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Chapter 6: Modulation and Envelopes
132 ANDROMEDA A6 REFERENCE MANUAL
gets brighter as it gets louder. This is harmonic modulation or, more precisely, filter
frequency modulation. The brightness of the sound (“something”) can be changed by
a pedal, an envelope, an LFO, velocity or other sources (“something else”).
The principle of “something/something else” is the key concept in understanding
modulation. The “something” is called the modulation destination (or simply the
destination). It is “what’s being modulated”.
The “something else” is called the modulation source (or simply the source). It is
“what’s doing the modulating”.
Throughout the rest of this manual, we’ll be discussing modulation in terms of
sources modulating destinations. This is called a modulation path or simply mod path
and we’ll use this term in the documentation as well.
Common Modulations
To further illustrate the source/destination concept, this is a good time to take a look
at some everyday modulations. Everything that is mentioned here will be covered in
detail throughout the manual.
Keyboard, Mod Wheels and Pedals
Used as often as any modulation source, but rarely perceived as one, the keyboard is
a legitimate source of modulation. Because a note played on the keyboard changes
the frequency of the VCOs (the key word here is “changes”), the keyboard (and
received MIDI Notes for that matter) can be counted among the mod sources in the
A6. Another common keyboard mod destination is the Filters, since we often want
the Filter to be more open on higher ranges of the keyboard, or even to track the
keyboard exactly because it's in self-oscillation.
However, the keyboard is most commonly recognized as a controller – a mechanical
component that affects the sound, rather than a mod source that’s electronic or
derived in the synth’s operating system. So we will refer to the keyboard in this
manual as a controller rather than a modulation source per se as well as the mod
wheels, pedals and ribbon controller.
Envelopes
Loudness and harmonic shaping, plus the amplitude-shaping of other sound
elements, make the envelopes indispensable modulation sources for every Program
in the A6.
Aside from the essential envelope-to-filter (
ENV 2) and envelope-to-loudness (ENV 3)
routings, envelopes are often used to affect VCO frequency (
ENV 1), shape the
amplitude of an LFO, or alter the shape of a VCO’s waveform.
LFOs
Low Frequency Oscillators are similar in design to the VCOs that are used as the
primary sound source of an analog synthesizer. They utilize periodic waveforms like
the VCOs (sine, triangle, sawtooth and pulse) and aperiodic waves (random and
noise) but that’s where the similarity ends. An LFO is not intended to be used as an
audio source but a modulation source and, as such, its output is not routed to any of
the A6’s audio paths. Rather, an LFO is routed to other elements of the sound as a
mod source, so while you can’t hear it directly, you can hear the effect of it on other
elements of the sound.
The most common use of an LFO is for vibrato. In fact, the modulation wheel on the
A6 controls the amplitude (amount) of an LFO that is routed to the frequency of the
VCOs and often to the VCFs. Similarly, one or more LFOs are typically used in string
ensemble Programs to simulate the animation of many stringed instruments playing
together.