4
Features and Functions
PROGRAMMABLE CONTROLS (CAN BE STORED IN MEMORY)
VCO
The Voltage Controlled Oscillator (VCO) is the basic sound source for the synthesizer. There are 6 VCOs in the
Polysix, one per voice. The VCO waveform you select has a large effect on the timbre or tone quality of a
particular sound. The VCO may be set to operate in several different octaves, extending the range of the
keyboard. Pulse width modulation and Sub OSC tones are included, allowing a wide range of fat, satisfying sounds
to be produced.
OCTAVE WAVEFORM PW/PWM PWM SPEED SUB OSC
1 OCT
OFF
2 OCT
VCO
1) OCTAVE
This control has three settings, 16’, 8’, and 4’. At the 8’ setting, the middle A on the keyboard produces A440
(with Tune control set properly). 16’ and 4’ settings produce sound one octave lower and one octave higher,
respectively. The keyboard is therefore extended to the equivalent of a 7 octave range.
2) WAVEFORM
A. Sawtooth
This waveform is rich in both even and odd harmonic overtones. Because of this, the VCF can be used to
"shape" the tone color over a wide range by selectively emphasizing different harmonics of the waveform (see
VCF section for more details). Sawtooth waveforms are good for bass, strings, brass, and many other sounds.
B. PW/PWM (Pulse Width/Pulse Width Modulation)
These settings produce various types of rectangular waveforms, such as square waves, pulse waves, "chorus",
etc., depending on the setting of the PW/PWM and PWM SPEED controls. An extremely wide range of sounds are
available using these controls.
• PW Waveform
The width, or "duty cycle" of the VCO waveform may be varied manually using the PW/PWM control (PWM
SPEED has no effect in this position). At 0, the VCO waveform is square wave (50% duty cycle), and possesses
the typical dull and "hollow" sound of the clarinet (only odd harmonics are present). Advancing the PW/PWM
control reduces the duty cycle, and hence the width of the VCO waveform. This produces a dramatic shift in the
tone quality towards a brighter and more "nasally" sound similar to oboe or harpsichord. At 8 or above the pulse
width becomes so narrow as to collapse, which produces sound and in effect shuts off the VCOs. This is useful
when the VCFs are used as sound sources in their self oscillating mode.
Note: The SUB OSC tone is not shut off when the VCO is shut off due to zero pulse width.
• PWM Waveform
The width of the VCO pulse waveform is continuously changed, or "modulated" by a variable speed oscillator.
This creates a fat "chorusing" type of sound, similar to multiple oscillators due to the constantly shifting harmonic
balance. The PW/PWM control now determines the depth of the effect. At 0, there is no modulation (constant
square wave). Between 8 and 10, modulation depth is so great that the VCO shuts off part of the time (because
pulse width becomes 0 for part of each cycle). The speed of the effect is controlled by the PWM SPEED knob.
The PWM oscillator is completely separate from the MG oscillator used for vibrato (see MG section), thus allowing
vibrato and PWM effects to occur simultaneously.
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