocean waves rolling in—when white noise is chosen as the waveform in the main oscillator.
•
Sync mode: Allows you to choose between free running—a user-dened LFO rate—or
synchronization with an external tempo source, such as a host application.
•
LFO Envelopes: The LFO can also be controlled with an envelope generator in some
synthesizers. For example, imagine a sustained string section sound where vibrato is
introduced a second or two into the sustained portion of the sound. If this can happen
automatically, it allows you to keep both hands on the keyboard. Some synthesizers include a
simple LFO envelope generator for this purpose. Often, this envelope consists only of an attack
parameter—some may also include decay or release options. These parameters perform in the
same way as the amplitude envelope parameters (see Attack, decay, sustain, and release on
page 486), but they are limited to control of LFO modulations.