Moog Music Minimoog Voyager XL - Manual (Page 89)

Page 90
Voyager XL User’s Manual - Appendices
Page 91
Voyager XL User’s Manual - Appendices
Returning to our Subtractive Synthesis model, the first of the auxiliary components is the keyboard. The
keyboard provides a familiar musical instrument ‘interface’ that produces a control voltage and trigger signal
whenever a key is pressed. The level of the control voltage signal is a function of which key is pressed - the
higher up on the keyboard you play, the higher the level of the control voltage.
The keyboard’s control voltage signal is commonly routed to the oscillators to control the pitch, and it can also
be routed to other voltage-controlled components like the filter, to vary the cutoff frequency. The keyboard
trigger signal is routed to the Envelope Generators to trigger the envelopes.
The second auxiliary component is the Envelope Generator, or EG. The
EG makes no sound by itself. Rather, it creates a time-varying control
voltage that is typically used to control the gain of the amplifier, or the
cutoff frequency of the filter. Many synthesizers, including the Voyager,
provide several EG’s for independent envelope control of the amplifier
and filter circuits.
The EG is triggered from a Gate signal that is generated every time a
key is pressed on the keyboard. Once triggered, as long as the key is
held down (i.e. the Gate signal is present), the EG envelope will evolve
according to the control settings.
The Voyager’s Envelope Generators have four stages that can be set individually:
Attack – The time to go from zero volts to the maximum voltage (the fade in time).
Decay – The time to go from the maximum voltage to the Sustain level.
Sustain – The maximum level of the envelope after completing the Attack and Decay stages (if the
key is held). When the Sustain level is zero, the envelope consists of just the Attack, Decay and
Release stages. With zero Sustain, if the Attack and Decay stages complete before the key is
released, the Release stage is ignored. If the Attack and Decay stages do not complete before
the key is released, the remainder of the envelope is controlled by the Release stage.
Release – The time to go back to zero volts when the key is released (the fade out time).
The Filtered signal is routed to the Amplifier, which controls the gain (volume) of the signal. The Amplifier
controls the dynamics of a sound, turning it on and off as you play. The Amplifier is usually paired with an
Envelope Generator (described below). The gain of the amplifier follows the contours of the Envelope
Generator signal, shaping the sound from start to finish.
The Oscillator, Filter and Amplifier are voltage controlled, meaning that they respond to changes in voltages.
For the Oscillator, it means the higher the voltage, the higher the pitch. For the Filter, it means the higher the
voltage, the higher the cutoff frequency. For the Amplifier, this means the higher the voltage, the greater the
volume. Since each of the three main components respond to a voltage, the entire synthesis system thus
has a common control element. This provides great flexibility for sound programming, and allows auxiliary
components, like Envelope Generators and Low Frequency Oscillators (which generate control voltages) to
further vary the sound.